Modifiers can help compounders produce materials that exhibit the physical characteristics their customers seek.
Recycled plastics entering a second or third life face some challenges. Repeated exposure to heat, light and processing can degrade mechanical properties, such as impact resistance.
Modifiers can help compounders produce materials that exhibit the physical characteristics, such as stiffness and strength, their customers seek, and some even make processing easier. Modifier manufacturers include Milliken Chemical, Addivant and DuPont.
“We look frequently at impact modification,” says Kevin Cronin, vice president of sustainability and R&D at Ultra-Poly. The company is a recycler and compounder based in Portland, Pennsylvania, that deals primarily with polypropylene (PP), polyethylene (PE) and polyvinyl chloride (PVC).
Ultra-Poly blends in elastomeric polymers that add impact strength in a PP compound, Cronin says.
PP is used in a wide variety of applications, ranging from car bumpers to pharmaceutical vials. When used in car bumpers, high impact strength is important to prevent cracking. Recyclers and virgin PP compounders often add rubber to increase impact strength. However, adding too much rubber to PP can reduce stiffness and increase viscosity, possibly making it more difficult to process. In addition, rubber, depending on the source, can be significantly more expensive than PP.
That has led companies like Milliken Chemical, Spartanburg, South Carolina, to develop modifiers that can improve impact strength without negatively affecting, and even perhaps improving, processability and stiffness. Milliken has created a new modifier called DeltaMax.
The product is unique in its ability to help improve all three properties, Patel says.
Milliken’s DeltaMax allows recyclers to eliminate or reduce the amount of traditional impact modifiers they add, he says.
DeltaMax will be available in powder form and as masterbatch pellets. Milliken is working with several recyclers and auto manufacturers on the new performance modifier, and the company hopes to introduce it to the market later this year, Patel says.
Impact modifiers also are available for other types of plastics. Additives manufacturer Addivant, headquartered in Danbury, Connecticut, supplies an additive that is designed for recycled acrylonitrile butadiene styrene (ABS) and polycarbonate (PC).
Between 5 percent and 20 percent of Addivant’s RoyalTuf 372P20 is blended with recycled ABS or PC. “It is used to recover the lost impact properties as well as the lost weather-resistant properties,” Yun says.
Also known as nucleating agents, these additives most commonly are used in PP to enhance mechanical properties and improve molding productivity and transparency. Nucleating agents also can be used in polyesters, including polyethylene terephthalate (PET) and polybutylene terephthalate (PBT).
Milliken’s Hyperform nucleating agents work at a molecular level to improve the structure of the PP, its stiffness and its processing characteristics. The addition of a nucleating agent can allow recycled plastic to be used for applications that require high-grade or virgin resins.
Some nucleating agents also can reduce cycle times associated with processing plastics in injection molding, extrusion or thermoforming.
“The overall time to heat it and cool it is much shorter,” Patel says.
Milliken’s Hyperform HPN-20 E improves the impact strength and stiffness of PP while reducing shrinkage and warping. Hyperform HPN-68 L is designed to improve crystallization and to reduce processing times for PP, while Hyperform HPN 210 M is designed for use with PE in injection molding.
Surlyn is an ionomeric ethylene copolymer manufactured by DuPont. Jose Torradas, a senior technical consultant with the DuPont Performance Materials division of DuPont, Wilmington, Delaware, says it can fit under more than one category of modifiers.
Surlyn, a well-known nylon impact modifier, also can be used as a compatibilizer. Additonally, it can be used to compatibilize nylon or PET with polyolefins, such as low-density polyethylene (LDPE) or linear LDPE, according to DuPont. It is available in a range of grades, each with a different balance of properties.
The author is a senior staff reporter with Plastics Machinery Magazine. He can be contacted at bgeiselman@plasticsmachinerymagazine.com.