Montmorillonite-reinforced nanocomposite from off-grade plastics materials using response surface analysis

Off-grade thermoplastic poly(ethylene terephthalate) of industrial manufacturers was partially depolymerized to synthesize poly(ethylene terephthalate) oligomers. Influences of reaction time, ethylene glycol/poly(ethylene terephthalate) molar ratio, catalyst concentrations and particle size of off-grade poly(ethylene terephthalate) on yield of partial glycolysis reaction were investigated based on Box–Behnken's design of experiment. Thermal analyses of glycolyzed products was carried out using differential scanning calorimetry. The optimum samples were also well characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy and carbon-13 nuclear magnetic resonance spectroscopy. The optimal conditions to synthesize poly(ethylene terephthalate) oligomer for a 120-min glycolysis reaction time were: using ethylene glycol/poly(ethylene terephthalate) of molar ratio of 2 with no catalyst and using granule-shaped poly(ethylene terephthalate). Then, endcapped poly(ethylene terephthalate) oligomer as a compatiblizer for preparing poly(ethylene terephthalate) nanocomposites was produced via reaction between maleic anhydride/phthalic anhydride composition and optimized poly(ethylene terephthalate) oligomers based on central composite design of experiment. The combination of reaction time of 106 min and phthalic anhydride/maleic anhydride molar ratio of 0.85 gave the best results based on d-spacing and peak intensity of nanocomposite samples. Hence, melt mixing of endcapped poly(ethylene terephthalate) with organoclay produced a good intercalation of layered silicate and good dispersion of clay in endcapped poly(ethylene terephthalate) matrix. Analysis of variance was studied for both glycolyzed products and functionalized poly(ethylene terephthalate) oligomers.