Monitor The Curing Process Of Thermosetting Resins

Thermosetting resin-based polymer composites,have many superior properties,such as high temperature resistance,high hardness,good chemical resistance,high size stability and so on.Thermosetting resin-based composites have been widely used in protective coatings,adhesives,casting materials,reinforced plastics and other fields.The properties of thermosetting resin-based composites are closely related to their molecular structure which largely depends on the resin type,curing temperature,curing time,curing degree and other factors related to the curing process.In order to develop thermosetting resin-based composites with high performance,it is necessary to effectively monitor the curing process of thermosetting resins,and investigate the effects of resin system and curing technology on curing process and curing degree.The curing processes of epoxy/amine system and epoxy/anhydride system were monitored and analyzed comprehensively for the first time by AC impedance spectroscopy.Effects of curing agent,accelerant,curing temperature and time on curing degree were investigated.A new equation used to estimate the curing degree of the epoxy resin system was proposed which takes impedance modulus at low frequency as the variable.Differential scanning calorimetry(DSC)method was used to verify the results of new equation,which shows that the curing degree measured by these two methods are in good agreement.Then the curing scheme for casting materials was optimized based on the monitoring results.The results show that epoxy-based casting material prepared by three-step curing scheme(80?/60min+120?/10min+160?/5min),the optimum curing scheme,exhibits best properties.The curing degree and tensile strength of this casting material prepared are98.0%and 72.3 MPa,respectively.This tensile strength increases by 23%compared with that of isothermal curing scheme(120?).Epoxy modified furan/polyaniline(PANI)protective coatings were prepared.The degradation processes of coatings in acid,alkali and salt solutions were monitored by Electrochemical Impedance Spectroscopy(EIS).The impedance spectra were simulated by equivalent electrical circuits,and changes in various parameters related to coating structure and protective performance during the degradation process were analyzed.Combined with XPS analysis and measurement of coating properties,the additive amount of PANI nanowires was optimized.Proper addition of PANI can increase the adhesion of the coating,promote the formation of dense passivation layer on the surface of carbon steel,and effectively delay the aging degradation of epoxy modified furan coating.In addition,the EMFA/PANI-1.0 coating containing 1.0%PANI exhibits the best overall performance.Several sets of epoxy/tephra micro-particle(TMP)and epoxy/basalt micro-plate(BMP)protective coatings were prepared.The degradation processes of these coatings under sever temperature shock cycles and in acid solution were monitored by EIS.Effects on coating protective performance and degradation of TMP and BMP were investigated.The experimental results show that TMP and BMP prevent the propagation of cracks in epoxy coating,significantly improve the temperature shock resistance and cracking resistance,and that can effectively delay the aging degradation of epoxy coatings under temperature shock from-80? to 230?.Besides,the degradation rate of E51/T31/BMP coating in salt solution is the slowest.In conclusion,AC impedance spectroscopy can effectively monitor the curing process of thermosetting resin and the degradation process of thermosetting resin-based composites.It can provide valuable theoretical guidance for the formulation optimization,curing process optimization,delaying degradation and evaluating lifetime of thermosetting resin-based composites.