Study On Reciprocating Friction And Wear Behaviors And Mechanism Of UHMWPE Modified With Schiff Base Copper Complex

Excellent dry friction and wear characteristic of ultrahigh molecular weight polyethylene(UHMWPE)modified with Schiff base copper complex against steel at higher sliding speed has been confirmed,but its reciprocating friction and wear behavior has not been carried out yet.This dissertation took development of new artificial joint materials and of potential application of polymer materials in nanopositioning as the background to go deep into studying reciprocating friction and wear behavior of UHMWPE modified with Schiff base copper complex against Ti6A14V under the condition of boundary lubrication with calf serum deionized water solution and discussing its wear mechanism.The optimization of type of Schiff base copper complexes as modified additives of UHMWPE,taking the tribological performance of modified UHMWPE as criterion,was carried out.New ways of improving the tribological characteristics of modified UHMWPE further were investigated through introduction of a ternary additive with a basic compound of Schiff base copper complex and of a new additive made up of micro-nano-powder of Schiff base copper complex.How the molecular weight of UHMWPE to influence on tribological performances of the pure UHMWPE and the modified UHMWPE with Schiff base copper complex was also investigated.Moreover,the sliding friction behavior at low speeds of UHMWPE modified by Schiff base copper complex was preliminary studied.The paper is going to do its best to provide a theoretical basis for application of the new tribomaterial,namely UHMWPE modified with Schiff base copper complex.The main conclusions and innovative points were as follows:1.Four types of Schiff base copper complex were synthesized as additives for modifying UHMWPE,they are Cu(?)complex with ethlenediamion-N,N'-bis(salicylidene);Cu(?)complex with N,N'-bis(salicylidene)-1,6-hexanediamine;Cu(?)complex with 1,2-cyclohexanediamion-N,N'-bis(salicylidene)and Cu(?)complex with 1,2-phenylendiamion-N?N'-bis(salicylidene).Their physical properties,chemical properties and micro-shape were identified and revealed by determination of M.p.,DSC,IR,UV,1HNMR and SEM.2.21 sets of representative data were tested with a homemade reciprocating friction and wear tester.Results showed that test parameters including surface roughness of titanium alloy,temperature of test environment,duration of test and components of some artificial synovia effected in evidence on reciprocating friction and wear behaviors of UHMWPE/Ti6A14V rubbing pairs.Testing parameters for investigating modified UHMWPE in the way of reciprocating friction and wear test with a short distance were designed and analyzed based upon this discovery,so the testing parameters for tests of this type were determined as:normal load(L)was 50N,surface roughness of titanium alloy(Ti6A14V)(R?)was 0.06±0.005?m,temperature of test environment(?)was 37?(simulate human body temperature),relative humidity of test environment was conditioned at 80%,duration of test(t)was 180min,and under the condition of boundary lubrication with 25vol.%calf serum deionized water solution(according to IS014242-1).Furthermore,this set of testing parameters was applied to investigate friction and wear behaviors of UHMWPE/Ti6A14V rubbing pairs,and results confirmed that the above determined testing parameters were right.3.A series of tests were carried out with the above determined testing parameters.For the tests the UHMWPE having a molecular weight of 2 million was modified with 5wt.%,1Owt.%and 15wt.%Schiff base copper(II)complex of 4 types of bissalicylaldehyde-diamine respectively,and the 12 types of modified UHMWPE were shaped for upper test specimens.Lower test specimens were all made from Ti6A14V.Friction and wear characteristics of these rubbing pairs were investigated.Their friction and wear mechanisms were analyzed by a confocal white light microscope(CWLM)and SEM,EDS and XPS.How the structural unit R of Schiff base copper complexes in modified UHMWPE to influence on their tribological modifying activity was also discussed.The main conclusions were as follows:a.Friction-reduction and anti-wear properties of the modified UHMWPE with 15wt.%Cu(?)complex with ethlenediamion-N,N'-bis(salicylidene)(in the abstract this modified UHMWPE was called“15%addl-UHMWPE" for short)were the best when additive content was range up to 15wt%.Friction coefficient of the 15%addl-UHMWPE/Ti6A14V had been reduced by 27%as compared with that of the pure UHMWPE/Ti6A14V.And in volume loss of wear the 15%addl-UHMWPE was only 74%as large as the pure UHMWPE.b.The law of the influence of the structural unit R of diamine Schiff base copper complex on the tribological modifying activity was that the smaller the group of the R was the higher the modifying activity was obtained.The Cu(?)complex with ethlenediamion-N,N'-bis(salicylidene)had the highest tribological modifying activity as its R group was the smallest.c.Wear mechanism of the pure UHMWPE/Ti6A14V and the 15%addl-UHMWPE/Ti6A14V was both three-body abrasive wear.Three-body abrasive wear could be decreased when content of Cu(II)complex with ethlenediamion-N,N'-bis(salicylidene)in the modified UHMWPE was up to 15wt.