Preparation And Mechanism Of Citric Acid Crosslinked Cellulose Hydrogel Materials

Cellulose based hydrogel material maintains the advantages of the hydrogel material,while it combines cellulose biodegradable and biocompatibility.Currently,hot point of the reaserch is the preparation of the hydrogel material with water retention and adsorption-release function through cellulose derivative.Because of the hydrogen bonding with weak bond energy,normal cellulose based hydrogel material obtained through physical crosslinking has low thermal stability and mechanical properties.Therefore,developing the cellulose hydrogel material with hydrogel material basic characterisitics,better thermal stability and mechanical properties will become the focus of the field.Citric acid is an organic ternary acid with high reactivity.In this paper,the role of citric acid and sodium citrate played in the fabric wrinkle finishing and timber structure modified is learned.Citric acid as crosslinking agent,sodium citrate as catalyst,prepared a kind of citric acid crosslinked cellulose hydrogel material through cellulose solution preparation,cellulose hydrogel obtained through sol-gel method,crosslinking reaction precursor preparation,precursor heat treatment and final disposal.Characterized the changes of material chemical structure,the crystalline form of cellulose aggregates,microscopic morphology,endothermic-exothermic characteristics when chemical reaction happened,thermal stability,thermal gravimetric stability,viscoelastic properties,mechanical properties and the basic macroscopic properties of the material by FTIR,XRD,SEM,DSC,TGA,DMA and mechanical testing machine.According to the characterization results,discussing the crosslinking reaction mechanism and kinetics,optimizing the preparation course of the material,analyzing the influence of cellulose amount on the basic macroscopic properties of materials,discussing the formation mechanism of the skeletal structure of the material,studying the response characteristics of the material skeletal structure network system on the linear temperature program and periodic stress,analyzing the influence of the cellulose amount and citric acid amount on the characteristics above and related mechanical properties of material.Through thess studies,the following conclusions were obtained:1.The mechanism of esterification crosslinking reaction is“cyclic anhydride-esterification" mechanism,both two stages is according to the first order reaction kinetic characteristics.2.Recrystallization occurred in cellulose aggregates during the preparation.With the increasing of the initial concentration of cellulose,the crystalline of material was more extent,cellulose microscopic structure is more structured,and with a certain extent genotyping in the local area.Forming of the material backbone structure is compliance "nucleation growth”partly.3.Glass transition,crystallization zone slacking,molecular chains crystalline rearrangement,crystalline regions collapsing and final pyrolysis occurred in the citric acid crosslinked cellulose hydrogel material successively when temperature is in the range of-30℃-350℃.With the increasing of the amount of cellulose and citric acid,energy required of the response was becoming large,quality loser of material is more stable in the dynamic heating process.Under the act of cyclical stress,the initial temperature of microscopic morphology changing is bigger with the increasing of the cellulose amount.When the citric acid amount is larger,material viscoelastic properties stable temperature range is wider,which is wide to 20℃-120℃.4.The larger the cellulose initial concentration,the larger the specific heat capacity of material,which is up to 15.660J/g·K.Thermal conductivity stable at 0.25W/m·K.This kind of material owes important application value on the special preservation packing materials which is needed to help with maintaining the packaging system’s temperature and humidity.5.Stress-strain curve shape confirmed the "nucleation growth" which is the forming mechanism of cellulose backbone structure from the side.When the amount of the cellulose is larger,material elastic modulus is larger and energy absorption is smaller.The modulus is up to 162.4Mpa,the energy absorption is up to 311.56KJ/m~3.