Preparation And Mechanism Of High Performance PVC Based On Multilayer Coextrusion

Polyvinyl chloride(PVC)has occupied an important place in the plastics industry due to its global availability and simple processing.However,the defects of its thermal stability,plasticizer migration and mechanical properties have prevented the promotion of PVC.The research of predecessors mainly aimed at improving the unilateral performance of PVC,but it could not meet the increasing demand for use.Based on the multilayer coextrusion extrusion technology,the macroscopic performance improvements of PVC were studied in this article,mainly including the extrusion plasticization behavior,effects of multilayer coextrusion and the addition of inorganic particles.Loss rate of plasticizer,mechanical strength and thermal stability are the three main properties to be characterized.Besides,typical cases of PVC further applications were anayzed.The contents and conclusions of this study are as follows:(1)The differences in basic properties,processing properties,mechanical properties and thermal stabilities of PVC resins in suspensions by different degrees of polymerization were studied.The thermal stabilities of various stabilizers were also compared and studied.This work provided basic data for special material configuration of PVC products.(2)We explored plasticizing effects of the extruder and layering actions of multilayer coextrusion on the properties of PVC products.The results showed that:When rotation speeds were constant,the crystallization property of PVC and tensile strength were improved with temperatures increased.When temperatures were constant,the crystallization property of PVC and tensile strength decreased with rotation speeds increased.With the number of micro-nano layers increased,the crystallization property of PVC was improved,yield strength,elastic modulus and tensile strength increased continuously,thermal stability was improved,but elongation at break decreased somewhat,heating loss rate and water extraction rate of plasticizer continuously decreased.Compared with 1-layer PVC samples,the heat loss rateo f 729-layer PVC samplesdecreased by 61.9%,the water extraction rate decreased by 46.4%,thermal weight loss decreased by 30.8‰ and the longitudinal tensile strength increased by 26%.(3)The PVC/nano-SiO2 composites were prepared based on multilayer coextrusion extrusion technology,which can effectively improve the uniform dispersion of nano-SiO2 in order to realize the high performance of materials.When the dosage of nano-SiO2 was 3%,the processability and usability were optimum.Compared with homogenous material samples,the heating loss rate of 729-layer composites decreased by 41.7%,the water extraction rate decreased by 73%,the weight loss decreased by 32.0%and the tensile strength in the longitudinal direction increased by 25.5%.The interface interaction reacheed the maximum.(4)The high-performance extrusion granulation pilot line for PVC with"one-to-four" micro-nano laminations was independently designed and torsional flow channels were simulatd by polyflow.The function equation of the maximum melt pressure in runners was also proposed to provide important reference for the model selection of PVC extruders and the usage of pressure sensors.(5)Based on multilayer coextrusion extrusion technology,soft PVC granules were used in blow molding and injection molding,and rigid PVC granules were applied in hot compression molding.The comparison results showed that soft PVC products could still remain the improvements of mechanical properties.Rigid PVC products had limited lifting effects on mechanical properties.