Preparation, Properties And Application Of Nanocellulose Crystal

Cellulose is a high-molecular weight linear homopolymer constituted of repeatingβ-D-glucopyranosyl units joined by 1→4-glycosidic linkages,is the most abundant,renewable and biodegradable natural polymer.This renewable natural polymer is present in all plants and tunicin,and it is also synthesized by some microorganisms.Manipulating cellulose molecules in the nanometer scale to create the nanocellulose crystal with excellent properties,has become a hotspot of cellulose science.In this thesis,microcrystalline celluose (MCC) was used as raw material for the preparation of nanocellulose crystal (NCC).NCC was prepared by two ways: sulfuric acid hydrolysis and cation exchange resin catalytic hydrolysis with the diameter size in the nanoscale (1-100 nm).Response surface mehtodology (RSM) and Box-behnken statistical experiment design method was employed for modeling and optimization of the influence of some operating variables on the yield of NCC were discussed.For the sulfuric acid hydrolysis,the results predicted by the developed model were in a very good agreement with the measured ones.The correlation coefficient (R2) of the regression models and the adjusted R2,was about 0.9931 and 0.9843,respectively.It also showed that when sulfuric acid contration, temperature and time seperately were 54 %,52°C,125 min,the yield of NCC would reach 69.31%,a highest value in our investigation extension.For cation exchange resin catalytic hydrolysis method,the R2 of the regression models and the adjusted R2,was about 0.9822 and 0.9592 respectively,which confirming the excellent accuracy of the model.The result also indicated that a maximum NCC yield of 50.04% was obtained under the optimal concitions of the ratio 10:1,48°C and 189min.The ultrastructure characterization and size distribution of microcrystalline cellulose (MCC) and nanocellulose crystal (NCC) were investigated using field emission scanning electron microscopy (FESEM),field emission transmission showed that NCC in water can form a very stable suspension.It can be observed that MCC has irregular shape with diameter about 15μm,length in the range of 20-80μm . Regular short rod-like NCC can be obtained by sulfuric acid hydrolysis.NCC was determined to have diameters in the range of 2-24 nm and lengths of 50-450 nm.Very long and thin crystals of cellulose obtained by cation exchange resin catalytic hydrolys.This NCC has the same diameter as sulfuric acid hydrolysis sample,but relatively longer length.It also can form an interconnected web-like structure.The size of NCC observed from AFM were a little bigger than that of FETEM,it can be contributed to the soft texture of cellulose.The X-ray diffraction (XRD) pattern showed that the NCC has the cellulose I crystal form.Compared with MCC,the crystallinity of NCC prepared from sulfuric acid hydrolysis and cation exchange resin catalytic hydrolysis increased from 72.25 % to 77.29 % and 84.26 %,respectively.On the other hand,NCC still keep with the basic chemical structure of cellulose analyzed with Fourier transformation infrared spectroscopy (FTIR).The rheological behavior of NCC was also studied.The result showed that NCC was the shear thinned pseudoplastic fluid.Furthermore,as the temperature increases,its viscosity decreases,and gradually tends to flat,it indicated that the sample enjoy nice stability.Incorporating nano-sized filler material in polymer matrices to obtain novel nanocomposites with excellent properties has been a rapidly expanding area of research . Polyvinyl alcohol (PVA) composite films were prepared by the reinforcement of NCC into a PVA matrix at different filler loading levels and subsequent film casting.The compatibility,mechanical and thermal properties were characterized and analyzed by FESEM , thermogravimetric analysis (TG) , differential scanning calorimetry (DSC) and other instruments.From FESEM images, it can be observed that PVA/NCC composite films were created by casting from a water suspension to produce a homogeneous dispersion of NCC in the polymer matrix.But it showd some agglomeration when the filler loading reached to 7 %,and the interaction between filler and matrix.PVA composite films reinforced by NCC exhibit improved mechanical properties as compared to the neat PVA film.When the NCC content was only 0.5 %,the tensile strength of composite film increaessess 45.7% compared to the neat PVA film,being up to 51 Mpa.TG and DSC analysis showed excellent interaction between NCC and PVA.The composite films filled with NCC exhibit improved thermal properties as compared to the pure PVA film.On the other hand,the thermal stability of PVA composites films was decreased with filler loading increased to 7 %.