Cellulose crystal density

Based on the unit cell structure for cellulose I, calculate its theoretical crystal density. (See Rgure 6.1.)... 

Lee KY, Bharadia P, Blaker JJ, Bismarck A (2012c) Short sisal fibre reinforced bacterial cellulose polylactide nanocomposites using hairy sisal fibres as reinforcement. Compos A 43 2065-2074 Lei Y, Wu Q (2010) Wood plastic composites based on microfibrillar blends of high density polyethylene/poly(ethylene terephthalate). Bioresour Technol 101 3665-3671 Liu D, Zhong T, Chang PR, Li K, Wu Q (2010) Starch composites reinforced by bamboo cellulosic crystals. Bioresour Technol 101 2529-2536 Liu H, Xie F, Yu L, Chen L, Li L (2009) Thermal processing of starch-based polymers. Prog Polym Sci 34 1348-1368... 

Cellulose in cotton is synthesized by the condensation of glucose monomers at enzyme complexes. Each enzyme complex produces 30 cellulose chains, which lie in the same direction to crystallize into long microfibrils. The microfibrils have an average diameter of several nanometers. From this aspect, the cellulose in cotton is considered to be 100% ciystalhne since all cellulose chains contribute to the formation of microfibrils. However, the density of cotton is lower than the crystal density, and experimental measirrements using diffraction, spectroscopic, thermal and other techniques show cotton is about 60% crystalline. This can be explained by the imperfect packing when the microfibrils are formed. Microfibrils consisting of aligned cellirlose chairts are the main structural components of cotton fibers. 

Manufactured cellulose fibers have a very different physical structure from natural cellulose fibers. The crystal lattice formed by native cellulose chains in natural cellulose fibers is called Cellulose 1 (Figure 5.2). When cellulose is dissolved and spun into fibers, the crystal lattice changes to Cellirlose 11. Table 5.3 compares the imit cell parameters and crystal densities of Cellirlose 1 and Cellulose 11. The... 

Table 5.3. Edge lengths, internal angles and crystal densities of Cellulose I and Cellulose II.

In the case of cellulose, these crystalline arrangements are usually imperfect, in terms of crystallinity, crystal dimensions, chain orientation and then the purity of the crystalline form must be taken into corrsideration. The crystal density can be gauged from the crystallographic data which leads to suggest the importance of the amorphous components generally present. By infrared spectroscopy, the degree of crystallinity can also be estimated as a function of the relative interrsity of specific bands [42]. 

The bulk properties of regenerated cellulose are the properties of Cellulose II which is created from Cellulose I by alkaline expansion of the crystal stmcture (97,101) (see Cellulose). The key textile fiber properties for the most important current varieties of regenerated cellulose are shown in Table 2. Fiber densities vary between 1.53 and 1.50. 

Combined X-ray and electron diffraction analysis led to an orthorhombic unit-cell, with a = 2.468 mn, 1) = 1.152 nm, and c = 1.054 nm. The space group is P2,2,21. Two parallel chains are related, pairwise, by a two-fold screw-axis parallel to the chain axis, and pairs of chains pack in an antiparallel array. The (110) growth planes ol the crystal are parallel to the direction of highest atomic densities. The transformation CTA II cellulose II was discussed. The R factor is 30% with the X-ray diffraction data, and 26% with the electron diffraction data. 

DEAE-cellulose column was further purified on Sephadex G-200 but resisted all efforts at crystallization. Figure 14 (4) shows the polyacrylamide gel electrophoretic pattern of crude rat liver extract with two bands, the resolution of these bands by DEAE-cellulose, and the crystalline peak I preparation. The crystalline enzyme had an approximate molecular weight of 100,000 estimated by sucrose density gradient... 

The first attempt to establish the crystal and molecular structure of CTA I was made by Stipanovic and Sarko, who suggested the occurrence of parallel-arranged cellulosic chains within an orthorhombic unit-cell. Later, the structural analysis of the diffraction pattern from an acetylated material derived from the green alga Cladophora sp. established it as a one-chain unit cell crystallizing in the P2i space group (fl = 5.94 A, = 11.43 A, c = 10.46 A, y = 95.4°, density = 1.375). 

Two interesting points are the number of cellobiose units per cell for cellulose triacetates I and II is 4, versus 2 for celluloses I and II and the measured density for cellulose triacetate II was 1.315 g/ cc, which is less than the calculated density of 1.348 g/cc as expected because cellulose triacetate is not 100% crystalline. The above studies on the crystalline structure of cellulose triacetate lead to the conclusion that commercial heat-treated cellulose triacetate is expected to have the cellulose triacetate II crystalline structure. Analysis of the crystal structure of cellulose triacetate continues [55]. 

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