Synthesis and application performance of environmentally-friendly plasticizer cardanol acetate for PVC

Abstract: As the plastic industry and the environmental awareness continuously grow, there is an urgent unmet need to develop new natural plasticizers with improved properties and cost competitiveness. Natural plasticizers from vegetable origin, such as modified or epoxidized vegetable oil, epoxidized fatty acid methyl eater and glycerin acetates, are alternatives for phthalate. Numerous raw materials have been used, like soybean, corn, sunflower, palm, flaxseed. As one of the most commonly used renewable raw material, cardanol, and its derivatives, have important applications in developing new eco-friendly materials. In this work, the cardanol-based polyvinyl chloride (PVC) plasticizer, cardanol acetate (CA) was prepared by the reaction of cardanol with acetic anhydride using potassium carbonate as a catalyst. 1H nuclear magnetic resonance (1H NMR) and 13C nuclear magnetic resonance (13C NMR) analyses were used to characterize the structure of the product. The results showed that the CA was obtained. The plasticizing effects of the obtained plasticizer on PVC formula were also investigated. The commercial phthalate plasticizer bis (2-ethylhexyl) benzene-1, 4-dicarboxylate (DOTP) was used as the control. Dynamic thermal mechanical properties, mechanical properties, thermal stability and compatibility were assessed by means of dynamic thermo mechanical analysis (DMA), tensile analysis, thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR), respectively. The results indicated that the glass-transition temperature of the plasticized PVC samples decreased from 41.52 to 36.35°C, reflecting a good compatibility of the CA with polyvinyl chloride resin. The reasons for this performance were that the plasticizers mixed with CA had higher ability to lubricate by incorporating itself among the polymer chains, and therefore reduced PVC-PVC interactions due to the replacing partly by plasticizer-PVC interactions. From the characteristic temperatures in TGA curves, it could be observed that the degradation of all the films consisted of 3 steps of weight loss. The degradation at the first stage was at around 80-220°C, which could be attributed to the evaporation of water and small molecules. The second stage at around 220-400°C was fast and due to dechlorination of the PVC, with the formation and evolution of HCl and a few chlorinated hydrocarbons. The third mass-loss step above 450°C, was corresponding to the degradation and decomposition of the complex structures resulting from aromatization. Furthermore, the mass of residual char of the PVC samples at 600°C was significantly increased with the adding of the CA. The results of tensile analysis suggested that the elongation at break increased with the CA content increasing, indicating the increase of flexibility and toughness for all the samples. And the tensile strength and elastic modulus were decreased in the same trend. These results were consistent with the DMA results, indicating that the CA had a significant effect on the flexibility property and exhibited the best toughness. FT-IR spectra of the PVC film samples were obtained. The results indicated that the mixed plasticizers of the CA and DOTP could interact with the PVC by hydrogen bonds between the polar parts of the CA (benzene ring, ester group) and the PVC (carbon-chloride bond). So, it can be concluded that this cardanol-derived plasticizer shows promise as a secondary plasticizer for soft PVC, as well as an alternative to partially replace petroleum-based plasticizers. Furthermore, more new type of PVC plasticizer based on cardanol might be developed on the basis of this study.