Study On Recycling Waste Carbon Fiber Epoxy Resin Composites By Subcritical Acetic Acid Swelling Method

In this paper,carbon fiber reinforced plastic（CFRP）was selected as the research object.Subcritical acetic acid was used as the main swelling medium to achieve the recovery and utilization of CFRP through swelling softened method,swelling layered method and swelling strengthening degradation method.The swelling and degradation characteristics of cured epoxy resin in subcritical acetic acid were studied.The main factors influencing the microstructure and mechanical properties of carbon fiber composites recovered by swelling softening method and swelling layered method were discussed.The main process and mechanism of synergistic catalytic degradation of epoxy resin by subcritical acetic acid and other organic solvents were studied.The main factors influencing the degradation rate of epoxy resin and the mechanical properties of recovered carbon fiber were studied.The recycle technical parameters of subcritical acetic acid were optimized.The main conclusions of this research are as follows:（1）CFRP can be rapidly softened and layered in acetic acid.CFRP was swelled and softened at the temperature of 100-180℃.The swelling rate of CFRP was around37.31%-68.42%.The swelled CFRP can be easily cutted into strips.Thses strips mixed with uncure epoxy resin can be prepared into new CFRP by hot pressing method.But the flexural strength of new CFRP is only 15%-46%of the original CFRP.CFRP was swelled and partially degraded at the temperature of 220-260℃,thus the dissociation can be observed.the swelling rate of epoxy resin was 114.74%-196.38%,and The degradation rate of epoxy resin was 12.7%-45.83%.New CFRP can be prepared from swelled and layered materials,and the flexural strength of the new CFRP was similar to the original CFRP.（2）Organic solvents such as formic acid,acetone,isopropanol can significantly enhanced the swelling degradation of epoxy resin by subcritical acetic acid.The subcritical acetic acid and formic acid had the best degradation effect on epoxy resin,and the degradation rate was 97.4%.With the increase of reaction temperature and time,the degradation rate of epoxy resin gradually increased.The degradation rate of epoxy resin increasesd first and then decreased with the addition of formic acid increased and the solid-liquid ratio decreased.In the subcritical acetic acid/formic acid mixed media,the epoxy resin was mainly degraded to phenol,isopropyl phenol and other small molecular substances.The degradation product composition can be regulated by controlling reaction conditions.（3）The main break bond degradation process of CFRP in the subcritical acetic acid and formic acid was as follows:the C-N in cured epoxy resin structure was broken first.With the increase of temperature,the ether bond（Ph O-CH₂）was broke lead to the formation of bisphenol A.After that,the temperature continued to increase,and the system energy caused Ph-CH₃ bond in bisphenol A begin to break bonds,and eventually phenol and isopropylphenol were formed.（4）According to the results of resin degradation rate,the optimal process parameters of subcritical acetic acid and formic acid were:the reaction temperature was240-260℃,the reaction time was 1-2 h,the addition of formic acid was about 10 ml,and the solid-liquid ratio of 1:50 g/ml.The degradation rate of epoxy resin was 97.4%.And the micromorphology of the recycled carbon fibers CFs is clean and there is almost no residual resin.At the same time,the tensile strength of the monofilaments can maintain 80%of the original CFs.