Study On The Structure And Properties Of Vitrimer Toughened And Reinforced Polybenzoxazine

The toughness of benzoxazine resin is poor and needs to be toughened and modified to meet the requirements of production development.At the same time,because the cured product has a permanently cross-linked three-dimensional network structure,it is difficult to recycle the waste of benzoxazine resin and its composite materials.The use of mechanical pulverization,high temperature pyrolysis and other methods to treat benzoxazine and its composite material waste has high cost,low added value,and is not conducive to energy conservation and environmental protection.Moreover,It is difficult to take into account the thermal properties and mechanical properties of the degradable benzoxazine prepared by introducing dynamic covalent bonds through molecular design,which will affect its further application.Therefore,for benzoxazine resin and its composite materials,it is very important to study how to improve the degradation ability of polybenzoxazine while maintaining good thermal and mechanical properties.In order to obtain the modified polybenzoxazine resin with good thermal properties,mechanical properties and more recycling value,the research idea of this paper is to use the associative dynamic covalent polymer material"Vitrimer"with good reprocessing and thermal stability as the second component,and use the basic method of blending to modify benzoxazine.The specific work is:The epoxy resin-based Vitrimer(EPv)based on transesterification and the vinylogous urethane-based Vitrimer(VUv)based on transamination reaction were combined with bisphenol A-aniline benzoxazine(BA-a)were respectively blended and cured with bisphenol A-aniline benzoxazine in different proportions to prepare the modified materials and its properties were studied.The main work is as follows:(1)A high-performance modified polybenzoxazine resin with recyclable second component(EPv)was prepared.Differential scanning calorimetry(DSC)and Fourier transform infrared spectroscopy(FT-IR)were used to study the curing reaction mechanism and chemical structure of the BA-a/EPv blend system.The thermal and mechanical properties of the cured product of the blend system were studied by dynamic thermomechanical analyzer(DMA),universal testing machine,electronic Izod impact testing machine and scanning electron microscope(SEM).The results show that the modified polybenzoxazine with EPv component has better thermal properties and mechanical properties,and the glass transition temperature(T_g)and storage modulus at room temperature can reach 224?and 5582 MPa,respectively,compared with Compared with pure polybenzoxazine,it is increased by 20?and 1060 MPa,respectively.When the addition amount of EPv component is 20%,the impact strength and flexural strength of the cured product of the blend system can reach 15.2 k J/m~2 and 169.3 MPa,respectively,which are 55.1%and 43.1%higher than those of pure polybenzoxazine,respectively.At the same time,relying on the dynamic transesterification of ethylene glycol(EG)and EPv,EPv components consistent with pure EPv can be recovered from the modified polybenzoxazine.(2)A degradable modified polybenzoxazine resin system that can achieve the recycling of high-value carbon fibers(CF)from its fiber-reinforced resin matrix composites was further prepared.The curing reaction mechanism of the BA-a/VUv system and the chemical structure of the cured product were studied by nuclear magnetic resonance spectroscopy(NMR),DSC and FT-IR.The thermal and mechanical properties of the cured product of the blend system were studied by DMA,thermogravimetric analyzer(TGA),universal testing machine,electronic Izod impact testing machine and SEM.The results show that the addition of VUv can catalyze the curing of BA-a,and the obtained polybenzoxazine has higher crosslinking density,and the storage moduli of T_g,T_d5 and room temperature can reach 236?,315?and4944 MPa,respectively,which are higher than those of pure polybenzoxazine(204?,230?and 4524 MPa).When the content of VUv component is 3%,the impact strength of the modified polymer can reach 16.91 k J/m~2,which is 71.85%higher than that of PBA-a.At the same time,relying on the transamination reaction between n-butylamine and VUv components,the modified polybenzoxazine can be degraded under mild conditions(at normal pressure of 70?),and the carbon fiber reinforced resin matrix composites can be degraded from its carbon fiber reinforced resin matrix.The monofilament tensile strength and surface morphology of the degraded CF in the material are basically consistent with the original CF.