Liquid-phase Catalytic Degradation Of UPR Composite And Recovery Of Carbon Fiber

Unsaturated polyester polyester（UPR）,as one of widely thermosetting composite materials,plays an important role in transportation,wind energy,construction,pressure vessels.However,UPR and its composite were hard to degrade again once cured due to stable cross-linking network structure.Therefore,a large number of damaged and discarded UPR waste thus led to serious environmental challenges.That virtually meant that a large number of costly carbon fiber（CF）which was employed in UPR waste was discarded.Compared with mechanical,advanced liquid chemical technologies provided an efficient solution for fiber recovery from composite,because the valuable fiber could be recycled under a relative mild condition with retaining its mechanical properties as much.Nevertheless,high temperature and pressure conditions were commonly required to achieve efficient degradation process in liquid phase chemical process.The performance of recycled fiber was thus damaged inevitably,significantly decreasing its commercial value of fiber.In view of the key science and technology problems in the degradation of thermosetting UPR composite,such as harsh conditions,low degradation efficiency and damaged recycling fiber,this paper designed an alkaline hydrolysis and Fenton/Fenton-like reaction combined strategy according to the characteristics of molecular structure for UPR composite degradation technology.A series of studies have been carried out on the degradation process of UPR carbon fiber composites,including the influence of catalytic methods on the degradation efficiency,the degradation system and the reuse of degradation products.There are plenty of ester groups and carbon-carbon bonds in UPR.A synergistic alkaline hydrolysis and Fenton oxidation catalytic degradation strategy was proposed for degrading UPR under mild conditions,aiming at the cleavage of ester group and carbon-carbon bond in UPR.The UPR was hydrolysed by using hydrazine hydrate and sodium hydroxide at 80^oC 60 min,and the hydrolysis-degradation efficiency of hydrolyzed UPR reached 75%.The hydrolyzed UPR was further degraded into amides,alcohols,aromatics,carbon dioxide gases and other substances by the strong oxidative free radicals produced in Fenton reaction.According to the theoretical simulation,the ester carbonyl group in hydrolysates was attacked by radicals preferentially because of the more negative potential.The free radical oxidation reaction mainly occurs in HOMO and LUMO concentration.In addition,the CF bundle in composite was recycled successfully by using this mild hydrolysis-oxidation strategy.The recycled CF bundle maintained its original surface microstructure,chemical structure and mechanical properties.The retention rate of tensile strength was more than 92%,indicating an efficient recovery of CF bundle.This strategy is expected to be used for the preparation of short fiber reinforced composite materials in the future.In order to achieve the recovery of carbon fiber cloth from composite,the unsaturated polyester carbon fiber composite was effectively degraded by Fenton-like reaction induced by in-situ formed nano zero-valent iron.UPR was hydrolysed at70^oC by using the hydrolysis system which the bialkaline catalyst of 1,2-diaminopropane/saturated potassium hydroxide methanol solution was selected as.The heterogeneous nano zero-valent iron catalyst was grown in situ on the surface of hydrolyzed UPR by loading-reduction method.The hydrolyzed UPR were further degraded under Fenton-like reaction,generating long chain hydrocarbons and aromatic substances.Compared with the addition of Fe²⁺and Fe⁰ nanoparticles,the Fenton-like reaction which triggered by in-situ grown nano zero valent iron exhibited higher degradation efficiency.The oxidation-degradation efficiency of hydrolyzed UPR was more than 90%under 80 min,80^oC.Most of the resin on the surface of the multi-layer UPR composites was removed by hydrolysis which initiated by 1,2-diaminopropane/saturated potassium hydroxide methanol solution.The CF cloth was recovered by the catalytic degradation strategy of supported loading-reduction and Fenton-like reaction.The resin removal rate on CF surface was close to 99%.The recovered CF maintained the original textile structure,microstructure,elemental composition and graphitization degree.The mechanical strength retention rate of CF single fiber was over 98%,achieving the recycled carbon fiber cloth.In order to realize the full recovery of UPR composite,the degradation of UPR was degraded by Fenton-like reaction triggered by iron-cobalt Prussian blue analogue.The recycling methods of degradation products were studied as well.UPR was first expanded with dichloromethane.The swelled UPR was then hydrolysed under mild conditions by using reaction which catalyzed by low-cost saturated potassium hydroxide solution at 100^oC.The heterogeneous iron-cobalt Prussian blue analogue catalyst was uniformly distributed on the surface of the hydrolyzed UPR by a wetting agent.Due to the synergistic effect between iron and cobalt in the catalyst and hydrogen peroxide,the hydrolyzed resin can be further degraded by the strong oxidative free radicals produced in Fenton-like reaction,achieving an over 90%oxidation degradation efficiency during 60 min.The recycled hydrolysis system and iron-cobalt Prussian blue analogue could trigger the reaction again after the reaction,showing a good reuse ability.The multilayer UPR composite was further degraded by using this strategy,and the resin removal rate was close to 99%.The CF cloth could be efficiently recycled via this strategy.The reclaimed CF reinforced UPR composite regained 98%and 96%retention rate of bending strength and interlaminar shear strength respectively,showing an excellent mechanical property.The degradation products could be used to prepare commercial polyurethane waterborne coating additives.The mixed coatings containing degradation products showed a good tensile strength,excellent stability and adhesion.This strategy offered the full recovery of UPR composite and provided a new solution for the treatment of commercial composites.