be decreased. The effect of plasticizers on elastic modulus is dependent on both temperature and plasticizer concentration. Below a certain concentration, referred to as the crossover concentration, a plasticizer can increase the modulus of a material. The material's glass transition temperature will decrease, however, at all concentrations. In addition to a crossover concentration, a crossover temperature exists. Below the crossover temperature the plasticizer will also increase the modulus. Selection Over the last 60 years more than 30,000 different substances have been evaluated for their suitability as polymer plasticizers. Of these, only a small number – approximately 50 – are today in commercial use. Ester plasticizers are selected based upon cost-performance evaluation. The rubber compounder must evaluate ester plasticizers for compatibility, processibility, permanence and other performance properties. The wide variety of ester chemistries that are in production include sebacates, adipates, terephthalates, dibenzoates, glutarates, phthalates, azelates, and other specialty blends. This broad product line provides an array of performance benefits required for the many elastomer applications such as tubing and hose products, flooring, wall-coverings, seals and gaskets, belts, wire and cable, and print rolls. Low to high polarity esters provide utility in a wide range of elastomers including nitrile, polychloroprene, EPDM, chlorinated polyethylene, and epichlorohydrin. Plasticizer-elastomer interaction is governed by many factors such as solubility parameter, molecular weight, and chemical structure. Compatibility and performance attributes are key factors in developing a rubber formulation for a particular application. Plasticizers used in PVC and other plastics are often based on esters of polycarboxylic acids with linear or branched aliphatic alcohols of moderate chain length. These compounds are selected on the basis of many critieria including low toxicity, compatibility with the host material, nonvolatility, and expense. Phthalate esters of straight-chain and branched-chain alkyl alcohols meet these specifications and are common plasticizers. Ortho-phthalate esters have traditionally been the most dominant plasticizers, but regulatory concerns have led to the move away from classified substances to non-classified which includes high molecular weight ortho-phthalates and other plasticisers, especially in Europe. Antiplasticizers Antiplasticizers are polymer additives that have effect opposite to those of plasticizers. They increase the modulus while decreasing the glass transition temperature. Safety and toxicity Substantial concerns have been expressed over the safety of some polymer plasticizers, especially because some low molecular weight ortho-phthalates have been classified as potential endocrine disruptors with some developmental toxicity reported. Plasticizers can escape plastics due to migration and abrasion of the plastic