Modified PETs Via In-situ Polymerization And Their Molten-state Foamability

In order to increase the melt viscosity and strength, PET has been modified via in-situ polymerization. The foamability of modified PET in the molten state was studied in the batch supercritical fluid foaming process. Meanwhile, Mucell injection molding process foaming with supercritical fluid were carried out, mechanical properties of modified PET and injection molding foamed PET were investigated.The third monomer such as alcohol N and acid M were added at the beginning of po-lymerization, the optimum content of the third monomer has been investigated. Batch melt polymerization results showed that the optimum content of alcohol N was 0.2%, the intrinsic viscosity of modified PET can increase to 0.95 dL/g, compared to the conventional linear PET of 0.68 dL/g, melt flow rate(MFR) decreased from 27.14 g/lOmin to 9.62 g/lOmin, die swell increased from 1.32 to 2.78, if further solid state polycondensation was followed, the intrinsic viscosity of modified PET can reach to 1.51 dL/g, MFR decreased to 5.23 g/10min, die swell increased to 2.92. The optimum content of acid M was 0.4%, the intrinsic viscosity of modi-fied PET can reach to 0.98 dL/g, MFR is 9.89g/10min, die swell is 2.48. The steady and dy-namic rheometric measurement showed that the storage modulus and loss modulus of PET modified with alcohol N and acid M increased.The batch molten depressurization foaming process with supercritical fluid demonstrated that, due to linear structure, low melt strength, cells of foamed conventional PET are easy to rupture and collapse; PETs modified with alcohol N and acid M, have long chain branching structure, high melt strength and viscosity, cells of their foams can keep good shape and the volume expansion ratio can reach more than 10 times.The tensile and impact strength of 80L-N-PET and 80L-M-PET modified by melt poly-condensation were higher than conventional PET, but the bending strength decreased, after continue solid state polymerization, the tensile, bending and impact strength all were much higher than conventional PET. The process of Mucell injection molding foaming of modified PETs with supercritical N2 were optimized by orthogonal experiment. With maintaining good cell morphology, weight of injection molding foaming PET could reduce 10% or more, the tensile, bending and impact strength normalized by weight ratio all increased, especially im-pact strength increased over 50%.