Polysaccharide Hybridization Of Vitrimer And Performance Study

Polysaccharides are naturally occurring macromolecules with enormous reserves and diverse sources.It has good biocompatibility and chemical modifiability as a renewable biomass resource,particularly in the manufacture of functionalized biomass-based polymer materials,and has significant application potential.Furthermore,numerous hydroxyl functional groups contained in polysaccharide molecular chain are beneficial to the formation of intermolecular and intramolecular hydrogen bonds,thus giving it good mechanical properties.However,the strong hydrogen bond makes polysaccharide difficult to dissolve or melt,limiting the moulding and processing of composite materials.As a result,based on the polyhydroxy structure of polysaccharide,vitrimer is used as the matrix in this thesis.Using an in-situ polymerization method,a series of vitrimer polysaccharide hybrid materials with good mechanical characteristics were created quickly and easily.The structure,characteristics,and uses of its hybrid materials were thoroughly investigated.First,utilizing natural cotton fiber(CF)as reinforcing material,polyhydroxyurethane vitrimer(PHU)with 3 D network structure was synthesized in situ in the fiber pore of CF,and the PHU@CF hybrid material was prepared.The transesterification process of its hybrid materials during UV radiation curing improves the crosslinking density of the crosslinking network,which benefits mechanical property enhancement.At the same time,the hydrogen bond between free hydroxyl groups in PHU and cotton fiber polysaccharide molecules further improved the mechanical properties of PHU@CF.The experimental results show that the tensile breaking strength of PHU@CF can reach 21.6 MPa after 8 minutes of ultraviolet irradiation,which is 2223%and 340%higher than that of pure PHU and CF,respectively.In addition,PHU shows excellent fluorescence characteristics after being irradiated by ultraviolet light.And on this basis,a new high-strength fluorescent anti-counterfeiting material for ink-free printing is developed.Secondly,in order to reduce the preparation cost and simplify the preparation process of hybrid materials,cheap and easily available cellulose filter paper(CP)is selected as the reinforcing material.Based on Epoxy vitrimer which is widely available,carboxyl groups were introduced into CP molecular chain by grafting modification,and obtain carboxylated filter paper(SCP,SDC)with grafting rates of 60%and 90%respectively.Epoxy vitrimer was synthesized in situ in the pore structure of paper by solvent-free method,and a series of Epoxy@SCP and Epoxy@SDC hybrid materials were obtained by further hot pressing.The carboxyl groups introduced into the molecular chains of SCP and SDC can cooperate to participate in the curing reaction of hybrid materials.The hybrid materials have excellent mechanical properties(the maximum breaking strength is 43.6 MPa)and intelligent characteristics such as repeatability,shape memory and self-healing.In addition,its hybrid materials have certain hygroscopicity because they contain free hydroxyl groups.With this characteristic,the new Epoxy@SCP-VMEG and Epoxy@SDC-VMEG based on Epoxy@SCP,Epoxy@SDC moist-electric generators are assembled and their voltage output can reach 0.6 V.Finally,in order to prove the universality of preparing high-strength hybrid materials at molecular level and expand the categories of polysaccharides as reinforcement materials.Bacterial cellulose(BC),a microbial polysaccharide different from the above plant polysaccharides,was selected as the reinforcing material.Carboxylated bacterial cellulose aerogels(SBC)were obtained by modifying the molecular structure of BC and introducing carboxyl groups.In-situ polymerization of epoxy vitrimer in its 3 D network structure was realized by solvent-free method,and a series of Epoxy@SBC hybrid materials were obtained by further hot pressing.The hybrid materials were characterized and analyzed by FT-IR and uniaxial tension.The results show that the obtained hybrid material has excellent mechanical properties,and the maximum breaking strength of DGEBA-SBC hybrid material can reach 30.8 MPa,which is 570%higher than that of SBC aerogel.Due to the existence of dynamic cross-linking network in epoxy vitrimer,its hybrid materials have good self-healing performance,and the self-healing rate can reach at least 90%within 10 s.At the same time,in order to expand the preparation scale of vitrimer humidity generator(VMEG),a series of humidity generators with stable open-circuit voltage were obtained by using Epoxy@SBC hybrid materials as energy conversion devices of humidity generators.