Preparation And Friction Properties Of Self-lubrication Polyurethane Materials

In this thesis,self-lubricating polyurethane composites were obtained by using different preparation routes and the relationship between the structure and tribological properties were evaluated:Porous self-lubricating polyurethane(PU)materials were prepared by non-solvent induced phase separation(NIPS);Oil-containing self-lubricating polyurethane was prepared by emulsion template method;Mesoporous silica(MS)with stimulation response features were prepared by surfactant-assisted sol-gel method,and addopting a lubricant container added into the PU matrix to prepared self-lubricating PU composite.The relationship between synthesizing parameters and structure of composites was studied.The influence of microstructure of composites on tribological properties have been investigated,the lubrication and wear mechanism of composites was discussed as well.(1)The porous self-lubricating polyurethane(PU)materials with micron-meter pores were fabricated by non-solvent induced phase separation(NIPS)method.The scanning electron microscopic(SEM)images and the intrusion/extrusion branches results demonstrated that the cross-section morphology of the materials is similar to that of the sponge and adjacent macropores were connected by interpenetrating pores which reveals the formation of 'ink-bottle'-type pores in porous PU films.Meanwhile,the porosity of the porous self-lubricating PU materials could be controlled by adjusting the PU solution concentrations and the oil content increased as the increasing of porosity.For the sample with PU solution concentration of 15 wt%,the porosity was found to be 69.93%.The results of centrifugation/heating test indicated that the porous self-lubricating PU materials have an excellent oil content performance owing to the“ink-bottle”type pore structure.Furthermore,the porous self-lubricating PU material will release the lubricating oil under the action of pressure and temperature which makes it exhibit excellent tribological properties.The tribological results show that the friction coefficient is 0.045 at 200 rpm,450N.In addition,it can be reasonably inferred that the lubricating oil contained in the self-lubricating porous material can only maintain the material in boundary lubrication regime during friction process based on the analysis of the Stribeck curves.(2)The oil-containing self-lubricating polyurethane materials were fabricated by emulsion template method,which realize the one-pot preparation of self-lubrication materials.The effects of emulsifiers with different HLB and dispersed phase fraction on the stability of emulsion system were investigated.The results show that the P123(HLB=8)can be used to stabilize the oil in oil(O/O)emulsion system.The SEM images show that the materials exhibit the spherical pore structure with the pore diameter falls in the micrometer range and the pore size of the material gradually increases with the increase of the inner phase fraction.Tribological tests show that the liquid paraffin storing in the polyurethane materials will be released to form a lubricating film on the friction interfaces.Meanwhile,the friction coefficient decreases with the increase of the dispersed phase fraction.When the dispersed phase fraction reaches 35%,the average friction coefficient of the self-lubricating composite decreases to 0.05 which is 93.06%reduce compared to pure PU.In addition,the formed lubricating film separates the frictional interfaces to avoid adhesive wear,thus PU-35 obtained the lowest wear rate.(3)Mesoporous silica(MS)with low density,high surface area and large interior space were synthesized by surfactant-assisted sol-gel method,and oil-laden mesoporous silica(OMS)were obtained by soaked into oil immersion.The as-prepared MS possesses high BET surface area(1542.35 m2·g-1)which satisfies the criterion for construction of ideal repository for storing enough lubricants.In addition,the thermal stimuli-responsiveness behavior of the OMS for lubrication has been investigated by thermogravimetric analyzer tester.The mechanical properties test show that methyl silicone oil has a toughening effect on the PU matrix,and the elongation at break of the OMS/PU composite increases compared with the MS/PU composites.But the tensile strength showed a downward trend with the increase of OMS content.Frictional tests show that the addition of OMS can effectively reduce the friction coefficient and wear rate of the material which is due to the fact that the lubricating oil in OMS is stimulated by frictional heat and released to form a lubricating film between the friction interfaces.Thus,PU composite with 10%OMS shows excellent lubrication performance(friction coefficient and wear rate weredecreased by 63.29%and 82.63%).Consequently,OMS can be used as a lubricating container to realize the friction reduction effect and antiwear properties of materials.