Processing Of Increasing Viscosity And Foaming Behavior For The Recycled PETG

As a new kind of non-crystalline copolyester,Poly(ethylene terephthalate glycol-modified)(PETG)products were applied to plate, sheet, high-performance shrink film, bottle and so on. Because it hashighly transparent, good toughness, good weather resistance, superior thermoforming properties. In recent years,the old PETG is also rapidly increasingwith the increase of the amount of PETG products. Because the reclamation can not only solve part of the problem of environmental pollution, but also saves natural resources and production costs. Therefore, as regards the recycled PETG has been modified that is a research hotspot in the field. In this paper,the vicosity of r-PETG was increased by the chain-extensionreaction,the modified r-PETG foam was prepared by the extrusion subsequently.Throughrotationalrheometer, torque rheometerand, gel permeationchromatography(GPC)and scanning electron microscope(SEM) measurernent, the mechanicalproperties, rheology properties and foamability of the modified r-PETG was studied. The main contents and results of experiments and described as follows:Phosphite-based(TPPi) and an epoxy-based(TGIC) for r-PETG have chain-extension effectiveness, acid anhydride(PMDA) does not expand its chain. On the contrary, it will accelerate degradation. There is greatefficiency bycomparing single-use TGIC and PMDA with the two-step method combined.The molecular weight, viscosity increases more remarkable. At themoment, The optimum processing conditions were reached(200 ℃,60 r/min,2.0 wt.% chain extender),with the melt index of the r-PETG decreased from 12.83 g/10 min to 4.24 g/10 min. But the number average molecular weight(Mn) of the r-PETG increased from 2.52×104 to 3.35×104. Simultaneously,the mechanical properties improve significantly.The structureandrheological properties were investigated thought rotationalrheometer.Theresults show the zero shear viscosity(η0) of the r-PETG increased from 3435.8Pa·s to 27944.5Pa·sby TPPi.The features relaxation time(τ0)increased from 0.94 s to 30.91 s. In this case, because TPPi as aesterifying promoter, the molecular chain of the r-PETG maintains linear structure. Whereas in two-stage chain extender combined with TGICand PMDA, the equilibrium torque value increased with the amount of TGIC. At the concentration of 0.25 wt.%PMDA+1.0wt.%TGIC, the zero shear viscosity(η0) and the features relaxation time(τ0) increasedfrom 3725.7Pa·s to 31578.6Pa·s and 3.35 s to 113.3s, respectively. Both of these methods could significantly improvethe complex viscosity and melt elasticity. The results show thatthe complex viscosity descreased with the increase of frequency, and the material presented the characteristics of pseudoplastic fluid.The r-PETG modified to produce the long chainbranching, whichleads to the formation of a system of entangled network structure and the "solid-like" structure make the relaxation time of the material is significantly longer, the chain relaxation was more difficult. Meanwhile, thedegree ofstress overshootincreases with the amount of TGIC. But no gel indicated that long-chain branched entanglement is not enough to form a crosslinked excesses.The results of extrusion foaming experimentshow that the cell size presented gradient distributionin the radial.At the same time, thecell size and cell density of the extruded rod wereclosely related to the screw speed. When the screw speed and the amount of chain extender are 50r/min and 0.25 wt.%PMDA + 1.0wt.%TGIC, respectively.