The invention provides an egg product having a reduced amount of free water comprising at least 30 wt-% whole egg; glycerol; maltodextrin; egg white powder; powdered shortening; liquid egg yolk, and salt. This egg product has a Aw of about 0.80 to 0.95. Further, the invention provides food products comprising this egg product, including baked goods and other products having the egg product as a filling or topping, that may be frozen and reheated without the egg product developing a tough or rubbery texture.

This invention is generally directed to an egg product having a high proportion of real egg. This egg product has a reduced free water content as compared to the free water content of natural whole eggs, and does not become tough or rubbery when frozen and reheated.
Eggs are a popular and nutritious food product. Their appealing flavor and texture have caused them to be prepared and consumed in numerous ways, particularly as a breakfast food. Traditionally, eggs have been prepared as a separate dish, or as part of a dish such as omelets, quiches, sandwiches, and recently in breakfast burritos.
As time becomes more and more valuable to the consumers of food products, and the demand for nutritious, quick and easy to prepare foods has grown, producers have sought to provide prepared food products that contain eggs. Because of the difficulty in storing and preserving fresh eggs, these products have often been stored in the freezer, to prevent the growth of undesirable microorganisms in the egg product.
Although freezer storage can be an effective method of storing egg products without growth of microorganisms, the method has given rise to other challenges in the production of egg-containing food products. Because a whole egg is made up of about 70% water by weight, when a prepared egg product is frozen ice crystals are formed. When these crystals melt the water is not completely reabsorbed into the egg product, and some of the water xe2x80x9cweepsxe2x80x9d out of the eggs. If the eggs are prepared separately, this results in the thawed eggs sitting in a puddle of water and may also result in the eggs having a rubbery texture. If the eggs are prepared as part of the filling of a food that has a crust or pastry component, this results in the transfer of water to the crust or pastry and a soggy texture. Further, the high levels of free water in most egg containing products result in relatively slow reheating times when the product is exposed to radiant heat, such as in a toaster. This is especially problematic when the egg product is used as part of a filling.
In the past, this problem had been addressed by the use of powdered eggs that are reconstituted when combined with additional ingredients. This system allowed the free water in the egg product to be easily controlled, but still resulted in the product having undesirable textural characteristics. The reconstituted egg product has a tendency to become tough or rubbery when it is frozen for storage and then thawed for consumption. This tough texture is believed to be caused by a loss of water when the egg protein is denatured in the dehydration process.
The prior art has attempted to overcome these problems in a number of different ways. Rapp et al., in U.S. Pat. No. 4,469,708, describe a freeze-thaw stable egg product and a process for preparing the product. The product comprises loosely cohered pieces of cooked egg in a batter coating. The egg mixture contains water binding carbohydrates such as a cold-water-insoluble starch and a hydrophilic colloid. The moisture content of the egg mixture is about 72 to about 80%.
In U.S. Pat. No. 3,640,731, Kaplow et al. disclose a shelf stable egg product wherein dried egg white, whole egg solids or egg yolks are blended with 20-40 wt-% of a polyhydric alcohol. This mixture is then combined with starch hydrolyzate solids and an antimycotic to form a shelf stable egg product having a moisture range of 14-32% and an Aw of between 0.65 and 0.80.
Kahn et al., U.S. Pat. No. 4,244,976 disclose an intermediate moisture content frozen egg yolk composition containing egg yolk, sugar, water and a stabilizer. In order to maintain the bacteriostatic effect of the mixture, the sugar to water ratio is at least about 1:1.
Each of the prior art methods of preparing a freezable egg product have certain undesirable features. For example, if large amounts of glycerol are used, the bittersweet taste of glycerol becomes very pronounced and it becomes necessary to mask the taste of glycerol. If large amounts of sugar are used, unless the product is a dessert product, it is necessary to reduce the flavor impact of the sweetness component, for example, by incorporating a bitterness principle such as quinine and caffeine.
Clearly, a substantial need exists for an egg based product that is suitable for freezing which does not become rubbery or tough during storage and may be quickly reheated.
In one aspect, the invention provides an egg product having low water activity (Aw) and a reduced free water content that does not become tough or rubbery during freezer storage, and can be easily reheated. The egg product comprises at least 30 wt-% of an egg source, a humectant system and a tenderizer. Unless otherwise specified, all weight percentages are based on the total weight of the product.
In the egg product of the invention, the free water ordinarily present in eggs is bound by the humectant system. The binding substantially reduces the amount of free water available to freeze and form ice crystals. The tenderizing component of the egg product of the invention enhances the organoleptic properties of the product, such as texture, mouthfeel, consistency and so on. The invention therefore also provides an egg product having a reduced amount of free water comprising at least 30 wt-% of an egg source, a humectant system, tenderizer and a flavor enhancing agent.
In the egg product of the invention, the free water ordinarily present in eggs is bound by the humectant system of the product. This substantially reduces the amount of free water available to freeze and form ice crystals. While a natural whole egg is made up of about 70% total water by weight, in the product of the invention about 48% to 52% of that water is bound, leaving about 18% to 22% total free water. This reduced free water content results in less water being available to freeze and form ice crystals when the product is stored in a freezer. These ice crystals must be melted before the water can be heated, resulting in increased heating times. This problem is solved by the product of the invention. Because of the reduced free water content up, less ice crystals form upon freezing the product and as a result, less time is needed to reheat the product to acceptable eating temperatures.
The invention also provides food products containing the egg product of the invention, such as a filled pastry product, either alone as the filling or with other ingredients in an egg sandwich, pita pocket, breakfast burrito, omelet, or quiche that may be conveniently stored in the freezer until needed.
The egg product of the invention having reduced amounts of free water comprises an egg source, a humectant system and a tenderizer.
The egg source component provides the egg product with the desirable organoleptic properties of real eggs. Use of a real egg source results in a composition with the appearance, texture, flavor, and mouthfeel of real whole eggs. In particular, the egg product of the invention may be frozen and reheated without the texture becoming rubbery or tough.
The egg source of the invention is preferably natural whole eggs and ingredients that are predominantly made up of natural egg components, such as dried egg yolk, liquid egg yolk, dried egg white, liquid egg white, dried whole egg solids, or combinations thereof. The egg source may contain minor amounts of additives. For example, the dried egg white may contain sodium lauryl sulfate as a whipping aid. Preferably, the liquid components of the egg source are from fresh eggs. The preferred egg source is real whole eggs. A preferred dried egg white is available from the M. G. Walbaum company of Wakefield, Nebr. A preferred dried egg yolk is available from Primegg Limited of Cameron, Wis.
Typically the total egg source comprises at least about 30 wt-% of the egg product to provide the desired qualities. If too little of the egg source is present, the egg product will not have the desired xe2x80x9creal eggxe2x80x9d taste. For optimal taste and texture, preferably the egg product contains about 30 to 70 wt-% of the egg source, and most preferably about 60 to 65 wt-%. In an especially preferred embodiment, fresh real whole eggs comprise about 40 to 65 wt-% of the composition.
The humectant system of the egg product provides the ability to absorb and retain water under conditions of medium or high relative humidity, thereby reducing the amount of free water available in the product. Generally, the humectant can be comprised of any material that is able to absorb and retain water, or bind water, such as, for example, alcohols, certain saccharides, salts and mixtures thereof. Examples of usable alcohols include monohydric alcohols, diols, and/or polyols. More specifically, glycerol, propylene glycol, sorbitol, manitol, 1,2-propanediol, and/or mixtures thereof are useable in the invention, with glycerol preferred. Examples of usable saccharides include corn syrup solids such as maltodextrin. Sodium chloride, carboxymethylcellulose, potassium polymetaphosphate, propionate, sodium lactate, monosodium glutamate, glycerine, and/or mixtures thereof are also useful as humectants or water binders. Humectant enhancers including starches such as corn starch or gums such as alginate may also be employed. Salts of any of the previously listed humectants or any other type of humectant and/or mixtures thereof are also useful.
The humectant system may comprise more than one of these humectant or water binding ingredients and is present in a proportion that allows a sufficient amount of water to be bound such that the free water content of the product is less than about 30%. Although the amount will necessarily vary with the preuse humectant system employed, this can be accomplished by the use of about 3 to 8 wt-% of a polyhydric alcohol; about 1 to 10 wt-% of a corn syrup solid; and 0.5 to 2.0 wt-% salt. Because the polyhydric alcohols can provide a bittersweet taste that might be considered unpleasant, preferably no more than about 20 wt-% of these components are present in the egg product.
Although sugar is known to be a humectant, it can impart an overly sweet taste to an egg product. To avoid the problem of over-sweetness caused by using sugar as a humectant, a low D.E. corn syrup solid such as maltodextrin is preferred. Preferably the corn syrup solids used in the egg product of the invention have a D.E. of about 1 to 10 or higher, with a D.E. of about 1 preferred. Maltodextrin is preferred as it functions effectively as a humectant but because of its low D.E. does not provide an overly sweet taste.
The corn syrup solids make up about 1 to 10 wt-% of the egg product, to provide a balance of its water binding properties without imparting too much sweetness. Preferably, about 1 to 5 wt-% maltodextrin or other corn syrup solid, is present to provide the desired balance of these properties. Because the water-binding efficiency of these corn syrup solids increases, as the D.E. increases, proportionately less high D.E. corn syrup solids are used.
Because the water activity, or Aw, is related to the amount of free water available in the system, the Aw of the egg product of the invention is also lower than the Aw of natural whole eggs. Water activity is a measure of the water vapor pressure generated by the product and is typically calculated by dividing the moles of water plus the moles of soluble solids into the moles of water. The water activity of the product has an impact on the amount of ice crystals formed upon freezing the product, as discussed above. The water activity of the product also has an impact on the stability of the product against microbiological contamination. If there is less water activity, and therefore less free water in the product, the product will have greater stability against the growth of microorganisms because it is difficult for microorganisms to grow under these conditions. The egg product of the invention, having a lower Aw, is thus also less susceptible to spoilage and microbiological contamination than natural whole eggs. The Aw of natural whole eggs is about 0.989, while the egg product of the invention has an Aw of about 0.80 to 0.95, and preferably about 0.84 to 0.91.
