Green plasticizers for PVC - An investigation of renewable alternatives to phthalates derived from vegetable oils or wood industry products
Polyvinyl chloride (PVC) is a very versatile thermoplastic because of its ability to solve a broad range of different concentrations of plasticizer. Phthalates are still the most commonly used plasticizer in PVC, but due to public opinion and legislation against phthalates there is a demand in the market for both old and new phthalate free plasticizers
Properties of epoxidized oils of soybean (ESBO), canola (ECO), sunflower (ESFO) and safflower (ESAO) were investigated to determine their suitability as plasticizers. The evaluation was performed using several methods, including mechanical evaluation and thermal ageing of PVC films highly plasticized with the four different epoxidized vegetable oils (EVOs). Diisononyl phthalate (DINP) was used as the reference plasticizer. The evaluation results showed that ESBO, ESFO and ESAO are good replacements for DINP for indoor applications. However, the current study also indicates that crosslinking takes place during thermal ageing of suspension PVC plasticized with ESBO, ECO and ESFO.
Also in this study the mechanism of hardening was further investigated. Analysis of the PVC films was made by measuring extractable amount EVO plasticizer before and after exposure to elevated temperature.
Further analysis of this hardening by exposing pure EVOs to elevated temperatures confirmed that the EVOs are crosslinking with themselves. Comparative analysis was performed on ESBO, ECO, ESAO and ESFO by using GC-MS, ACPI-MS, XRF, NMR, DSC and FTIR.
The results of this part of the study is that the rate of crosslinking is positively correlated with the degree of epoxidation of the EVOs, their content of epoxidized polyunsaturated fatty acids and the storage time of the EVO.
A third part of this study was to explore the possibilities of using lignin as source for plasticizers. Lignin molecules themselves are typically too large and would require fractioning to be a useful source. Eugenyl acetate and vanillic acid were used as model substances of lignin. These model substances were modified by epoxidation and by esterification with octanoic acid. The results show promise with plasticizing effect achieved with both model substances. There are however challenges in the compatibility with PVC and fractioning of the lignin source.
Epoxidized vegetable oils
Tall oil fatty acid