Study On Preparation And Moclification Of Functional Nanocrystal Cellulose And Its Application

Cellulose is one of the most abundant natural polymer on earth. With thegradual depletion of oil, natural gas and other resources, study on renewable naturalresources used for industrial production has become a new trend. As one derivativesof cellulose, nanocrystalline cellulose(NCC) has characteristics of large surface area,strong adsorption capacity, high reactivity, big Young’s modulus, goodbiocompatibility and prominent nano features, so it has broad application prospects infields of nano-composite materials, biological medicine, catalytic carrier etc.Firstly, we study NCC preparation and modification. It is essential for NCC torecover the unique suspension and particle properties after drying, so we need tostudy the redispersion of NCC in aqueous solution. Moreover, owning to the richhydroxyl groups on the NCC, NCC particles can easily aggregate through hydrogenagglomeration in the process of drying, and it is difficult to use physical methods toredisperse after aggregation. So it limits NCC’s application in the polymer system. Inthis paper, NCC prepared by sulfuric acid hydrolysis of MCC were modified throughcrosslinking, esterification and dual modification of crosslinking and esterification toadjust the surface polarity of NCC. Then we study the redispersion of dried NCC inaqueous solution and improve the redispersion in non-polar or low polar solvent byincreasing hydrophobicity. The results show that: NCC can be modified throughcrosslinking with borax and glutaraldehyde in water. The crystalline structure of NCCis completely or partially preserved after the crosslinking modification and theaggregation among NCC is significantly reduced. So the modified NCC can be welldispersed in water. NCC can also be modified through esterification by using aceticanhydride. The ester groups are introduced onto the NCC and the polarity of NCC isreduced, so NCC can be well dispersed in water and organic solvents such asdichloromethane, suggesting that the esterified NCC has amphiphilicity. Thecross-linked NCC by glutaraldehyde is further modified through esterification withacetic anhydride. After the dual modification of crosslinking and esterification, NCCalso has amphiphilicity.Secondly, we conduct research on enhanced modification of PUA by NCC. Byincorporating different mass percentage of NCC, its effect on the overall performance of the polymer matrix is observed. The results showed that with the increase of theamount of NCC, the tensile strength of the composite films first increases and thendecreases; when the amount of NCC is5%, it displays the best enhancement effectwith the tensile strength reaching12.91MPa, improved54.98%compared to purePUA. The water absorption of modified composite film reaches a minimum when theamount of NCC is5%. Futhermore, thermal properties and light transmission of thecomposite films are hardly affected when the amount of NCC is5%. However, theNCC improves the high temperature properties of matrix.Thirdly, we prepared hollow silica with microbeam rod structure. Used NCC as atemplate and a cationic surfactant as the bridging agent, the NCC surface is coveredwith a layer of silica nanoparticles. Then remove the template and get hollowmicrobeam through calcination. SEM and TEM images show that a hollow SiO2isprepared, with a shape substantially similar to NCC, length of100-200nm, diameterof20-30nm, shell thickness of10-15nm, forming hollow rod-like structure. Thehollow silica has no collapse but some aggregation after calcination. BET testshows the hollow micro-beam possesses an enormous specific surface area reaching980m2/g, much larger than that of the core-shell structure before calcination.