Study On A New Wear Resistant Material Of UHMWPE Modified With Schiff Base Cu(Ⅱ) Complex

Due to its innocuity and excellent wearability, Ultra-high molecular weight polyethylene(UHMWPE) is ideal for medical polymer materials. But gradually it is found in the course of using UHMWPE that it has many defects, such as low strength, surface hardness, and low heat distortion temperature. Therefore application of Schiff base metal ionic complexes as additives to the physical modification of UHMWPE's wearability attracts research interest.Experimental investigations and theoretical exploration about disc of UHMWPE and modified UHMWPE with Schiff Base Cu(Ⅱ) complexes against pin of 45# steel were developed involved in the scientific problems of project "Study on a new wear resistant material of UHMWPE modified with Schiff base Cu(Ⅱ) complexes" in this paper. It was tested by a pin-disk tester (surface-surface contact) under the condition of dry friction, with the rotational speed of 60 rpm, normal load of 40 kg±3 and testing time of 1.5h, at 20℃and 60% RH (relative humidity).Firstly, friction and wear behaviors of UHMWPE with molecular weight of 2 million, 3 million, 5 million, 9 million were tested, and in order to investigate wear mechanism, topographies of worn surface were observed by SEM. It was found that friction coefficient of UHMWPE with molecular weight of 3 million was minimal; with the increase of molecular weight, the weight loss of wear of UHMWPE was first reduced and then increased, and the weight loss of wear of UHMWPE with molecular weight of 3 million was minimum; in addition, abrasive wear and adhesive wear were showed in wear mechanism of UHMWPE, thereinto, the wear of UHMWPE with molecular weight of 3 million was the least. So the UHMWPE with molecular weight of 3 million whose friction and wear properties were better than other three pure UHMWPE can be choosed as basic material in study of Schiff base Cu(Ⅱ) complex modifying UHMWPE.Secondly, five additives modifying UHMWPE were successfully synthesized, they are bis-salicylaldehyde-ethylenediamine Schiff base Cu(Ⅱ) complex, bis-salicylaldehyde-1,3-propanediamine Schiff base Cu(Ⅱ) complex, bis-salicylaldehyde-1,6-hexanediamine Schiff base Cu(Ⅱ) complex, bis-salicylaldehyde-1,2-cyclohexanediamine Schiff base Cu(Ⅱ) complex and bis-salicylaldehyde-1,2-benzenediamine Schiff base Cu(Ⅱ) complex; friction and wear behaviors of UHMWPE with molecular weight of 3 million modified by five bis-salicylaldehyde diamine-type Schiff base Cu(Ⅱ) complexes with different content (2.5%, 5.0%, 10%, 15%) were tested respectively, in order to investigate wear mechanism, topographies of worn surface were observed by SEM and the main element composition of the worn surface was determined by EDS, and the law of tribological modifying activity influenced by structural units was analysed. It was found that the friction and wear properties of modified UHMWPE can be effectively improved by adding the bis-salicylaldehyde-ethylenediamine, bis-salicylaldehyde-1,3-propanediamine Schiff base Cu(Ⅱ) complex and bis-salicylaldehyde-1,6-hexanediamine Schiff base Cu(Ⅱ) complex, and the friction coefficient and weight loss of wear of modified UHMWPE againet steel pin decreased with the content increasing of Schiff base Cu(Ⅱ) complex in UHMWPE within the range of 10 wt%,namely, the effect of reducing wear of modified UHMWPE with 10 wt% additive was the best, thereinto, the friction coefficient and weight loss of wear of UHMWPE modified with 10 wt% 1,6-diamine Schiff base Cu(Ⅱ) complex was minimum; but the friction and wear properties of UHMWPE modified by bis-salicylaldehyde-1,2-cyclohexanediamine Schiff base Cu(Ⅱ) complex modified and bis-salicylaldehyde-1,2-benzenediamine Schiff base Cu(Ⅱ) complex were not improved; abrasive wear was showed in wear mechanism of modified UHMWPE disc specimen with bis-salicylaldehyde-1,6-hexanediamine Schiff base Cu(Ⅱ) complex and steel pin specimen, and selective transfer effect, of Cu element from its additives was found, which can reduce friction and wear of the surface of steel pin against it. It seems that diamine Schiff base Cu(Ⅱ) complex which contains open chain structure with relatively more carbon atoms has more activity of tribological modification, due to its similar methylene unit in the structure of UHMWPE, and the activity of open chain is better than that of alkyl and aromatic ring.