Crystallinity index cellulose

O.D. Bemardinelh, M.A. Lima, C.A. Rezende, 1. Polikarpov, E.R. deAzevedo, Quantitative 13C multiCP sohd-state NMR as a tool for evaluation of cellulose crystallinity index measured directly inside sugarcane biomass, Biotechnol. Biofuels 8 (2015) 1-11. 

Bleached cotton stalk pulp is treated with different concentrations of ethylene diamine (50-100%) for 20 min. It is clear that the crystallinity index (CrI) of these treated pulps is decreased by increasing the concentration of ethylene diamine that is, the decrystallization increases. The degree of polymerization is nearly the same, but some increase is shown in the sample treated with 100% ethylene diamine. This indicates that 100% ethylene diamine may act as a dissolving agent for low degree of polymerization (DP) of cellulosic chains and hemicellulose. 

FIGURE 5.21 Infrared (IR) crystallinity index (Cl) 1429 versus accessibility by the Br2 method for different cellulose fiber. 

Cellulosic materials usually form crystal structures in part, and water cannot penetrate the inside of crystalline domains at room temperature. Native celluloses form crystalline microfibrils or bundles of cellulose chains 2-5 nm in width for higher plant celluloses and 15-30 nm for algal celluloses, which are observable by electron microscope. Almost all native celluloses have X-ray diffraction patterns of cellulose I with crystallinity indexes (Cl) 13] of about 40-95 %. 

Other researchers have evaluated the crystallinity index by using IR spectrophotometry. This method requires the KBr pellet technique of sampling. The X-ray diffraction method was investigated for its potential as a nondestructive technique for recording changes in cellulose as it ages. 

Crystallinity indexes calculated according to the method described by Segal et al. (32) showed that the old cotton has a crystallinity of about 38 . Aqueous treatments increased the crystallinity of the historic cotton sample to about 45 . However, the crystallinity of contemporary cotton, which is about 70 , was not reached (30). This increase suggests that water acts as an internal plasticizer and allows a segmental reorientation which leads to an increase in crystallinity. Water-induced crystallization of amorphous cellulose fibers has been reported (17). Kalyanaraman (33) investigated orientation factors of cotton fibers from historic samples and found that the orientation values of the museums samples are smaller than the values of present-day cottons. He opined that cotton may have lost its orientation over time. In view of this... 

Crystallinity index was calculated based on data of X-ray diffractometry [14], The degree of polymerization was determined by the viscosity measurements from cellulose cadoxen solutions (the relative error of the method was 5 %) [15]. 

Effect of interaction of acid and cellulose at the stages of impregnation and thermal pretreatment depends on the cellulose properties. The celluloses under study have different ratios of ordered and amorphous regions. They differ also by their degree of polymerization (Table 1) and hydrophilic properties. The presence of phosphoric acid affects the system of the cellulose hydrogen bonds, the crystallinity index and leads to the formation of esters [11,12, 19],... 

Determination of infra-red crystallinity index at different wavelengths (1429 cm V893 cm ) by the usual base line technique can be used [38]. When cellulose-II samples are considered, the 1372 cm 72900 cm" ratio is more reliable index [39, 40]. A rapid method for estimation of the degree of mercerization has been developed using a near IR diffuse reflection technique [41]. 

The two most dominating characteristics of cellulose are the specific surface area, SSA, and the crystallinity index, CrI. Specific surface area is defined as the amount of surface area per mass of cellulose. Crystallinty index is the relative amount of crystalline cellulose as opposed to the amount of amorphous cellulose [15]. In biomass, cellulose is closely associated with hemicellulose and lignin. Agricultural residues are composed of 30 - 40 % cellulose, 25 - 35 % hemi-... 

Increased specific surface area would thus increase the rate of hydrolysis. The increase in specific surface area is hkely due to endoglucanase action of fragmenting the cellulose and opening pores thus increasing the amount of enzymes adsorbed. The crystallinity index, on the other hand, increased greatly in the first 12 h but then slowly decreased but not to its initial level. The crystallinity index increased due to the fast removal of the amorphous cellulose in relation to the crystalhne cellulose. 

Fig. 4. Changes in specific surface area and crystallinity index by enzymatic hydrolysis (reproduced from [18]). Specific surface area (SSA) and crystallinity index (CrI) change quickly as enzymatic hydrolysis proceeds until leveling out at a constant level. Initial enzymatic action breaks cellulose into smaller particles (increased SSA) and attacks amorphous regions (increased CrI)... 

