Preparation And Performance Of PTFE Matrix Composites Reinforced By Fibers And Powders

As thermoplastic, polytetrafluoroethylene (PTFE) which is famous as "The King of Plastic" has been widely used as antiseptic and friction materials for excellent chemical stability and lubricating properties. However, the application of PTFE is limited due to poor wear resistance and mechanical properties. Hence, methods of filling modification, surface modification and mixing modification have been employed to improve PTFE properties. In the study, PTFE matrix composites were prepared and reinforced by filling fibres, powders or graphite. Fibers, powders and graphite were used as reinforcing component to prepare PTFE composites. Effect of composition ratio on the properties of PTFE matrix composites was analyzed and the reinforced mechanism was also investigated.The mechanical properties of pure PTFE and PTFE matrix composites were characterized through tensile, impact, hardness and compression tests. The results showed that the hardness of PTFE matrix composites was increased twice times more than that of PTFE by filling PPS and PPTA fibers, or by filling SiO₂ powder, while the hardness was increased slightly by filling GF. Adding PPS or PPTA fiber into PTFE, the tensile strength of composites was increased about 10 percent. However, the tensile strength was decreased about 30-70 percent by filling GF, powder of PPS fiber, PPS powder or SiO₂ powder. The impact strengths were increased for 27, 47 and 23 percent when GF, powder of PPS fiber and PPS powder were filled, respectively. The compression strength was increased about 17 and 15 percent when filled GF and SiO₂, respectively. However, the compression strength was decreased for 21-44 percent when filled PPS and PPTA. Compression strength could be enhanced by filling graphite, but hardness, tensile strength and impact strength were decreased. PTFE composites, cooperatively reinforced by fibers, powders and graphite, have higher tensile strength and impact strength, but have a little lower compression strength than those of pure PTFE.The friction and wear properties of pure PTFE and PTFE composites were determined by scanning electron microscopy (SEM). The friction mechanism of PTFE composites which reinforced by fibers, powders or graphite was studied. The results indicate that fibers and powders which embedded in PTFE matrix preferentially support the external load and can pass the compressive stress and shear stress on friction surface to inner of PTFE matrix, and avoid stress concentration. Hence, it is effective for preventing large-scale fragmentation of PTFE and improving wear resistance. However, fibers and organic powder are prone to congregate on wear surface, resulting in high friction coefficient. At the same time, due to external load, fibers may shed off and cause particle abrasion. Graphite can form a lubricating film on wear surface and reduce friction coefficient while improve wear resistance. The friction force of fibers can be reduced by filling graphite which can act as lubricant to prevent fibers shed off. Friction coefficient and wear rate were decreased by filling SiC>2, while other fillers made friction coefficient increase and wear rate decrease. The PTFE composites, cooperatively reinforced by fibers, powders and graphite, have better friction and wear properties.Hence, the conclusion can be drawn that the PTFE matrix composites reinforced by fibers, powders and graphite have better wear properties and comprehensive mechanical properties. The optimized mass ratios of raw materials are 15wt%PPS fiber+15wt%Gr+70wt%PTFE, 10wt%Powder of PPS fiber+20wt%Gr+70wt%PTFE, 10wt%PPS powder+20wt%Gr+70wt%PTFE, 20wt%PPTA+10wt%Gr+70wt%PTFE, 20wt%GF+10wt%Gr+70wt%PTFE and 15wt%SiO₂+15wt%Gr+70wt%PTFE.