Tenderizing components can be added to maintain the water holding capacity of the egg product, to enhance the texture of the egg product and to prevent the product from becoming tough or rubbery after being frozen and reheated. One such tenderizer is shortening, such as vegetable shortening. The shortening is preferably a vegetable shortening in powdered form, although other forms known in the art may be acceptable.
Shortening powders used in the invention contain a major proportion of fat, usually about 75 to 85 wt-%. The fat component of the shortening is typically a hydrogenated vegetable oil, such as hydrogenated soybean oil, vegetable oil, coconut oil, cottonseed oil, sunflower oil, and the like. Vegetable shortenings useful in the preparation of the egg products of the invention may also include other ingredients and additives, such as saccharides, milk proteins or solids, and preservatives.
Another useful tenderizing and texture enhancing ingredient is a powdered cheese blend. Such blends typically comprise dehydrated cheese, such as blue, cheddar, and the like; whey; reduced lactose whey; fat such as partially hydrogenated soybean or vegetable oil; maltodextrin; salt; and various other additives. Such powders not only help maintain the egg-like texture of the product, but provide additional flavoring that is desirable on its own or may help mask any xe2x80x9coffxe2x80x9d flavors present in the product. Preferably the cheese powder is uncolored, to avoid altering the color of the egg product, and has a relatively mild flavor so the egg flavor is not overpowered. Suitable cheese powders are commercially available from Kraft Food Ingredients of Memphis, Tenn.
The tenderizer, such as the shortening, cheese powder, or a mixture thereof, is generally present in the egg product in amounts ranging from about 10.0 to 40.0 wt-%, in order to maintain good texture. Preferably, about 15 to 35 wt-% of the tenderizing agent is present, and most preferably about 20 to 30 wt-%.
Optionally, flavorings may be included in the egg product, both to provide a variety of desirable flavors and to mask any xe2x80x9coffxe2x80x9d flavors that may be present in the product. The flavorings may be either natural or artificial. Such flavorings include, but are not limited to, natural egg flavor, salt (which also may comprise part of the humectant system), natural and artificial butter or cheese flavor, pepper, onion, garlic, and so on. If such flavorings are used, they typically comprise about 0.5 to 5.0 wt-% of the egg product, preferably about 1.0 to 3.0 wt-%, although the actual amount will vary with the type of flavoring used.
The composition of the egg product of the invention may be summarized as follows. All amounts shown are by weight percent of the total composition:
The egg product is prepared by first preparing a real egg mixture by combining the liquid egg sources, such as whole egg or liquid egg yolk. Powdered egg sources, such as powdered egg white or egg yolk, are then added and allowed to rehydrate. The remaining dry ingredients are blended and added to the real egg mixture. Mixing continues until the dry ingredients are fully incorporated. The polyhydric alcohol and other liquid ingredients, if any, are then added and blended until well incorporated. Mixing is preferably performed at about 40xc2x0 F.
When prepared, the egg product will have a consistency approximating that of pancake batter. The pH of the product should be close to neutral or only slightly acidic, from about 5 to 7, to remain at approximately the same pH as natural eggs. Preferably, the product has a pH of about 5.5 to 6.8. The egg product is then ready for inclusion in a prepared food product that can be stored in a frozen state and easily reheated by the consumer.
The egg product may be cooked before its incorporation into the food product, or it may be cooked after combined with the other ingredients of the food product. Whether the egg product is cooked before or after combination with other ingredients, the internal temperature should reach at least 150xc2x0 F., and preferably about 190xc2x0 F., to meet applicable safety standards.
The egg product of the present invention is particularly suitable for cooking by microwave energy. Cooking shelled natural eggs using microwave energy provides a transient increase in volume during cooking, but the final egg volume remains unchanged because the natural cooked egg collapses after it is cooked and removed from the microwave cooker. Surprisingly, cooking the egg product of the present invention by microwave energy results in a 60% increase in volume after the egg product is cooked and removed from the microwave cooker. It is believed that the ingredients added to the egg source sustain the increased volume and hold the resulting structure after the egg product has been cooked.
After the egg product is cooked, it can be further processed using conventional methods to provide desired product characteristics such as shape, size and further processability. In one embodiment, the cooked egg product is cooled after cooking, diced and/or shredded, and then frozen in liquid nitrogen using conventional IQF (xe2x80x9cindividual quick frozenxe2x80x9d) techniques. An egg product of this embodiment exhibits an appearance similar to a fresh scrambled egg product and is readily integrated with other ingredients of a food product.
The egg product of the invention may be used as a substitute for real eggs in the preparation of any food product that calls for eggs. For example, they may be used as a filling in a pastry product, either alone or with ingredients such as ham, bacon, sausage, cheese, onions, red or green peppers, and combinations thereof. The egg product together with such other ingredients could also be used in an egg sandwich, pita pocket, breakfast burrito, or omelet. The egg product may form part of a complete prepared breakfast, or it may be used in the preparation of quiches or other products that may be conveniently stored in the freezer until needed.


The disclosure relates to a packaging container for long-term cold storage of liquid foods for retaining superior flavor and aroma properties in the packed product, and produced from a packaging laminate including a core layer of paper or paper-board, an inside aroma barrier layer of PET and a gas barrier layer, by fold formation and sealing of a planar packaging blank so that all contact surfaces vis-a-vis the packed product consist of the PET layer. The disclosure also relates to a method of fold forming and sealing the packaging laminate into a packaging container according to the invention. Good shelf-life after cold storage for at least six weeks at 8xc2x0 C., or at least 10 weeks at 4xc2x0 C. will be attained using the packaging container according to the invention.

The present invention relates to a packaging container for the cold storage of liquid foods, for retaining superior flavour and aroma properties in the packed product, the container being of the type which is produced by fold forming and sealing of a planar, substantially rectangular or quadratic packaging container blank comprising side wall panels, top panels and bottom panels, for the formation of a tubular blank with a longitudinal sealing joint between the overlapping longitudinal incision edges of the packaging container blank, the tubular blank thereafter being given the desired bottom and top closures by fold forming and sealing of the bottom and top panels, respectively, of the packaging container blank, the packaging container blank being produced from a laminated packaging material comprising a core layer of paper or paperboard, an outer, aroma barrier layer of PET and a gas barrier layer disposed between the core layer and the aroma barrier layer. The present invention also relates to a method of producing such packaging containers.
Use has long been made within the packaging industry of packages of a single-use nature (so-called single-use disposable packages) for packing and transporting products such as liquid foods. A very large group of these single-use disposable packages is produced from laminated packaging material based on an interjacent core layer of paper or paperboard and outer laminate layers of some thermosealable plastic possessing superior liquid barrier properties, normally such as low density polyethylene (LDPE).
Depending on what food product is to be packed, i.e. its composition and storage sensitivity, its shelf-life, additional laminate layersxe2x80x94or laminate layers of other types than LDPExe2x80x94may be included in the laminate structure. Examples of such additional or other laminate layers may be material layers possessing superior gas barrier properties, such as an aluminium foil or a layer of polyamide or of copolymers of ethylene and vinyl alcohol. Certain food products, such as juice, moreover place more stringent requirements to the effect that the packaging material possess superior aroma barrier properties, i.e. prevent flavour deterioration as a result of non-polar flavour and aroma substances being absorbed from the packed product into the packaging material. At the same time as the package must afford the product the best possible product protection properties, production of such single-use packages must also be simple and rational in order to be economically viable.
Within the prior art technology, polyethylene terephthalate (PET) has often been proposed as a material possessing superior aroma barrier properties, suitable for the inside layer in a packaging container for direct contact with the packed product, as opposed to, for example, LDPE. PET possesses extremely good barrier properties against essential oils such as D-limonen and other non-polar flavour and nutrient substances in, for example, orange juice and is, therefore, a highly desirable material for this purpose. However, PET suffers from the major drawback in employment as the innermost laminate layer in a packaging container for direct contact with the packed product in that it is difficult to thermoseal at rational production speeds, in particular on sealing of the longitudinal joints in a packaging container produced from a sheet-shaped packaging laminate blank in which the longitudinal edges of the sheet-shaped blank overlap one another and are exposed such that the outside of the inner edge is sealed against the inside of the outer edge. In rational production of conventional packaging containers, such longitudinal joint sealing takes place at very high speeds, in that the sheet-shaped blanks in rapid sequence are advanced, reformed and longitudinally sealed by means of thermosealing into tubular packaging container blanks. The term xe2x80x9ctubularxe2x80x9d is hereafter taken to signify tubes of both circular and quadratic or rectangular cross section. For thermosealing of PET, it is necessary that the pressure from the sealing jaws is maintained during the heating process, at least up to approximately 165xc2x0 C., which takes roughly 0.5 sec. However, the available stay time during the sealing process on sealing of longitudinal joints, i.e. the time during which the pressure from the sealing jaws is maintained, is only approx. 0.01 sec., and thereby insufficient. On the other hand, sealing of the top and bottom of the same packaging containers takes place intermittently in connection with the product being filled into the container, which permits longer stay times in the sealing operation proper, and thereby makes for thermosealing by means of surface fusion between two PET layers.
Attempts have been made to overcome these difficulties in various manners, for example by employing a modified PET which facilitates thermosealing. From, for example, European Patent Application EP 0 237 235, it is known that glycol-modified PET, so-called PETG, may be thermosealed. However, a serious drawback inherent in this glycol-modified PET is that it results in a more brittle material layer with less flexibility and durability and is thus not as desirable in a packaging laminate as normal, amorphous, non glycol-modified PET. Moreover, nor can thermosealing take place using PETG at such high production speeds as are actually desirable.
