Plasticizers
According to the ASTM D-883 definition, a plasticizer is a material incorporated into a plastic to increase its workability, flexibility, or dispensability. The addition of a plasticizer may lower the melt viscosity, elastic modulus, and Tg. It should be relatively non volatile, non mobile, inert, inexpensive, nontoxic, and compatible with the system to be plasticized. The plasticizers are chemically and thermally stable organic solvents or low melting solids which when mixed with a polymer modifies its flow as well as the mechanical and electrical properties. Waldo Semon patented the use of tricresyl phosphate as a plasticizer for PVC in 1933.
This was later replaced by the less toxic di-2-ethylhexyl phthalate (DEHP), which is now the most widely used plasticizer. The worldwide production of plasticizer is approximately 3.2 million tons annually. Volume wise, about 90% of the plasticizers are used with PVC and PVC containing systems.
Plasticizers can be broadly classified into four types according to their chemical constitution; phthalates, aliphatic esters, phosphates and miscellaneous. The USEPA regulates many phthalates and adipates by methods 606, 506-1, and 8061. There is a balance between compatibility and migration. Generally, the larger the ester grouping the less the migration up to a point where compatibility becomes a problem and where compatibility now becomes the limiting factor. The development of plasticizers has been plagued with toxicity problems. Thus, the use of highly toxic polychlorinated biphenyls (PCBs) has been discontinued. Phthalic acid esters, such as DEHP, may be extracted from blood stored in plasticized
PVC blood bags and tubing. These problems have been solved by using oligomeric polyester as non migrating plasticizers instead of DEHP, inappropriate situation. Recently, some limited tests have indicated a relationship of prenatal exposure to phthalates and reproductive abnormalities of male babies.
