Cellulose crystallite length

Material Cellulose hydrolyzed, percent Moisture-Regain reduction,° percent Crystallite length, DP... 

The best-known renewable primary sources for natural fibers are wood and cotton. Both of these natural materials consist of basic fibrous units known as fibrils, the diameter of which is probably equivalent to that of the cellulose crystallites. Crystalline and amorphous regions alternate along the length of the fibrils. Several elementary fibrils may also be united in fibrillary structural units [84]. 

The recent interest in using stiff nanometric particles as reinforcement materials in polymeric matrixes, composites, or nanocomposites has been increasing. Two good examples of these types of particles are carbon nanotubes and cellulose nanofibers. Cellulose nanofibers, also reported in the literature as whiskers, nanocrystals, cellulose crystallites, or crystals, are the crystalline domains of ceUulosic fibers, isolated by means of acid hydrolysis, and are called in this way due to theb physical characteristics of stiffness, thickness, and length (Souza and Borsali 2004). 

To calculate the length of cellulose crystallites, width of the (004)-peak at 29 of 34.6-34.8° should be measured. The updated Eq. (7.14) is not suitable for this purpose since the length of cellulose crystallites might exceed 100 nm. Therefore, a special equation was proposed in order to calculate the actual length (Lc) of crystallites (loelovich, 1991a) ... 

The actual lateral sizes of crystallites are greater than the supposed Scherrer s sizes by 10-30%. At determining the longitudinal sizes, the actual length of cellulose crystallites may exceed the estimated Scherrer s dimensions of 5-6 times. The actual length of cellulose crystallites can be also estimated from level-off DP (LOOP] of the hydrolyzed cellulose samples (loelovich, 1991a) ... 

Treatment of the algal cellulose (mixture of la—IP) from Valonia in ethylenediamine to give Cellulose IIIj simultaneously induced sub fibrillation in the initial microfihril (75). Thus crystallites 20 nm wide were spHt into subunits only 3—5 nm wide, even though the length was retained. Conversion of this IIIj back to I gave a material with an electron diffraction pattern and nmr spectmm similar to that of cotton Cellulose ip. 

The findings suggest that shortening of the cellulose molecule ceases in 30 minutes but hydrolysis does not. A possible explanation is that disordered hygroscopic cellulose between crystallites is first attacked and that thereafter attack occurs mainly on the lateral surfaces of crystallites. If this is indeed the case, then the effective length of crystallites is indicated by the minimum viscosity attained. 

The exact length of the cellulose molecule is not known but it is variable and very large. Cellulose threads possess micellar structure and consist(according to x-ray diagrams) of numerous rod-like crystallites, which are oriented with their long axis parallel to the thread axis, forming a fiber... 

Cellulose is found not to be uniformly crystalline. However, the ordered regions are extensively distributed throughout the material and these regions are called crystallites [27]. Cellulose exists in the plant cell wall in the form of thin threads with an indefinite length. Such threads are cellulose micro-fibrils, playing an important role in the chemical, physical, and mechanical properties of plant fibers and wood. 

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