One method of attempting to circumvent the difficulties of longitudinally sealing normal PET by means of thermosealing has been instead to seal the longitudinal lap joints by means of hot melt glue sealing, by applying a hot melt glue along one edge and then compressing it with the other edge in the lap joint between the two edges. However, it has not hitherto been possible to achieve rational sealing speeds using this technique. It has not hitherto been possible to use hot melt glue application at acceptable speeds, and serious problems have been encountered with large spillage of hot melt glue and with the fact that the application of the hot melt glue becomes uneven, with tacky outflows as a result. Another difficulty in the striving to produce a packaging container possessing superior aroma barrier properties is that such a hot melt glue sealed longitudinal joint is not durable in cold storage. Such a packaging container has thus not hitherto been capable of being stored for a lengthy period of time with good liquid-, gas-, and aroma barrier properties, because of the fact that the hot melt glue sealed longitudinal joint becomes untight.
In respect of liquid-, gas-, and aroma barrier properties, such incision edges of the sheet-shaped packaging blank which are freely exposed to the packed product create problems in that gas and liquid molecules, like non-polar flavour substances, are slowly absorbed in the packaging material through the thus freely exposed incision edges.
Another drawback is that configurationally stable, strong and durable packaging containers according to the prior art technology normally require larger quantities of the materials included in the package in order to achieve improved stability and improved barrier properties, despite lengthy cold storage, and thus command a higher price.
Hence, it has not hitherto been possible in the prior art technology, in a cost effective and rational manner to longitudinally joint seal and produce fold-formed packaging containers from sheet-shaped blanks of a paper-based packaging laminate with inside layers of PET which possess retained superior gas and aroma barrier properties also in the lengthy cold storage of liquid foods.
One object of the present invention is therefore to realise a novel packaging container of the type described by way of introduction without the attendant problems of the type intimately to the prior art technology.
A further object of the present invention is to realise a configurationally stable packaging container possessing superior gas and aroma barrier properties for packing and lengthy cold storage of liquid foods, from a sheet-shaped blank of a packaging laminate.
One particular object of the present invention is to realise a fold-formed packaging container which, in terms of material consumption and production process, is cost effective and which, also during lengthy cold storage of liquid foods, maintains good configurational stability and good gas and aroma barrier properties.
Yet a further object of the present invention is to realise a simple and rational method of producing a packaging container possessing superior lengthy cold storage properties according to the present invention.
The point of departure for attaining the desired aroma barrier properties in a packaging container for lengthy storage of liquid foods is thus a packaging laminate comprising an inside layer, i.e. that layer which is turned to face inwards in a packaging container produced from the packaging laminate, for direct contact with packed product, possessing superior aroma barrier properties, such as polyester, suitably PET, and preferably amorphous PET. Certain current process-facilitating additives employed in the prior art technology may be added to amorphous PET for facilitating extrusion and application of such a film or layer of PET.
Suitable core layers in packaging laminates for packaging containers according to the invention consist of paper or paperboard of suitable packaging quality.
To obtain superior gas barrier properties for protecting the packed product, such as, for example, the vitamin C content of orange juice, a separate layer is required of a material possessing superior gas barrier properties. Polymer gas barrier materials are today most desirable in the new development of packaging materials, since, from both the point of view of recycling and the environment, and from the point of view of costs, they are deemed to be preferable. Well-known polymer gas barrier materials are, for example, polyamide (PA) or copolymers of ethylene and vinyl alcohol (EVOH). The most preferred material alternative for the packaging container according to the pertinent invention is polyamide or a mixture of different polyamides because of their excellent gas barrier properties and inherent material rigidity. Mixtures of substantially polyamide and PET or EVOH are well-functioning gas barrier alternatives in a packaging container according to the present invention.
A further surprising advantage with a packaging laminate including an inner layer of PET and a gas barrier layer of substantially PA is that such aroma and gas barrier layers independently make considerable contributions to the total rigidity of the packaging laminate and that the rigidity of the core layer is, as a result, not as critical. By optimising the material quantity in the core layer and each respective barrier layer, a cost effective packaging laminate can be obtained given the qualitative advantages which are achieved at the same time. It has surprisingly proved that, when a PET layer with a grammage of approx. 18-30 g/m2 is combined with PA layer with a grammage of approx. 5-15 g/m2, it is possible, with retained overall rigidity, to employ a xe2x80x9cweakerxe2x80x9d and therefore cheaper paper for the core layer. By such means, the rigidity of the paper core layer may be reduced from 360 mN to between 280 and 340 mN. A preferred paper core layer according to the invention thus has a rigidity of approx. 280-340 mN, preferably approx. 290-330 mN.
Preferably, the PET layer has a grammage of approx. 18-25, most preferably approx. 20 g/m2 for optimum aroma barrier properties, which, in measurement tests, has been defined as an at least 90% retention of D-limonen in the packed product. The grammage should preferably not be less than 20 g/m2, but the aroma barrier layer functions well even at approx. 18 g/m2.
The gas barrier layer is thus constituted preferably by PA and is then applied preferably in a quantity of approx. 8-12 g/m2, most preferably approx. 10 g/m2, which gives optimum gas barrier and rigidity properties.
The gas barrier layer may be laminated to the core layer by means of an interjacent layer of LDPE and/or an adhesive layer of an adhesive polymer, such as, for example, an acid-modified polyethylene. For example, adhesives of the type maleic acid anhydride-modified polyethylene function very well according to the invention. Preferably, the gas barrier layer is laminated to the core layer by means of a lamination layer of LDPE most proximal the core layer and an adhesive layer between the LDPE layer and the gas barrier layer, for obtaining optimum adhesion and laminate strength. However, it is also conceivable, depending on the quality and properties of the polyamide layer, that this is applied direct on the core layer by means of extrusion.
Preferably, the inside/aroma barrier layer is laminated to the gas barrier layer with the aid of an interjacent adhesive layer of the same type of acid-modified polyethylene.
On the outside of the packaging laminate, i.e. that side which forms the outside of a packaging container produced from the packaging laminate, a layer of a thermosealable polymerxe2x80x94preferably LDPExe2x80x94is suitably applied.
With a view to achieving the requisite superior gas and aroma barrier properties in lengthy cold storage of the packaging container according to the present invention, it is important to protect the incision edges of the sheet-shaped packaging blank from contact with the packed product in the packaging container. This may be put into effect in different, per se known manners, for example by applying separate protective strips over the incision edges. Since the problem with difficultly sealable PET layers remains unsolved, the covering of the incision edges with separate strips is not a good solution.
By, instead, splitting and partly removing, by so-called xe2x80x9cskivingxe2x80x9d, the longitudinal edge of the sheet-shaped packaging laminate blank which is on the inside of a container produced from the packaging blank, i.e. the inner edge, for the formation of a projecting strip of half of the thickness of the packaging laminate including the inside layer of PET and folding back and sealing the projecting strip against the outside of the packaging laminate, the incision edge is concealed behind the outer edge (see FIG. 2) and, thus, does not come into contact with the packed product. The skived and double folded strip is sealed against the outer overlapping edge""s PET inside, which avoids the situation that incision edges and other material than PET come into direct contact with the packed product in the longitudinal joint region of the inside of the packaging container.
The skived and double folded strip including the inside layer of PET is sealed to the outside of the inner edge partly by means of thermosealing along a narrow region in which the outermost longitudinal edge of the strip meets the non-skived outside layer of LDPE of the packaging laminate, and partly in that the hot melt glue applied for the longitudinal joint sealing flows out to the outermost edge of the strip and seals this against the unsplit packaging laminate in the inner edge.
The top and bottom portions of the packaging container are also fold formed in such a manner that exposure of incision edges to the packed product is precluded. One example of possible top and bottom fold formation techniques according to the invention is represented by a gable top package of the xe2x80x9cTetra Rexxe2x80x9d(copyright) type. In order to avoid incision edge exposure in the fold formed bottom in such a packaging container, one of the bottom panels may, in a per se known manner, be provided with a small projection which may be folded outwards towards the outside of the packaging container and sealed in beneath the outermost bottom panel in order to turn the incision edge outwards away from the inside of the packaging container.
By, for example, such methods of skiving and panel folding, a packaging container is obtained in which all contact surfaces vis-à-vis the packed product on the inside of the filled and sealed container consist of the outer layer of PET.
The above-described packaging laminate, intended for a packaging container according to the present invention, is preferably produced by multilayer co-extrusion of two or more of the gas barrier layer, the adhesive layers and the aroma barrier layer on the one side of the core layer. It is naturally also possible to prefabricate a film of the inside layer of the packaging laminate which is laminated to a core layer or an LDPE-coated core layer. According to one preferred manner of manufacture, all layers are co-extruded on the inside of the packaging laminate by means of a five-layer extrusion nozzle on the core layer. According to another preferred manner of manufacture, the gas barrier layer, the adhesive layers and the aroma barrier layer may be co-extruded as four layers on a core layer coated with LDPE. According to an alternative, preferred manner of manufacture, it is possible to apply the gas barrier layer, the polyester layer and an interjacent adhesive layer by means of co-extrusion direct on the core layer.
