the following examples are provided for illustration only , and not intended to be limiting in any aspect . 189 g n -( 2 - oxoethyl ) phthalimide , 221 g 2 -( 2 , 3 - dihydroxypropyl ) isoindole - 1 , 3 - dione , 5 g anhydrous p - toluene sulfonic acid and 1 l toluene were mixed at room temperature , then the solution was heated to reflux with dean - stark apparatus to distill the evolved water . after 20 hours , the reaction was completed . the solution was cooled to room temperature , 2 l petroleum ether ( bp : 60 - 90 ° c .) was added , filtered , the solid was washed with 1 l petroleum ether ( bp : 60 - 90 ° c .) and dried to give 950 g crude . then 3 . 4 l 20 % aq . naoh was added and the solution was heated to reflux , after 10 hours at reflux , cooled , extracted with chloroform / isopropyl alcohol , separated , the organic phase was dried with anhydrous sodium sulfate , then distilled at reduced pressure to give 80 g curing agent 1 . 800 g methylbenzene and 440 g 3 - chloro - 1 , 2 - propanediol were placed in the reaction bottle , 548 g dimethylchloroacetal and 3 g p - toluenesulfonic acid were added under stirring . the solution was slowly heated to reflux with dean - stark apparatus to distil evolved methanol . after 12 - 16 hours , the reaction was completed , and the solution was cooled to below 40 ° c ., a moderate amount of sodium carbonate was added into the reaction bottle , the solution was neutralized to ph close to 7 . the reaction solution was concentrated at reduced pressure ; toluene was recycled to give 760 g chlorinated intermediate . 400 ml n , n - dimethylformamide was placed into the three flask , while stirring 231 g potassium phthalimide and 86 . 5 g chlorinated intermediate were added . the solution was heated to 150 ° c ., after 8 hours ( the reaction was completed ), concentrated at reduced pressure and dmf was recycled . the residue could be used for the next step without purification . 320 g naoh and 960 g water were added into the residue at room temperature , then the solution was heated to reflux , after reflux for 12 hours , cooled to room temperature , extracted with chloroform / ethanol ( volume ratio 3 : 1 ) for 3 times . the organic phase was combined and dried with anhydrous sodium sulfate , filtered , concentrated at reduced pressure , then distilled at reduced pressure to give 50 g curing agent 1 . 300 g liquid ammonia was placed into the high pressure reactor and 30 g intermediate of method 2 was added while stirring at room temperature , then the solution was slowly heated to 90 ° c . after 6 hours , the reaction was completed by tlc monitoring . most of solvent were concentrated at reduced the pressure , then the residue was transferred to the reaction bottle , 30 % aq . naoh was added and the residue was neutralized to ph ≧ 10 , then extracted with 100 ml chloroform / ethanol ( volume ratio 3 : 1 ) for 3 times , the organic phase was combined and dried with anhydrous sodium sulfate or anhydrous magnesium sulfate , filtered , the filter cake was washed with small amount of solvent , then the filtrate was concentrated and distilled at reduced pressure to give 15 g curing agent 1 . 1 h - nmr ( cdcl 3 , 400 mhz ): 5 . 13 ( t , 1h ), 4 . 13 ( m , 1h ), 3 . 73 ( d , 2h ), 2 . 90 ( d , 2h ), 2 . 83 ( d , 2h ) 221 g sodium hydroxide was dissolved in 1 . 5 l ethyl alcohol , the solution was added in a 5 l stirring reactor while the temperature was controlled below 40 ° c . then 700 g 4 - nitrophenol and 3 l ethanol were added and , during the procedure , the precipitate was formed . after 2 hours at 40 ° c ., the reaction solution was concentrated to give sodium 4 - nitrophenoxide . 800 g toluene and 480 g 3 - chloro - 1 , 2 - propanediol were placed into the reaction flask , while stirring , 660 g nitroacetophenone and 1 . 