Potential Replacement of Toxic PVC Plasticizers with Urea, Its Derivatives, and Related Compounds

The primary plasticizers for the world’s most plasticized polymer, poly(vinyl chloride) (PVC), are organic phthalates, this despite being categorized as probable human carcinogens by the EPA. Di-2-ethylhexyl phthalate (DEHP or DOP) is such a typical PVC plasticizer. We sought to find an alternative plasticizer that lowered the glass transition temperature (Tg) and softened PVC, but was not as harmful to the environment and for our health as the currently employed phthalate plasticizers. We recently discovered that urea (U) could complex with amorphous polymers, such as atactic poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc). Compared to neat samples, the Tgs of the PMMA-U and PVAc-U complexes were increased and decreased, respectively. However, when complexed with dimethylurea (DMU), the Tg of the PMMA-DMU complex was lowered. Since Tgs of PMMA and PVAc were lowered by either U or one of its derivatives, this prompted us to investigate whether they could interact and complex with another largely amorphous polymer PVC, that is often plasticized, to soften and lower its Tg. Shifts in the vibrational frequencies observed by Fourier-Transform Infrared spectroscopy and Differential Scanning Calorimetry thermograms indicated that U, its derivative tetramethylurea (TMU)], and the related compound Acetamide (AC) were complexing with PVC. All three complexes (PVC-U, -TMU, and –AC) showed significantly lowered Tgs. Preliminary mechanical property measurements of PVC-U and PVC-AC films showed they were softer and more pliable than PVC films. Consequently, we believe our preliminary results warrant further examination of U, AC, and TMU as potential effective and less harmful PVC plasticizers.