Preparation And Properties Of Modified CaCO₃ Filled Ptfe Composites

As a kind of relatively widely used special engineering plastic,Polytetraflouroethylene?PTFE?possesses excellent properties of chemical stability,high temperature resistance,good corrosion resistance,good self-lubricating,and anti-adherence.It has the extremely widespread application in machinery manufacturing,electronics,aerospace,petrochemical industry,and many other industrial sectors.Literatures about reducing its cost while maintaining high performance have been one of the hot research topics in the field of materials science and engineering.The modification of PTFE by incorporating inorganic fillers is one of the important methods to enhance the ultimate properties of PTFE.As the current most used inorganic filler in polymer matrix composites,heavy calcium carbonate?CaCO₃?and glass fiber?GF?were selected as the two fillers to fill the PTFE matrix out of their being relatively unexplored.Paraffin was used to modify the heavy CaCO₃ and GF by means of surface-coating.The inorganic fillers'surface properties,modification process and filling amount has obvious effects on the structure and properties of composite materials,therefore,so the investigation of the effect of the surface properties,surface modification technology of inorganic filler and filling amount on the structure and properties of composite will help to design and apply new PTFE matrix composites.The main research content of this thesis is as follows:Paraffin was used to modify the heavy CaCO₃ by means of surface-coating,including dry modification and wet modification methods.PTFE/CaCO₃ composites were prepared by die pressing and sintering,and its mechanical properties were studied.The structure of modificed and unmodified CaCO₃ were analyzed by infrared spectrum analysis characterization,static experiments and water contact angle results showed the surface polarity changes of modified CaCO₃.The effect of two different surface modification methods on the mechanical properties of PTFE/CaCO3 binary composites was investigated.Results showed that both two modification methods can lead to the improvement of the elongation at break and tensile strength of PTFE/CaCO₃ composites,wet modification showed better effects than that of dry modification with the same CaCO₃ content.Through DSC analysis,the existence of the modified CaCO₃ has heterogeneous nucleation effect on PTFE,which improved the thermal stability of the composite.Modification in CaCO₃ has greatly increased their dispersion in PTFE matrix by SEM observation and BSE images,,and effectively avoided agglomeration phenomenon between filler particles.Based on the research of PTFE/CaCO₃ binary composites,GF was introduced to further explore the relationship between composite'performance in order to gain greater performance breakthrough.After GF wet modification,a series of PTFE/GF binary composites,PTFE/CaCO₃/GF ternary composites were prepared.Through the comparison of mechanics performance and thermodynamic performance under different composites formula,the suitable modification process and conditions for this research system were explored,the cause of the differences between composites properties were analyzed by SEM photographes.Existence of wet modified GF obviously improved the tensile strength of composite,especially after the GF were wet modified,composites reinforced with wet modified CaCO₃ and GF had better performance than that of the composites reinforced with only CaCO3 or GF,and PTFE/CaCO3/GF ternary composites remained high mechanical performance with high filler content.Clear and coincident dispersity of filler particles and interface bonding strength improvements were proved through SEM photographs for the composites with modified fillers.Vicat softening temperature?VST?test data showed great improvement,which means thermal stability of the composites were improved by wet modified fillers.