Preparation And Surface Modification Of Nano-crystalline Cellulose

Cellulose is the most abundant natural polymer in the world, which mainly derived fromthe photosynthesis of plants. Nano-crystalline cellulose (NCC) suspensions were prepared bythe method of acid hydrolysis of sisal, cotton and microcrystalline cellulose (MCC). Thecharacterization results show that the NCC prepared by sisal owns the largest size distribution,which has the average particle size distribute from50~500nm. The average size of NCCobtained from the cotton40~200nm. The NCC prepared by MCC has the smallest sizedistribution, which distribute from20~50nm. The rheological measurements were applied toNCC suspensions with different viscosities in order to explore their rheology and flowbehavior. The steady-state shear viscosity was measured in the shear rate range of0.1to1000rad/s. Result shows that suspension with low concentration was easy to be influenced bythe change of shear rate, the curve is typical of a “three-region” model. Curve behavior asshearing thinning at the whole range of shear rate if increase the concentration of suspension,which suggest that the gel structure may emerge in the suspension.NCC particles are easy to agglomerate because of their large specific surface area andabundant hydroxyl group. The surface modification of NCC will decrease the content ofhydroxyl group, and also bring in a new functional chain, which may give NCC new features.3-chloro-2-hydroxypropyl-trim-ethyl ammonium chloride (CHMAC) is a kind of cationicagent, which is low-priced and stable. NCC was grafted with CHMAC in two differentreaction systems: water and water mixture with DMSO. Elemental analysis results show thatthe NCC in the water/DMSO system has higher graft ratio. Reducing the water content in thereaction system can effectively improve the graft ratio of NCC. The grafted product wascharacterized using several analytical techniques such as FTIR, TEM, and XRD. Results showthat the grafted product owns the same structure as the prototype cellulose, and has a betterdispersion in water, a lower content of crystallinity can be observed for the grafted NCC.On the basis of the first step graft modification of NCC, hydro-propyl quaternaryammonium salt (NPES) was grafted onto the surface through the principle of ionic exchange.TEM results showed that NCC grafted with NPES still has whiskers structure, and a betterdispersed; XRD tests show that they all owns the basic crystal structure of cellulose. NCCgrafted with NPES has lower content of crystallinity, maybe which should attribute to therandom conformation of NPES on the surface of the NCC.