Study On Thermal Stability And Repairability Of PVC

PVC is widely used due to its flame retardancy,wear resistance,chemical corrosion resistance,low gas permeability,comprehensive mechanical properties,transparent products,electrical insulation,thermal insulation and sound insulation.However,due to defects in the chemical structure of PVC,resulting in poor thermal stability and low impact strength,PVC stabilization,high performance and functionalization have been receiving much attention.In this paper,the degradation and aging of PVC were first simulated,and then the D-A reaction of ethyl bismaleamic acid(DMA)with degradation of PVC was carried out to achieve the mechanical property repair at the molecular level.The furan ring and PVC were realized by Friedel-Crafts reaction.And D-A reversible reaction with DMA was carried out to realize the thermal reversible self-repair of PVC.The main research work is as follows:(1)DMA-based materials were synthesized,and simulated the aged degradation of PVC.The tensile properties of the tensile strength and elongation at break were 109.8%and 150.3%,respectively.The FTIR before and after the repair of-PVC proved that the mechanism of the repair reaction was the Diels-Alder reaction of the conjugated polyene in the degraded PVC with DMA.(2)The Friedel-Crafts grafting reaction of furan and PVC was carried out by microwave irradiation,and the reaction conditions were optimized.The unstable structure of PVC was modified by the replacement of abnormal structure chlorine atoms by furan ring,and PVC was realized from the source.Stabilization.The optimum conditions for the grafting reaction of furan and PVC with Friedel-Crafts were as follows:reaction temperature was 45℃,microwave irradiation for 15 min,Fur:PVC:AlCl3=1:1:0.01,graft ratio was 11.47%,and the grafting reaction was repaired.The structural defects of PVC delayed the elimination reaction of HCl and improved the thermal stability of PVC:Congo red heat stabilization time was extended by about 4 min.By calculating the thermal degradation kinetic parameters,the activation energy of the first degradation stage(de-HCl)of furan grafted PVC was increased compared with PVC.(3)Based on the thermoreversible D-A reaction between the introduced furan ring and DMA,a Fur-PVC-DMA self-repairing system was constructed.The polarized microscope was used to observe the repair of scratches at different temperatures and at different times.It was proved that the D-A bond with thermal reversibility was successfully introduced,and the self-repair of the material was achieved.The heat treatment temperature was 120℃.The 60℃ heat treatment repair experiment was carried out on the pull-off dumbbell self-repairing system,and the tensile strength repair rate was 52.6%.