PTFE Nanocomposites In Situ Fabricated With Different Dimension Hydroxyapatites And Their Tribological Performance

Polytetrafluoroethylene(PTFE)possesses good chemical stability,corrosion resistance and self-lubrication,which is widely used in chemical,mechanical and biological materials.Although PTFE is a plastic with excellent comprehensive properties,its low mechanical strength and hardness and poor wear resistance also limit its application.Hydroxyapatite(HAP)is an inorganic material with good biocompatibility and bioactivity which is widely used in biological materials and drug fields.However,its low strength and high brittleness limit its use.HAP can be filled into other materials to make up for its inherent defects while maintaining its biological activity.The size and morphology of HAP affect the properties and application fields of the material.The specific surface area of nanometer HAP is large and the bone conductivity and solubility are strong and it has good biological activity and biocompatibility,and its mechanical properties are better than that of micron HAP.By hydrothermal synthesis,zero,one and two dimensions of nanoscale HAP were in situ filled into PTFE,improved nanometer hydroxyapatite dispersed in matrix and the interface bonding ability.We studied the influence of the dimensions on the physicochemical and tribological properties of nanocomposites.The nanocomposites were prepared with the bioactivity of HAP and good toughness of PTFE,expand the HAP in the range of application in the field of biological materials.1.PTFE composite in situ filled with hydroxyapatite nanoparticles and its tribological performanceHAP nanoparticles are easy to be synthesized and widely used.In this paper,Ca(NO3)2·4H2O and(NH4)2HPO4 were used as calcium and phosphorus sources.HAP nanoparticles were synthesized by hydrothermal synthesis under the condition of 60?water bath and filled into PTFE in situ to prepare HAP nanoparticles/PTFE complex(HAP-NP/PTFE).Through SEM,TEM,XRD,XPS,FT-IR,DSC,TG,video optical contact Angle measuring instrument,universal testing machine,high-speed ring friction and wear testing machine,3D laser microscope and other instruments,the structural properties,thermal properties,hydrophobic properties,mechanical properties and tribological properties of HAP nanoparticles/PTFE composites were studied.The HAP nanoparticles synthesized in the experiment have a particle size of 20-30 nm and are highly dispersed on the material surface.They had a good interaction and interface with PTFE matrix material.The addition of hydroxyapatite nanoparticles increased the glass transition temperature,crystallinity,hydrophobicity and elastic modulus of the composites.Under the lubrication of simulated body fluids,the average tribological coefficient volume wear rate of the composite was also effectively reduced,and reached the minimum when the filling amount of HAP nanoparticles was 1%,which was 55.0%and 60.7%lower than that of pure PTFE.HAP nanoparticles prepared by hydrothermal synthesis were filled into PTFE in situ to produce the composite material.The filler had good dispersion in the matrix,and effectively improved the tribological properties of the material,and promoted the heat resistance of the material.2.PTFE composite in situ filled with hydroxyapatite nanowires and its tribological performancesOne-dimensional nanomaterials have the characteristics and properties of both nanometer and micron scale materials,with high crystallinity and length-diameter ratio,which has shown a good application prospect.In this chapter,CaCl2 and NaH2PO4 were used as calcium source and phosphorus source,and oleic acid was used as template.HAP nanowires were filled into PTFE in situ for 24 h under constant temperature hydrothermal synthesis at 180? to prepare HAP nanowires/PTFE complex(HAP-NW/PTFE).The diameter of the prepared HAP nanowires is between 100-300 nm,the ratio of length to diameter is about 50-150,the size distribution is uniform,the filler and the substrate material have good interaction,and the HAP nanowires were highly dispersed.The vitrification transition temperature,melting point and crystallinity of HAP-NW/PTFE composite were all higher than that of PTFE matrix,Hydrophobicity and mechanical properties of the material were also improved at lower filling quantity.Compared with the PTFE,the tribological properties of HAP naowires/PTFE composites under the lubrication of simulated hody fluids were significantly improved.When the filling amount of HAP nanowires was 0.5%,the friction coefficient and volume wear rate of the prepared HAP/PTFE nanowires were only 34%and 6.7%of that of the matrix.Compared with HAP nanowires/PTFE complex prepared by