5 g p - toluenesulfonic acid were added , the reaction solution was slowly heated to reflux with dean - stark trap to distil the water . after the reaction was completed by tlc monitoring , the solution was cooled to below 40 ° c ., moderate amount of sodium carbonate was added into the reaction flask , the reaction solution was neutralized to ph close to 7 , concentrated at reduced the pressure , most of the toluene was recycled , hot water was added to crystallize , filtered , dried to give 1100 g crude solid . the crude solid prepared by the above step can be used without further purification . in a 1 l three round bottom flask , while stirring , 400 ml n , n - dimethylformamide ( dmf ) and 180 g sodium 4 - nitrophenoxide prepared by step ( 1 ) and 260 g crude solid prepared by step ( 2 ) were added , the reaction solution was heated to 120 ˜ 130 ° c . after the reaction was completed by tlc monitoring , dmf was recycled at reduced pressure , after the residue was cooled , water was added till yellow precipitate was appeared , filtered , the solid was dried at vacuum to give 325 g yellow solid . in a 2 l three round bottom flask , the yellow solid prepared by step ( 3 ) dissolved in 1 . 3 l tetrahydrofuran , 8 . 2 g 10 % pd / c and 200 g 80 % hydrazine hydrate were added . the reaction solution was heated to reflux . after the reaction was completed by tlc monitoring , the solution was cooled , filtered , and 10 % pd / c was recycled . mother solution was evaporated by rotary evaporator , and the residue was recrystallized with petroleum ether / ethyl acetate to give 230 g curing agent 2 . 1h - nmr ( cdcl3 , 400 mhz ): 7 . 13 ( t , 1h ), 6 . 74 ( d , 2h ), 6 . 72 ( d , 1h ), 6 . 68 ( s , 1h ), 6 . 66 ( d , 2h ), 6 . 56 ( d , 1h ), 4 . 40 ( m , 1h ), 4 . 08 ( d , 2h ), 3 . 86 ( d , 2h ), 1 . 74 ( s , 3h ) 800 g toluene and 440 g 3 - chloro - 1 , 2 - propanediol were placed into the reaction flask , then while stirring 660 g nitroacetophenone and 3 g p - toluenesulfonic acid were added . the reaction solution was slowly heated to reflux with dean - stark trap to distil the water . after the reaction was completed by tlc monitoring , the solution was cooled to below 40 ° c ., moderate amount of sodium carbonate was added into the reaction flask , the reaction solution was neutralized to ph close to 7 , concentrated at reduced pressure , most of toluene was recycled , hot water was added till precipitate was prepared , filtered , dried to give 1000 g crude solid . the crude solid prepared by the above step can be used without further purification . in a 1 l three round bottom flask , while stirring , 400 ml n , n - dimethylformamide ( dmf ), 180 g sodium 4 - nitrophenoxide , and 244 g crude solid prepared by step ( 1 ) were added , the reaction solution was heated to 120 ˜ 130 ° c . after the reaction was completed by tlc monitoring , the solution was concentrated at vacuum and dmf was recycled . after the residue was cooled , water was added till yellow solid was appeared , filtered , the solid was dried at vacuum to give 315 g yellow solid . in a 2 l three round bottom flask , the yellow solid prepared by step ( 2 ) dissolved in 1 . 26 l tetrahydrofuran , then 7 . 8 g 10 % pd / c and 250 g 80 % hydrazine hydrate were added , the reaction solution was heated to reflux . after the reaction was completed by tlc monitoring , the solution was cooled , filtered and 10 % pd / c was recycled , mother solution was evaporated by rotary evaporator , and the residue was recrystallized with petroleum ether / ethyl acetate to give 220 g curing agent 3 . 1 h - nmr ( cdcl 3 , 400 mhz ): 7 . 11 ( d , 2h ), 6 . 74 ( d , 2h ), 6 . 66 ( d , 2h ), 6 . 56 ( d , 2h ), 5 . 79 ( s , 1h ), 4 . 40 ( m , 1h ), 4 . 08 ( d , 2h ), 3 . 86 ( d , 2h ) degradable cross - linked polymer polymerized by the curing agent and epoxy resin 10 g curing agent 1 in example 1 ( aew ≈ 3 . 03 n — h eq ./ 100 g ) and 57 . 1 g liquid bisphenol a type epoxy resin e52d ( eew 0 . 52 ˜ 0 . 54 eq ./ 100 g ) were mixed and stirred evenly at room temperature . as tested , gel time was longer than 4 hours at 70 ° c . the mixture could be stored for more than one month at room temperature . appropriate amount of the mixture sample was painted on a glass slide , the reaction was heated to 120 ° c . for 2 hours , then to 160 ° c . for 2 hours until fully cured , and then then was prepared to the sample of cured degradable epoxy resin . degradable cross - linked polymer polymerized by the curing agent and epoxy resin 10 g curing agent 2 in example 2 ( aew ≈ 1 . 33 n — h eq ./ 100 g ) and 25 . 1 g liquid bisphenol a type epoxy resin e52d ( eew 0 . 52 ˜ 0 . 