Crystallinity of cellulose materials

Pulverization can reduce the size as well as the crystallinity of cellulosic materials and increase the surface area and bulk density. It is also possible to separate part of the hgnin from carbohydrates which makes it easier for microorganisms to digest cellulose. Various equipment, such as a compression mill, a bead mill, an extruder, a roll mill and disc refiners, etc., can be used for pulverization. Unfortunately these methods tend to be very expensive and too energy intensive. For sohd-state fermentation, if the particles are too fine, the oxygen mass transfer will become a big problem therefore, hghtly crushed or just ground raw material will suffice. 

Jayme, G., and Knolle, H. (1964). Introduction into empirical X-ray determination of crystallinity of cellulose materials. Das Papier, 18, 249-255. 

It has grown increasingly apparent that the non-crystalline portions of cellulose structures may play as important a role in the properties and behavior of cellulosic materials as the crystalline parts. X-ray diffraction studies have greatly extended knowledge of crystalline cellulose but in the case of the amorphous or disordered fraction the methods of study have necessarily been indirect and not completely reliable. 

A series of estimates of non-crystalline cellulose in various types of cellulosic material is presented in Table II. These estimates were obtained by extrapolating the relatively flat portions of curves such as those given in Figure 2 to zero time and are admittedly first approxima-... 

Relative crystallinity undoubtedly influences such properties of cellulosic materials as rigidity, flexibility, plasticity and extensibility. Likewise the amount and reactivity of intercrystalline cellulose are major factors in common processing treatments such as bleaching, dyeing, pulping and wet finishing. Further refinement of measuring methods and the development of further correlations between crystallinity and fiber properties would contribute much to this important field. 

The use of Cl to represent the percentage of the crystalline component is unjustified among such a diversity of cellulosic materials, whose lignin components vary from 0 to about 30%. Cl, as used here, is not intended to represent the proportion of the crystalline component. Rather, Cl provides a means of quantifying the characteristics of the x-ray diffraction patterns. When applied to a set of similar samples, Cl is a convenient measure of the degree of lateral order. 

A major problem in the commercialization of this potential is the inherent resistance of lignocellulosic materials toward conversion to fermentable sugars (4). To improve the efficiency of enzymatic hydrolysis, a pretreatment step is necessary to make the cellulose fraction accessible to cellulase enzymes. Delignification, removal of hemicellulose, and decreasing the crystallinity of cellulose produce more accessible surface area for cellulase enzymes to react with cellulose (5). 

Similar analyses of moisture uptake data available in the literature for other cellulose and starch derivatives used as pharmaceutical excipients are presented in Table 5. Considering the uncertainties associated with the estimated moisture uptake values from published graphs, the values of are all quite consistent with each other and with a stoichiometry of one water molecule per anhydroglucose unit. It is interesting to note that the two samples derived from cellulose, sodium carboxymethylcellulose and sodium croscar-mellose, did not require any correction for degree of crystallinity to conform to close to a 1 1 stoichiometry. It appears quite likely, therefore, that the change in chemical structure and the processing of these materials essentially eliminates the crystallinity of cellulose. 

Viscose rayon is inherently a weak fibre, particularly when wet, therefore it is highly susceptible to damage if enzymatic hydrolysis is not controlled. The enzymatic hydrolysis of viscose fibres causes a decrease of the intrinsic viscosity from 250 to 140 ml/g and an increase in crystallinity from 29 to 39% after 44 h [34]. Strong changes of the structure, however, are not typical for the enzymatic hydrolysis of cellulosic materials. Neither cotton nor wood pulp show an essential decrease of the DP during enzymatic hydrolysis [35-37]. The kinetics of the enzymatic hydrolysis of regenerated cellulose fibres before and after acid prehydrolysis changes the kinetics from a monophasic to a biphasic first order reaction [38]. 

Structural features of cellulosic materials that determine their susceptibility to enzymatic degradation include (1) the moisture content of the fiber (2) the size and diffusibility of the enzyme molecules involved in relation to the size and surface properties of the gross capillaries, and the spaces between microfibrils and the cellulose molecules in the amorphous regions (3) the degree of crystallinity of the cellulose (4) its unit-cell dimensions (5) the conformation and steric rigidity of the anhydroglucose units (6) the degree of polymerization of the cellulose ... 

Since it is essentially impossible to prepare Celluloses II, III, and IV without also altering the degree of crystallinity of the material, it is difficult to determine whether their modified susceptibility to enzymatic degradation is owing to changes in the unit cell dimensions of the crystallites alone or also to differences in the amount of amorphous material present. 

---