The skived and double folded edge is sealed against the overlapping outer edge""s inside with the aid of a hot melt glue possessing superior application, gluing and tightness properties, these properties being thoroughly retained even after lengthy cold storage, i.e. storage at refrigeration temperatures of approx. 4-8xc2x0 C. for at least six weeks. A suitable hot melt glue for the present invention must provide good adhesion to different substrates and good resistance to cold, i.e. be flexible even at low temperatures. In the practical application according to the invention, it is thus desirable that the hot melt glue does not become brittle and lose its tacky and adhesion capabilities at cold storage temperatures, i.e. at approx. 4-8xc2x0 C., even after a time as long as at least six weeks. At the same time, it is necessary that the glue has a high so-called tacking point and high viscosity in order to give sufficiently good adhesion properties to PET which in turn means that the molten glue must be applied at a relatively high temperature. Furthermore, a high tacking or softening point ensures that the longitudinal hot melt sealing joint will not be negatively influenced by the high sealing temperature of the subsequent intermittent transverse, or top and bottom, heat sealing operation, by re-melting or re-softening of the hot melt in the joint. A well-functioning example of such a hot melt glue is based on a copolymer of ethylene and vinyl acetate (EVA) in a composition with a tackifying rosin ester resin, the hot melt glue having a preferred thermal viscosity (xe2x80x9cThermoselxe2x80x9d) of approx. 30000-40000 cp, more preferably 36500 cp at 190xc2x0 C. (375 F) (27/5.0) (alternatively less preferably, a Thermosel viscosity of approx 60000 cp at 177 C (350 F) (27/2.5) or approx. 25000 cp at 204 C (400 F) (27/5.0)), and a plasticising or softening temperature at approx. 80-100xc2x0 C., preferably approx. 90-100xc2x0 C. Preferably, for sake of optimal properties at cooling temperature, the hot melt composition comprises 50-70% by weight of EVA, 20-40% by weight of rosin ester resin and 5-15% by weight of a synthetic plasticising polymer, which has a similar type of plasticising effect as mineral oil, and has a density of about 0.96-0.98, more preferably about 0.97-0.98 g/cm3.

Packaging container for the cold storage of liquid foods and a method of producing the packaging container


An enclosure for sheltering a small aircraft, provides an arcuate roof frame supported by a base frame. The roof frame has a fixed roof portion engaging a movable roof portion and a crank system for adjusting the position of the movable roof. Wing cushions contact the wings of the small aircraft as it is backed into the enclosure and assure that the craft is properly placed. The fixed and movable roof portions are mutually engaged by a rolling clamping system enabled for directing arcuate motion of the movable roof portion relative to the fixed roof portion. A spring-biased awning is engaged with the movable roof portion and extends forwardly. A fabric cover is mounted between the fixed and movable roofs so as to deploy the fabric cover when the movable roof portion is extended.

1. Field of the Invention
This invention relates generally to light weight and portable shelters and more particularly to an enclosure for sheltering a small aircraft.
2. Description of Related Art
The following art defines the present state of this field:
Ahlborn, U.S. Pat. No. D75,199 relates to the ornamental design for an airplane hanger.
Clark, U.S. Pat. No. D138,436 relates to the ornamental design for an implement shed.
Goodrich, U.S. Pat. No. 1,350,493 describes a knock down building, including joists, supports, and a connecting member for securing the supports to the joists comprising a body portion, wings extending along the longitudinal edges of the body portion and bent at right angles thereto to form a socket for the reception of the end of a joist and spaced apart wings at one end of the body portion bent at right angles thereto and spaced from the first mentioned wings and lying in a plane at right angles to the planes of said first wings and forming a socket for the reception of the end of the supports.
Merritt, U.S. Pat. No. 2,532,456 describes an in door construction, a door member, an inwardly projecting frame carried by said door member, means for pivotally mounting the inner end of said frame for swinging movement about a horizontal axis, and arcuate extension movably bodily with said door member and forming a component part thereof, a vertically disposed cantilever-type supporting post structure having one end thereof secured to a stationary foundation and disposed immediately adjacent to said door member extension in concentric relation about the axis of turning movement of said door member, an arcuate guide formed by said post structure, antifriction devices carried by said extension and engageable in the guide of said post structure, and counterbalancing means for said member carried by said extension.
McKee et al., U.S. Pat. No. 2,610,366 describes a building having a wall formed substantially horizontally disposed cylinder, said wall having an opening to form a doorway therein, a door for closing said opening, said door also being formed as a portion of a cylinder and being located within said building and behind said wall, said door being sufficiently rigid to be self-supporting, a single horizontal pivot to the rear of said door and adjacent each end thereof, supports for said pivots, a pair of arms attached to the door at each end thereof and rotatably mounted on the adjacent pivot whereby said door can be swung into an overhead position about an axis established by said pivots, sealing means on the peripheral edges of the front face of said door and cooperating curved jambs bordering said doorway opening, the vertically extending peripheral edges of said door and said sealing means conforming in curvature to the curvature of the jambs to adapt the door to be brought into sealing engagement with said jambs when the door is in its lowermost position, one arm of each pair being shorter than the other whereby said pivots are eccentrically located relative to the axis of curvature of said doorjamb so as to break the bond between said sealing means and said jamb upon initial upward movement of the door from closed position.
McKee et al., U.S. Pat. No. 2,664,597 describes a counterbalanced door for a building having a wall formed substantially as a portion of a substantially horizontally disposed cylinder, and wherein the wall has an opening to form a doorway therein, said door being located within the building and behind said wall, said door being sufficiently rigid to be self-supporting and having rearwardly extending A-shaped supporting arms at opposite ends thereof, said arms having horizontal pivot points adjacent their apices whereby said door can be swung into an overhead open position about an axis established by said pivot points, a pair of counterweights, a cable attached to each counter weight, and overhead pulley for each cable, and means attaching each cable to one of said arms intermediate its apex and said door, said means being constructed so that the total weight of the counterweights multiplied by their effective lever arm about said pivotal axis is equal to the total weight of the door times its effective lever arm about said pivotal axis for all positions of the door.
Younger, U.S. Pat. No. 2,837,780 describes an airplane hangar having a floor level and a door opening above said floor level, a door panel adapted to register with said opening when said panel is closed, a compartment below said floor level for receiving said panel when the latter is open, said door panel being curved along its vertical extent to a circular arc, said panel being provided with a rigid extension extending into said compartment when said panel is closed, a pair of rollers in said compartment and respectively engaging opposite side of said extension for providing a couple resisting the couple due to the action of gravity on said panel when said panel is closed, means for swinging said panel through its circular arc about the center of curvature of said panel between said open and closed positions with said rollers in rolling engagement with said panel at all times.
Ray, U.S. Pat. No. 3,766,691 describes a swimming pool enclosure comprising a plurality of arched supporting beams which extend from ground level up over an area to be enclosed, and a series of panel members arranged between each adjacent pair of supporting beams and hinged to one another for movement along such beams between extended enclosing positions and retracted open positions, the panels in the latter positions being folded and stacked relative to one another.
Pierce, U.S. Pat. No. 3,818,652 describes a portable apparatus for shelter and protection of small airplanes which may be utilized with standardized mooring ring arrays existing at small craft mooring areas of airports. The apparatus is of inexpensive, light-weight pre-fabricated design such that it is capable of rapid assembly and disassembly, ease of tranport, yet strudy weather-resistant stability; the components of the pre-fabricated structure are constructed along essentially planar design with rectangular/parallel bracing, and in assembled form they constitute a main housing for receiving the fuselage of the airplane and oppositely extending wind coverage nacelles extending on each side of the main housing in position to receive the wings of the airplane. The structure is readily adaptable to receive any of the many types of small aircraft or it may be converted with aid of special accessory structure to receive the larger twin engine aircraft.
Brown, U.S. Pat. No. 4,014,133 describes a greenhouse structure for growing vegetables, flowers, and like plants inside under good conditions particularly in the fall, winter, and early spring portions of the year includes a building structure having a rear wall and opposite end walls and a roof defining an enclosed space having an open front side and a closure member movable between an open position and a closed position with the closure member being adapted to close the open front side of the building structure. Power means are operatively connected to the closure member for moving same between the open position and the closed position in response to temperature measurement within the building structure for controlling some growing conditions of the plants.
Kumode, U.S. Pat. No. 4,175,361 describes an openable canopy housing having a series of movable, telescoping transparent arched panels which form the combination roof and sides. Part of the roof of the housing is formed by a horizontal beam which runs the length of the structure. The transparent panels can be selectively opened or closed to provide a structure which can be used for indoor as well as outdoor use.
Milinic, U.S. Pat. No. 4,280,306 describes a convertible tennis-court enclosure, comprising a plurality of parallel supporting beams and two closure elements between two of the supporting beams to be extended simultaneously along the supporting beams, each element including a series of purlins arranged to slide on the supporting beams and connected in two""s by a portion of a canvas fixed to the purlins, of which the length is equal to half that of the beams.
Kyner, Jr., U.S. Pat. No. 4,542,759 describes a geodesic type shelter having the shape of a semi-ellipsoid of revolution having a large opening in one side and being constructed of elements which are all removably connected together so that it is particularly useful as a portable airplane hangar.
Taylor, U.S. Pat. No. 5,507,121 describes a garage generally comprises a pair of side walls that are vertical, parallel and semi-circular, and a peripheral wall spanning between the periphery of the side walls to form an enclosure. The peripheral wall includes a front door and a rear door. Front and rear door support paths are located on the inside of each side wall near the wall""s peripheral edge. Each door path is parallel, semi-circular and supports a side edge of a door. The front and rear door paths are of different radius such that the door panels may overlap. Latching mechanisms, located at approximately midway up on the marginal side of each side wall are moveable to a latching position connecting a door to side walls such that the door cannot slide and such that the door prevents the side walls from outward movement at that location.
Meyer, WO 98/06625 describes a sound proof hangar for airplanes with a wide entrance for aircraft. To provide a sound barrier at the open side, the entrance opening is limited, at least on one side, by a series of deflecting surfaces, the inner edges of which are directed, in horizontal section towards the hangar interior and the external edges of which are directed laterally. The deflecting surfaces can be moved between a closed position which partly or completely closes the entrance opening and a position which opens the entrance opening.
The prior art teaches a variety of enclosures and hangers and especially doors for such, knock-down buildings, portable structures, and especially teaches arcuate door structures. However, the prior art does not teach a structure as herein disclosed and claimed having advantages as described in the following summary.
