Durability Study Of Epoxy Resins And Their Carbon Fiber Reinforced Composites

Epoxy resins are broadly considered in civil engineering,marine,and aerospace applications as coatings,adhesives,and reinforcement matrices for fiber reinforced polymer(FRP)composites.Recently,FRP composites have attracted significant interest in many areas,owing to their low density,spectacular mechanical strength,lightweight,anticipated long service life,simple installation,and high corrosion resistance.Since FRP composites while applied in civil engineering applications they are anticipated to use for over 50 years so,those materials’ long-term service life performance under aggressive conditions is essential to study.Therefore,the degradation caused by the hygrothermal aging of such composites would adversely affect their safety,economic efficiency,and potential applications.Different formulations of epoxy resins were prepared in this study,and the superior properties performed three epoxy resins and their FRP composites were extracted for the further study.The aging study revealed that epoxy resins are more vulnerable to acidic environments.The medium glass transition temperature epoxy exhibited superior properties,which can be applied to various civil engineering applications.The main research contents and results were as follows:The thermal,mechanical,moisture absorption of low glass transition temperature epoxy resin system(LTEP)and its CFRP composites in water,acid,and alkaline solutions at 20 ℃,40 ℃,and 60 ℃ soaking temperatures were studied.The higher degradation of LTEP resin and composite specimens has happened in acidic solution,than alkaline medium.The service life of LTEP resin and composites in harsh environments was predicted by applying the Arrhenius equation.The mechanical and thermal analyzes results revealed that the immersion temperature and solution can influence the degradation of resin and composites showing a higher service life for the samples immersed in water and alkaline solution.The durability of LTEP resins in acid medium were exhibited around 4.9% after 10 years which is the least durable.LTEP/CFRP composites,prediction results were revealed that the composites exposed in water exhibited around 42.6–26.8% of tensile strength retention values for 20 years.The tensile strength retention of CFRP composites in acid medium were indicated around 11.8–5.3% after 15 years which is the least durable.The effects of water,acid and alkaline solution at different soaking temperatures like 20 ℃,40 ℃,and 60 ℃ on the thermal,mechanical,moisture absorption of medium glass transition temperature epoxy resin(MTEP)and its CFRP composites were studied.The thermal and mechanical analysis results reveal that the CFRP composites were more vulnerable to HCl owing to the higher moisture absorption and diffusion of HCl into their cracks.The service life of the MTEP/CFRP composites predicted by the Arrhenius equation showed that the tensile strength retention values varied from 63.6-48% in water for 20 years.The durability of the samples in the alkaline medium was better than that in acid and lower than that in water,and ranged from 49.8-32.7%.The MTEP/CFRP composites exhibited low durability in the acidic solution,with the tensile strength retention after 15 years ranging from 44.9-29.1%.However,compared with LTEP resin and composite,the MTEP resin and related composite exhibited less degradation.The effects of immersion in water,acid,and alkaline solution at temperatures of20 ℃,40 ℃,and 60 ℃ on the thermal,mechanical,moisture absorption behavior of a high glass transition temperature epoxy resin(HTEP)and its CFRP composites were studied.The formation of broad secondary peaks at elevated temperatures and the lowering of tan delta peaks were remarkably observed due to the high damping and additional crosslinking.The prediction results revealed that the tensile strength retention values varied from 62.9-15% for composites in water for 20 years.The durability of the composites in the alkaline solution was much better than that in acid and lower than that in water,and ranged from 45.7-4.4%.The composites exhibited lower durability performance in the acidic medium,with the tensile strength retention for 15 years ranging from 24.3-1.4%.Compared with LTEP and MTEP,the HTEP resin and composites exhibited higher deterioration.From the durability performance analysis,superior performance was observed in MTEP resins,so multi-walled carbon nanotubes(MWCNTs)were incorporated into it to improve mechanical and thermal properties.The thermal,mechanical,microscopic,and water uptake behaviors of neat epoxy and epoxy/CNT nanocomposites were analyzed.The addition of surfactant-modified MWCNTs into the epoxy caused an evident increase in the mechanical and thermal properties.Additionally,the MWCNTs could impart a reduction in the surface’s wettability of the epoxy matrix,leading to an increase in the contact angle and a reduction in the water uptake,which is significant to improving the durability of the epoxy resin systems.Moreover,the higher weight concentration of the MWCNTs indicated a greater water uptake owing to agglomeration,which may cause the formation of plenty of microcracks and microvoids in the nanocomposites.