Effects of Two Phosphonium-Type Ionic Liquids on the Rheological and Thermomechanical Properties of Emulsion Poly(vinyl chloride)-Based Formulations Plasticized with DINP and CITROFOL

Industrial poly(vinyl chloride) (PVC) plastisols are often formulated using phthalate plasticizers due to their cost-effectiveness and high compatibility with PVC. However, there is a current need to replace these additives by plasticizers that (i) present reduced migration/leaching and volatilization profiles, (ii) can optimize production processes while maintaining the performance of the final plasticized materials, and (iii) reduce toxicological risks to consumers and to the environment. The main objective of this work was to evaluate the effects of the partial replacement (15 and 30% (w/w)) of two conventional plasticizers (diisononyl phthalate (DINP) and acetyltri-2-ethylhexyl citrate (CITROFOL AHII)) by two low-volatility ionic liquids of the phosphonium-type (trihexyl(tetradecyl) phosphonium dicyanamide and trihexyl(tetradecyl) phosphonium bis(trifluoromethylsulfonyl)imide) on the rheological and thermomechanical properties of an emulsion-grade PVC which is usually employed in the production of automotive industry upholsteries. Rheological profiles and plastisols’ particle size distributions were monitored over time (up to 14 days) to study the effects of plastisols aging on the thermal stability and thermomechanical properties of PVC films obtained after gelation of the plastisols. Obtained results showed that the incorporation of these two phosphonium-type ionic liquids into DINP- and CITROFOL-based PVC plastisols significantly reduced their viscosities and changed their rheological profiles (from pseudoplastic to near-Newtonian behavior). Plastisols aging had a noticeable impact on the final thermomechanical properties of PVC films plasticized with DINP while no significant effects were observed for films plasticized with CITROFOL. These results are in good agreement with the correspondent time-dependent rheological profiles.