The present invention teaches certain benefits in construction and use which give rise to the objectives described below.
The present invention is an enclosure for sheltering a small aircraft, and provides an arcuate roof frame supported by a base frame. The roof frame has a fixed roof portion engaging a movable roof portion and a crank system for adjusting the position of the movable roof. Wing cushions contact the wings of the small aircraft as it is backed into the enclosure and assure that the craft is properly placed. The fixed and movable roof portions are mutually engaged by a rolling clamping system enabled for directing arcuate motion of the movable roof portion relative to the fixed roof portion. A spring-biased awning is engaged with the movable roof portion and extends forwardly. A fabric cover is mounted between the fixed and movable roofs so as to deploy the fabric cover when the movable roof portion is extended.
A primary objective of the present invention is to provide a shelter or enclosure for small aircraft having advantages not taught by the prior art.
Another objective is to provide such an invention having a relatively small footprint.
A further objective is to provide such an invention manufacturable at low cost.
Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.

Portable shade shelter for small aircraft


Isopycnic or asymmetric mixed matrix hollow fiber membranes for gas separation can be made by a continuous spinning process. Mixed matrix membranes are characterized by a continuous phase of selectively gas permeable polymer in which are uniformly dispersed discrete absorbent particles such as molecular sieves that also have selectivity enhancing properties. The fibers can be monolithic in which the fiber wall is entirely mixed matrix, or composite in which an active mixed matrix layer is positioned adjacent to a supporting substrate layer. The novel mixed matrix hollow fiber membranes provide higher selectivity than dense film membranes of the continuous phase polymer.

This invention relates to a spinning process for making hollow fiber membranes that are used in gas separation processes. More specifically, it relates to a process for spinning hollow fibers having mixed matrix membrane compositions.
The use of selectively gas permeable membranes to separate the components of gas mixtures is a well developed and commercially very important art. Such membranes are traditionally composed of a homogeneous, usually polymeric composition through which the components to be separated from the mixture are able to travel at different rates under a given set of driving force conditions, e.g. transmembrane pressure and concentration gradients.
Gas separation membranes are provided in various forms such as flat, spiral wound and pleated sheets and tubes. The hollow fiber membrane module is a commercially preferred form of gas separation membrane equipment because it presents an extremely large gas transfer area per unit volume and especially per unit of module cross section area. The basic element of such a module is a very small diameter hollow fiber comprising a selectively gas permeable material. Typically hundreds or thousands of the hollow fibers are aligned substantially parallel to each other in bundles and positioned within a cylindrical housing to form a module. The ends of the bundles are xe2x80x9cpottedxe2x80x9d usually in a polymeric resin and the fiber ends are kept open. The module is thus structured much like a conventional tube and sheet style fluid heat exchanger. U.S. Pat. No. 3,339,341 to J. M. Maxwell et al. the entire disclosure of which is hereby incorporated herein by reference provides a thorough description of the structure of certain hollow filament membrane modules.
Many embodiments of gas separation membrane modules use fibers of asymmetric structure in which the selectively gas permeable material forms an ultra-thin fiber skin that ideally fully covers the gas transfer area, i.e., the external generally cylindrical surface of the fiber. The skin is the active gas separation portion of the fiber.
In other embodiments, the hollow fibers can be a composite structure in which the selectively gas permeable material is in a layer on one surface of a microporous substrate material layer. The separating material can be in the form of an ultra thin dense layer or an asymmetric layer. The separating material can be deposited either on the outside surface of the fiber or the inside surface of the fiber.
A relatively recent advance in this field utilizes mixed matrix membranes. Such membranes are characterized by a heterogeneous, active gas separation layer comprising a dispersed phase of discrete particles in a continuous phase of a selectively permeable polymeric material. The dispersed phase particles are microporous materials, such as zeolites, carbon molecular sieves and other molecular sieve materials, that have discriminating adsorbent properties for certain size molecules. Chemical compounds of suitable size can selectively migrate through the pores of the dispersed phase particles. In a separation of gases involving a mixed matrix membrane, the dispersed phase material is desirably selected to provide separation characteristics which provide improved permeability and/or selectivity performance of the mixed matrix membrane relative to that of a homogeneous polymeric membrane of the continuous phase material.
The fabrication of hollow fibers for gas separation modules typically involves extruding the nascent fiber through narrow channel extrusion dies, occasionally called xe2x80x9cspinnerettesxe2x80x9d, at very high shear rates. The manufacture of mixed matrix hollow fibers also normally calls for axially drawing the nascent fibers to provide them with precise and uniform cross section dimensions. For these and other reasons, the production of hollow fiber mixed matrix is highly problematic and conventional hollow fiber membranes do not utilize mixed matrix compositions. It is very desirable to provide hollow fiber which utilize mixed matrix compositions for the active gas separation membrane portion of the fiber so as to obtain better permeance and selectivity than polymer-only membrane compositions.
Accordingly there is now provided a process for making mixed matrix hollow fiber membrane for gas separation comprising,
(A) providing a spinnerette adapted to extrude at least one nascent hollow fiber,
(B) feeding a bore fluid through the spinnerette to form a cylindrical fluid stream for each hollow fiber,
(C) feeding through the spinnerette to an annular channel surrounding the fluid stream for each hollow fiber a suspension comprising molecular sieve particles uniformly dispersed in a polymer solution comprising a selectively gas permeable polymer and a solvent for the selectively gas permeable polymer, and
(D) immersing the nascent hollow fiber in a coagulant for a duration effective to solidify the selectively gas permeable polymer, thereby forming a monolithic mixed matrix membrane hollow fiber.
This invention also provides a process as just described which further comprises feeding through the spinnerette to a second annular channel surrounding the fluid stream for each hollow fiber a core polymer solution comprising a core polymer dissolved in a core solvent, thereby depositing a nascent annular core layer of core polymer solution around the bore fluid stream and a nascent annular sheath layer of the suspension around the nascent annular core layer, to form a nascent composite mixed matrix membrane hollow fiber, in which the nascent composite mixed matrix membrane hollow fiber is immersed in a coagulant for a duration effective to solidify the core polymer and the selectively gas permeable polymer, thereby forming a composite hollow fiber having an inner polymer core and an outer mixed matrix membrane sheath.
There is further provided a mixed matrix hollow fiber membrane for gas separations comprising a monolithic annular wall comprising a continuous phase of a selectively gas permeable polymer and a discrete phase of selectively gas permeable molecular sieve particles uniformly dispersed throughout the continuous phase in which the weight ratio of selectively gas permeable molecular sieve particles of the discrete phase to selectively gas permeable polymer of the continuous phase is within the range of about 0.05-0.4.
Yet additionally the invention provides a mixed matrix composite hollow fiber membrane for gas separations having an annular core comprising a core polymer and an annular, mixed matrix sheath externally adjacent to the core, in which the sheath comprises a continuous phase of a selectively gas permeable polymer and a discrete phase of selectively gas permeable molecular sieve particles uniformly dispersed throughout the continuous phase in which the weight ratio of selectively gas permeable molecular sieve particles of the discrete phase to selectively gas permeable polymer of the continuous phase is within the range of about 0.05-0.4.
The invention still further provides a method of separating components of a gas mixture utilizing a hollow fiber gas separation module having a tube side and a shell side, the method comprising feeding the gas mixture through the tube side or the shell side of the hollow fiber gas separation module and withdrawing a permeate gas mixture from the shell side or tube side, in which the module comprises a plurality of mixed matrix hollow fiber membranes each of which comprises a monolithic annular wall comprising a continuous phase of a selectively gas permeable polymer and a discrete phase of selectively gas permeable molecular sieve particles uniformly dispersed throughout the continuous phase and in which the weight ratio of selectively gas permeable molecular sieve particles of the discrete phase to selectively gas permeable polymer of the continuous phase is within the range of about 0.05-0.4.
In a particular aspect of the invention the nascent fiber is drawn from the spinnerette through an air gap and a liquid coagulation bath at a draw ratio of about 1-6 to produce a monolithic or composite asymmetric hollow fiber mixed matrix membrane having an outer diameter of about 100-500 xcexcm.
This invention is directed to the manufacture of hollow fibers that are suitable for use in multiple fiber gas separation modules. Such fibers are generally tubular in form and have an outside diameter of about 75 to about 1000 xcexcm, preferably about 100 to about 500 xcexcm, more preferably about 100 to about 400 xcexcm, and most preferably about 125 to about 250 xcexcm. The wall thickness can be in the range of about 25 to about 300 xcexcm, and preferably about 25 to about 75 xcexcm. Preferably the diameter of the bore, i.e., the inner diameter of the fiber is about one-half to about three-quarters of the outside diameter and will preferably lie in the range of about 50 to about 200 xcexcm and more preferably about 60 to about 150 xcexcm.
In one embodiment of gas separation hollow fibers, the fiber is monolithic. By xe2x80x9cmonolithicxe2x80x9d is meant that the whole of the fiber wall is a single element, sometimes referred to as a layer. The wall structure can be completely nonporous such that the entire wall thickness is selectively gas permeable. For many practical reasons, primarily that the flux associated with completely nonporous walled fibers is very low, asymmetric wall structure is preferred. Asymmetric walled hollow fibers are characterized by a thin, nonporous, selectively gas permeable skin at one surface of the fiber and a porous, less dense structure adjacent the skin. Usually, porosity increases and density decreases with radial distance from the skin. The skin is frequently on the outside of the fiber but alternatively can be on the inside. The thickness of the skin is usually less than about {fraction (1/10)}th of the wall thickness.
