| Petroleum-based chemical raw materials are generally considered unsustainable,while bio-based raw materials and materials are considered sustainable and environmentally friendly.In the field of polymer materials,the connotation of "sustainable development" includes the sustainability of raw materials and the extension of material life cycle.In recent years,the highperformance and functionalization of sustainable polymer-based materials and their composites have become a cutting-edge field in materials science.Cellulose is the most widely distributed natural polymer material in nature,characterized by low cost,stable structure,and good mechanical properties.In the preparation of composite materials using cellulose as a sustainable filler,the formation of a good interfacial interaction between the matrix and the filler is a key issue.Usually,a chemical environment suitable for the chemical structure of the matrix is constructed on the surface of the filler for preparation.However,the formation of hydrogen bonds by a large number of hydroxyl groups in the chemical structure of cellulose is an obstacle to chemical modification of the cellulose surface.At present,the types of chemical groups grafted on the surface of cellulose and high degree of substitution modification methods are still being explored and developed by researchers.Epoxy resin is generally considered a thermosetting material until the concept of vitrimer was proposed.Vitrimer combines the macroscopic properties of thermosetting and thermoplastic materials,with both repairable and recyclable "sustainable" properties,and is expected to gradually be widely applied.The preparation of vitrimers from bulk biobased raw materials,exploration of the structure performance relationship of vitrimers and optimization of their properties,as well as the preparation of functional vitrimers,are research directions that have received attention in the field of vitrimers.This thesis started from the sustainability of polymers,focusing on the high degree of substitution functionalization of cellulose surface and its reinforcement of epoxy resin or epoxy vitrimer,and conducted research on the structure performance relationship and functionalization of epoxy resin cellulose composites.The research content and main achievements are as follows:(1)A high degree of substitution surface epoxidation preparation method for microcrystalline cellulose was designed.The surface of the cellulose was modified by epoxidation without damaging its crystal structure,and a reactive epoxidized microcrystalline cellulose(EP-MCC)filler was prepared.The modified epoxy resin composites were studied in detail.Microcrystalline cellulose(MCC)was treated with sodium hydroxide solution to obtain sodium microcrystalline cellulose(Na-MCC),which was then subjected to a one-step heterogeneous reaction with epichlorohydrin,sodium hydroxide,and phase transfer catalyst to synthesize EP-MCC.A characterization method for the degree of surface epoxidation modification of MCC was established.The thermosetting epoxy/anhydride curing system was reinforced with MCC and EP-MCC,respectively.Comparative studies showed that the epoxy groups on EP-MCC could better form covalent bonds between the filler and matrix,thereby forming an interface layer.In addition,the hydrophilicity of EP-MCC was significantly reduced compared to MCC,and its dispersion in epoxy resin was good.The phase transfer catalyst method proposed in this study was a promising method for heterogeneous epoxidation modification of Na-MCC,which could achieve high epoxidation of cellulose surface.The resulting EPMCC was a green,convenient,and inexpensive epoxy resin filler that could improve the performance of epoxy resin composites and had the potential to replace traditional fillers.(2)In response to the limited types of small molecule tertiary amine catalysts and poor compatibility controllability with epoxy resin matrix,a "covalent integration" method was adopted to prepare a catalyst containing tertiary amine structure(TAP)with adjustable alkyl chain structure and molecular weight by reacting epoxy resin with secondary amine compounds with equal functional group ratio.This catalyst had long storage life,low toxicity,low corrosion,high catalytic activity,and good compatibility with resin matrix.Further,we used the catalyst for the preparation of transesterification vitrimers containing self-catalytic structures.A comparative study was conducted between this strategy and several methods for preparing transesterification vitrimers containing self-catalytic structures that have been published in literature,including mixing small tertiary amine molecules directly with epoxy curing systems and preparing epoxy-tertiary amine coexisting resins with built-in tertiary amine structures before curing.The results showed that the vitrimer system prepared by TAP had excellent comprehensive performance,and the covalent integration method optimized the performance of epoxy transesterification self-catalytic vitrimers.The performance of TAP catalyzed vitrimer system was mainly reflected in three aspects: first,the curing reaction conditions were relatively mild;Secondly,the mechanical properties of the cured material were good;The third was that the cured material had good properties such as self-healing and hot-pressing recovery.Finally,the new selfcatalytic vitrimer proposed in this chapter was filled with EP-MCC from the previous chapter,and a series of experiments confirmed that EP-MCC could also be used as a good enhancing reactive low-cost biobased filler in the vitrimer resin system.The data and conclusions obtained from this study could provide guidance and reference for the development of self-catalytic vitrimers and their composites based on tertiary amine structures.(3)Guided by the principles of cellulose surface epoxidation and covalent integration mentioned above,the low-cost,flexible,and high biomass content epoxy resin was modified and the vitrimer structure was designed to achieve performance improvement,material reuse,biodegradability,and conductivity functionalization.A matrix(CNSLV)of sustainable vitrimer composites based on cashew nut shell liquid was prepared using cashew nut shell liquid-based epoxy resin(NC-514s),glutaric anhydride derived from glucose fermentation,and di-n-hexamine as raw materials.The filler of composites was made of bamboo fiber r-BF,which was subjected to physical and chemical treatment,crushed,and then chemically modified to obtain surface epoxidized modified bamboo fiber EP-r-BF(EBF)particles.A recyclable,high bio-based carbon content,flexible,and self-catalytic vitrimer composite was prepared by combining the matrix and filler,and further functionalization research was conducted.This study successfully provided a modular preparation strategy for epoxy vitrimer-cellulose sustainable composites.Based on this strategy,a series of epoxy vitrimer-cellulose sustainable composites can be prepared,and the performance of the composites can be further optimized according to the structure-performance relationship. |
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