mechanical mixing(HAP-NW/PTFE-M),HAP nanowires/PTFE composite prepared by in-situ filling showed better thermal properties,mechanical properties and tribological properties.This should be attributed to the good dispersion and interfacial bonding of HAP nanowires in the matrix3.PTFE composite in situ filled with hydroxyapatite nanowires with adjustable length to diameter ratio and its tribological performanceThe properties of hydroxyapatite nanowires are closely related to the size of their length-diameter ratio,which is affected by the reaction conditions in the reaction system On the synthesis method of HAP nanowires,HAP nanowires with different length-diameter ratios were synthesized by changing the amount of ethanol(alcohol-water ratio)and filling them into PTFE matrix in situ to obtain HAP nanowires/PTFE complex(HAP-NW/PTFE).The SEM figure showed that the length-diameter ratio of the hydroxyapatite nanowires synthesized in the experiment decreased with the increase of the alcohol-water ratio.The vitrification transition temperature,melting point and crystallinity of HAP nanowires/PTFE composites with different length-diameter ratios were all higher than that of the pure PTFE,and the crystallinity of the composites increased with the decrease of the length-diameter ratio of HAP nanowires.The tensile strength and elongation at break of HAP nanowires/PTFE composite with larger diameter were higher than those with smaller length-diameter ratio.The average friction coefficient and volume wear rate of the composite were lower than that of the pure PTFE,indicating that the addition of HAP nanowires with different length-diameter ratios played an anti-friction and anti-wear role.Therefore,the average friction coefficient and volume wear rate of PTFE composites with larger diameter HAP nanowires were lower than those filled with smaller length-diameter ratio.4.PTFE composite in situ filled with hydroxyapatite nanosheets and its tribological performanceHydroxyapatite with two-dimensional morphology has a unique lamellar main structure,showing good compatibility and lubrication.In addition,the flake material has a good role in promoting on the mechanical property of material.Based on CaCl2 and NaH2PO4 for calcium and phosphorus source,sodium acetate as a buffer solution,under the condition of 75? water bath.Hydroxyapatite nanoparticles were filled in situ to PTFE by hydrothermal synthesis method,obtained HAP nanosheets/PTFE composites(HAP-NS/PTFE).The length and width and thickness of the prepared HAP nanosheets tablet are about 1 ?m-2.5 ?m,200 nm-400 nm and about 50 nm respectively.The in-situ filling of HAP nanosheets increased the glass transition temperature and melting point of the composite.Under the condition of low filling amount,HAP nanosheets played the role of heterogeneous nucleation and improves the crystallinity of the composite.The hydrophobic properties of the compounds were also improved.Compared with the substrate material,the tribological properties of HAP nanosheets/PTFE composite were improved under the lubrication of simulated body fluids.When the filling amount of HAP nanosheets was 1%,the friction coefficient and volume wear rate were only 34.3%and 24.5%of the pure PTFE.In addition,PTFE composites prepared by in-situ filling had better tribological and mechanical properties than mechanically mixed PTFE composites.In summary,in this paper,zero-dimensional HAP nanoparticles,one-dimension HAP nanowires with controllable length-to-diameter ratio and two-dimensional HAP nanosheets were prepared by hydrothermal synthesis under different conditions and filled into PTFE in situ.Compared with the method of mechanical mixing,the nano-HAP prepared by in-situ filling were highly dispersed in PTFE,which played a filling enhancement.The filling effect of nano-HAP in different dimensions is different,the heat resistance,hydrophobicity,mechanical properties and tribological properties of the composite were improved to different degrees compared with the pure sample at low filling amount.In terms of mechanics,HAP nanowires had the strongest toughening effect on the composite.In terms of tribological properties,HAP nanowires had the best anti-friction effect on the composite,followed by HAP nanosheets.In terms of thermal properties,the improvement effect of three kinds of nanometer HAP were similar.In terms of hydrophobic properties,HAP nanowires had the best enhancement effect,followed by HAP nanoparticles.In this paper,the structure-activity relationship of three morphologies of nanometer HAP was investigated and discussed in order to provide a feasible reference for the application of nanometer HAP in the direction of bio-wear-resistant materials.