Study On Structure And Properties Of UHMWPE Prepared By Eccentric Rotor Extruder

Ultra-high molecular weight polyethylene(UHMWPE),as a comprehensive engineering plastic with excellent impact resistance,friction and wear resistance and good biocompatibility,has been used in pipeline transportation,aerospace,biomedical engineering and other fields.Above the melting point,UHMWPE still cannot flow appealing to be elastomer,in contrast to other thermoplastics with low molecular weight.The extremely poor processability of UHMWPE,so makes it difficult to processed UHMWPE via conventional methods like injection molding,screw extrusion.As a novel polymer processing apparatus,the eccentric rotor extruder(ERE)greatly change the way of plastic processing by changing traditional shear flow to elongational flow.The eccentric rotor extruder is a positive-displacement device and less dependence on the material’s own characteristics.Study the microstructure and performance evolution of UHMWPE in the extrusion process of ERE,provides a reference for the property control of UHMWPE.The development and innovation of polymer processing theory and application of extreme rheology has important value in science sense and engineer.In this paper,the UHMWPE with a molecular weight of 2.5×10~6 g/mol is extruded by ERE.By comparing the compression molded UHMWPE samples that have been pretreated by the ERE(CM-UHMWPE)with the non-pretreated compression molded samples(CM-UPE30),it is found that the elongational flow reduces the entanglement of molecular chains within particles,promotes the diffusion of interparticle chains,and decreases the melt defects of UHMWPE.The eccentric rotor extruder can also maintain the molecular weight of UHMWPE.Compared with CM-UHMWPE,the mechanical properties and friction resistance of CM-UPE30 increased,the yield strength increases from 21 MPa to 23 MPa,the tensile strength increases from 36 MPa to 46 MPa,the elongation at break increases from 610%to 700%,and the abrasion loss decreases from 1.73 mg/1000r to 0.93 mg/1000r.The influence of processing temperature and rotor speed on the structure and properties of UHMWPE is studied.With the increase of processing temperature,the yield strength and elongation at break of UHMWPE increase gradually,but the tensile strength increases firstly and then decreases,and reaches the maximum when the processing temperature is 180-200-220℃.Increasing the rotor speed,reduces the residence time of UHMWPE in the extruder which is inversely proportional to the rotor speed,linearly increases the output,and the increases melt temperature.When the rotor speed is increase from 10 rpm to 35 rpm,the yield strength of UHMWPE increases from 22 MPa to 24 MPa,the tensile strength increases from48 MPa to 54 MPa,and the elongation at break increases from 662%to 713%.As the rotor speed increases,the elongational strain rate and the force of the elongational flow increases,which contributes to the disentanglement of the UHMWPE molecular chain,improves the crystallization ability of UHMWPE,increases the crystallinity and grain size,and reduces the melting defects.In eccentric rotor extruder,UHMWPE can also maintain the molecular weight of UHMWPE well at high processing temperature and high rotor speed.Based on the above experimental results,the effects of material properties(molecular weight and processing aid)on the structure and properties of UHMWPE were further studied using fixed processing parameters.With the increase of molecular weight,the yield strength and elongation at break of UHMWPE decrease,and the tensile strength increases first and then decreases.When the molecular weight of UHMWPE is low,the UHMWPE extruded by the eccentric rotor extruder has a good melt plasticization effect.The higher the molecular weight,the more physical entanglement points and more stress points during the stretching process.When the molecular weight is higher than a certain value,the melting effect of UHMWPE in the extruder is deteriorated,the melting defects are increased,and the tensile strength is lowered.With the increase of rotor speed,the molecular weight has little effect on the tensile strength of UHMWPE.GUR X205 is a kind of modified UHMWPE with a molecular weight of 4.5×10~6g/mol.The volumetric tensile deformation produced by the ERE has an efficient dispersive mixing effect on GUR X205.Compared with the direct molded sample,the tensile properties of the GUR X205 molded sample extruded by the eccentric rotor extruder increased overall,the yield strength increases from 22 MPa to 23 MPa,the tensile strength increases from 37 MPa to 41 MPa,and the elongation increased from 643%to 747%.Due to the high melt plasticization efficiency of the eccentric rotor extruder,the thermomechanical history of UHMWPE in the extruder is short,and thermal degradation due to long heating time is avoided,which is favorable for the maintenance of its excellent performance.In addition,the elongational flow promotes the disentanglement of the UHMWPE molecular chain along the tensile direction,which can improve the processing performance of UHMWPE and reduces the melting defects of the sample,which contributes to the improvement of the mechanical properties of UHMWPE.Compared with other traditional polymer processing apparatus,ERE can process pure UHMWPE with higher quality and efficiency.