Chain Extension Of The Condensation Polymer For Melt Foaming With Supercritical CO₂

Condensation polymer of poly(ethylene terephthalate) (PET) and polyamide 6 (PA6) are widely used in the field of engineering plastics due to their excellent performance and preparing polymer foams by foaming is very important for its further application. For ordinary linear PET and PA6 with a low molecular weight and a narrow molecular weight distribution, they display very low melt strengths in the molten state that they have very poor foamability. The chain extending is a fast and effective method to increase the molecular weight, broaden the molecular weight distribution and enhance the degree of long chain branching of polymer, significantly improving its viscoelasticity, melt viscosity and melt strength. Thus, the foamability of polymer can be greatly enhanced by means of chain extending.In this study, PET and PA6 were chosen as the raw materials which were chain extended by chemical method to prepare the modified PET and PA6 with high melt strength, and the viscoelastic behavior was analyzed by rheological method. The batch melt foaming experiments with supercritical CO2 as blowing agent were performed on the modified products, and the microcellular foam with excellent cell morphology were obtained. PMDA was used as the chain extender to modify the raw PET material by the combination of reactive extrusion with solid-state polycondensition (SSP). The results showed that the intrinsic viscosity greatly increased, the melt flow rate drastically declined to 2.37 g/10 min and high viscoelasticity and quite obvious shear thinning phenomenon was observed. The foaming experiment results revealed that PET foams with the average cell diameter of 30 ?m and the cell density of 108 cell/cm3 were obtained. 1,1'-Isophthaloyl-biscaprolactam(IBC),2,2'-Bis(2-oxazoline)(BOZ) and KL-E4370(EP) were all used to modify the raw PA6 material and it displayed that the melt torque and viscoelasticity of modified products were significantly improved. The modification effects of the different chain extenders are in sequence of EP> IBC&BOZ> BOZ> IBC.The foaming experiment results exhibited that PA6 foams with the average cell diameter less than 10?m, cell density of 1010 cell/cm3 and expansion ratio about 20 times were obtained.