UHMWPE Powder Grafted Acrylic Acid And Tribological Properties Research Of Bulk Material

Ultra-high molecular weight polyethylene (UHMWPE) get more and more widely appreciated as replacement of the bone because of its excellent comprehensive mechanical properties and biocompatibility. In the present work, aiming at the current failure of UHMWPE, UHMWPE powder is grafted with the method of UV and solution grafting, and then it is molded. A series of experimental approaches were used to investigate performances of the treated and untreated samples, the results are as following:1. The result of graft rate test shows that, when the reaction was carried on under the UV, the graft rate rised with the ppm of photosensitizer. And the graft rate reached the maximum,5.5%, when the photosensitizer is 4phr.After that, the graft rate keep steady. In the solution graft, when the acrylic acid(AA) concentration is 10phr, the graft rate is the highest, and then if we went on improve the concentration of AA, the graft rate declined.2. The wetting angle of the untreated UHMWPE is 83-84°, and the wetting angle declined with the improvement of grafting, the lowest was 34-35°, which illustrated that the hydrophilicity of UHMWPE was improved.3. The hardness of the grafted samples were also improved and the solution grafted samples were the highest. When the graft rate is 2.16% using the UV, the tensile strength and elongation were improved. However, the tensile strength of all samples solution grafted were declined, and the lowest was just the 1/20 of the untreated samples.4. Under the lubricating fluid, the initial friction coefficient was higher, but it declined with the increasement of the sliding distance. Because the surface of samples was grafted with polar polymer and then format lubricating film, which prevented the direct contact between the basis material surface and the grinding material. The wear rate declined greatly, the wear rate of the sample with 3.5% grafting was just 1/4 of the untreated sample. Although the solution grafted samples had the lower friction coefficient, the wear rate is the highest and twice untreated, because the graft process broke the original properties of UHMWPE.5. Surface grafting of UHMWPE has a low friction coefficient, but with the increasement of the sliding distance, the grafted polymer layer was grinded off and the friction coefficient rised. The powder grafted samples had the different case. The graft polymer existed everywhere of the samples. When the dermal polymer was grinded off, the polymer from the subsurface could form the polymer brush, which could guarantee the stability and durability of lubricity. The result showed that, the wear rate of powder grafted samples is just half of the surface grafted after 24h worn.6. The worn surface morphology was observed, the grafted samples looked smoother, the untreated ones had a lot of furrow and peeling, which were the result of adhesion wear and abrasion wear. The major wear mechanism of grafted samples is fatigue wear because of the lubricating film of the polymer brush.