Study On The Properties Of Vitrimer Composites Doped With Linear Polymers And Carbon Nanotubes

Traditional thermosetting materials are widely used in life because of their good mechanical properties and thermal stability.However,thermosetting materials are difficult to recycle and reprocess.Most of thermosetting materials are used as a disposable material and it will greatly waste resources and pollute the environment.In 2011,Leibler et al.found that the thermosetting epoxy resin obtained by curing the bisphenol A epoxy resin and the fatty acid / polybasic acid,which can occur transesterification reaction at Tv.Leibler named this material vitrimer.The Tv for vitrimers,similar to the glass-transition temperatures(Tg)for conventional materials,are transition temperatures for the topological rearrangement resulting from transesterification.At Tv and below,transesterification is so slow that the vitrimer behaves like thermosetting material.Above Tv,transesterification becomes accelerated so that materials are able to relax their stress and mend.2 Vitrimers have the excellent mechanical properties of thermosetting materials and can be self-healing and recyclable,and they are becoming one of the most popular materials research in recent years.In this paper,Vitrimer materials are studied in the following aspects.1.Effect of vitrimer material doping with different contents of methyl methacrylateIn this study,we synthesized poly(methyl methacrylate)(PMMA)epoxy vitrimer composites by doping methyl methacrylate(MMA)and benzoyl peroxide into a curing system of epoxy resin and citric acid.The vitrimer composites were characterized with dynamic mechanical thermal analysis(DMA),field emission scanning electron microscopy(SEM),and stress-relaxation analysis(SRA)and lap-shear testing.The test results show that with increasing amount of MMA,the existence of PMMA in the epoxy vitrimer matrix in the form of intermiscible,slightly soluble,and phase separation became more evident.When the doping amount of PMMA reached 10–25 wt %,the bonding strength of the PMMA–epoxy vitrimer composites was about two times that of the epoxy vitrimer(from 2.3 to 4.3 MPa).This showed that the self-healing strength of the vitrimer composites was better than that of the pure vitrimer.When the PMMA in the epoxy matrix was in a slightly soluble form,the linear PMMA improved the mechanical properties of the epoxy vitrimer by physical winding.At the same time,the doping of PMMA promoted the transesterification rate of the epoxy vitrimer and enhanced the bonding strength of the composites without lowering the epoxy vitrimer glass-transition temperature2.Effect of vitrimer material doping with different linear polymersThree kinds of polymer monomers(methyl methacrylate,hydroxypropyl methacrylate and styrene)were added to the epoxy vitrimer respectively to prepare three different epoxy vitrimer composites,the vitrimer composites were characterized with DMTA,SEM,test of stress relaxation and lap-shear.The results show that the three different kinds of polymers can be uniformly dispersed in the epoxy vitrimer matrix.Methyl methacrylate and hydroxypropyl methacrylate which contain polar pendant have a strong interaction with polar epoxy matrix,while the interaction force between nonpolar styrene and epoxy vitrimer matrix is weak.The bonding strength of vitrimer materials was enhanced and the stress relaxation time was reduced by doping the PMMA or hydroxypropyl methacrylate.From the test data we can see the properties of PMMA epoxy vitrimer composites are the best.3.Simultaneous doping of vitrimer with carbon nanotubes(CNT)and methyl methacrylate(MMA)In the previous work,the composite material obtained by doping with 20 wt% MMA in virimer had the best performance.In this work,vitrimer composite material was prepared by doping with MMA and polypyrrole-coated carbon nanotubes(0.15CNT/PPY)in vitrimer.The test shows that 0.15CNT/PPY reduces the Tv of the vitrimer composites,making the bonding temperature of the composites drop to 100°C,and its bonding strength at 100 degrees is almost the same as that of pure vitrimer materials at 120°C.And 0.15CNT/PPY reduces the surface tension between PMMA and epoxy vitrimer,improves the dispersion of PMMA in the virimmer matrix.And the microphase structure of PMMA disappear,PMMA is evenly dispersed in the vitrimer matrix and interface between 0.15CNT/PPY and vitrimer matrix.The simultaneous dopping of 0.15 CNT/PPY and PMMA to the Vitrimer material reduces the Tv temperature of the vitrimer and promotes the transesterification of the vitrimer material.