Study On The Degradation Mechanism Of Brominated Epoxy Resins In Waste Printed Circuit Board By Subcritical Acetic Acid

In this paper,the waste printed circuit boards?WPCBs?containing large amounts of brominated epoxy resins?BERs?was selected as the research object.Subcritical acetic acid was used to efficiently catalyze the degradation of BERs in WPCBs.Oil phase products without bromine wasobtained and the main components of degradation products were phenol and bisphenol A.By studying the main degradation products of BERs in different subcritical acetic acid environments and the migration and transformation pathway of bromine,the main mechanism and process of BERs catalytic degradation by subcritical acetic acid were revealed.The main factors affecting the degradation of BERs in subcritical acetic acid environment were discussed,and the technological parameters of BERs degradation by subcritical acetic acid were optimized.The main conclusions of this research are as follows:?1?BERs can be rapidly swelled and degraded in subcritical acetic acid system.BERs only degraded slightly at lower temperatures of 200?,but the acetic acid cause the swelling and softening phenomenon of BERs which resulted in copper foil falling off automatically from the surface of WPCBs.This phenomenon facilitated the recovery and utilization of metal components.After that,the degradation rate of BERs increased rapidly with the increase of temperature,acetic acid mass concentration and holding time.When the treat temperature was higher than 220?,the mass concentration of acetic acid was higher than 49.9%,and the reaction time was more than 1 h,the BERs contanined in WPCBs was almost completely degraded,and the glass fibers and metal copper foils with smooth surface were obtained.?2?At lower temperatures,BERs were partially degraded,and the bromine in the degradation product was mainly rich in the solid phase in the form of organic bromide,while the rest was in the form of inorganic bromide?HBr?in the aqueous phase.When the temperature increased to 220?,BERs were completely degraded,and the solid phase debromination rate was 100%.Except for a small amount of bromine was enriched in the oil phase,the remaining bromine mainly existed in the form of HBr in the aqueous phase.Increasing the reaction temperature or prolong the treatment time,all organic bromide in the oil phase was transformed into inorganic HBr and enriched in the aqueous phase.?3?BERs were degraded completely for 1 h at 220 C with 49.9%acetic acid And the main organic degradation products were bisphenol A and phenol whose relative contents were 50.36%and 23.00%,respectively.With the increase of reaction temperature and holding time,bisphenol A was further decomposed into phenol and isopropylphenol.When the temperature was raised to 260?,the main organic degradation products were phenol and isopropylphenol whose relative contents were45.37%and 25.17%,respectively.Therefore,different types and contents of the BERs degradation products can be obtained by controlling the reaction conditions.?4?The main bond-breaking degradation process of BERs in subcritical acetic acid environment was as follows:with the increase of temperature,the ether bond?PhO-CH₂?energy of BERs is the lowest and was first broke lead to the formation of tetrabromobisphenol A and bisphenol A.Then Ph-Br bond in tetrabromobisphenol A began to break and debrominate to form bisphenol A.After that,Ph-CH₃ bond in bisphenol A begin to break bonds after increasing temperature,and eventually phenol and isopropylphenol were formed.In addition,the Ph-CH?CH₃?₂ bond in tetrabromobisphenol A can be broken before the Ph-Br bond to form 2,6-dibromophenol and 2,6-dibromo-4-isopropylphenol,and then gradually debrominated to form phenol and isopropylphenol.?5?Acetic acid acts as catalyst and swelling agent in BERs degradation.Under subcritical conditions,acetic acid can offer a large amount of H₃O⁺?hydrogen hydrate?,which can enhance the acid-base catalytic degradation of BERs by subcritical water.Acetic acid can rapidly swell the BERs in subcritical environment.The swelling phenomenon helps H₃O⁺and other degradation products of BERs migrate rapidly in the swelling BERs lead to the rapid degradation of BERs.?6?Base on the considering of BERs degradation rate,debromination rate,main organic degradation products and bromine distribution in subcritical acetic acid,the optimum processing parameters for catalytic degradation of BERs by subcritical acetic acid were determined as follows:reaction temperature 220-260?,reaction time 1-2 h,mass concentration of acetic acid 49.9%.