This work describes synthetic approaches and spectroscopic and thermal characterization of aramid polymers prepared from waste PET via sustainable processes. Direct depolymerization of PET with aliphatic diamines under melt conditions resulted in decomposition without substantial formation of any aramid polymer. The Higashi-Ogata methodology direct polycondensation of terephthalic acid (TPA) and p-phenylenediamine resulted in oligomerization and formation or aramids with low degree of polymerization. The highest molecular weight polymers, as determined spectroscopically, were obtained via the acid chloride of TPA, the traditional method. A proprietary solvent enabled the dissolution of five (out of fifteen) polymers and subsequent gel permeation (GPC) analysis in the same solvent. The apparent molecular weights of the soluble polymer ranged between 10-35kDa (Mn) and 28-81kDa (Mw). Several analogs were prepared utilizing commercially available diamines and amine combinations, to improve the solubility of the aramid products. The obtained solid powders were dissolved in D2SO4 and analyzed spectroscopically to qualitatively evaluate degrees of polymerizations, while the solids were characterized via TGA and DSC. Many reaction conditions were employed to improve the solution polycondensation reaction, and it was found that pyridine (2eq) and CaCl2 (5% g/mL) addition to the NMP reaction medium was crucial in preventing the precipitation of the polymer. Both room temperature and 0 °C reactions generated similar polymers via NMR, however the cold conditions enhanced gel formation, an important attribute in the future processing of these materials to obtain fibers. All analogs had high degradation temperature at 5% and 10% weight loss (T5% and T10%), above 400 °C, along with high percent char values. A glass transition (Tg) was not detected in any of the analogs prepared.
Published: October 6, 2022
Cosimbescu L., D. Malhotra, M. Pallaka, and M.S. Swita. 2022.Kevlar-Like Aramid Polymers from Mixed PET Waste.ACS Omega 7, no. 36:32026–32037.PNNL-SA-169420.doi:10.1021/acsomega.2c03059