Abstract
Herein, we produced a series of ultrahigh molecular weight polyethylene/polypropylene (UHMWPE/PP) blends by elongational-flow-field dominated eccentric rotor extruder (ERE) and shear-flow-field dominated twin screw extruder (TSE) respectively and presented a detailed comparative study on microstructures and tribological properties of UHMWPE/PP by different processing modes. Compared with the shear flow field in TSE, the elongational flow field in ERE facilitates the dispersion of PP in the UHMWPE matrix and promotes the interdiffusion of UHMWPE and PP molecular chains. For the first time, we discovered the presence of the interlayer phase in blends with different processing modes by using Raman mapping inspection. The elongational flow field introduces strong interaction to enable excellent compatibility of UHMWPE and PP and induces more pronounced interlayer phase with respect to the shear flow field, eventually endowing UHMWPE/PP with improved wear resistance. The optimized UHMWPE/PP (85/15) blend processed by ERE displayed higher tensile strength (25.3 MPa), higher elongation at break (341.77%) and lower wear loss of ERE-85/15 (1.5 mg) compared to the blend created by TSE. By systematically investigating the microstructures and mechanical properties of blends, we found that with increased content of PP, the wear mechanism of blends varies from abrasive wear, fatigue wear, to adhesion wear as the dominant mechanism for two processing modes.
Highlights
The crystallinity of blends was acquired by differential scanning calorimetry (DSC), and the crystallinity of Ultrahigh molecular weight polyethylene (UHMWPE)
We propose by the twin screw extruder (TSE), which to betterbased compatibility of blends processed by ERE.asWe propose reason forattributes strong interactions on the principles underlying the process; shown in Figure 6a, under the shear flow field in TSE, the velocity gradient is perpendicular to the direction of the flow field, which tends to form a flow with weak interaction between the layers
UHMWPE/PP with with different differentcomponent component ratios developed by TSE
Summary
Ultrahigh molecular weight polyethylene (UHMWPE) has multiple advantages including good self-lubricating ability, low friction coefficient, high impact strength, fatigue resistance, and biological inertness, which demonstrates its potential use as a wear-resistant material in industrial bearings, protective layer, and artificial joints [1]. Owing to the relatively high average of UHMWPE, irregular inter-chain entanglement results in high regional chain density and low mass flow rate (MFR), making UHMWPE difficult to be processed by common injection molding or extrusion processes. The low surface hardness, low modulus of elasticity, and bending strength, and poor abrasion resistance of UHMWPE greatly limit its application [2]. It is of great significance to develop industrially viable UHMWPE-based wear resistant materials through the regulation of polymer composition and the optimization of processing technology [3]
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