Study On New Epoxy Vitrimer And Its Application In Pultrusion Process Of Carbon Fiber Composites

In recent years,carbon fiber composites(CFRP)have developed vigorously.In 2021,the global demand for carbon fiber has reached 118,000 tons and maintained a high growth rate of10.4%.Among them,the demand of wind power industry accounts for 28%,ranking first.Pultrusion technology has become the most important production technology for wind turbine blades due to its advantages such as high degree of automation,low cost,unlimited product length and controllable quality of finished products.Thermoset epoxy resin is widely used as matrix resin of wind turbine blades because of its excellent mechanical properties,heat resistance and solvent resistance.However,the service life of wind turbine blades is only about 15～20 years.The highly cross-linked and insoluble network structure of epoxy resin makes it difficult to recycle and repair wind turbine blades.At present,most of the waste wind turbine blades are processed by mechanical recycling,heat treatment,chemical recycling and other inefficient,energy-consuming and high-cost methods.From the perspective of environmental protection and sustainable development,developing epoxy resin with recyclable function is an important way to solve the recycling problem of wind turbine blades.In 2011,Professor Leibler used zinc ions to catalyze the transesterification reaction to construct a thermoset resin with thermoplastic polymer properties,named Vitrimer.This discovery provides a new direction for the recycling of thermosetting composites.In recent years,the vitrimer system has been continuously developed and enriched,and new structures and catalysts are constantly emerging,but most of them are still in the laboratory stage,and their practical application and industrialization research are relatively lacking.At present,there are no mature glass-like polymer products in the market.Based on the current CFRP market and the research status of vitrimers,this paper takes commercial matrix epoxy resin system of wind turbine blades as a reference sample,constructs and prepares a replaceable vitrimer by transesterification,systematically studies its various properties,and fits its pultrusion process conditions,so as to further push the new epoxy vitrimer to industrialization.The research of this paper is mainly divided into the following three aspects:(1)Based on the commercially available epoxy anhydride resin system for pultruded CFRP of wind turbine blades,the effects of different accelerator contents on the viscosity,curing kinetics and mechanical properties of casting body were investigated.It is found that the content of accelerator has obvious influence on the viscosity and gel time of resin system.The curing kinetics of different formulations was explored by non-isothermal DSC,the curing kinetics model was established,the process window was determined,and the curing mechanism was further understood.The curing kinetics of different accelerator formulations are slightly different,and there is an optimal ratio of thermal mechanical properties and mechanical properties of the casting body,which is used as a reference sample.(2)Through comparison and optimization,trihydroxylamine(TEOA)was selected from four catalysts as the catalysts for transesterification reaction to prepare a vitrimer with the same manufacturability and casting properties as the reference epoxy resin.The vitrimer is easy to relax at high temperature,has good solvent resistance,good shape memory,repairable,weldable and recyclable properties.The pultrusion process conditions of the new vitrimer were further explored.The results showed that the curing characteristics were similar to those of the reference sample,and the process conditions were close to each other,meeting the actual production requirements.(3)Two kinds of epoxy resin-based CFRP,the reference sample and the epoxy vitrimer,were prepared by hand lay-up molding process.The results showed that tensile and flexural properties of these two resin systems were basically the same.The degradation experiment showed that the vitrimer can be degraded in ethylene glycol,and then the carbon fiber can be recycled.The SEM micro-morphology,Raman spectrum and single fiber strength analysis were conducted on the carbon fiber before and after recycling.The results showed that the tensile strength retention rate of the recycled carbon fiber was 94%,the surface smoothness was good,there was no resin residue and no damage,and the graphitization degree was the same as that before recycling,which basically realized the nondestructive recycling of carbon fiber.