Study On Processing And Molding Of Small Hollow High-density Polyethylene Materials

High-density polyethylene?HDPE?has been widely used in various hollow containers for its excellent mechanical and processing properties.At present,small hollow HDPE materials from domestic petrochemical enterprises are basically unimodal products.In order to improve market competitiveness,a petrochemical company developed a new bimodal HDPE product.This dissertation focuses on the analysis the performance of the bimodal product to explore its processing parameters and the factors related to its further processing and molding.Firstly,the basic properties including molecular structure,thermal and rheological properties of the bimodal HDPE were analyzed and compared with other typical commercial HDPE materials in the dissertation.The characterization results show that the mechanical properties of the bimodal HDPE product are superior to those of unimodal commercial HDPE materials,and bimodal HDPE possesses better environmental stress cracking and rigidity.The processing fluidity of the bimodal HDPE is good,but its processing stability is poor leading to a relatively limited processing scope.The critical shear rate of unimodal products is 444 s^-1 at 170°C,while the critical shear rate of bimodal products is 208 s^-1.The critical shear rate of unimodal products is more than 2000 s^-1 at 190°C and the critical shear rate of bimodal products is 444 s^-1.Secondly,the blow molding process of bimodal HDPE was also studied by orthogonal test.The effect of process parameters,such as wall thickness,processing temperature,blowing time and mould temperature,were investigated.According to different requirements of product quality,the optimal processing temperature of the product is 160°C or 180°C,the optimal blowing time is 20³0 s,and the optimal mold temperature is 10²0°C.Finally,based on the trial of bimodal HDPE in the market,the products were improved and developed,and the problems in the processing of products were analyzed and solved.