In a preferred embodiment, the hollow fiber has a multilayer structure comprising a porous substrate and a layer of selectively gas permeable composition adjacent to the substrate. This type of hollow fiber is referred to as a xe2x80x9ccompositexe2x80x9d fiber. The substrate provides structural integrity for the selectively gas permeable layer which is usually much thinner than the substrate. The pores of the substrate provide an unrestricted path for the permeating components of the gas mixture being separated and thus do not appreciably reduce transmembrane flux. The substrate is also frequently much less expensive than the selectively gas permeable material and accordingly, using a substrate reduces the cost of the membrane module without negatively affecting separation performance.
A diverse variety of polymers can be used for the substrate. Representative substrate polymers include polysulfone, polyether sulfone, polyamide, polyimide, polyetherimide, polyesters, polycarbonates, copolycarbonate esters, polyethers, polyetherketones, polyvinylidene fluoride, polybenzimidazoles, polybenzoxazoles, cellulosic derivatives, polyazoaromatics, poly(2,6-dimethylphenylene oxide), polyarylene oxide, polyureas, polyurethanes, polyhydrazides, polyazomethines, cellulose acetates, cellulose nitrates, ethyl cellulose, brominated poly(xylylene oxide), sulfonated poly(xylylene oxide), polyquinoxaline, polyamideimides, polyamide esters, blends thereof, copolymers thereof, substituted materials thereof and the like. This should not be considered limiting since any material which can be fabricated into an anisotropic substrate membrane may find utility as the substrate layer of the present invention. Preferred materials for the substrate layer include polysulfone, polyethersulfone, polyetherimide, polyimide and polyamide compositions.
The continuous phase polymer for the gas separating layer is usually chosen to provide high flux and selectivity with respect to components of a gas mixture which is desired to be separated. The range of gas mixtures suitable for separation by selectively permeable membranes is too broad to describe. Some gas mixtures which present a high degree of industrial utility include, for example, He/N2, O2/N2, CO2/CH4 and H2/CH4. Many other gas mixture compositions can be used.
A wide range of polymeric materials have desirable selectively gas permeating properties and can be used as the continuous phase polymer gas separating layer. Representative materials include polyamides, polyimides, polyesters, polycarbonates, copolycarbonate esters, polyethers, polyetherketones, polyetherimides, polyethersulfones, polysulfones, fluorine-substituted ethylene polymers and copolymers such as polyvinylidene fluoride, tetrafluoroethylene, copolymers of tetrafluoroethylene with perfluorovinylethers or with perfluorodioxoles, polybenzimidazoles, polybenzoxazoles, polyacrylonitrile, cellulosic derivatives, polyazoaromatics, poly(2,6-dimethylphenylene oxide), polyphenylene oxide, polyureas, polyurethanes, polyhydrazides, polyazomethines, polyacetals, cellulose acetates, cellulose nitrates, ethyl cellulose, styrene-acrylonitrile copolymers, brominated poly(xylylene oxide), sulfonated poly(xylylene oxide), tetrahalogen-substituted polycarbonates, tetrahalogen-substituted polyesters, tetrahalogen-substituted polycarbonate esters, polyquinoxaline, polyamideimides, polyamide esters, blends thereof, copolymers thereof, substituted materials thereof, and the like. In addition, suitable gas separating layer membrane materials may include those found useful as the dense separating layer of composite gas separation membranes. These materials include polysiloxanes, polyacetylenes, polyphosphazenes, polyethylenes, poly(4-methylpentene), poly(trimethylsilylpropyne), poly(trialkylsilylacetylenes), polyureas, polyurethanes, blends thereof, copolymers thereof, substituted materials thereof, and the like. It is further anticipated that polymerizable substances, that is, materials which cure to form a polymer, such as vulcanizable siloxanes and the like, may be suitable gas separating layers for the multicomponent gas separation membranes of the present invention. Preferred materials for the dense gas separating layer include aromatic polyamide and aromatic polyimide compositions.
Preferred aromatic polyimides for the gas separating layer are disclosed in U.S. Pat. No. 5,085,676, especially at column 4, line 22 through column 7, line 27. Preferred substrate polymers and continuous phase polymers are also described in detail in U.S. Pat. No. 5,085,676, the entire disclosure of which is hereby incorporated herein by reference.
The hollow fiber structure for use in this invention can include a monolithic mixed matrix structure in which the single layer of the fiber comprises the discrete absorbent particles dispersed in the continuous phase polymer. When an asymmetric monolith is used, the discrete particles may be dispersed throughout the monolithic layer, including the less dense portions thereof. To achieve desired results it is important that the discrete particles should be substantially dispersed uniformly in the skin formed by the continuous phase of the asymmetric membrane. For a composite membrane the discrete particles are preferably dispersed only in the active, selectively gas permeable polymer layer. The active layer can be a uniformly dense element or it can be an asymmetric element and the discrete absorbent particles should be dispersed in the active layer as described for a monolithic hollow fiber membrane.
The molecular sieve particle size should be small enough to provide a uniform dispersion of the particles in the suspension from which the mixed matrix membrane will be formed and also to obtain uniform distribution of the dispersed phase particles in the continuous phase of the mixed matrix membrane. The median particle size should be less than about 10 xcexcm, preferably less than 3 xcexcm, and more preferably less than 1 xcexcm. Large agglomerates should be reduced to less than about 10 xcexcm and preferably less than about 3 xcexcm. Very fine molecular sieve particles may be made by various techniques such as by choosing appropriate synthesis conditions or by physical size reduction methods well known to those of ordinary skill in the art, such as ball milling, wet-milling and ultrasonication. In some cases, the size reduction process, e.g., ultrasonication or wet-milling can be advantageously carried out at the same time as reaction of the molecular sieve with a monofunctional organosilicon compound in accordance with certain embodiments of this invention.
The preferred adsorbent materials utilized as the discrete phase particle in the present invention are molecular sieves. Molecular sieves exist in both natural and synthetic forms. They are well known in the art to encompass an extensive variety of species and are described in Atlas of Zeolite Structure Types W. M. Meier, D H Olson and Ch. Baerlocher, Zeolites 1996, 17 (A1-A6), 1-230 (hereinafter xe2x80x9cIZAxe2x80x9d), in Molecular Sieves: Principles of Synthesis and Identification, R. Szostak, Van Nostrand Reinhold, (1989), and in Zeolite Molecular Sieves, D. Breck, John Wiley and Sons, 1973, (Breck). Molecular sieves that are suitable for use in this invention are also disclosed in U.S. patent application Ser. No. 09/960,194, now U.S. Pat. No. 6,503,860 which is assigned to the same Assignee as this application and the complete disclosures of these references are hereby incorporated herein by reference. Zeolites are a subclass of molecular sieves based on an aluminosilicate composition. Non-zeolitic molecular sieves are based on other compositions such as aluminophosphates, silico-aluminophosphates and silica. Molecular sieves of different chemical compositions can have the same framework structure.
The zeolite framework structure has corner-linked tetrahedra with Al or Si atoms at centers of the tetrahedra and oxygen atoms at corners. Such tetrahedra are combined in a well-defined repeating structure comprising various combinations of 4-, 6-, 8-, 10-, and 12-membered rings. The resulting framework structure is one of regular channels and cages, which has a pore network that is useful for separation. Pore dimensions are determined by the geometry of the aluminosilicate tetrahedra forming the zeolite channels or cages, with nominal openings of 0.26 nm for 6-member rings, 0.40 nm for 8-member rings, 0.55 nm for 10-member rings and 0.74 nm for 12-member rings (these numbers assume ionic radii for oxygen). Those skilled in the art will recognize that zeolites with the largest pores being 8-member rings, 10-member rings, and 12-member rings are considered small, medium, and large pore zeolites, respectively. Pore dimensions are critical to the performance of these materials in catalytic and separation applications, since this characteristic determines whether molecules of certain size can enter and exit the zeolite framework. In practice, it has been observed that very slight decreases in ring dimensions can effectively hinder or block movement of particular molecular species through the zeolite structure.
Representative examples of zeolites are small pore zeolites such as NaA, CaA, Erionite, Rho, ZK-5 and chabazite; medium pore zeolites such as ZSM-5, ZSM-11, ZSM-22, and ZSM-48, and large pore zeolites such as zeolite beta, zeolite L, NaX, NaY, and CaY.
A useful type of molecular sieves is based on carbon. Carbon molecular sieves (xe2x80x9cCMSxe2x80x9d) are a special class of activated carbons, which have the ability to discriminate between molecules on the basis of size. Carbon molecular sieves are typically used to separate molecules based on differential rates of adsorption rather than on the differences in adsorption capacity. Unlike inorganic-oxide molecular sieves which have a well ordered crystalline structure, carbon molecular sieves are non-crystalline or amorphous. CMS can be prepared by pyrolysis of a variety of natural or synthetic polymer precursor materials as is well known in the art.
Another class of molecular sieves is characterized by AlO2 and PO2 units (AlPO4 or aluminum phosphates) of which at least some Al or P constituents optionally may be substituted by other elements such as Si (called silicoaluminophosphates or SAPO""s), or metals (called metallo-aluminophosphates or MeAPO""s) or combinations thereof (called metalloalumino-phosphosilicates or MeAPSO""s). These AlPO4, SAPO, MeAPO, and MeAPSO materials are crystalline and have ordered pore structures which accept certain molecules while rejecting others.
A particularly preferred type of molecular sieve used in the mixed matrix membrane of this invention is iso-structural with the mineral zeolite known as chabazite. That is, they are characterized by the chabazite framework structure designated as CHA by the IZA reference. The chabazite type (CHA) molecular sieves are distinguished by channels based on 8-member rings with about 3.8 xc3x85xc3x973.8 xc3x85 (0.38 nmxc3x970.38 nm) dimensions.
Additional illustrative examples of CHA type molecular sieves suitable for use in this invention include SSZ-13, SAPO-34, and SAPO-44. SSZ-13 is an aluminosilicate molecular sieve material prepared as disclosed in U.S. Pat. No. 4,544,538, the entire disclosure of which is hereby incorporated by reference.
