Curing behaviour and mechanical property of unsaturated polyester based on recycled PET

Abstract

PET was depolymerized by glycolysis, and obtained glycolized product and free glycol reacted with maleic anhydride to get unsaturated polyester. The unsaturated polyester was dissolved in styrene monomer and then the curing reaction was carried out. Curing behaviour and kinetics were investigated at that time. The glycolysis was carried out with the DEG contents change as the 0wt%(0mol%), 5wt%(3.64mol%) and 10wt%(7.4mol%) of PG. PET whose number average molecular weight is depolymerized to the monomer and higher oligomer of 400 - 900 molecular weight. There is no severe difference in molecular weight on DEG contents in PG for glycolysis. The molecular weight of synthesized polyester is ranged about from 400 to 1400, there is main peak above the 1000 of molecular weight on each glycol compositions from GPC results. As the contents of DEG in PG increase, the portion of the low molecular weight increases. Synthesized unsaturated polyester from depolymerized PET are cured at 80℃ - 100 ℃ range. Curing conversion could be obtained using DSC, and the kinetic parameter and activation energy are evaluated by fitting into Kamal``s semiempirical kinetic equation. The maximum conversion and the reaction rate constant increase as the curing temperature increase as expected. But the difference of the maximum conversion is not severe, and the all near to 1. Gel point detected by three different methods and are compared with each other. The gel points detected by steady shearing test and crossover point of G`` and G" are quite similar, but the gel time detected by tan δ method suggested by Winter et al. is slightly larger than other methods. The tensile property of cured polyester decreases as the curing temperature increases and DEG contents increase in PG. This tensile property is closely related with gel fraction. The sample which has the higher gel fraction shows the higher tensile property.