Modification Of Microcrystalline Cellulose And Research On Its Enhanced Polymer Composite Materials

Composite material has the advantages such as the properties of each components and extra functional characteristics based on the synergistic effects of the components.It has attracted widely attention during the social development to meet people's expanding demands.Among them,the composite material strengthened with reinforcements is the most important and is used most widely.Up to date,various reinforcement materials have been developed,such as glass fiber,quartz,carbon black,but many of them are not biodegradable or toxic,and are not suitable for biomedical materials or food related products.Cellulose is the most abundant natural polymer material on earth.The properties of such as non-toxic,renewable,biodegradable,and high crystallinity of cellulose has endowed it with very high strength.Moreover,the hydroxyl groups on the cellulose chain can be modified,and cellulose can also be processed into microcrystalline cellulose(MCC)or nanocrystalline cellulose(CNC)with a size of micron or nanoscale,so cellulose is expected to become the ideal reinforcement materials.However,large scale natural cellulose fiber is difficult to disperse evenly in matrix and its enhancement effect is not good.CNC is expensive to prepare.Although MCC is cheap,its particle size is large,and it is easy to aggregate in matrix,and its enhancement effect is not obvious.Moreover,MCC has strong interactions between molecular chains,making it difficult to dissolve in general solvents.This work aims to use the microwave radiation for the surface modification of MCC,and then it was added into chitosan solution as a reinforcing material to prepare chitosan composite,which is hoped to overcome the disadvantages of low mechanical properties and large water vapor transmission rate of chitosan membrane,and to extend the application prospects in the fields of the packaging.Moreover,acrylamide was mixed with MCC and irradiated under microwave to prepare acrylamide,modified MCC,and its application as flocculates was carefully investigated.In addition,the acrylamide-modified MCC was mixed with acrylamide monomer,which was inniated to polymerize to prepare a polyacrylamide composite hydrogel.The properties of the samples prepared by various parts are characterized and tested with advanced instruments and equipment,and the mechanisms are also studied.The detailed research work is as follows:Microcrystalline cellulose modified with urea for the reinforcement of chitosan filmThe commercial MCC with particle size of about 50?m was mixed with urea and was then irradiated under microwave for the modification.The obtained urea-modified MCC(u-MCC)was dispersed in a chitosan solution without precipitation for over 48h,which provided a time window for its processing.Through casting the mixture slurry followed by coagulating,a full natural polymer composite film has been prepared.The mechanical properties of the obtained composite film have been carefully measured and discussed.Our results indicate that the mechanical properties reaches the highest when the urea-modified MCC is 7 wt%in the composite film:the tensile strength,the elongation at break,the Young's modulus and the fracture energy are respectively about 2.0,2.1,2.4 and 6.0 times of those of the pure chitosan film.The reinforcement of the composite material with the u-MCC particles was understood through scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FT-IR)and X-ray diffraction(XRD)results,and has been attributed to the strong interaction between the surface modified MCC particles and the neighboring chitosan chains in the film matrix.Moreover,the water vapor permeability and the transparency of the composite films have been determined to evaluate potential applications such as packaging material.Preparation and study on flocculation properties of microcrystalline cellulose grafted polyacrylamide by microwave irradiationMCC and acrylamide(AM)water solution are mixed with magnetic stirring for 24h.After drying,the product is subjected to microwave irradiation without catalyst and initiator,and acrylamide modified microcrystalline cellulose(am-MCC)is obtained.The results of study on the composition of the reaction product by Fourier transform infrared spectroscopy(FT-IR)show that PAM was successfully grafted onto the MCC.The observation of the morphology by scanning electron microscopy(SEM)shows that the surface of modified MCC is more loose than the surface of pure MCC.The characterization results of X-ray diffraction(XRD)show that microwave modification does not change the crystal structure of MCC and the reaction only occurs on the surface of MCC.The effects of microwave power,radiation time and mass ratio of reactants on grafting rate were discussed.The results showed that the highest grafting rate was 95.5%when radiation power was 800W,radiation time was 3min and MCC/AM was 1/4.5.The flocculation performance was tested.The results showed that the graft product had good flocculation performance.In this part,a sMCC and PAM to get environmentally friendly flocculants.imple and low cost method is used to combineStudy on modified microcrystalline cellulose reinforced polyacrylamide hydrogelMCC and AM(MCC/AM(WT)1/4.5)water solution was mixed with magnetic stirring for 24h as the study of the upper part.After drying,the product was microwave irradiated under the condition of 800W and 3min,and the product was am-MCC.And am-MCC was added into the aqueous solution of AM and joined with initiator and crosslinking agent to induce monomer polymerization to get the hydrogel.Fourier transform infrared spectroscopy(FT-IR)and scanning electron microscopy(SEM)were used to characterize their composition and morphology.The results showed that there was strong hydrogen bonding interaction and crosslinking between the modified MCC and PAM matrix,and the composite hydrogel had good pore structure.The mechanical properties and water absorption properties of the hydrogels were tested,and the results show that when the content of modified MCC was 4%(percentage of PAM matrix)the compressive strength of the composite hydrogel reached the maximum compression strength which is 69%higher than pure PAM hydrogel,and the composite hydrogel had good water absorption performance as pure PAM hydrogel.Repeat compression experiment results show that the composite hydrogel has good shape recovery properties and strength did not change obviously,repeated water absorption test results show that the composite hydrogel has good water absorption performance and the maximum swelling rate has not changed significantly.Therefore,the am-MCC reinforced PAM hydrogel prepared in this part makes polyacrylamide hydrogel can be used as absorbent material under high pressure and can be reused.