Studies On The Modification Of R-PET By Chain Extension And Toughness Enhancement And The Crystallization Of PET

The post-consumer poly(ethylene terephthalate) (PET) becomes the most important component of municipal solid waste(MSW) due to its wide usage as a package material. The post-consumer PET recycling conserves both material and energy and provides a comparatively simple way to make a substantial reduction in the overall volume of MSW. However, recycled poly(ethylene terephthalate) (R-PET) usually undergoes chemical, mechanical, thermal, oxidative and hydrolytic degradation or biodegradation during the recycling process and reprocess. These degradation reactions result in loss of molecular weight, decrease in melt strength, intrinsic viscosity and thermal properties, render R-PET unsuitable particularly for applications of long fiber-spinning and blow moulding. As a matter of fact, virgin poly(ethylene terephthalate)(PET) is also limited to apply as an engineering plastic for injection moulding due to its low crystallization rate, long crystallization period and inferior dimensional stability. In this work, chain extension and toughening of R-PET were investigated and the crystallization of PET and theses composite were studied.A multi-functional linear chain epoxide(ADR4370S) was employed as a chain extender to increase the molecular weight of R-PET in a single step by melt banburying reaction. The effects of ADR4370S content on the molecular structure (molecular weight(MW), molecular weight distributions (MWD), branching and gel-like structures) of modified R-PET were investigated by DSC, torque and rotation rheological analyses. The results showed that the viscosity, MW, MWD, the branch degree, melt strength, intrinsic viscosity and solid-like behavior of the modified R-PET were enhanced after reactive modification with increase in content of the chain extender. The intrinsic viscosity was enhanced from 0.59 dL/g to 0.61 dL/g with raising the concentration of ADR4370S from 0 to 0.5 wt%. The value approaches to that of the virgin PET (Trademark BG80 with 0.62 dL/g). However, further increase the concentration to 1.5 wt% resulted in a polymeric structure near the sol-gel transition point and to 2.0 wt% led to form gel structure. The decrease in the crystallization speed and mechanical-thermal stabilityof the modified R-PET was responding to the presence of chain branching.A series of maleic anhydride-grafted poly(acrylonitrile-butadiene-styrene) (ABS-g-MAH) and the blends of the amorphous tri-block copolymer ABS and semicrystalline R-PET were prepared via a melt banburying process in a RM-200B torque rheometer. The ABS-g-MAH with about 5% of grafting degree was prepared and used as a compatibilizer to improve the compatibility of R-PET/ABS blends. differential scanning calorimeter(DSC), dynamic mechanical analysis(DMA), SEM and rotation rheological analyses were carried out to investigate the morphology of R-PET/ABS blends with various viscosities of R-PET and with difference weight ratios of ABS and R-PET. The results showed that R-PET was partially miscible with ABS and ABS-g-MAH was an efficient compatibilizer for R-PET/ABS blends with proper concentration. Continuously raising the concentration of ABS in R-PET/ABS blends resulted in conversing phase sturcture of blends from sea-island to partial continuous and coexisting structure. It was also clear that the morphology of blend could be changed by changing viscosity of R-PET.Lanthanum coordination compound (LaC) used as a heterogeneous nucleating agent to prepare PET/LaC composite. The experiments were carried out in torque rheology by melt banburying. Morphology, non-isothermal and isothermal crystallization kinetics of LaC-modified PET were investigated by polarizing optical microscopy (POM), wide-angle X-ray scattering(WAXD), differential scanning calorimeter(DSC), dynamic mechanical analysis(DMA) and rotation rheological analysis, respectively. The results illuminated that LaC can act as heterogeneous nucleating agent to accelerate the rate of crystallization, shorten the crystallization period and reduce the crystal dimension during no-isothermal process. The concentration of LaC was optimized to 0.85 wt%. The loss modulus and storage modulus of PET/LaC, the energy consumption during PET/LaC process and the glass-transition temperature of PET decreased with increase in LaC content, whereas the Newtonian fluid behavior increased with raising LaC content.