The Process Of Single Screw Extrusion Of Ultra-High Molecular Weight Polyethylene

Ultra high molecular weight polyethylene(UHMWPE) is a kind of engineering thermoplastics, whose viscosity-average molecular weight is extremely high. Its performance is outstanding, compared with other kind of plastics, such as wear resistance, impact strength, low temperature resistance and low friction coefficient. UHMWPE has been used in more and more fields. The need for it, throughout the world and China, is also growing. Meanwhile, the need for manufacture, process technology and industrialization of UHMWPE is becoming higher and higher.In this article, we investigate the theory of the single-screw extrusion of UHMWPE, including residence time, conveying theory, melting theory and phenomenon and theory of degradation, which can be used to guide the real single-screw extrusion production of UHMWPE. Below are the detailed content and conclusion of this research.(1) Analyze the extrusion conveying theory, based on the performance of UHMWPE and predecessors’research achievements. First, we assume the whole conveying process of UHMWPE extrusion is "solid plug" conveying, and the motion of material is one-dementioanl. Based on Darnell and Mol theory and frictional static equilibrium, UHMWPE theoretical residence time is calculated. Real residence time in different rotational speed was measured through experiments and experimental curves were made. The theoretical and experimental curves are compared to prove the assumed conveying theory.(2) The melting process and status was observed through screw ejection experiments and the melting physical model was built, based on which melting mathematical model was built, which was proved by experiments. The radial melting film thickness formula δ=f(Z) and melting zone length formula z=G/ωAW is concluded, which can guide the production.(3) Get extrusion samples in different rotational speed and temperature and measure the molecular weight, which is used to indicate the degradation extend of UHMWPE, to analyze the degradation trend with the change of temperature, rotational speed and with or without extruder mold. The extrusion degradation theory of UHMWPE is analyzed according to the experimental phenomenon and results.