| PFA is a copolymer of tetrafluoroethylene (TFE) and perfluoroalkyl vinylether (PAVE), which is also known as the meltable polytetrafluoroethylene. PFA not only have outstanding thermal and chemical resistance, excellent flame retardant, waterproof and self-lubricating properties as well as low coefficient of friction, but also can be processed by the traditional way of thermoplastics.In this paper, TGA, DSC, DMA, XRD, TG-FT1R, capillary rheometer, polarizing microscope as well as some other test methods were used to characterize the thermal performance, rheological properties and kinetics of thermal decomposition of the PFA. The optimal key processing parameters for melt spinning and hot-drawing of PFA fiber were explored. In addition, the influence of processing condition on the crystalline and orientation structures as well as mechanical properties of PFA fiber was also studied.Without any observed thermal degradation before470℃. PFA exhibits excellent thermal stability. Only when the temperature is higher than500℃significant decomposition occurs and the decomposition rate reaches the maximum of19.23%/min at553.5℃.When the temperature raises to510℃, PFA begins to decompose with the emission of CO2. tetrafluoroethylene (TFE) and hexafluoropropylene (HFE). When the temperature elevates to540℃fluorine phosgene (COF2) can also be detected. The maximum concentration of the gas generated by thermal decomposition happens at about600℃. When the temperature elevates to620℃. fluoride. phosgene, tetrafluoroethylene. hexafluoropropylene began to disappear and only absorption peak of CO2and C-F bond can be observed. In addition, the non-isothermal kinetics study has revealed that the thermal degradation of PFA resin belongs to second order reaction according to the Coats-Redfern method and the activation energy E-;237.4k.J/mol.The content of comonomer (perfluoropropyl vinylether, PPVE) of the used PFA is about4.62%. Due to the introduction of the comonomer, the degree of crystallinity is reduced to41.51%compared to PTFE, which made PFA can be melt-processed with a melt index of15.2g/10min. The melting point and melting enthalpy of PFA is about308℃and26.63J/g respectively. PFA spherulites is formed in the crystallization process of cooling from the melt when the temperature dropped from350℃to300.9℃.PFA melt is a non-Newtonian fluid. The non-Newtonian index of PFA melt is between0.154and0.187and increased with increasing temperature. Melt viscosity PFA decreases as the shear rate increases at different temperatures. And with increasing shear rate, the apparent viscous flow activation energy of PFA is gradually reduced, which indicates that temperature sensitivity of viscosity decreases with increasing shear rate. The structural viscosity index of the PFA melt is between1.29and1.41and the value of structural viscosity index increased, in another words, spinnability is improved under higher temperature.WXRD and DSC results show that the melting point and degree of crystallinity of the PFA fibers increased with increasing drawing ratios, which means the crystal structure is getting perfect. rate. At the same time, as the drawing ratio increased, orientation factor and sound modulus is gradually improved.Spinning experiments show that continuous and uniform PFA fibers can be prepared under the spinning temperature of390℃, with a winding speed of53m/min and screw speed of38r/min.The tensile strength and elongation at break of the as spun PFA fiber is0.89cN/dtex and57.3%respectively. The optimal heat drawing temperature of the PFA fiber is about280℃, under which PFA fibers can be drawn of3.4times. The mechanical property got to the maximum value with a tensile strength of2.45cN/dtex and elongation at break of32.7%. |
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