Modification Of PET By Reactive Extrusion For Microcellular Foaming

Poly(ethylene terephthalate)(PET) foams have a wide application prospects due to their good mechanical, high temperature resistance, good solvent resistance and recyclable characteristics. However, foaming from ordinary PET resins is impracticable for fabrication of PET foams due to their low melt strength at the processing temperatures. In this work, reactive extrusion followed with solid-state polycondensation were applied for ordinary PET to improve its viscoelasticity. The modified PET with high melt strength has the intrinsic viscosity as high as1.37dL/g and melt flow index as low as2.5g/10min. Its DSC traces upon heating shows two melting peaks. Its rheological behavior shows higher viscoelasticity than ordinary PET and shear thinning phenomenon as well, indicating the modified PET has branched structure of macromolecular chains. Recycle PET was modifed by three chain extenders and the modification process conditions were optimized. The resulted high melt strength PET has the intrinsic viscosity as high as1.15dL/g and melt flow index as low as3.7g/10min with the chain extender TGIC. It was found that the effect of the chain extender for the modification process, in sequences, is TGIC, PMDA and ADR4370. In comparison with the recycle PET, the modified PET has much better foamability.Two modified PETs with different melt strength were foamed by using Mucell injection molding process with supercritical nitrogen (SCN2) as the blowing agent. The effects of the process conditions on the cell structure and mechanical properties of the specimens were carefully investigated. The results show that the optimization processing conditions for obtaining the best mechanical properties of the two PETs are the same. The specific tensile, impact and bending strength to weight ratio of the two different PET foamed specimens are all improved in comparison with the unfoamed ones. The specific tensile strength of PET-2prepared under the optimization conditions is improved18%with the weight loss of20.98%, the specific impact strength5%with the weight loss of4.69%, and the specific bending strength improved18%with the weight loss of12.21%.