Crystal, cellulose

An important chemical finishing process for cotton fabrics is that of mercerization, which improves strength, luster, and dye receptivity. Mercerization iavolves brief exposure of the fabric under tension to concentrated (20—25 wt %) NaOH solution (14). In this treatment, the cotton fibers become more circular ia cross-section and smoother ia surface appearance, which iacreases their luster. At the molecular level, mercerization causes a decrease ia the degree of crystallinity and a transformation of the cellulose crystal form. These fine stmctural changes iacrease the moisture and dye absorption properties of the fiber. Biopolishing is a relatively new treatment of cotton fabrics, involving ceUulase enzymes, to produce special surface effects (15). 

Cheng Q (2010) Green nanocomposites reinforced with cellulosic crystals isolated from juvenile poplar. In Proceedings International Convention of Society of Wood Science and Technology and United Nations Economic Commission for Europe - Timber Committee October 11-14, Geneva, Switzerland, Paper NT-6 1... 

Attempts to examine the process of cellulose crystallization have frequently involved culturing Acetobacter in the presence of fluorescent brighteners, direct dyes, carboxy-methyl-cellulose, or other agents which compete for interchain hydrogen bond sites, thereby disrupting microfibril formation... 

Next, a correlation among Sa, Xam(X), the fraction of the accessible part (by heavy water) at equilibrium, as determined by the deuteration IR method, Xac(IR)> ar)d the relative amount of the higher field peaks of the C4 carbon peaks, Xh(NMR), were examined for samples having cellulose crystal form II, so as to clarify the factors contributing to Sa. In this case, Xi,(NMR) was estimated from Eq. (60) ... 

Alkaline treatment causes lignocellulosic materials to swell increased swelling leads to higher susceptibihty of cellulose to saccharification. In the presence of alkaline chemicals (e.g., NaOH or NHj), cellulose, hemicellulose, and hgnin bonds can be disrupted. This permits cellulose to swell beyond normal water-swollen stages. Consequently, the pore size, the intraparticle porosity, and the capillary size are increased. There is also a phase change in the cellulose crystal-hne structure [33]. 

Stout has written a detailed review on jute and kenaf. X-ray diffraction patterns show the basic cellulose crystal structure, although in jute and kenaf the crystalline orientation is high and the degree of lateral order is lower than in flax. Batra" in a comprehensive review has highlighted the morphological structures and physical, mechanical and chemical properties of other long vegetable fibers. 

Like this, the decomposition of cellulose crystal structure initiated and finished at lower temperatures in C, grafted cellulose, and stannic chloride treated cellulose than those in M. 

In perfect crystals these faces are fairly small - the major exposed faces along the fibre crystal are 100 and 010, which are hydrophilic - and are not large enough to account for the amount of CBM adsorbed. However, cellulose crystals will be damaged and this damage will be associated with removal of glucan chains from the corners of the crystal, increasing the effective hydrophobic area. 

Cell Symmetry. For many years. It was accepted that the cellulose molecule embodied 2-fold screw symmetry (space group F2 ). Later, Honjo and Watanabe (12) showed electron diffraction diagrams that Indicate that Valonla cellulose crystallizes In the FI space group that does not contain symmetric chains. The unit cell also contained 8 chains. Other diffraction work showed the presence of faint meridional reflections on the odd layer lines that also Indicate that the chains do not have exact 2-fold screw symmetry. While the validity of this evidence has been accepted for Valonla, It has not been used In structural studies because of the low Intensities of the spots that Indicate the large cell and that break the symmetry. It has been argued that the deviations from symmetry must be relatively small (11) assumptions regarding the cell size have been necessary In order for the needed computations to be manageable. 

Fig. 1. Transformation pathways between cellulose and Na-cellulose crystal structures. (Reproduced with permission from ref. 1. Copyright 1986 John Wiley Sons, Inc.)...

The polymorphism and morphology of cellulose precipitated from solutions in amine oxide by the slow diffusion of water vapors, was Investigated, as functions of the temperature of recrystallization and the degree of polymerization (DP) of the material to be recrystallized. At temperatures around 90°C, low DP cellulose crystallized almost exclusively as cellulose IV, whereas higher DP material was found in the form or cellulose II. Substantial differences were also found in the morphologies of the various samples with cellulose II, rod-like crystals were obtained with low DP material while a crystalline fibrillar gel precipitated when high DP scimples were recrystallized. In all cases, cellulose was obtained as a granular precipitate. 

Cellulose Crystallization. For crystallization below 100 C, the solutions were poured into petri dishes and positioned inside a closed vessel containing an excess of water. The vessel was then fitted into a temperature controlled oil bath and brought to the crystallization temperature. Crystallization of cellulose resulted from the diffusion of water into the solution. Crystallization was complete within a few minutes at 90 C whereas several days were necessary at room temperature. For crystallization between 100 C and 120 C, a similar principle was used except that a thick-wall sealed glass vessel was used to prevent water vapor from escaping. 

Figure 1. X-ray diagram of cellulose crystals recrystallized at 90°C. lA from cotton cellulose (DP 2000) solution. IB from microcrystalline cellulose (DP 34) solution.

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