%,because in this case few low valance oxide TiO existing originally on the surface of the counterpart(Ti6A14V)was oxidized to high valance oxide TiO2 and generating TiC phase on the surface of the counterpart(Ti6A14V)was restrained effectively,so that the formation of wear debris containing high-hardness TiO and TiC was avoided and the three-body abrasive wear extent of the rubbing pair was reduced.At the same time a transfer of the main composition of calf serum as a boundary lubricant to the friction surface of Ti6A14V was inhibited effectively during reciprocating friction and wear,so that an early failure of lubrication of the calf serum was avoided.As a result,wear of the 15%add1-UHMWPE/Ti6A14V was obviously lower than that of the pure UHMWPE/Ti6A14V and other rubbing pairs of modified UHMWPE with 5wt.%and 10wt.%Cu(II)complex with ethlenediamion-N,N'-bis(salicylidene)respectively against Ti6A14V.4.Besides excellent friction-reduction and anti-wear properties,15%addl-UHMWE had a better thermal conductivity and an increased deformation resistance as compared to the pure UHMWPE.Moreover,its bio-compatibility was also clinically acceptable,so that it might be used as a new type of artificial joint material.5.Tribological characteristics of UHMWPE modified with 15wt.%Cu(II)complex with ethlenediamion-N,N'-bis(salicylidene)+ 5wt.%glycerol-polyethylene microencapsules(in the abstract this modified UHMWPE was called "SCG-UHMWPE" for short)were better than that of the 15%addl-UHMWPE when they paired up with Ti6A14V under the condition of boundary lubrication with calf serum,due to the addition of glycerol-polyethylene microencapsules to the former.According to the characteristics that the glycerol kept still its original properties and was distributed in the UHMWPE matrix,requirements for releasing glycerol from the SCG-UHMWPE were present.Releasing of glycerol enabled the SCG-UHMWPE to gain a self-lubricating ability.Results of tribological tests showed that the released trace glycerol was compatible with the boundary lubricant of calf serum;and their contribution to boundary lubrication was positive when they existed together,that is,their effect was synergistic.Because of its bio-compatibility,glycerol was acceptable for establishing artificial joint's self-lubricating ability through using it as a modifying additive of UHMWPE of artificial joint material.6.A kind of stable dispersed micro-nano-powder of copper(II)complex with ethlenediamion-N,N',bis(salicylidene)was successfully prepared,and its structure and partial size were identified by IR and SEM.It was confirmed that in the case of copper(II)complex with ethlenediamion-N,N'-bis(salicylidene)with 5wt.%.10wt.%and 15wt.%additive amount respectively the micro-nano-powder of copper(II)complex with ethlenediamion-N,N'-bis(salicylidene)was more effective for improving anti-wear property of the modified UHMWPE itself than the one with micro size when modified UHMWPE paired up with Ti6A14V during reciprocating friction and wear tests under the condition of boundary lubrication with 25vol.%calf serum deionized water solution.When additive amount was lower,such as 5wt.%,the micro-nano-powder of copper(II)complex with ethlenediamion-N,N'-bis(salicylidene)was more effective for improving anti-wear property of the modified UHMWPE itself and the counterpart(Ti6A14V)and for reducing friction of modified UHMWPE/Ti6A14V than the one with micro size.Besides the above mentioned two cases,when using same additive amount to modify UHMWPE,effects of the both additives with different powder size for improving tribological properties were corresponding.7.Influences of molecular weight of UHMWPE were obvious on friction and wear characteristics of pure UHMWPE and 15%addl-UHMWPE.It was demonstrated that when pure UHMWPE with a molecular weight of 2 million,3 million,5 million and 9 million was tested respectively against steel with a pin-disc tribometer in dry,the lowest friction coefficient of rubbing pair and the minimum wear of UHMWPE itself appeared in the case of 3 million.Moreover,reciprocating friction and wear tests were carried out for investigating influences of UHMWPE's molecular weight(2 million,3 million,5 million and 9 million)on tribological behaviors of pure UHMWPE/Ti6A14V and 15%addl-UHMWPE/Ti6A14V under the condition of boundary lubrication with 25vol.%calf serum deionized water solution.See from the function results,it was best for 3 million molecular weight also on increasing friction-reduction of rubbing pairs,enhancing wear resistance of the pure UHMWPE and the 15%addl-UHMWPE themselves and improving mating properties=of the pure UHMWPE/Ti6A14V and the 15%addl-UHMWPE/Ti6A14V.8.Influences of normal load(L),sliding velocity(v)and testing duration(T)on friction and wear of rubbing pairs of UHMWPE modified with 5wt.%,10wt.%and 15wt.%copper(II)complex with ethlenediamionN,N'-bis(salicylidene)respectively against a steel(100Cr6)sphere were investigated by a micro-tribometer under the condition of stroke(s=)lmm,v=50?m/s?1600?m/s,L?600mN and T?7600s.And for comparison testing of pure UHMWPE is were carried out under the same conditions.Results showed that under the condition of dry friction and at low speed the friction coefficient of modified UHMWPE with 5wt.%?15wt.%copper(?)complex with ethlenediamion-N,N'-bis(salicylidene)was independent from normal load and testing duration,and independent basically from sliding velocity;their values were obviously less than that of the pure UHMWPE;and their wear resistance was very excellent.These characteristics of the modified UHMWPE with 5wt.%?15wt%copper(?)complex with ethlenediamion-N,N'-bis(salicylidene)appearing in the case of friction at low speed accord to required performance of accurate friction control of a material used as rubbing pairs that nanopositioning technique expects of.