Design,Preparation And Performance Study Of Epoxy Vitrimer Composites

Thermosets exhibit various excellent properties and are widely used in many fields ranging from high-end technology to civil life due to their permanent three-dimensional covalently cross-linked networks.However,they can not be re-processed or recycled after shaping or damage,which has brought about terrible resources waste and environmental pollution.In recent years,the introduction of dynamic exchange reactions（DERs）into the cross-linked networks of thermosets has attracted extensive attention.And the as-prepared polymer materials,named vitrimers,have the ability to rearrange topological networks,be reprocessed and reused.In order to modify the structure and properties of the classic epoxy resin vitrimer,reduce the dependence on fossil resources and environmental pollution,fully develop bio-based raw materials and explore the blend-processing methods of different thermosets,in the present thesis,the design,preparation and performance studies of vitrimer composites based on dynamic exchange reaction were carried out in the following aspects.And the relationship between structure and properties of polymer materials is explored and explained.1.In order to modify the shortcomings of classic bisphenol A-epoxy vitrimer,such as high rigidity,slow stress relaxation rate,poor mechanical toughness and high reprocessing temperature,the epoxidized soybean oil（ESO）,a flexible fatty molecule containing epoxy groups,was introduced into the rigid networks of epoxy dynamic polymer networks（DPNs）.The purpose of this modification is to make epoxy DPNs meet the needs of practical applications.The introduction of ESO reduces the crosslinking density,network rigidity and T_gof the epoxy-ESO DPNs,as a result,they show good mechanical toughness,fast stress relaxation and significantly reduced reprocessing temperature.In addition,the prepared epoxy-ESO DPNs also show outstanding self-healing,welding and chemical degradation properties.2.The ESO DPNs was prepared by using the bio-based ESO as epoxy monomer and dual DERs as crosslinking bonds.The hydroxylated silica（OH-Si O₂）nanoparticles were introduced into the ESO networks as reinforced and functional nanofillers to improve their mechanical properties and further accelerate the stress relaxation rate.The obtained ESO/Si O₂composites show enhanced mechanical strength and thermal stability as the OH-Si O₂has uniform dispersion and strong interfacial interaction with the ESO matrix,especially at the optimal amount of 3 wt.%.In addition,the rich-OH groups on the surface of Si O₂can participate in and promote the transesterification reaction.So the ESO/Si O₂composites also show accelerated stress relaxation,rapid self-healing,welding and reprocessing properties.3.A fully biobased elastomer vitrimer composite was prepared by using epoxidized natural rubber（ENR）as matrix,carboxymethyl chitosan（CMCS）as functional fillers and dynamic covalent bonds as crosslinking bonds.The CMCS can be uniformly dispersed and form strong interface interaction with the ENR matrix due to the abundant hydroxyl and carboxyl active groups on its surface,which increases the tensile strength of the resulted ENR/CMCS composites.Due to the dual DERs in the networks,the ENR/CMCS composites exhibit rapid stress relaxation and good reprocessability.In addition,the raw materials are both bio-based and non-toxic,so the ENR/CMCS composites exhibit good biocompatibility and have application prospects in the field of biomaterials.4.DERs not only endow thermosets with some dynamic features,but also provide a new pathway for their processing method.Two incompatible and dissimilar cross-linked polymers（ENR and EV）are uniformly mixed together by physical blending,and the ENR-EV blends are obtained after a thermal treatment process.The ENR and EV networks can achieve good blending and compatibility due to the rapid transesterification reaction at the interface.And the obtained ENR-EV blends exhibit excellent mechanical properties,thermal stability and vitrimeric properties.In this work,we systematically studied the effects of EV content and thermal treatment conditions on the microstructure-evolution and macro properties of the final ENR-EV blends.Besides,we also explored the relevant mechanism and finally obtained binary vitrimer blends with excellent comprehensive performance.This work provides guidance for realizing the blend-processing of different cross-linked polymers and promoting the practical applications of vitrimer materials.