Another type of molecular sieve suitable for use with this invention is silicalite. Silicalite is a hydrophobic, crystalline silica-based molecular sieve. Silicalite I can be prepared according to the procedure described in U.S. Pat. No. 4,061,724, the disclosure of which is hereby incorporated herein by reference.
A prominent feature of this invention is that the dispersion of discrete phase absorbent particles is uniform throughout the continuous phase despite high shear processing. Another key feature is reduced formation of voids between the continuous phase polymer and the discrete absorbent particles. In one aspect, the invention seeks to achieve these features by adhering the absorbent particles to the continuous phase polymer. Sometimes this is referred to as xe2x80x9ccompatibilizingxe2x80x9d the absorbent particles with the continuous phase polymer.
In one aspect of the invention, compatibility between sieve and polymer is achieved by treating the sieves with a monofunctional organosilicon compound in which this compound becomes bonded to the surface of the molecular sieve. This bonding occurs at only one of the four bond sites of the silicon atom in the compound. The monofunctional organosilicon compound also has one or more substituent moieties, occasionally referred to herein as xe2x80x9clinking groupsxe2x80x9d. These are groups which have affinity for the polymeric continuous phase or which chemically react with the polymer of the continuous phase. Hence, attraction between molecular sieve treated with monofunctional organosilicon compound and the continuous phase is enhanced. This reduces the formation of voids at the dispersed phase-continuous phase interface.
The term xe2x80x9cmonofunctionalxe2x80x9d emphasizes that the organosilicon molecule has a single tetravalent silicon atom to which only one silanol group of the molecular sieve can bond. The single functional group is sometimes referred to herein as a xe2x80x9cdisplaceable radicalxe2x80x9d. The monofunctional organosilicon compound can have other substituent groups which are functional in different ways. For example, the linking groups can bond or associate with the polymer. This monofunctional aspect of the organosilicon compound is designed to cause the organosilicon compound to attach to the surface of the molecular sieve in a mono-molecular thickness layer and preferably without substantial crosslinking between neighboring attached organosilicon compound molecules. Without wishing to be bound by a particular theory, it is contemplated that the monofunctional organosilicon compound attaches to the sieve largely without blocking the pores.
Polyfunctional organosilicon compounds can also provide desired interfacial adhesion. Polyfunctional compounds can block the molecular sieve pores, build up a network over the molecular sieve surface to an excessive thickness or otherwise interfere with the transport of the migrating molecules through the membrane. Nevertheless, polyfunctional compounds can be effective for enhancing interfacial adhesion in the mixed matrix. With rigorous control of reaction conditions, e.g., by scrupulously maintaining an anhydrous system, polyfunctional organosilicon compounds can form a mono-molecular layer of comparable morphology to that obtained readily by a monofunctional organosilicon compound.
Mixed matrix membranes having improved gas separation performance can be produced by using molecular sieve treated with the monofunctional organosilicon compound which permits the treated sieve particles to bond or associate with the continuous phase polymer. Broadly stated, the procedure for using the compound to join the sieve particles to the polymer includes two major steps. One involves reacting the monofunctional organosilicon compound at the site of the displaceable radical with free silanol on the molecular sieve surface. This step, often called xe2x80x9csilanationxe2x80x9d of the sieve, typically results in substitution of the displaceable radical of the compound by the silanol of the molecular sieve. A molecular sieve having been treated in this fashion may be said to be xe2x80x9csilanatedxe2x80x9d. The monofunctional organosilicon compound thus becomes chemically bonded to the molecular sieve particle via the single silicon atom formerly bonded with the displaceable radical.
The other major step relates to the interaction of the silanated molecular sieve particles with the continuous phase polymer. Two mechanisms for obtaining affinity between the silanated sieve and the polymer are contemplated. Firstly, the linking groups can react with the polymer to form direct chemical bonds therebetween. Alternatively, when the chemical compositions of the linking groups and the polymer are selected to be mutually attractive, the linking groups can associate with the polymer. For example, the linking groups and polymer can be populated with moieties which have mutually attractive polar or dipolar interactions. Affinity can also be attained by reacting or associating the linking groups with a monomer of the continuous phase polymer. That is, the linking groups are caused to react or associate with free monomer so that the sieve-monomer adduct has enhanced affinity for the polymer by virtue of the chemical compatibility of the monomer and the polymer. The step of joining the silanated molecular sieve to the polymer by either reacting or associating the linking groups with the polymer or monomer of the polymer is sometimes referred to herein as xe2x80x9csizingxe2x80x9d.
The term xe2x80x9cassociatexe2x80x9d is used here to mean that the linking groups and polymer have strong attraction but the bond is less than that which results from chemical reaction. A way to determine whether a linking group is suitable for associating with the polymer calls for silanating a molecular sieve with a monofunctional organosilicon compound having the candidate linking group substituted thereon. The treated sieve is then intimately mixed with the continuous phase polymer, usually by blending a dispersion of the sieve particles in a solvent with a solution of the polymer. After removing the solvent, the mixed matrix material is cross-sectioned by cryo-fracturing and then gold coated. The section is examined by scanning electron microscopy (xe2x80x9cSEMxe2x80x9d) at 10,000-20,000 power magnification. If no gaps are seen between the continuous phase polymer and the embedded particles, then the linking group is deemed to acceptably associate with the polymer for purposes of this invention.
In a preferred embodiment, the monofunctional organosilicon compound has chemical composition of the formula Si(XYR1R2) which also may be represented diagramatically by the following structure:
in which X is a displaceable radical,
Y is a linking group, and
R1 and R2 are each independently any radical other than a displaceable radical.
xe2x80x9cDisplaceable radicalxe2x80x9d means an active functional group capable of reacting with silanol groups on the molecular sieve such that X is displaced leaving the molecular sieve bonded to the monofunctional organosilicon compound at the Xxe2x80x94Si bond position. Preferably, the displaceable radical can be a halogen, a hydroxyl group, or an ester or alkoxy radical having from 1-8 carbon atoms. Any halogen, i.e., fluorine, chlorine, iodine, or bromine atom can be used. A representative ester is the acetoxy radical. Illustrative examples of alkoxy radicals of substituent X include methoxy, ethoxy, n-propoxy and t-butoxy radicals.
The chemical composition of Y will largely depend upon the composition of the continuous phase polymer. The linking group is selected for capability of reacting or associating with the polymer or a monomer of the polymer. Knowing the latter, one of ordinary skill in the art can identify functional groups that can react with the polymer or with a monomer of the polymer. Similarly, the likelihood that a functional group is able to associate with a particular polymer or monomer composition can be estimated by one of ordinary skill in the chemical arts. The usefulness of a particular candidate linking group to react or associate with the polymer can be verified by the method described above. Typical examples of Y which can be used with polymer of suitable co-reactivity include amino radicals, such as aminopropyl and aminophenyl, amido radicals, such as methacrylamido and ethacrylamido, ureido radicals, such as ureidopropylepoxy, epoxy radicals, such as epoxycyclohexyl and glycidoxypropyl, and isocyanoato radicals, such as cyanoethyl and cyanopropyl. R1 and R2 can be non-reactive hydrocarbon radicals including straight chain and branched alkyls, such as methyl, ethyl, n-propyl, isopropyl, n-butyl and t-butyl radicals. Optionally, R1, R2 or both can be a linking group. Illustrative of suitable monofunctional organosilicon compounds include the silanes 3-aminopropyldimethylethoxysilane (APDMS), 3-isocyanatopropyldimethylchlorosilane (ICDMS), 3-aminopropyldiisopropylethoxysilane (APDIPS) and mixtures thereof.
The silanation step for treating the molecular sieve according to this invention typically involves a chemical reaction to condense the monofunctional organosilicon compound onto the molecular sieve at silanol groups on the molecular sieve surface. Usually this is carried out in a suspension of the molecular sieves in a liquid medium of a solvent containing the dissolved compound.
The solvent utilized for the silanation medium is chosen primarily for its ability to dissolve the monofunctional organosilicon compound. It is also desirable that the compound and solvent can form a solution of viscosity which is satisfactory to permit easy mechanical or ultrasonic dispersion of the compound in the medium at desired solution concentrations and temperatures. Preferably temperature of the silanation reaction is about 15-80xc2x0 C., and more preferably about 25-50xc2x0 C. The concentration of the compound in solution is preferably about 0.1 to about 5 wt. % and more preferably about 1-2 wt. %. Representative solvents which can be used for dissolving monofunctional organosilicon compound having either alkoxy, hydroxyl or ester displaceable radicals according to this invention include ethanol, methanol, isopropanol, water and mixtures thereof. A preferred solvent is 95:5 ethanol:water solution. For halogen displaceable radicals, anhydrous aprotic solvents should be utilized. Tetrahydrofuran or toluene are representative. Anhydrous aprotic solvents should also be used when the monofunctional organosilicon compound contains hydrolytically unstable linking groups, such as cyano radicals.
The liquid medium ingredients can be agitated to form a completely miscible mixture. The organosilicon compound is added in amount in excess of the stoichiometric amount required to fully react with silanol groups on the molecular sieve to be treated. When the homogeneous liquid medium has been formed, the molecular sieve is added while maintaining the medium in a state of agitation effective to disperse the molecular sieve particles uniformly throughout the liquid. Heat can be applied prior to, during or after addition of the molecular sieve to attain reaction temperature. These conditions are maintained for a duration effective to substantially completely condense the monofunctional organosilicon compound onto the molecular sieve. For monoflmctional organosilicon compounds with alkoxy, hydroxyl or ester displaceable radicals, preferably the silanation reaction conditions are continued for about 1 to about 60 minutes. Silanation with compounds having halogen displaceable radicals may call for longer reaction time, i.e., up to about 24 hours, and preferably at a temperature near the boiling point of the solvent. After reaction is completed, the temperature of the reaction mass can be lowered to ambient and the treated molecular sieve particles are then filtered free of excess reactants and washed, preferably repeatedly, in clean solvent to remove trace residual reactants.
