Prevention of poly(vinyl chloride) degradation through organic terephthalamides generated from poly(ethylene terephthalate) waste

Abstract

The use of organic compounds as thermal stabilizers for poly(vinyl chloride) (PVC) stabilization is the current state of art worldwide owing to their high efficiency and nontoxic residues after degradation. Terephthalamide, N,N′‐dimethylterephthalamide and N,N′‐dibutylterephthalamide have been prepared via depolymerization of poly(ethylene terephthalate) through an economical and environmentally friendly approach. These compounds have been examined as thermal stabilizers for PVC formulations and found to exhibit high thermal stabilizing effects. Thermal stability measurements were performed using conventional Congo red test method. Color change experiments were conducted by heating the samples at 200 °C in air, and the colored compounds formed were extracted and compared with the help of UV–visible spectroscopy. Fourier transform infrared spectroscopic studies of organic terephthalamides incorporated PVC samples have been performed in order to insight the probable mechanistic aspects involved in thermal stabilization process. Thermogravimetric analysis (TGA) thermograms of PVC sheets loaded with 10 wt % organic terephthalamides have been recorded and were found stable below 200 °C. SEM and energy dispersive X‐ray analysis of char residues of TGA samples were performed supporting the proposed thermal stabilizing action of the organic terephthalamides. Furthermore, specific gravity and mechanical performance of the PVC sheets have also been reported assisting in finding suitable commercial applications of PVC formulations. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48022.

Chemical recycling of polyesters

“…Of the nitrogenous compounds, ammonia is relatively rarely proposed as a degrading agent for PET macromolecules, which can be explained by its lower reactivity compared to amines and the limited possibilities of economically justified utilization of the produced terephthalic acid diamide (TPADA) [54]. Literature data show that TPADA can be used as an additive increasing the thermal resistance of PVC [137,138] or transformed, in the process of pyrolytic dehydration, into a number of other aromatic nitrile compounds (1,4-dicyanobenzene, 4-cyanobenzoic acid and its amide) [139,140]. It is worth emphasizing that aromatic nitriles can be further hydrogenated to the appropriate reactive aminomethyl derivatives [p-xylene diamine, 4-(aminomethyl)benzoic acid], which are attractive monomers in the synthesis of polyamides -they can improve the economy of the entire process of PET ammonolysis [60,141].…”

“…It was shown that ammonolytic degradation of PET can be carried out with high efficiency in the presence of EG [139][140][141] and water [137,[142][143][144]. Table 1 summarizes the literature data on PET ammonolysis.…”

“…Usually this process does not require heating or pressure reactors, and ammonia is used in the form of an aqueous solution [137,138,[142][143][144]. However, a fairly long time is required to achieve a complete conversion of PET waste (up to 45 days).…”

“…Among the tested systems were both simple derivatives with monofunctional alkyl groups (e.g. Me [137,142,144,147,148], Et [147], n Bu [137,147,148]) or phenyl substituents [146], as well as more complex compo- [145,146]. Due to their potential applications, two groups of reactive, N-substituted terephthalamides containing the OH or amino groups are of particular interest to researchers.…”

“…Aminolytic degradation of PET does not require the use of extreme process conditions and advanced apparatus or anhydrous environment. However, depending on the amine used, a simple mixing of substrates at atmospheric pressure and ambient temperature (25-40 °C) results in a complete conversion of waste PET only after a several days [137,142,144,147,148]. This time can be reduced to few hours by increasing temperature and using suitable catalysts, which increase the electrophilicity of carbonyl carbon in an ester bond [151].…”