Preparation And Performance Research Of Natural Polymer Derivative Materials With Anti-ultraviolet And Anti-oxidation Function

Polymer materials play an important role in the development of the national economy and society;however the large-scale application of polymer materials has arose serious resource and environmental problems.It is agreed that the development of new polymer materials using abundant renewable biomass resources as raw materials is one of the important ways to realize the sustainable development of polymer industry.Cellulose,lignin and chitosan have good biodegradability and biocompatibility,and they are easy modification and are regarded inexhaustible bio-renewable resources.Therefore,the development of new,green and efficient modification strategies have attracted much attention towards new materials development by taking advantage of their polymer backbone.In this thesis,CO₂-based solvents and water were used as green solvent systems,for cellulose and cheitosan,and novel,green,and efficient derivatization and composition strategies were developed.The relationship between material hierarchical structure and properties were systematically studied in order to establish the new theories and technologies for the controllable derivatization and functionalization of cellulose and chitosan.Firstly,based on the new solvent properties of the newly developed CO₂-based solvents system,as well as taking the structural advantages both of cellulose and DHC,a novel cellulose-3-（2-hydroxyphenyl）propionate ester（CHP）with satisfactory antioxidant and UV-resistant properties was successfully designed and prepared via a green organocatalytic ring opening reaction of dihydrocoumarin（DHC）with the hydroxyl groups on cellulose,without adding exterior catalyst.The degree of substitution could be simply adjusted by changing the reaction conditions（molar ratio of DHC to AGU,reaction temperature and time）,and the DS reached 2.35 at 3 h when the molar ratio of DHC to AGU is 6/1 at 120°C and 3h.The introduced 3-（2-hydroxyphenyl）propionate group enabled CHP to have excellent UV absorption properties and antioxidant capacity.When the concentration of CHP-3 was 40 m M,the DPPH free radicals scavenging activity was 68.1%instantaneously and reached 100%in 30 min.The kinetic study of scavenging effect showed that the reaction followed a pseudo-first-order kinetic model,and the activation energy Ea and Arrhenius frequency factor A of CHP-3 for DPPH were 24.24 k J/mol and 2.5918/s,respectively.The cytotoxicity test results showed that even at 200μM,CHP had no significant cytotoxicity to L929 cells,indicating good biocompatibility.In addition,the CHP showed strong ultraviolet absorption in the ultraviolet UVB and UVA regions,and a color enhancement effect with the increase of DS.The excellent UV-absorbing and antioxidant properties,as well as biocompatibility make CHP has potential applications in personal care,medicine,cosmetics and food.Secondly,taking the advantages of the solvent properties of the newly developed CO₂-based solvents system,a serials of cellulose graft alternating copolyester have been designed and prepared via anionic ring-opening alternating copolymerization reaction by using DHC and epoxy compounds.The organic base DBU not only participated in the dissolution of cellulose,but also acted as a catalyst for the cellulose initiated ring-opening copolymerization of DHC and epoxides.The structural characteristics,monomer conversion,total polymerization degree and molecular weight distribution of the cellulose grafted-alternating copolymers（Cell-g-P（DHC-alt-EPO））were elucidated by various characteriation methods.When the molar ratio of DHC,epoxide,and cellulose was set to 10/10/1,the monomer conversion,DP and Mn1 of DHCSO5were 80.48%,11.64 and 224.8 k Da at 100°C,24 h.Meanwhile,the MALDI-TOF MS and GPC results demonstrated that the final Cell-g-P（DHC-alt-EPO）was a composition of a cellulose graft alternating copolyester and a copolyerster via self-polymerization of the DHC and epoxide.The findings also indicate that the Cell-g-P（DHC-alt-EPO）s had good UV absorption and antioxidant ability,fluorescence,and antibacterial properties.For example,the Cell-g-P（DHC-alt-EPO）was identified to has satisfactory UV absorption properties at 282 and 295 nm.The DHCSO5 in DMSO showed obvious both AIE and ACQ behaviors with the increasing of concentration.However,the solid state of DHCSO5 still showed strong photoluminescence with QY of 2.4%andτ_ave of3.39 ns.The radiative（k_r）rate constants was 7.71×10⁶ and nonradiative(k_nr)rate constants was 2.88×10⁸,respectively.In addition,the Cell-g-P（DHC-alt-EPO）had good photobleaching resistance.The antioxidant capacity was also evaluated by DPPH-based colorimetric protocol,and the instant DPPH radicals scavenging activity was up to 65%at 40 mg/m L,100%in 30 min in the case of DHCSO5.Thirdly,with the successful dissolution of cellulose in CO₂-based reversible ionic liquids system（TMG/EG/DMSO/CO₂）,a gel film of cellulose was prepared through a solution-gel transmition protocol,and then a serials of self-assembled cellulose/lignosulfate salts（LS）composited films with satisfactory mechanical properties and excellent UV-shielding properties were prepared through cellulosic gel films in LS aqueous solution.It is believed that the hydrogen bonding interaction among of the hydroxyl,sulfate and metal cations on LS and cellulose endow their satisfactory mechanical properties,and a maximum tensile strength was 94.7 MPa for MCC3LS,and a best breaking strain was 11.6%for MCC1LS.The permeability of the films to oxygen was almost 0,and the permeability to water vapor could be as low as 5.3×10^-3g·μm/m²·day·k Pa.The findings also demonstrate that LS is easy to self-assemble into uniform nanoparticles in the cellulose chain,which endow the composited films with excellent UV shielding properties.The composited films could shield 100%of the UVC and UVB regions.Finally,a biobased levulinic acid（LA）aqueous solution was successfully developed for the dissolution of chitosan（CS）,in association of the use of a biobased Vanillic acid（VA）as a functional carboxylic acid.With the successful dissolution of chitosan in the aquesous solution with different molar ration of LA and VA,a serials of functional compositied polyelectrolyte membranes（CS/VA/LA）were prepared via a solution-gel transmition protocol and suitable drying processes.The findings indicated that the as-prepared membranes havd good mechanical properties,UV shielding effect and satisfactory biocompatibility.The NMR and FTIR results demonstrate that there were not only hydrogen bonds and ionic bonds,but also Schiff-base structural moiety in membranes.The mechanical test results showed that with the increasing of VA content,the tensile strength of the CS/VA/LA polyelectrolyte composite membrane increased from 25 MPa to 54 MPa,but the breaking strain first increased and then decreased from 9.3%to 4.9%.Due to the introduction of the VA group,the composited membranes almost had excellent shielding of the UVC and UVB regions.For example,when the molar ratio of VA/LA was 2/8,the composited membrans can achieve full shielding in UVC.With the increasing of VA content,the shielding efficiency also increased gradually.The transmittance of CS-V10L0 composited film was only 2.8%in UVB region and 28.8%in UVA region.In addition,the composited membranes also had excellent antioxidant properties.The DPPH free radicals scavenging activity of CS-V2L8 wass evaluated to 45%,and the value of CS-V5L5 and CS-V10L0 was 78%,and90%in 300 min,respectively.In addition,the composited membranes also had good biocompatibility.Towards new sustainable materials development by using natural polymers,this dissertation integrates the disciplines of natural polymers,green chemistry,organic chemistry,and polymer chemistry.The achievements provide significant insights for the design and preparation of new derivatized and composited new materials from natural polymers,by taking the advantages of newly developed solvent system,which has significant scientific value and social benefits.