Cotton cellulose crystallinity

Wakelin, J. H., Virgin, H. S., and Crystal, E. (1959). Development and comparison of two X-ray methods for determining the crystallinity of cotton cellulose. Journal of Applied Physics. 30,1654-1662. 

Crystallinity. Diffraction traces of the cellulosic materials are presented in Figures 1-4. Table I lists the crystallinity indices obtained from the diffraction patterns. Also included in Table I are the crystallite sizes of the unmilled materials obtained from measurement of the half widths of the 002 reflections. The 002 reflection is noticeably sharper in the case of the cotton cellulose. Crystallite size measures 54 A for the cotton cellulose compared to an average of 29 A from the wood celluloses. 

The relative influence of vibratory milling on the course of enzymatic and dilute acid hydrolysis of four cellulosic substrates was investigated. The four substrates—cotton linters, newsprint, Douglas fir, and red oak— were vacuum-dried and then milled for various time periods ranging up to 240 min. Assays were then made of rate and extent of hydrolysis, maximum yield of reducing sugar, and cellulose crystallinity. 

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. 

The proportions of ordered and disordered regions of cellulose vary considerably depending on the origin of the sample (cf. Table 9-1). Cotton cellulose is more crystalline than cellulose in wood. 

Some cotton cellulose is noncrystalline or amorphous in the sense of lacking definite crystalline form. One reason is that cotton cellulose has a broad molecular weight... 

The response of the cotton fiber to heat is a function of temperature, time of heating, moisture content of the fiber and the relative humidity of the ambient atmosphere, presence or absence of oxygen in the ambient atmosphere, and presence or absence of any finish or other material that may catalyze or retard the degradative processes. Crystalline state and DP of the cotton cellulose also affect the course of thermal degradation, as does the physical condition of the fibers and method of heating (radiant heating, convection, or heated surface). Time, temperature, and content of additive catalytic materials are the major factors that affect the rate of degradation or pyrolysis. 

PROP Fine white fibrous particles from treatment of bleached cellulose from wood or cotton. Insol in water and most org solvs. SYNS ABICEL n P-AMYLOSE ARBOCEL ARBOCEL BC 200 ARBOCELL B 600/30 AVICEL AVICEL 101 AVICEL 102 AVICEL PH 101 AVICEL PH 105 CELLEX MX a-CELLULOSE CELLULOSE 248 CELLULOSE (ACGIH.OSHA) CELLULOSE CRYSTALLINE CELUFI CEPO CEPO CFM CEPO S 20 CEPO S 40 CHROMEDIA CC 31 ... 

Cellulose crystallinity is not uniform. A simple experiment of immersing cellulose in cold concentrated alkali, a process used for enhancing the dye-absorbing quality of cotton fabrics called mercerization, was found already in the 1930s on the basis of X-ray diffraction to produce a cellulosic allomorph with different unit cell dimensions [13,14]. This was given the... 

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. 

Crystallinity of cotton cellulose was measured using a density method by means of a density gradient column (Techne Inc., Model DC-2). Xylene and carbon tetrachloride were used to make up the solution. Based on the density data, crystallinity of cellulose can be calculated from the following equation (13) ... 

Much of the chemical behavior of cellulose fiber can be attributed to cellulose structure. Since cellulose is a highly crystalline polymer, it can absorb mechanical energy efficiently for mechanical stress reaction ( 5, 19). The mechanically activated thermal energy, in addition to rupture of main chains, may alter morphology or microstructure of cotton cellulose. Accordingly, the crystallinity and accessibility of cotton fiber may be influenced. 

As mentioned earlier, a fiber fraction and a powder fraction of cotton cellulose were formed during milling the changes in crystallinity for these two fractions are different For the fiber fraction, the loss of crystallinity was critical for the initial 100 hrs of milling, as shown in Figure 4. The rate of change in crystallinity was then levelled off after 100 hrs of... 

Figure 4. Change in crystallinity of cotton cellulose during cutting and milling. Key V, cut fiber , milled fiber O, milled powder.

The Unit Cell Dimensions of the Crystallites Present. Cellulose occurs in four recognized crystal structures designated Cellulose I, II, III, and IV (27). These can be distinguished by their characteristic x-ray diffraction patterns. Cellulose I is the crystal form in native cellulosic materials. Cellulose II is found in regenerated materials such as viscose filaments, cellophane, and mercerized cotton. Cellulose III and IV are formed by treatment with anhydrous ethylamine and certain high temperatures, respectively. These four crystal forms differ in unit cell dimensions—i.e., the repeating three-dimensional unit within the crystalline regions. These dimensions are shown in Table VI for the four crystal forms. 

Chemical Changes that Occur when Hardwoods Are Treated with Dilute NaOH. Cellulosic materials swell in aqueous NaOH. Under certain conditions the swelling is intramicellar (as well as intermicellar) and leads to a transformation of Cellulose I to Cellulose II. Sisson and Saner (30) developed a phase diagram describing the combinations of NaOH concentration and temperature that produce this transformation in cotton cellulose. At room temperature the concentration must exceed about 15%. Because of poorer lateral order of crystalline regions in wood cellulose, the minimum concentration for wood is probably lower, perhaps 8%. With lesser concentrations the phase transformation does not occur although some intermicellar swelling does occur. 

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...

The existence of an ordered structure in cellulose is shown conclusively by wide-angle x-ray diffraction (WAXD) and electron diffraction studies (3). The diffraction patterns exhibit reasonably well-definid reflections for which unit cells have been defined. There are four basic recognized crystalline modifications, namely, cellulose I, II, III and IV. By the WAXD method as proposed by Hermans (4,5) it has been found that native celluloses of different biological origin vary in crystallinity over wide limits, from A0% in bacterial cellulose to 60 in cotton cellulose and 70 in Valonia cellulose. 

S. O. Rowland and E. J. Roberts, Disposition of D-glucopyranosyl units on the surface of crystalline elementary fibrils of cotton cellulose, J. Polym. Sci. Polym. Chem. Ed., 10 (1972) 867-879. 

Some cotton cellulose is noncrystalline or amorphous in the sense of lacking definite crystalline form. One reason is that cotton cellulose has a broad molecular weight distribution, making high-crystalline perfection impossible. The small crystallites constitute deviations from ideal crystals that are infinite arrays. The remaining amorphous character of most polymers is often thought to arise from the fringed micelle model of the solid structure. In... 

---