Development Of Biobased Plasticizers From Vegetable Oils For Poly(Vinyl Chloride), PVC

Abstract

Phthalate plasticizers have long been used in poly(vinyl chloride), PVC formulations until recent studies have shown they can cause adverse health effects when ingested. Alternative plasticizers are available but they do not match the cost and performance of phthalates. Vegetable oils are ubiquitous, nontoxic, low cost materials that can be chemically modified to function as plasticizers in PVC. To be compatible, vegetable oils must be modified to reduce molecular weight, balance of polarity, and introduce branching along the fatty acid backbone. Readily available soybean oil was used as the primary starting material to meet these structural requirements. The oil was transesterified with different alcohols to reduce molecular weight and change its overall polarity. To increase polarity and add branching, estolides were introduced onto the fatty acid ester backbone at the site of unsaturation by two synthetic methods. The perchloric acid method provided estolides with low estolide number and higher crosslinking products, while the epoxy method resulted in higher estolide numbers which imparted better compatibility with PVC. Separation and characterization of the components of the epoxy method found they contained cyclic tetrahydrofuran ether estolides in significant quantities. These were formed by the ring opening reaction of diepoxy linoleate by acetic acid. To reduce the formation of these cyclic ether estolides castor oil epoxy fatty acid alkyl ester estolides were synthesized and evaluated as plasticizers. These epoxy fatty acid alkyl ester estolides from castor oil had excellent plasticizing properties but the higher cost and limited availability of castor oil would make them prohibitive. Considering the better performance of castor oil based epoxy fatty acid ester estolides, soybean oil derived epoxy fatty acid alkyl ester estolides with reduced cyclic ether content were prepared. These compounds with medium molecular weight head group (butyl and pentyl) provided good functionality in PVC. Based on their performance, these epoxy fatty acid ester estolides would be useful replacements for phthalates in low water contact applications such as wire and cable coatings or wall coverings.