Preparation Of Cellulose Nanocrystalline Particles And Their Aggregation Properties

In recent years, building carrier system with special functions using cellulose nanocrystals(CNC) as a template,has become the hotspot of food, medicine and other fields. While the preparation of CNC and study on their aggregation characteristics are of great significance for the design of function of supports. In this thesis, microcrystalline celluose was used as raw material for the preparation of CNC particles with different morphology and size.CNC was prepared by sulfuric acid hydrolysis and Na OH/urea system, respectively.The differences on aggregation behavior of the CNC particles have been analyzed and compared. The effects of different conditions on the formation and transformation of the CNC aggregate structures also has been investigated. Moreover, the relationship among macroscopic rheological properties, microstructures and driving forces in the CNC aggregates are clarified. The main contents include the following points:(1) The effects of the sulfuric acid concentration, hydrolysis temperature, hydrolysis time and concentration of Na OH and urea on the yield, purity, and the average degree of polymerization of CNC particles have been investigated. The properties of CNC particles were characterized using scanning electron microscopy, transmission electron microscopy, nanoparticle size and Zeta analyzer, fourier infrared spectrum, X-ray diffraction, thermogravimetric analysis, and other means. The results show that with the increase of sulphuric acid concentration, hydrolysis temperature and hydrolysis time, the yield of CNC decreases, while the crystallinity increases. Three rod-shaped nanoparticles(CNP1, CNP2 and CNP3) were obtained by the sulfuric acid hydrolysis method, and A spherical submicron particle(CMP) was obtained by the Na OH/urea method. CNP1, CNP2 and CNP3 have typical of cellulose I,and CMP has typical of cellulose II. Sulfate ester can be introduced in cellulose crystal surface during the process of sulfuric acid hydrolysis.(2) Based on the special response of CNP gathering system with multi-scale structure on the rheological parameters, rheological and small angle laser scattering method, supplemented by scanning electron microscopy, was used to analyze and compare the differences of aggregation behavior of the particles. The effects of particle concentration, p H and ionic strength on the steady shear viscosity and the parameters characteristic(size and aspect ratio) of the CNP suspensions have been investigated. The relationship between difference of macroscopic rheological properties and evolution of the microstructure in system was also discussed. The results showed that steady shear viscosity of the CNP suspensions affected by shear stress, exhibiting the classic model of "three zones" and a shear-thinning behavior. Scanning electron microscopy results showed the presents of cumulus aggregate morphology under the condition of strong acid or alkali. The change in CNP morphology and structure has direct influence on the aggregation behavior. The sulfate ester on the particle surface increases with the increases with the decrease in its size. The effects of p H and ionic strength on the CNP aggregation behavior reduce. CNP and CMP have different responsiveness to the changes of ionic strength, which can be explained that the sulfate ester introduced may effectively enhance the electrostatic repulsion between CNP. The shielding on electrostatic repulsion by salt causes the aggregation of the CNP, hence changs their rheological properties and characteristics parameters.