A different approach to mathematical analysis of the solid-state C NMR spectra of celluloses was introduced by the group at the Swedish Forest Products Laboratory (STFI). They took advantage of statistical multivariate data analysis techniques that had been adapted for use with spectroscopic methods. Principal component analyses (PCA) were used to derive a suitable set of subspectra from the CP/MAS spectra of a set of well-characterized cellulosic samples. The relative amounts of the I and I/3 forms and the crystallinity index for these well-characterized samples were defined in terms of the integrals of specific features in the spectra. These were then used to derive the subspectra of the principal components, which in turn were used as the basis for a partial least squares analysis of the experimental spectra. Once the subspectra of the principal components are validated by relating their features to the known measures of variability, they become the basis for analysis of the spectra of other cellulosic samples that were not included in the initial analysis. Here again the interested reader can refer to the original publications or the overview presented earlier. ... 

Table 2 Crystallinity index and degree of orientation of crystals of regenerated cellulose fibers calculated from their X-ray diffraction patterns...

Cellulose solvent Crystal structure Crystallinity Index (%) Degree of orientation of crystals (%)... 

In ARP pretreatment of hybrid poplar, deUgnification is increased with the treatment severity, but xylan removal occurs only to a certain extent. Increase of temperature from 175 to 195 °C in ARP does not affect xylan/lignin removal in hybrid poplar, yet the glucan digestibility of treated solid is increased. This is caused by an increase of cellulase accessibility to cellulose created by breakage of certain bonds and reconfiguration of the components in hemicellulose-lignin matrix. Crystallinity index of hybrid poplar increases after the ARP treatment. It is primarily caused by the removal of amorphous components,... 

In the case of cellulosics percentage, crystallinity and crystalline index are calculated as follows [23] ... 

Sample Preparation. Cellulose powders, Whatman CFll, short fibrous cellulose powder with mean particle size 50-350 pm (Whatman International, Ltd.) and microcrystalline cellulose Avicel, mean particle size 27.6-102 pm, crystallinity index 0.60 (Avicel PHlOl, obtained from FMC, Ireland), were milled separately in a vibratory mill filled to 80% of volume with steel balls for 0 to 60 min. After milling, the samples were rubbed gently through a 50 pm sieve. All the treatments were performed at room temperature which is far below Tg temperature. The PAL temperature dependence data up to 200 do not show Tg onset Detailed information about sample preparation was described elsewhere(i0). 

The structural properties of the nanocomposites such as the size of the cellulose crystallites and the crystallinity index can be characterized using X-ray diffraction. X-ray diffraction is used to elucidate the eventual modifications in the crystalline structure of the matrix after the addition of the whiskers. 

Microfibrillar structure of bacterial cellulose is responsible for most of its properties such as high tensile strength, higher degree of polymerization and crystallinity index. 

Zhou et al. [53] studied the effect of nanocellulose isolation techniques on the quality of nanocellulose and its performance in reinforced nanocomposites. They employed three different techniques including acid hydrolysis (AH), TEMPO-mediated oxidation (TMO) and ultrasonica-tion (US) to isolate nanocellulose from microcrystalline cellulose (MCC) and to evaluate the quality of nanocellulose and the reinforcing ability of these nanocelluloses in PVA matrices. The characterization of nanocellulose indicated that nanocellulose with higher aspect ratio, surface charge (-47 mV) and yields (37%) was obtained by TMO treatment, while acid hydrolysis treatment resulted in higher crystallinity index (88.1 %) and better size dispersion. 

It is important to mention that the chemical composition of each type of fibers and the orientation of microfibrils about the fiber axis, called microfibrillar angle (Table 8.1), may significantly differ. Similarly, depending on the cellulose and lignin contents, crystallinity index of each type of fiber differs. In view of these, when lignocellulosic fibers are tested for their tensile properties, their fracture mode differs, which may be intercellular or intracellular or mixed modes of fracture. Accordingly, the tensile properties and fractographs are different for each type of fiber. These are also listed for some fibers in Table 8.1 and Fig. 8.3, respectively. 

An X-ray diffractogram of pineapple crown fibers is shown in Figure 10.6. It shows two peaks, which are well defined. The presence of these diffraction peaks indicates that the fiber is semicrystalline. According to several authors [30] the two peaks situated at 20 = 15.4° and 20 = 22.5° can be attributed to cellulose I and IV. These two peaks are attributed to the (2 0 0) and (1 1 0) crystallographic planes, respectively. Crystallinity index (Cl) is estimated using the Equation 9.2 ... 

Figure 7 The spectrum of biomass pretreated with 1% H2SO4 contains signals from both native cellulose and lignin (hemicellulose has been removed). Subtraction of a lignin spectrum provides a spectrum of native cellulose which can provide the crystalline index by focusing on the crystalline signal at 88 ppm and on the amorphous signal at 84 ppm. Data were acquired at 9.4 T using a 14 kHz spinning frequency. Reproduced from Bemardinelli et al. [114] published under the CC-BY license.

Although bacterial cellulose has the same chemical composition but different structures and physical properties, it is preferred over the plant cellulose as it can be obtained in higher purity and exhibits a higher degree of polymerization and crystallinity index. Its fibrils are about 100 times thinner, have higher tensile strength and better water holding capacity than those of plant cellulose. ... 

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