Research On Extrusion Processing Characteristics Of Modified Polyethylene Terephthalate(PET)

Polyethylene terephthalate(PET)is widely used in polyester containers,packaging,textiles,electronics and automobiles due to its excellent comprehensive properties.However,due to the defects of PET itself,in the extrusion process,PET shows low melt strength and melt viscoelasticity,which makes it difficult to be extruded and molded,thus limiting its application in extrusion processing fields such as extrusion plate and foam molding.In this paper,aiming at the above defects of PET,a twin-screw extruder was used to improve the melt strength and melt viscoelasticity of PET by reactive extrusion chain extension modification and blending modification to meet the extrusion processing requirements of PET.On this basis,the extrusion rheological properties of modified PET were studied by torque rheometer,and the extrusion formability of modified PET was studied by single screw extruder.The main work and conclusions of the project are:(1)The effects of three kinds of epoxy chain extenders KLX,KLR and KLW on the intrinsic viscosity,melt flow rate,rheological properties and crystallization of PET were studied by reactive extrusion chain extension modification.The results showed that the chain extender KLX had the best modification effect,which increased the intrinsic viscosity of PET from 0.69d L/g to 0.92d L/g by 33.3%.At the same time,the modified PET had the highest complex viscosity,storage modulus and loss modulus,and the melt viscoelasticity was the best.(2)On the basis of chain extension modification,the effect of chain extension PET and HDPE blending viscosity enhancement was studied by blending modification and viscosity enhancement.Then the effects of two compatibilizers(POE-g-GMA and PE-g-MAH)on the chain-extended PET/HDPE blend system were studied.Combined with melt flow rate,dynamic thermomechanical,crystallization performance,mechanical properties test and scanning electron microscope,the compatibilizer with good modification effect and the optimum dosage were determined.Adding 7%POE-g-GMA had the best compatibilization effect,and the MFR of the blend was reduced from 10.5g/10min of chain-extended PET/HDPE without compatibilizer to 4.05g/10min,a decrease of 61.9%,which effectively improved the viscosity of the blend and achieved the purpose of increasing the viscosity of the blend.(3)The extrusion rheological properties of modified PET were studied by using a capillary rheometer.The torque of the material during stable extrusion by torque rheometer shows that the chain extension modification improves the melt strength of PET.The torque of pure PET is increased from 2.2 N·m to 7.3N·m,which is 2.3 times higher.Blending and tackifying further improved the melt strength of PET.After adding POE-g-GMA,the maximum torque was 10.0N·m,which was 3.5 times higher than that of pure PET.On-line capillary rheological test shows that GMA7 component of chain-extended PET/HDPE/POE-g-GMA(80/20/7)has the best modification effect and the highest melt strength.The viscosity of modified PET decreases and its fluidity increases with the increase of temperature.Higher temperature is not conducive to the extrusion molding of PET.(4)The effects of die temperature and process routes(one-step molding and two-step molding)on the forming properties of extruded splines(maximum tensile force at traction fracture,traction distance and apparent density of splines)were studied by using a single screw extruder.The results show that GMA7-7has the highest melt strength among the tested components,and the maximum tensile force required for pulling to fracture is 57N,the longest spline pulling distance is 40cm,and the maximum density is 1.21 g/cm~3.Under the same composition,too high or too low die temperature is unfavorable to extrusion processing,and the optimum die temperature is 260℃.The modified PET extrusion processing using two-step molding process has better formability,denser extrusion spline and longer traction distance.