Test And Performance Evaluation Of PTFE Sewing Thread

The atmosphere is increasingly polluted by the high-temperature flue gas.Polytetrafluoroethylene materials are widely used in high-temperature filtration because of their excellent physical and chemical properties.However,during the application,more and more cases of PTFE sewing thread failing are found under the effect of long-term hot smoke.For example,the PTFE sewing thread is weakened to failure due to the continuous high temperature effect,and the pinhole is gradually enlarged due to the friction of the sewing thread,thereby causing the leak of ash and the filtering effect to be deteriorated.Therefore,this paper takes 8 kinds of PTFE sewing thread as the research object,including PTFE/PPS composite sewing thread designed to improve the above problems.Their structure,tensile properties,wear resistance and thermal properties were tested and evaluated,which can provide reference for the research and application of PTFE sewing thread.The main research contents and conclusions of this paper are as follows:(1)Structure and tensile properties of PTFE sewing threadThe structure of the PTFE sewing thread was observed using SEM scanning electron microscope.It was found that the surface of the PTFE sewing thread was smooth and uniform in structure.PTFE/PPS composite sewing thread has many hairiness on the surface,which can form the plugging of the pinhole,increase the friction between the filter cloth and reduce the cutting of the filter bag by the smooth surface;PTFE sewing thread and PTFE/PPS composite sewing thread have different degrees of damage etching on the surface after high temperature effect.The tensile properties of the PTFE sewing thread were tested using a YG061FQ electronic single yarn strength meter.The results show that the rupture strength of PTFE sewing thread of 1540D?4230D at normal temperature is 1.89-2.70cN/dtex,and the elongation at break is 3.87-6.52%.The 2360D PTFE/PPS composite sewing thread has a breaking strength of 1.80 cN/dtex and an elongation at break of 5.95%.By comparing the tensile properties of PTFE sewing threads of different linear density and plying modes,it was found that the higher the linear density,the stronger the sewing thread,and the smaller the elongation at break,and the sewing thread with secondary ply is stronger.(2)Wear resistance of PTFE sewing threadThe self-made wear-resistant instrument was used to test the wear resistance of the PTFE sewing thread.The residual strength of the PTFE sewing thread and the residual strength after a certain times of friction were tested.The wear and fracture process were analyzed,and the effects of different structural parameters,frictional speed and preload on the wear resistance of the sewing thread were comparedThe results show that the times of friction of PTFE sewing thread of 1540D-4230D is between 1260 and 30258,and the times of friction at break increases with the increase of linear density.The performance of wear resistance of the one-ply sewing thread is better than the second-ply sewing thread.The PTFE/PPS composite sewing thread has a significantly improved wear resistance compared to a pure PTFE sewing thread which has the same linear density.The residual strength of the PTFE sewing thread decreases as the times of frictions increases.The wear and fracture process can be divided into four stages:fuzzing-filament bulging-partial rupture-complete rupture,and the third stage is the early warning stage,where a strong sudden decrease occurs.The times of friction at the break point will decrease with the increase of the preload and the speed,and the change can be predicted by a mathematical model of exponential function(3)Thermal properties of PTFE sewing threadThe sewing thread is subjected to high temperature treatment using a DHG-9240A electric thermostat blast drying oven.After the PTFE sewing thread was treated at the set five temperatures of 130?,160?,190?,220?,and 250? for 2 hours,the tensile properties of the sewing thread after heating were measured using an electronic single yarn strength meter.The results show that the PTFE sewing thread has a small heat shrinkage rate and hardly shrinks.The PTFE/PPS composite sewing thread added with PPS material has a large heat shrinkage rate of up to 10.12%,and it has good mechanical stability when it is cooled after being treated at a temperature of 130?to 250?After the PTFE sewing thread was treated at 190? for 2h,4h,6h,8h,and 10h,the tensile properties of the sewing thread after heating were tested by an electronic single yarn strength meter The results show that the PTFE sewing thread and the PTFE/PPS composite sewing thread have a small shrinkage after two hours of high temperature effect,and the heat shrinkage rate does not change significantly after prolonging the treatment time,and the sewing thread can maintain good mechanical properties after long-term high temperature effectThe PTFE sewing thread was treated at the set 5 temperatures for 2 hours using an INSTRON 5967 universal testing machine to test the tensile properties of the PTFE sewing thread under a thermal field.The results show that the breaking strength of the sewing thread under the thermal field is significantly reduced.When the temperature reaches 250?,the strength retention rate of the PTFE sewing thread is less than 30%.The PTFE sewing thread has obvious etching and grooves on the surface and has thermal creep phenomenon under the thermal field.The PTFE molecules are decomposed and oriented under the effect of high temperature.The thermal decomposition temperature of the sewing thread and the thermal stability of the material was tested using the temperament-synchronous thermal analysis instrument GCMS-STA.The results show that the initial decomposition temperature of the PTFE sewing thread is 572.9 C.The weight loss rate of the PTFE/PPS composite sewing thread at 650 C is lower than that of the PTFE sewing thread,which means the thermal stability of the composite is improved.