Preparation And Properties Of Recyclable Carbon Fiber Composites Based On Thermosets

With the development of carbon fiber(CF)reinforced thermosetting advanced composites,it has been widely employed in many high-tech fields including aerospace,wind power,transportation,etc.in recent decades.However,their massive application,meanwhile,engender a substantial amount of waste of such CF-reinforced composite(CFRC).This prove to be a bottleneck restricting the further application and development.In essence,researches on the recycling and reuse of waste of advanced composites is turned to be an ideal way to prolong the service life of materials(especially for the expensive carbon fibers).Many researchers have made great efforts for this.Whereas,owing to the inherent properties of tranditional thermosetting resin matrices(e.g.epoxy),the requisite harsh degradation conditions such as oxidation and pyrolysis would unavoidably damage the properties of CFs.Consequently,such reclaimed CFs can never be used for the preparation of advanced composites again.In view of this,herein we adopted hexahydrotriazine skeleton as the functional group with the aim to solve problems of recovery for both thermosetting resins and its composites.In this paper,we have designed a new synthesis scheme and successfully prepared a new thermosetting resins of poly(hexahydrotriazine)(PHT)via the addition and condensation reactions between aromatic diamines and formaldehyde.First,we’ve studied on the mechanism and influencing factors of the reaction.The results suggested that the contents of formaldehyde and/or water both erert significant effects on the reaction.But the catalytic efficiency of water on the reaction,under the same conditions,is superior than that of formaldehyde.It pertains to water-promoted self-catalyzed sequential addition condensation.Water accelerated the reaction process by forming hydrogen bonds with intermediates,such as acetal,imine,diamine and triamine,and thus facilitate all transformations involving C-N formation or C-O bond breaking.The hemiaminal dynamic covalent networks(HDCNs)was pre-prepared by the polymerization of aromatic diamines with formaldehyde at low temperatures(~50 °C).Then,by high temperature processing,highly cross-linked PHT covalent networks formed as a result of solvents and water removing.Comparatively,nearly completely cured PHT resin sheets can be obtained at 200 °C for 2 h.The obtained PHT resins exihibit good mechanical properties,excellent heat resistance and favourable chemical corrosion resistance.And more importantly,it can be completely depolymerized into its raw materials under certain special gentle conditions.On this basis,this paper empolyed CFs as the reinforcement and prepared a new class of advanced composite which can be recycled and reused for many times.This is the first time to realize non-retrive and multiply recycling of CFs from its application in the field of advanced composites.In addition,the mechanical and thermal properties of this new composite is comparable or even superior to some of its commercial counterparts.Because the important characteristics of CFs(performance,length and weave structure)can be perfectly preserved during the recycling process,the performance of regenerated composites prepared with these reclaimed CFs remains almost unchanged.In a word,this research has provided scientific basis for improving the comprehensive performance,prolonging the service life and ehdowing its with environmental friendliness of CFRC.