Abstract:

Polyethylene terephthalate(PET) resin was hydrolyzed to terephthalate acid(TPA) and ethylene glycol(EG) under microwave irradiation.The effects of crystallinity on the depolymerization of PET was investigated.PET resin was isothermal crystallized at temperature of 140,170,200 and 230℃ for 5 hours,the crystallinity of the resin was 25.7%,29.5%,33.9% and 40.6%,respectively,then the resin with different crystallinity was hydrolyzed under microwave irriadition. Under the same conditions of hydrolytic depolymerization,the degree of PET depolymerization decreased from 72.8% to 69.34% with the increase of crystallinity of PET resin,the rate of depolymerization varied little with the increasing of crystallinity of PET,this indicated that the crystallinity of PET has little effect on the hydrolytic depolymerization.The crystallinity of PET was increased during the temperature elevating process of the hydrolytic depolymerization.Investigation by DSC proved that the crystallinity of PET resin increased notability during the same temperature elevating process as the hydrolyzed depolymerization.According to the theory that depolymerization was firstly proceed in the amorphous phase,the crystallinity should increase during the reaction.However,the crystallinity of PET residue was decreased during all the reaction process,this indicates that the hydrolysis did  not preferentially occur in the amorphous phase.

Key words: Polyethylene terephthalate(PET);Microwave irradiation;DSC;Crystallinity;Depolymerization rate, Polyethylene terephthalate(PET), Microwave irradiation, DSC, Crystallinity, Depolymerization rate