Cellulose ball-milled

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 conversion of ball-milled cellulose, glucose and fructose into micro-ciystalline lactic acid and 5-hydro g methylfurfural in water, catalysed by lead(ii) nitrate, has been reported (Scheme 22.5). The process involves a multistep cascade including the hydrolysis of cellulose to glucose, the isomerisation of glucose to fructose, retro-aldol fragmentation of fructose to trioses and their subsequent conversion to lactic acid lead(ii) catalyses both the conversion of glucose to fructose and the multistep cascade from fructose to lactic acid. The capacity of lead(ii) to be chelated by... 

Liu et al. used the same pathway to produce hexane from cellulose. With an Ir-ReOySiO catalyst combined with a H-ZSM-5 zeolite in a biphasic system (H O—dodecane), they were able to convert ball-milled cellulose and microcrystalline cellulose to hexane in one pot with yields up to 83% and 78%, respectively [179]. The catalytic reaction proceeds via the formation of sorbitol from cellulose afterward it undergoes hydrogenolysis into hexane. Independently... 

Besides, powders of microciystalline and nano-cellulose, ball-milled cellulose and some others also can be used. The dry samples of the equal mass are pressed into tablets that are used for WAXD experiments. The conditions for preparation of the tablets should... 

The degree of crystallinity can vary from 0 for non-crystalline sample (e.g., ball-milled cellulose] to 1 for hypothetical macrocrystals of cellulose. Minimal and maximal values of crystallinity index (CrI] of MCC Avicel PH-101 obtained by various researchers using different methods (Park et al., 2010 Terinte et al., 2011] and degree of crystallinity of this sample are shown in Fig. 7.6. 

Interestingly, the ball-milling studies of microcrystalline cellulose by Nakai (Table 4 [53]) have shown that the Wm values obtained from water sorption... 

Deters (14) vibromilled a blend of cellulose and cellulose triacetate. The acetic acid content of cellulose acetate decreased with grinding time (40 h) while that of the cellulose increased, suggesting the formation of a block or graft copolymer or of an esterification reaction by acetic acid developed by mechanical reaction. Baramboim (/5) dissolved separately in CO polystyrene, poly(methyl methacrylate), and poly(vinyl acetate). After mixing equal volumes of solutions of equivalent polymer concentration, the solvent was evaporated at 50° C under vacuum and the resultant product ball-milled. The examination of the ball-milled products showed the formation of free radicals which copolymerized. 

The effect of ball milling is similar in all cases. Within the first 10 min of milling, the 002 reflection is considerably broadened and appears slightly shifted to a smaller angle. This apparent shift is probably the result of the superposition of the broadened 002 peak upon the rising, broad, amorphous peak which centers about 18.5° (2 ). As ball milling continues, the crystalline characteristics decrease and the amorphous characteristics increase. After about 1 hr of milling time, the crystalline characteristics of all the cellulosic materials have disappeared. 

The effect of ball milling on the dilute acid hydrolysis of cellulose is similar in many ways to the effect electron irradiation has on enhancing saccharification (18). In the case of cotton linters, for example, maximum irradiation lO d) resulted in a half life of hydrolysis of about 7 min... 

It is not clear, however, whether electron radiation would have beneficial effects upon the enzymatic hydrolysis of cellulose. It has been shown that the particle size reduction and surface area increase upon ball milling are probably more important than the reduction of crystallinity (19). Electron irradiation may not disrupt the shielding layer provided by the lignin to expose fresh cellulose to the action of large enzyme molecules. 

In contrast to the usual blending of cellulose via a solution medium, a fine-powdered composition was obtained by ball-milling a dry mixture of fibrous cellulose and granulated PEG without any solvent [63]. A certain extent of compatibilization of PEG with cellulose appears to occur even in their solid state, probably by insertion of parts of PEG molecules into the cellulose domains, followed by the formation of hydrogen bonds between cellulose hydroxyls and polyether oxygens. It was shown that such a mechano-chemically prepared powder was moldable three-dimensionally by facile hot-press treatment, e.g., at 120 °C for a composition of CELL/PEG = 80/20 (wt/wt) [64],... 

Mintova et al. studied deposition of zeolite A on various cellulose fibers pretreated chemically and/or mechanically [151]. It was shown that the amount of zeolite deposited was controllable by suitable fiber pretreatment with ball-milling or with diethyl ether under ultrasonic action. The reactive high-concentration hydroxyl groups on the structurally loosened celluloses seem to interact with aluminosilicate species and thus promote the formation of nuclei for zeolite crystallization. Pretreatment of natural cellulose fibers with alkali provides another simple route for anchoring preformed zeolite crystallites onto the cellulose surface. 

Most MAS rotors require between 0.1 and 0.5 g of sample. Samples should be ground to sufficiently small size for uniform packing in the MAS rotor. Wiley milling of wood to 40 or 60 mesh has been commonly used, but ball-milled wood is undesirable because the severe physical damage to cellulose fibers broadens NMR signals (Kolodziejski et al. 1982). 

Solid-state cellulose can also be noncrystalline, sometimes called amorphous. Intermediate situations are also likely to be important but not well characterized. One example, nematic ordered cellulose has been described [230]. In most treatments that produce amorphous cellulose, the whole fiber is severely degraded. For example, decrystallization can be effected by ball milling, which leaves the cellulose as a fine dust. In this case, some crystalline structure can be recreated by placing the sample in a humid environment. Another approach uses phosphoric acid, which can dissolve the cellulose. Precipitation by dilution with water results in a material with very little crystallinity. There is some chance that the chain may adopt a different shape (a collapsed, sixfold helix) after phosphoric acid treatment. This was concluded because the cellulose stains blue with iodine (see Figure 5.12), similar to the sixfold amylose helix in the starch-iodine complex. 

The degree to which the internal volume has been expanded or contracted is deduced. Similar information is obtained from the static and chromatographic methods. Cellulose has been evaluated in the forms of decrystallized, ball-milled cotton, chopped cotton, cotton batting, and whole fabric. 

Ball milling of native celluloses under dry conditions decreases their Cl together with severe depolymerization and is sometimes used for preparing amorphous cellulose samples [7]. Noncrystalline celluloses with virtually no depolymerization and with a stable noncrystalline structure under aqueous conditions can be prepared from various native celluloses by regeneration from their nonaqueous cellulose solutions in water [8]. 

The amorphous or disordered component plays an enormous role in the physicochemical properties of cellulose. Its nature is still poorly defined [66-69] and like crystallites is influenced by physical and chemical treatments as reflected in solubility and reactivity characteristics [14-17]. The alkali solubility of cotton cellulose cannot be correlated entirely with its apparent amorphous content [16]. A regenerated sample prepared from a cuprammonium solution having a 94% amorphous content was totally soluble in 10% NaOH while a powdered cellulose obtained by ball milling to a similar amorphous content (92%) had an alkali solubility of only 58%. 

Accessibility. The extent of etherification is often determined by the accessibility of a substrate under a given environment. As Segal discussed [8], the extent of methylation with ethereal diazomethane (indicated by methoxyl contents) increased in the order hydrocellulose (5.9%) < cotton (7%) < mercerized cotton (14.9%) < cuprammonium rayon (18.6%) < ball mill-ground cotton (20.6%). Crystallinity of the cellulose was considered to be a significant factor. 

---