Degradable Thermosets And Its Application In Carbon Fiber Composites

Recent years,carbon fiber reinforced composites(CFRC)have attracted increasing attention due to their excellent properties and have been widely used in many fields.However,the resin matrix of traditional CFRC is derived from petroleum-based sources,which will limit its development as the unsustainability of petroleum and its damage to the environment.In addition,the post-processing issues of CFRC also become growing severe as its output and application fields gradually expand.How to reasonably dispose of scrapped CFRC,non-destructive recycling of valuable carbon fiber not only has great commercial value,but also conforms to the sustainable development strategy.In order to solve these two problems,we have done the following works:(1)A bio-based degradable intermediate monomer was synthesized and it can be easily used to prepare bio-based degradable thermosets.The monomer is synthesized from bio-based resources vanillin(lignin derivative)and glycerin through solvent-free acetalization,and has high conversion rate and high selectivity.Afterwards,its structure,degradation mechanism and cytotoxicity were characterized in detail by means of infrared spectroscopy,nuclear magnetic,mass spectrometry,computer simulation,etc.,which provided a basis for the further preparation of bio-based degradable resins.(2)The monomer was used to prepare epoxy monomer which was cured with a commercial amine-type curing agent.Commercial bisphenol A epoxy resin(DER-331)was used as the control.The basic properties of this material,such as glass transition temperature(T_g),thermal stability,mechanical properties and free volume,were studied using differential scanning calorimetry,thermogravimetric analysis,tensile experiments and positron annihilation test.It was proved that the performance of this material is comparable to and even better than the control,which means the monomer can be a promising substitute to bisphenol A.Subsequent degradation and stability experiment prove that although the material can degrade rapidly in a specific acidic solution,its chemical stability and hygrothermal aging resistance are comparable to the control.It provided a basis for the further preparation of CFRC.(3)The monomer was directly reacted with trifunctional isocyanate to obtain a cross-linked polyurethane,and the cured product of bisphenol A was used as the control.After that,these two materials were used to prepare CFRC.Results showed that the thermal and mechanical properties of these two materials and their CFRCs are comparable.In the degradation and recycling experiments,the non-destructive recovery of carbon fibers was successfully achieved.The reclaimed carbon fibers maintain the original texture structure,micro-morphology,chemical structure and mechanical properties,and there is almost no resin residue on the surface of fibers.This bio-derived building block exhibits great potential to be as a sustainable and upgraded alternative to petroleum-sourced aromatic chemicals such as BPA to address the source and recycle issues of carbon fiber composites.