Abstract
The major hurdle in melt-processing of ultra-high molecular weight polyethylene (UHMWPE) nanocomposite lies on the high melt viscosity of the UHMWPE, which may contribute to poor dispersion and distribution of the nanofiller. In this study, UHMWPE/cellulose nanofiber (UHMWPE/CNF) bionanocomposites were prepared by two different blending methods: (i) melt blending at 150 °C in a triple screw kneading extruder, and (ii) non-melt blending by ethanol mixing at room temperature. Results showed that melt-processing of UHMWPE without CNF (MB-UHMWPE/0) exhibited an increment in yield strength and Young’s modulus by 15% and 25%, respectively, compared to the Neat-UHMWPE. Tensile strength was however reduced by almost half. Ethanol mixed sample without CNF (EM-UHMWPE/0) on the other hand showed slight decrement in all mechanical properties tested. At 0.5% CNF inclusion, the mechanical properties of melt-blended bionanocomposites (MB-UHMWPE/0.5) were improved as compared to Neat-UHMWPE. It was also found that the yield strength, elongation at break, Young’s modulus, toughness and crystallinity of MB-UHMWPE/0.5 were higher by 28%, 61%, 47%, 45% and 11%, respectively, as compared to the ethanol mixing sample (EM-UHMWPE/0.5). Despite the reduction in tensile strength of MB-UHMWPE/0.5, the value i.e., 28.4 ± 1.0 MPa surpassed the minimum requirement of standard specification for fabricated UHMWPE in surgical implant application. Overall, melt-blending processing is more suitable for the preparation of UHMWPE/CNF bionanocomposites as exhibited by their characteristics presented herein. A better mechanical interlocking between UHMWPE and CNF at high temperature mixing with kneading was evident through FE-SEM observation, explains the higher mechanical properties of MB-UHMWPE/0.5 as compared to EM-UHMWPE/0.5.
Highlights
Ultra-high molecular weight polyethylene (UHMWPE) is a long linear engineered thermoplastic with extremely high molecular weight of approximately 3 × 106 g/mol [1]
The tensile strength of MB-UHMWPE/0 reduced by almost half of the value exhibited by Neat-UHMWPE while no significant difference was observed in EM-UHMWPE/0 sample
Addition of cellulose nanofiber (CNF) through ethanol mixing reduced the tensile strength by 34% from 55.4 MPa (EM-UHMWPE/0) to 36.6 MPa (EMUHMWPE/0.5) whereas by melt blending, the reduction was only 11% which was from 31.8 MPa (MB-UHMWPE/0) to 28.4 MPa (MB-UHMWPE/0.5)
Summary
Ultra-high molecular weight polyethylene (UHMWPE) is a long linear engineered thermoplastic with extremely high molecular weight of approximately 3 × 106 g/mol [1] It possesses high resistance against impact, fatigue, chemical corrosion and abrasion, which stemmed from effective load transfer to its long linear backbone. Relatively low Young’s modulus and surface hardness of UHMWPE could limit the sustainability of this polymer against wear as a result of contact and slip with harder counterpart such as metal under repeated motion [8]. This results in abrasion where generated debris in turns may accelerate cracks leading to component loosening and failure [4,5]. These properties of nanocellulose make it an excellent material as UHMWPE fillers, for artificial joint application
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