54 eq ./ 100 g ) were mixed and stirred evenly at room temperature . as tested , gel time was longer than 4 hours at 70 ° c . the mixture could be stored for more than one month at room temperature . an appropriate amount of the mixture was painted on a glass slide , heated to 120 ° c . for 2 hours , then to 160 ° c . for 2 hours until fully cured , and then was prepared to the sample of cured degradable epoxy resin . degradable cross - linked polymer polymerized by the curing agent and epoxy resin 10 g curing agent 3 in example 3 ( aew ≈ 1 . 40 n — h eq ./ 100 g ) and 24 . 8 g liquid bisphenol f type epoxy resin ( eew 0 . 5 ˜ 0 . 63 eq ./ 100 g ) were mixed and stirred evenly at room temperature . as tested , gel time was longer than 4 hours at 70 ° c . the mixture could be stored for more than one month at room temperature . appropriate amount of the mixture was painted on a glass slide , heated to 70 ° c . for 2 hours , then to 125 ° c . for 2 hours until fully cured , and then was prepared to the sample of cured degradable epoxy resin . 0 . 5 g cured sample in example 4 , 10 ml concentrated hydrochloric acid and 90 ml ethylene glycol were placed in a one - neck round flask , stirred and heated to 180 ° c ., completely degraded after 10 hours to give transparent clear solution , which was neutralized with 20 % sodium hydroxide solution . precipitated solid was filtered and the solid was washed with water and dried to give 0 . 49 g of degradation products of thermoset epoxy resin , mass recovery ratio was 95 %. 0 . 6 g cured sample in example 4 , 0 . 1 ml concentrated hydrochloric acid , and 90 ml ethylene glycol were placed in an autoclave , stirred and heated to 350 ° c ., completely degraded after 0 . 5 hours to give transparent clear solution , which was neutralized with 20 % sodium hydroxide solution . precipitated solid was filtered and the solid was washed with water and dried to give 0 . 57 g of degradation products of thermoset epoxy resin , mass recovery ratio was 95 %. 0 . 06 g cured sample in example 4 , 90 ml concentrated hydrochloric acid , and 10 ml ethylene glycol were placed in a one - neck round flask , stirred and heated to 20 ° c ., completely degraded after 120 hours to give transparent clear solution , which was neutralized with 95 % sodium hydroxide solution . precipitated solid was filtered and the solid was washed with water and dried to give 0 . 059 g of degradation products of thermoset epoxy resin , mass recovery ratio was 95 %. 0 . 7 g cured sample in example 5 , 10 ml concentrated hydrochloric acid , and 90 ml ethylene glycol were placed in a one - neck round flask , stirred and heated to 190 ° c ., completely degraded after 6 hours to give transparent clear solution , which was neutralized with 95 % sodium hydroxide solution . precipitated solid was filtered and the solid was washed with water and dried to give 0 . 67 g of degradation products of thermoset epoxy resin , mass recovery ratio was 95 %. 0 . 61 g of the samples of cured sample in example 5 , 10 ml concentrated hydrochloric acid and 90 ml ethylene glycol were placed in a one - neck round flask , stirred and heated to 190 ° c ., completely degraded after 6 hours and transparent clear solution was obtained , which was neutralized with 2 % sodium hydroxide solution and precipitated solid was filtered and the solid was washed with water and dried to give 0 . 58 g of degradation products of thermoset epoxy resin , mass recovery ratio was 95 %. 0 . 65 g cured sample in example 5 , 10 ml concentrated hydrochloric acid , and 90 ml octanol were placed in a one - neck round flask , stirred and heated to 155 ° c ., completely degraded after 4 hours to give transparent clear solution , which was neutralized with 10 % sodium hydroxide solution , and precipitated solid was filtered and the solid was washed with water and dried to give 0 . 62 g of degradation products of thermoset epoxy resin , mass recovery ratio was 96 %. 0 . 75 g cured sample in example 6 , 10 ml concentrated hydrochloric acid , and 90 ml hexanol were placed in a one - neck round flask , stirred and heated to 155 ° c ., completely degraded after 4 hours and to give transparent clear solution , which was neutralized with 20 % sodium hydroxide solution , and precipitated solid was filtered and the solid was washed with water and dried to give 0 . 71 g of degradation products of thermoset epoxy resin , mass recovery ratio was 95 %. 