Preparation And Properties Of Epoxy Vitrimer Composites With Segregated Structure

Constructing a segregated network by the three-dimensional distribution of fillers is efficient to improve the performance of composite materials and reduce the percolation threshold.Conventionally,most segregated composites were based on thermoplastics and precisely controlled processing conditions to prevent the migration of filler into the interior matrix,resulting in the complex preparation process,poor performance stability and other shortcomings.Moreover,the filler located on the interface between particles would hinder molecular diffusion and entanglement,resulting in inferior interfacial adhesion and poor mechanical strength.Therefore,solving the above problems are the key to preparing high-performance segregated structure composites.Vitrimers,as a new group of crosslinked polymers,behaves as a thermosetting material at low temperature,and can be melt-processed and recycled like thermoplastic at high temperatures,owing to associative dynamic covalent bond mechanism.In this thesis,using epoxy vitrimer as the matrix to study the alcoholysis-reesterification reaction assisted by ethylene glycol to enhance interfacial fusion,successfully prepared the segregated structure composites with a wide processing conditions,and the microstructure characteristics and various properties of the composites were investigated,which could have great development in electromagnetic shielding and thermal insulation field.The main content of the thesis is divided into the following three parts:1)The epoxy vitrimer was prepared,and the stress relaxation measurements revealed that the epoxy vitrimer has the rheological characteristics based on the associative covalent bond mechanism,and the viscosity only experienced marginal change within a broad temperature range.Studying the fusion process of epoxy vitrimer particles,which showed that ethylene glycol molecules participate in the alcoholysis-reesterification reaction of epoxy vitrimer,assisted the process of particle interface fusion and improved the interface strength.Moreover,owing to the plasticization of short-chain oligomers formed by alcoholysis,the toughness and ductility of the welding products were significantly improved.2)The segregated epoxy vitrimer/MWCNTs composites(s-EV/MWCNTs)was successfully prepared with different compression molding conditions,indicating that the composites has a wide processing window.The MWCNTs in the composite material were closely contacted and formed three-dimensional network structure.The tensile strength of s-EV/MWCNTs-2 maintains 90% of its parent matrix.and the elongation at break was increased by nearly 50%.The product has excellent electrical conductivity and electromagnetic shielding effectiveness(EMI SE).When the filler content was only 4 wt%,the electrical conductivity of the composites reached 6.8 S/m,and the EMI SE reached31 dB,which was much higher than other composites.Moreover,owing to the dynamic crosslinking characteristics,the composites can be processed again,and the EMI SE of the recycling sample can be restored to more than 90%.3)The segregated epoxy vitrimer composites(s-EV/MWCNTs/h-BN)with selective distribution of MWCNTs and h-BN was prepared by compression molding.The microscopic morphology the s-EV/MWCNTs/h-BN composite were characterized by SEM,which showed that MWCNTs with high aspect ratio like a "bridge" to connect the h-BN segregated network,shortening the heat transfer path.The thermal conductivity of s-EV/MWCNTs/h-BN-8 composites is 0.83 W/m K,which is much higher than other polymer-based composites.The reprocessing results showed that the elongation at break of the recycled s-EV/MWCNTs/h-BN-8 composites decreased by only 9%,the tensile strength increased by 50%,and the thermal recovery rate exceeded 70%.