When the molecular sieve is silanated with an organosilicon compound having reactive linking groups, the linking groups coupled to the molecular sieve during the silanation step can be further reacted with monomer or polymer in the subsequent sizing step. Sizing step temperature is preferably in the range of about 35-200xc2x0 C., and more preferably about 120-160xc2x0 C. The reaction duration is usually about 30 to about 300 minutes. The particles can then be filtered free of excess reactants, washed, dried and stored for later use. This provides molecular sieve particles with monomer or polymer bound to the sieve surface by the organosilicon compound linkage.
In a preferred method of sizing the treated molecular sieves, filtered and cleaned particles of treated molecular sieve from the silanation step are suspended in fresh, dilute solution of about 0.2-5%, preferably about 0.5-1% continuous phase polymer. Representative solvents suitable for this polymer solution include N-methyl pyrrolidone, dimethyl acetamide, dioxane and mixtures thereof The treated molecular sieve particles are added to the dilute solution while maintaining the solution in a state of agitation effective to disperse the particles uniformly throughout the solution. Then this suspension is subjected to sizing step conditions mentioned above. Thereafter, if desired, the treated particles can be filtered, washed and stored as before.
In another aspect, the sizing step can be bypassed. This is an option when the monofunctional organosilicon compound contains reactive linking groups and the continuous phase polymer contains active sites to react with the linking groups under normal membrane formation temperature conditions.
Formation of the mixed matrix membrane is completed typically by dissolving the polymer for the continuous phase in a suitable solvent and dispersing the silanated or silanated-and-sized molecular sieve particles in the resulting polymer solution. The particles can be added to the solution as a powder or as a suspension in a liquid medium. The order of combining ingredients is not critical. In yet another optional process variation, if the reactive linking groups have not yet been reacted with monomer or polymer, the sizing step can be carried out at this time by raising temperature and holding while maintaining the particles dispersed in the reaction medium, as above.
Much attention of this disclosure has been directed to compatibilizing the discrete phase molecular sieve with the continuous phase polymer by using a monofunctional organosilicon compound. Moieties other than monofunctional organosilicon compounds can be used to achieve the desired compatibility and it should be understood that the present invention is not limited to silanation and sizing that involves such monoftmctional organosilicon compounds only. The composition of the compatibilizing agent utilized in any particular application will depend upon the chemical nature of the specific discrete and continuous phase materials. In circumstances for which the chemistry is suitable, the discrete phase molecular sieve particles may be intrinsically compatible with the continuous phase polymer. One of ordinary skill in the art applying the principles described herein should be well apprised of other compatibilizing agents and methods for using them. An example of non-monofunctional organosilicon compound compatibilizers that can be used is 3-aminopropylmonomethyldiethoxysilane (xe2x80x9cAPPMSxe2x80x9d).
Although materials selection and treatment represent an important aspect of this invention, processing the materials to fabricate hollow fiber membranes constitutes another important aspect. A typical procedure for producing a composite mixed matrix hollow fiber selectively gas permeable membrane according to this invention involves simultaneously coextruding a sheath suspension of mixed matrix composition and a core solution by utilizing a composite hollow fiber spinnerette design to form a nascent composite hollow fiber membrane which travels through an air gap into a nonsolvent coagulation bath, followed by windup on a drum, roll or other suitable device. Various additional steps such as, post treatment, packaging, and storage may be utilized. It should be noted that a monolithic, i.e., non-composite hollow fiber can optionally be fabricated as above by leaving out steps associated with forming the core solution.
The foregoing description merely juxtaposes certain basic elements. Exemplary conventional processes for producing non-mixed matrix composite hollow fibers are disclosed in U.S. Pat No. 5,085,676 and U.S. Pat. No. 5,141,642, the entire disclosures of which are hereby incorporated by reference herein. Hollow fiber mixed matrix membranes according to this invention can be produced by such conventional processes with modifications as are further described, below.
The composite hollow fiber membranes of this invention preferably comprise a thin outer sheath layer of asymmetric structure containing a selectively permeable continuous phase polymer and a molecular sieve material. The hollow fiber membranes further comprise a microporous polymeric core layer that structurally supports the sheath layer. The choice of the continuous phase polymer is primarily based on the intrinsic gas separation properties and the chemical compatibility of the polymer with the molecular sieve material. The choice of the core layer polymer is largely determined by its mechanical properties, compatibility with the continuous phase polymer of the sheath, and the ability to be processed into a microporous structure.
It is an advantageous feature of the present invention that the novel mixed matrix composite hollow fiber membranes which include discrete molecular sieve particles dispersed in the continuous phase polymer of the selectively permeable layer can be produced by using, basically conventional spinnerette designs. A number of different existing designs for spinnerettes adapted to extrude hollow fiber suitable for gas separation are known in the art. Suitable embodiments of the composite hollow fiber spinnerette designs are disclosed in U.S. Pat. No. 5,320,512 and aforementioned U.S. Pat. No. 5,141,642 the entire disclosures of which are hereby incorporated by reference herein.
In the novel composite hollow fiber spinning process, the mixed matrix suspension for the sheath and core solution may be subjected to high rates of shear, especially in the narrow spinnerette flow channels. Depending on the particular spinnerette design employed and the solution/suspension flow rates utilized, shear rates can reach many thousand reciprocal seconds. It is not unexpected for sheath suspension and core solution are to encounter shear rates in a broad range from about 100 secxe2x88x921 or less to about 50,000 secxe2x88x921 during fiber spinning. The microstructural stability of the suspension under applied shear stresses becomes very critical. Moreover, interparticle collision of molecular sieves, especially in converging flow fields, can promote agglomeration which can block the spinnerette channels and/or adversely affect performance of the membrane. The stability of the mixed matrix suspension can be evaluated by measuring the particle size distribution of the mixed matrix slurry prior to feeding to the spinnerette and at the spinnerette exit. If the distributions are substantially alike, the suspension is deemed to be sufficiently stable for use in the spinning process according to this invention.
Other processing factors that can profoundly affect shear stability of the suspension are the concentration of the dispersed phase particles in the suspension and the concentration of the dispersed phase particles relative to the concentration of the polymer in the suspension. The polymer concentration in the spinning solution should be maintained sufficiently high to provide for formation of a substantially completely defect-free integral skin during the spinning process. The upper limit for concentration of the polymer in the spinning solution is dictated by the viscosity of the solution and processing conditions. The upper limit for concentration of the dispersed phase particles is based on these same considerations, and in addition, on the shear stability of the resulting suspension under processing conditions. At higher dispersed phase particle concentration, the shear stress of the solution during processing can increase dramatically and this can cause shear instability of the dispersion. Within practical limits, it has been found that an optimum weight ratio of dispersed phase particles to continuous phase polymer in the suspension, and consequently, in the product membrane, is preferably within the range of about 0.05 to 0.4, and more preferably, about 0.1-0.25. At lower values than 0.05 weight ratio, the desired increase in selectivity resulting from the presence of the dispersed phase is significantly diminished. At higher values, the suspension tends to become unstable under fiber spinning conditions and this causes plugging of the fiber production equipment and/or excessive formation of defects in the separating layer of the fiber. This defect formation occurs as a result of agglomeration of dispersed phase particles or of void formation between the dispersed phase particles and the continuous phase polymer. The optimum ratio of dispersed phase particles to continuous phase polymer as well as the concentration of each within spinning solution for any particular hollow fiber spinning application depends upon such considerations as polymer composition and molecular weight; dispersed phase composition, particle size and particle size distribution; surface area of the dispersed phase particles; composition and fluid dynamic properties of the solvent; presence of additives; processing temperature; type of processing equipment, processing conditions and the like.
After leaving the spinnerette, the fiber velocity is accelerated in the air gap from the extrusion velocity at the spinnerette exit to a wind-up velocity which is determined by the speed of the wind-up device. The wind-up velocity is usually adjusted to elongate the fiber and to draw down the diameter of the nascent composite hollow fiber in the air gap to essentially the desired finished fiber diameter. During draw down the polymer chains of the fiber can also undergo extensional orientation. Upon entering the coagulation bath, the nascent fiber undergoes phase inversion and the fiber structure is thereby solidified before being wound up on the wind-up device.
A commonly used parameter for characterizing the degree of extensional deformation that the fiber experiences in the air gap is referred to as the xe2x80x9cdraw ratioxe2x80x9d. This is defined as the ratio of wind-up velocity to the average extrusion velocity. The average extrusion velocity is defined as the volumetric flow divided by the cross sectional area of the annular fiber channel. According to this definition, the fiber inner and outer dimensions are reduced with increasing draw ratio for a particular spinnerette geometry and total volumetric flow rate of bore fluid, core solution, and sheath suspension. Fiber deformation resulting from draw down is beneficial because it provides increased surface area for permeation per unit volume of the hollow fiber module. Another potential advantage is that the fiber mechanical properties may be enhanced due to the extensional orientation of the polymer chains.
Increasing draw ratio results in an increase in the fiber extensional stress profile in the air gap and an increase in the distance between the molecular sieve particles in the axial direction. It is anticipated that during extensional deformation the sheath suspension experiences extensional as well as shear stresses which may affect the polymer solution/molecular sieve interface.
Decreasing draw ratio on the other hand results in larger fiber diameters. In the limit, wind-up velocity approaches the so called free-fall spinning velocity at which the fiber elongates in the air gap only due to the force of gravity. During spinning at free-fall or low-draw ratio velocities, the nascent fiber experiences significantly reduced extensional stress and reduced polymer extensional orientation.

Process for making hollow fiber mixed matrix membranes

L""Air Liquide Societe Anonyme a Directoire et Conseil de Surveillance pour l""Etude et l""Exploitation des Procedes Georges Claude