0 . 9 g cured sample in example 6 , 5 ml methanesulfonic acid , and 90 ml ethylene glycol were placed in a one - neck round flask , stirred and heated to 135 ° c ., completely degraded after 6 hours and transparent to give clear solution , which was neutralized with 0 . 1 % sodium hydroxide solution , and precipitated solid was filtered and the solid was washed with water and dried to give 0 . 88 g of degradation products of thermoset epoxy resin , mass recovery ratio was 98 %. 0 . 95 g cured sample in example 6 , 5 ml methanesulfonic acid , and 90 ml octanol were placed in a one - neck round flask , stirred and heated to 135 ° c ., completely degraded after 6 hours to give transparent clear solution , which was neutralized with 90 % sodium hydroxide solution , and precipitated solid was filtered and the solid was washed with water and dried to give 0 . 91 g of degradation products of thermoset epoxy resin , mass recovery ratio was 96 %. bisphenol a epoxy resin e51 ( eew 0 . 48 ˜ 0 . 54 eq ./ 100 g ), e20 ( eew 0 . 18 ˜ 0 . 22 eq ./ 100 g ), and e44 ( eew 0 . 41 ˜ 0 . 47 eq ./ 100 g ) were mixed and stirred evenly in the mass ratio ( 3 . 5 : 5 : 1 . 5 ) at 100 ° c . the mixture is cooled to 70 ° c ., the equivalent amount of curing agent 2 in example 2 ( aew ≈ 1 . 33 n — h eq ./ 100 g ) was added , then the resin mixture was stirred at high speed . at 70 ° c ., gel time was longer than 6 hours . the viscosity of the resin mixture is 18000 - 24000 cps at 70 ° c . similarly , after the resin mixture was stored at − 18 ° c . for 7 days and 30 days , the viscosity and gel time of the resin mixture at 70 ° c . had no significant change ; after the resin mixture was stored at 25 ° c . for 7 days and 30 days , the viscosity and gel time at of the resin mixture at 70 ° c . had no significant change . bisphenol a epoxy resin e52d ( eew 0 . 52 ˜ 0 . 54 eq ./ 100 g ), e20 ( eew 0 . 18 ˜ 0 . 22 eq ./ 100 g ), and e44 ( eew 0 . 41 ˜ 0 . 47 eq ./ 100 g ) in the mass ratio ( 3 . 5 : 5 : 1 . 5 ) were mixed and stirred well at 100 ° c ., and then cooled to 70 ° c ., the equivalent amount of curing agent 3 in example 3 ( aew ≈ 1 . 40 n — h eq ./ 100 g ) was added , then the resin mixture was stirred at high speed . at 70 ° c ., gel time of the resin mixture was longer than 6 hours . the viscosity of the resin mixture is 18000 - 25000 cps at 70 ° c . similarly , after the resin mixture was stored at − 18 ° c . for 7 days and 30 days , the viscosity and gel time of the resin mixture at 70 ° c . had no significant change ; after the resin mixture was stored at 25 ° c . for 7 days and 30 days , the viscosity and gel time of the resin mixture at 70 ° c . had no significant change . preparation of degradable epoxy resin carbon fiber prepreg and carbon fiber composite laminate 20 g bisphenol a epoxy resin e51 ( eew 0 . 48 ˜ 0 . 54 eq ./ 100 g ), 25 . 8 g curing agent 2 in example 2 ( aew ≈ 1 . 33 n — h eq ./ 100 g ) were weighed and mixed in the blender , then grinded in three - roll mill for 30 minutes as standby . 15 g bisphenol a epoxy resin e51 ( eew 0 . 48 ˜ 0 . 54 eq ./ 100 g ), 15 g bisphenol a epoxy resin e44 ( eew 0 . 41 ˜ 0 . 47 eq ./ 100 g ), and 50 g bisphenol a epoxy resin e20 ( eew 0 . 18 ˜ 0 . 22 eq ./ 100 g ) were placed into the oven , and preheat for 3 hours at 120 ° c ., then the heated resin was put into the kneader to knead for 1 hour , cooled to 70 ° c ., then the resin was put into the mixing blender , vacurated , former standby e51 / curing agent 2 mixed system which had been grinded in the three - roll grinder was added at 70 ° c ., then the resin mixture was stirred at high speed for 30 minutes , discharged , and cooled to room temperature , then frozen in store . the gel time of the prepared degradable epoxy resin matrix as prepared above was longer than 4 hours at 70 ° c . it can be stored longer than one month at room temperature , half a year at 0 ° c ., or one year at − 18 ° c . step 2 : preparation of degradable epoxy carbon fiber prepreq and carbon fiber composite laminate the epoxy system prepared by the above step was heated to 70 ° c ., and carbon fiber prepreg was made using 3k carbon fiber cloth by wet method . the prepregs were slightly tacky at room temperature and pressed on the tablet pressing machine at 150 ° c . to give laminate of carbon fiber composite . preparation of the degradable epoxy resin uni - directional carbon fiber prepreg and carbon fiber composite laminate 20 g bisphenol a epoxy resin e52d ( eew 0 . 