Cotton cellulose crystalline components

We have spent some time investigating possible heterogeneity in the Ci components of F. solani, T. koningii, and P. funiculosum. This has been done by testing for both Ci activity (defined as the enzyme that acts in synergism with the Cx enzymes to solubilize cotton cellulose or other crystalline cellulose) and cellobiohydrolase (release of cellobiose from H3P04-swollen cellulose) during different fractionation studies on the various Ci components. 

Gel-permeation chromatography" is used to compare the pore structure of jute, scoured jute and purified cotton cellulose. Both native and scoured jute have shown greater pore volumes than cotton. The effects of alkali and acid treatment on the mechanical properties of coir fibers are reported." Scanning electron micrographs of the fractured surfaces of the fibers have revealed extensive fibrillation. Tenacity and extension-at-break decrease with chemical treatment and ultraviolet radiation, whereas an increase in initial modulus and crystallinity is observed with alkali treatment. FTIR spectroscopy shows that the major structural changes that occur when coir fibers are heated isothermally in an air oven (at 100, 150 and 200 °C for 1 h) are attributable to oxidation, dehydration and depolymerization of the cellulose component. 

The crystalline component of ramie and cotton differs In chemical shift and line splittings from that of valonia and bacterial cellulose. This suggests that there Is some difference in crystal structure among these samples, although the crystalline form Is generally assumed to be cellulose I for all these materials. 

Figure 6b shows the spectrum of the crystalline component of cotton soaked in H OCwater content=161%), which was obtained by Torchia s pulse sequence(27,28). The delay time between two ir/2 pulses in the pulse sequence was set to be 100 s. As is clearly seen, the spectrum shown in Figure 6b reflects the components corresponding to the downfield sharp lines of C4 and C6 carbons in the whole spectrum shown in Figure 6a. A similar crystalline spectrum was obtained by others(29) using almost the same technique. On the other hand. Figure 6c indicates the spectrum of the noncrystalline component of the cotton cellulose, which was obtained by subtracting the spectrum of the crystalline component shown in Figure 6b from the whole spectrum shown in Figure 6a. This spectrum evidently corresponds to the components associated with the upfield broad resonances of C4 and C6 carbons.

Figure 7 shows the spectra of the crystalline components of cotton celluloses with the water contents of 0% and 161%, which were obtained by the method described in the previous section(4). The multiplet of the Cl resonance is clearly seen in these spectra in the dry state two nonequivalent lines seem to constitute this resonance but they split into one doublet and one small singlet centered at the doublet in the hydrated form. Moreover, C4 and C6 resonances tend to split into a triplet and a doublet, respectively. Almost the same spectra were obtained for ramie cellulose in both dry and hydrated forms. 

CP/MAS C NMR spectra of the crystalline components of cotton cellulose with the water contents of 0% (a) and 161% (b). (Reproduced from Ref.4. Copyright 1985 Academia Republicil Socialiste Romania,)... 

Figure 10 shows the spectra of the noncrystalline components of cotton cellulose with water contents of 0% and 161%(4), These spectra were obtained by subtracting the spectra of the crystalline components from the corresponding whole spectra as shown in Figure 6. It is clearly seen that the linewidths of the Cl and C4 resonances become markedly narrower upon absorbing water, while holding the chemical shifts unchanged. For instance, the half-value widths of the Cl resonance lines are 50 Hz and 150 Hz, respectively. Such a...

Glycol cleavage. The initial periodate oxidation of cellulose, like other chemical reactions, was largely limited to the readily accessible component and has also been used to indicate the accessibility of cellulose substrates [151] (Table 1). Rowland and Cousins [232], based on the influence of periodate oxidation in the crystallinity of cotton, observed about 40% of the component being noncrystalline. Since the m-diol unit is generally more reactive than the /ran.9-diol, the cleavage of the mannose residues would proceed faster than that of the glucose or xylose residues. 

On the basis of fractionation studies made at this time, Ci-type enzyme was envisaged as the only component capable on its own of solubilizing highly ordered forms of cellulose cotton was used by Mandels and Reese (10) and in some of Flora s work (2) and crystalline hydrocellulose (an acid-hydrolyzed cotton) by Li, Flora, and King (8). Addition of Cx to Ci caused about threefold increases in solubilization. Contemporary work at the Shirley Institute centered on rigorous fractionation of the cellulase system of T. viride into components displaying single... 

Cellulase is a complex of enzymes showing various types of activities. Cellulose substrates include highly resistant crystalline forms such as cotton, various types of microcrystalline cellulose such as Avicel and hydrocellulose, sulfite pulps such as Solka Floe, as well as filter paper and cotton fabrics. More susceptible substrates include swollen or reprecipitated cellulose, cellophane, and ball-milled cellulose. Most susceptible are the soluble derivatives (of low D.S.) such as carboxymethylcellulose and cellulose sulfate. It is not surprising that there are many assay methods to detect or measure cellulase (9). These methods differ markedly in sensitivity, and in cellulase components detected, depending on the substrate used, the effect measured, and the duration and conditions of... 

The finer details of secondary and tertiary cellulose structure remain somewhat controversial and in any case will not concern us here. It will suffice to say that the chains align themselves side by side to form a substructure of microflbrils 35 A in diameter, and these in turn are linked together in more complex arrangements to form the main cellulose fibres. The microfibrils are believed to contain both amorphous and crystalline regions of aligned cellulose chains and the latter may adopt helical configurations. As a result of the presence of other components, differences exist between wood, cotton and synthetic cellulose fibres. 

Fig. 16. Integrated fraction of the downfield component of the C4 resonance line versus degree of crystallinity, /, determined by X-ray analysis., Native cellulose O, regenerated cellulose , mercerized cotton and ramie. (The data for regenerated cellulose samples, except for cupra rayon fibres, were reproduced from ref. 45).

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. 

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