Chemical modification of virgin and recycled poly(ethylene terephthalate) by adding of chain extenders during processing

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The processing of recycled poly(ethylene terephthalate) (PET) involves thermal and hydrolitic degradation of a polymer, which reduces the molecular weight, the intrinsic viscosity, and the mechanical properties of recycled materials. Degradative effects can be limited by using chain extenders. Preliminary tests show that the diisocyanates are more reactive toward the end groups of virgin PET than are bis-oxazolines or diepoxides under the experimental conditions used. So, samples of modified virgin PET with diisocyanates possess molecular weight and intrinsic viscosity (Mw > 60,000 g/mol and [η] > 1 dL/g) superior to those of virgin PET (Mw > 40,000 g/mol and [η] > 0.70 dL/g). Chemical modification of recycled PET by diisocyanates leads to an increase in the molecular weight from 30,000 to 51,000 g/mol, the intrinsic viscosity from 0.60 to 0.84 dL/g, and the mechanical properties, particularly the elongation at break, from 5 to 300%. Chemical modification of recycled PET by injection molding is an interesting method from an industrial point of view because it provides a recycled material possessing properties close to virgin PET in one-step processing.