52 ˜ 0 . 54 eq ./ 100 g ), 24 . 6 g curing agent 3 in example 3 ( aew ≈ 1 . 40 n — h eq ./ 100 g ) were weighed and mixed in the blender , then grinded in three - roll mill for 30 minutes as standby . 15 g bisphenol a epoxy resin e52d ( eew 0 . 52 ˜ 0 . 54 eq ./ 100 g ), 15 g bisphenol a epoxy resin e44 ( eew 0 . 41 ˜ 0 . 47 eq ./ 100 g ), and 50 g bisphenol a epoxy resin e20 ( eew 0 . 18 ˜ 0 . 22 eq ./ 100 g ) were placed into the oven , and preheated for 3 hours at 120 ° c ., then the heated resin was put into the kneader to knead for 1 hour , cooled 70 ° c ., then the resin was put into the mixing blender , then vacurated , former standby e52 / curing agent 3 mixed system , which has been grinded in the three - roll mill was added at 70 ° c ., then the resin mixture was stirred at high speed for 30 minutes , discharged , cooled to room temperature , then frozen in store . the gel time of the above degradable epoxy resin matrix is longer than 4 hours at 70 ° c . it can be stored longer than one month at room temperature , half a year at 0 ° c ., or one year at − 18 ° c . step 2 : preparation of degradable epoxy carbon fiber prepreq and carbon fiber composite laminate the above prepared epoxy system was heated to 70 ° c ., and carbon fiber prepreg was made using 3k carbon fiber cloth by wet method . the prepregs were slightly tacky at room temperature and pressed on the tablet pressing machine at 150 ° c . to give laminate of carbon fiber composite . 1 . 5 g of the samples of the carbon fiber composite laminate in example 18 , 10 ml concentrated hydrochloric acid and 90 ml phenylcarbinol were placed in a one - neck round flask , stirred and heated to 190 ° c ., epoxy resin matrix was completely degraded after 3 hours , filtered when the solution was hot , the carbon fiber and the degradation solution were separated , the solution was neutralized with 20 % sodium hydroxide solution and precipitated solid was filtered and the solid was washed with water and dried to give 1 . 47 g of degradation products of thermoset epoxy resin and carbon fiber , mass recovery ratio was 98 %. the surface of recycled fiber was clean and basically has no defect . 1 . 5 g of the samples of the carbon fiber composite laminate in example 18 , 10 ml concentrated hydrochloric acid and 90 ml ethylene glycol were placed in a one - neck round flask , stirred and heated to 160 ° c ., epoxy resin matrix was completely degraded after 3 hours , filtered when the solution was hot , the carbon fiber and the degradation solution were separated , the solution was neutralized with 30 % sodium hydroxide solution and precipitated solid was filtered and the solid was washed with water and dried to give 1 . 46 g of degradation products of thermoset epoxy resin and carbon fiber , mass recovery ratio was 97 %. the surface of recycled fiber was clean and basically has no defect . 1 . 5 g of the samples of the carbon fiber composite laminate in example 18 , 10 ml concentrated hydrochloric acid and 90 ml hexanol were placed in a one - neck round flask , stirred and heated to 135 ° c ., epoxy resin matrix was completely degraded after 4 hours , filtered when the solution was hot , the carbon fiber and the degradation solution were separated , the solution was neutralized with 20 % sodium hydroxide solution and precipitated solid was filtered and the solid was washed with water and dried to give 1 . 43 g of degradation products of thermoset epoxy resin and carbon fiber , mass recovery ratio was 95 %. the surface of recycled fiber was clean and basically has no defect . 1 . 5 g of the samples of the carbon fiber composite laminate in example 18 , 10 ml concentrated hydrochloric acid and 90 ml octanol were placed in a one - neck round flask , stirred and heated to 135 ° c ., epoxy resin matrix was completely degraded after 4 hours , filtered when the solution was hot , the carbon fiber and the degradation solution were separated , the solution was neutralized with 40 % sodium hydroxide solution and precipitated solid was filtered and the solid was washed with water and dried to give 1 . 