Preparation Of Oligocellulose And Study On The Structure And Properties Of Its Graft Copolymer Elastomers

In the era of great challenges in energy,resources,and the environment,how to use renewable resources and reduce the dependence on non-renewable petrochemical raw materials is essential to the sustainable development of the world economy.As the most abundant natural polysaccharide in nature,cellulose has attracted much attention because of its inherent sustainability,biocompatibility,and biodegradability.However,due to the complex hierarchical structures of cellulose and the strong intra-and intermolecular hydrogen bonding interactions,many physical and chemical properties remain to be revealed.Oligocellulose(OC)can be used as a model molecule to clarify the chemical and physical properties of cellulose and its derivatives,as well as for different applications in biomedical and food industries.Therefore,an easy-to-implement,well-characterized OC production process is essential.Moreover,OC can be used to prepare novel thermoplastic elastomer materials with star topology by controlled free radical polymerization,which further expands the application range of OC.Thermoplastic elastomers are a kind of polymer material with excellent ductility and elasticity.The macroscopic properties of elastomer materials are closely related to their composition,microstructure,and network structure.For most unfilled elastomers,the main limiting factor for their application is insufficient tensile strength.In addition to improving mechanical properties by the introduction of natural or synthetic nanofillers into the elastomer materials,the tensile strength can also be improved through topological design.This thesis is aimed to prepare OC with narrow molecular weight distribution by mild hydrolysis method,construct star-like bio-based elastomer materials with excellent mechanical properties by grafting polymerization strategy and reveal the structure-property relationship of these elastomers via various characterization means.The detailed contents are as follows:(1)OC usually consists of 2-30 glucose repeating units and can be obtained by synthesis or depolymerization.OC can be used as a model compound to reveal some of the physical and chemical properties of cellulose with high degrees of polymerization(DP).However,so far,there is still no simple,fast and efficient production process to prepare OC with DPs ranging from 5 to 12,which greatly limits the further applications of such materials in food,agriculture,medicine,chemical industry,energy environment,and other fields.OC with narrow molecular weight distribution can be prepared by hydrolyzing microcrystalline cellulose(MCC)with phosphoric acid at different temperatures under a homogeneous condition.Hydrolysis kinetics at different temperatures showed that increasing the temperature could significantly reduce the hydrolysis time.When the hydrolysis temperature was 60 ℃,the yield of OC could reach 21.5% in 2.5 hours.Compared with traditional methods of cellulose hydrolysis,this method is fast,simple,and efficient,which can provide a new idea for the large-scale production of OC.(2)How to use renewable biomass resources to develop high-performance bio-based materials instead of traditional petroleum-based materials has become a global research hotspot.The mechanical properties of elastomers are determined by their composition,topology,and network structure.Compared with linear elastomers,star-like elastomers can exhibit significantly enhanced mechanical strength and elasticity due to their topological structure.Therefore,a series of OC-g-P(IBOMA-r-BA)star-like copolymers were synthesized by grafting polymerization using OC as the initiator,and these elastomers were well characterized.The results show that these star-like polymers have excellent thermal stability and controllable mechanical properties.The glass transition temperature,tensile strength,ductility,and elasticity can be systematically adjusted by monomer feed ratio and OC content.As these star-like elastomers are synthesized by random copolymerization,there is no microphase separation structure,and each sample has only one glass transition temperature,indicating that the material is relatively uniform inside.These elastomers can be easily processed by hot pressing.The combination of OC and controlled free radical polymerization can provide theoretical guidance for the development of star bio-based elastomers shortly.(3)The development and application of bio-based elastomers can not only reduce the over-dependence on petrochemical resources but also avoid environmental pollution and realize the sustainable development of the thermoplastic elastomer industry.A fully substituted cellulose oligomer initiator(OC-Br)was obtained by the full reaction of its hydroxyl groups,and then a bio-based monomer acrylate(SA)was synthesized.Combined with another bio-based monomer tetrahydrofurfuryl acrylate(TA),fully bio-based OC-g-P(SA-r-TA)star-like elastomers the excellent performance was successfully prepared by grafting polymerization.These elastomer materials also have excellent UV absorption and adhesion ability,which can be used as UV shielding materials and hot melt adhesives.This simple and efficient grafting polymerization method can provide new avenues for the development of green,clean,sustainable,and high-performance bio-based elastomer materials.