Investigation on the Thermo-Oxidative Degradation of Polyethylene, Poly(vinyl chloride), and Polystyrene Using NiPIm_1.5 and NiPIm₂ Nanocomposites

Abstract

In this work, we report the synthesis of two nanoscale composites of nickel, NiPIm1.5 and NiPIm2 (NiPIm1.5 = [Ni­(C3H4N2)­(H2O)5]­(HPO4)­(H2O)·0.3­(C3H4N2) and NiPIm2 = [Ni­(C3H4N2)­(H2O)5]­(HPO4)­(H2O)·0.4­(C3H4N2)·H2O), characterization by various instrumental methods and the investigation of the thermo-oxidative degradation of polyethylene (PE), poly­(vinyl chloride) (PVC), and polystyrene (PS) in the presence of both nanocomposites. All of these polymers are subjected to thermal treatment with and without composites at 353 K for 120 min. The rate of degradation is maximum with NiPIm2 for all three polymers, PE13.1522%, PS13.6152%, and PVC8.04%, whereas with NiPIm1.5, PE7.3128%, PS11.9837%, and PVC4.9106%. The percentage of degradation in the presence of composites is much greater than the percentage of degradation without composites. The specific heat capacities of NiPIm1.5 and NiPIm2 are −148.42 and −348.64 J kg–1 K–1, respectively. The degradation process takes place by free radical mechanism. Thermogravimetric and differential thermal analyses revealed that the temperatures corresponding to the formation of composite materials with NiPIm2 are 338.76, 331.78, and 354.30 K for PE, PVC, and PS, respectively. The temperatures of formation of the above composites are found to be less than that of NiPIm1.5. The degraded residues of polymers indicate that ester is formed in each case along with other byproducts containing imidazole. Infrared studies revealed the thermal oxidation of hydroperoxides and the formation of ketone.

Recent advances in oxidative degradation of plastics

“…Apart from transition metal catalysts, nanoparticles, carbon-based materials, and other alternatives can also be used in the thermocatalytic oxidative degradation of polymers. 102–105…”

“…After the oxidative degradation of lignin with 10 wt% catalyst under 35 bar in air with 6% O 2 at 190 1C, they recovered 15 wt% of small molecules phenolic products ranging from aldehydes to carboxylic acids in 12 h. Although the yield is not incredibly high, using a one pot system and acetone as a benign solvent is advantageous over traditional methods with multistep degradations and harsher conditions. Apart from transition metal catalysts, nanoparticles, carbon-based materials, and other alternatives can also be used in the thermocatalytic oxidative degradation of polymers [102][103][104][105].…”