44 g of degradation products of thermoset epoxy resin and carbon fiber , mass recovery ratio was 96 %. the surface of recycled fiber was clean and basically has no defect . 1 . 5 g of the samples of the carbon fiber composite laminate in example 19 , 10 ml concentrated hydrochloric acid and 90 ml ethylene glycol were placed in a one - neck round flask , stirred and heated to 135 ° c ., epoxy resin matrix was completely degraded after 4 hours , filtered when the solution was hot , the carbon fiber and the degradation solution were separated , the solution was neutralized with 20 % sodium hydroxide solution and precipitated solid was filtered and the solid was washed with water and dried to give 1 . 42 g of degradation products of thermoset epoxy resin and carbon fiber , mass recovery ratio was 95 %. the surface of recycled fiber was clean and basically has no defect . 1 . 5 g of the samples of the carbon fiber composite laminate in example 19 , 5 ml methylsulfonic acid and 90 ml ethylene glycol were placed in a one - neck round flask , stirred and heated to 190 ° c ., epoxy resin matrix was completely degraded after 3 hours , filtered when the solution was hot , the carbon fiber and the degradation solution were separated , the solution was neutralized with 10 % sodium hydroxide solution and precipitated solid was filtered and the solid was washed with water and dried to give 1 . 43 g of degradation products of thermoset epoxy resin and carbon fiber , mass recovery ratio was 95 %. the surface of recycled fiber was clean and basically has no defect . 2 g of the samples of the carbon fiber composite laminate in example 19 , 5 ml methylsulfonic acid and 90 ml octanol were placed in a one - neck round flask , stirred and heated to 160 ° c ., epoxy resin matrix was completely degraded after 3 hours , filtered when the solution was hot , the carbon fiber and the degradation solution were separated , the solution was neutralized with 50 % sodium hydroxide solution and precipitated solid was filtered and the solid was washed with water and dried to give 1 . 94 g of degradation products of thermoset epoxy resin and carbon fiber , mass recovery ratio was 97 %. the surface of recycled fiber was clean and basically has no defect . 2 g of the samples of the carbon fiber composite laminate in example 19 , 5 ml methylsulfonic acid and 90 ml hexanol were placed in a one - neck round flask , stirred and heated to 135 ° c ., epoxy resin matrix was completely degraded after 4 hours , filtered when the solution was hot , the carbon fiber and the degradation solution were separated , the solution was neutralized with 20 % sodium hydroxide solution and precipitated solid was filtered and the solid was washed with water and dried to give 0 . 95 g of degradation products of thermoset epoxy resin and carbon fiber , mass recovery ratio was 1 . 9 %. the surface of recycled fiber was clean and basically has no defect . 0 . 5 g of the samples of the carbon fiber composite laminate in example 19 , 0 . 1 ml concentrated hydrochloric acid and 90 ml ethylene glycol were placed in an autoclave , stirred and heated to 350 ° c ., epoxy resin matrix was completely degraded after 0 . 5 hours , cool down to 100 ° c ., filtered when the solution was not cooled down , the carbon fiber and the degradation solution were separated , the solution was neutralized with 0 . 1 % sodium hydroxide solution and precipitated solid was filtered and the solid was washed with water and dried to give 0 . 47 g of degradation products of thermoset epoxy resin and carbon fiber , mass recovery ratio was 95 %. 0 . 15 g of the samples of the carbon fiber composite laminate in example 19 , 90 ml concentrated hydrochloric acid and 2 ml ethylene glycol were placed in an autoclave , stirred and heated to 20 ° c ., epoxy resin matrix was completely degraded after 120 hours , cool down to 100 ° c ., filtered when the solution was not cooled down , the carbon fiber and the degradation solution were separated , the solution was neutralized with 100 % sodium hydroxide solution and precipitated solid was filtered and the solid was washed with water and dried to give 0 . 143 g of degradation products of thermoset epoxy resin and carbon fiber , mass recovery ratio was 95 %.