Recycling of polyethylene terephthalate using high-pressure steam treatment

In this study, polyethylene terephthalate (PET) was broken into fine particles during high-pressure steam treatment without crushing or using acidic or alkaline catalysts and solvents. Scanning electron microscopy (SEM) images showed that PET was decomposed from the surface by the high-pressure steam. H-1 NMR and CP/MAS C-13 NMR spectra revealed that the molecular weight of PET gradually decreased to that of an oligomer with increasing the high-pressure steam treatment time, and then reacted to a monomer. Differential scanning calorimetry (DSC) showed a decrease in the glass transition temperature (T-g), crystallization temperature (T-c), and melting temperature (T-m). X-Ray diffraction (XRD) measurements indicated that crystallinity increased with high-pressure steam treatment time. Decomposed PET consisting of hydroxyl groups and carboxylic acid thus repolymerize into new products. This investigation showed that a PET recycling method can be established easily, which had no adverse effect on the environment.