Preparation And Properties Of Reshapeable And Degradable Recycled Bio-based Epoxy Resin

Epoxy resins can be used in a wide range of applications due to their excellent physical and chemical stability,and are found everywhere in everyday life.However,the commonly used BPA-based epoxy resins are restricted in their application because they are derived from conventional petroleum-based bisphenol A with biological toxicity.Hence,the urgent need to find bio-based epoxy resins by utilization of sustainable resources instead of BPA.In addition,petroleum-based epoxy resins are susceptible to mechanical,thermal,chemical and UV radiation,which can create deep micro-cracks in the resin matrix,resulting in the deformation or damage on the materials.Due to the formation of permanently cross-linked three-dimensional network,the reuse or recycling composites will be a huge challenge.In this paper,two different bio-based epoxy monomers were designed from green energy plant monophenols to investigate the reprocessing,recycling degradation and self-healing properties of epoxy materials by introducing dynamic covalent bonds through curing.The main work is described as follows:In Chapter 2,a new guaiacol-based epoxy resin(BGF-EP)was prepared using renewable resources instead of the traditional petroleum-based bisphenol A and cured with 4-aminophenyl disulphide(AFD).The curing mechanism was investigated by DSC non-isothermal method and the cured BGF-EP-AFD exhibited good thermal stability and mechanical strength as well as rapid stress relaxation(only 27.5 s at200 °C).At the same time,BGF-EP-AFD vitrimer can be remoulded and reprocessed to form a complete shape by hot pressing.It is also possible to closed-loop recycle carbon fiber-reinforced epoxy composites at room temperature by an efficient method.Experimental results showed that the epoxy powder and structurally undamaged carbon fibers can be recovered by degradation in a 50%DMF/50%β-ME mixture,and the obtained epoxy powder remained good reprocessability under hot pressing conditions.However,BGF-EP-AFD contains only one dynamic covalent bond,which limits its dynamic mechanical properties such as long relaxation time.For optimizing the mechanical and self-healing properties,new vitrimers based on double reversible covalent bonds are investigated in Chapter 3.A bio-based epoxy monomer(BVF-EP)was synthesized via plant monophenol vanillin,the double dynamic bond(S-S and C=N)were introduced using AFD curing and the effect of three different ratios of BVFEP/AFD on the properties of the epoxy system was investigated in detail.All three kinds of epoxy resin materials with different feed ratios had good thermal stability.Especially,BVF-EP-AFD with R=1.5 possessed fast stress relaxation(only 6 s at 200 °C)due to the higher contents of dynamic S-S and C=N bonds,and can be reprocessed at lower temperatures(140 °C)and degraded for recovery in two kinds solvent mixtures.And its self-healing efficiency can reach 50.10% when heating at 200 °C for 20 min.Excellent self-healing,degradability and recyclability under simple and mild conditions,without the need to add additional catalysts,provide BVF-EP-AFD vitrimer with significantly reduced production costs and environmental concerns.