Decrystallization of cellulosic

Recovery of properties already lost through aging would require efforts to modify molecular order along two lines. The first would involve a decrystallizing treatment that can reduce the dimensions of the brittle domains and increase the capacity of fibers to respond to deformation in an elastic mode. Although a number of approaches to decrystallization of cellulosic materials are available, most are unsuited for conservation applications. This approach might be pursued in search of suitable methods. 

More recently, Ohkoshi et al. [103] studied the mechanism of thermoplasticization of wood by allylation. They considered that decrystallization of cellulose within wood during allylation permits the wood to soften thermally and the allylated lignin within wood increases the softening through acting as a plasticizer. 

To the extent possible, this chapter will deal with the changes in physical properties of wood as a direct result of chemical modification of the cell wall and not as a result of the reaction conditions used to modify the wood. For example, strong acid or base catalysts used in some chemical modification reaction systems will result in a reduction in physical properties due to hydrolysis or decrystallization of cellulose and these changes are not due to the... 

Decrystallization of cellulose by swelling agents or solvents can be brought about by concentrated sodium hydroxide amines me-tallo-organic complexes of copper, cadmium, and iron quaternary ammonium bases concentrated mineral acids (sulfuric, hydrochloric, phosphoric) concentrated salt solutions (beryllium, calcium, lithium, zinc) and a number of recently investigated mixed solvents (J6). 

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. 

Of samples swollen with ethylene diamine, the graft yield at a 50 1 liquor ratio increases as the concentration of ethylene diamine increases. This is due to the increase of decrystallization of swollen samples, which helps the penetration velocity of the chemicals through the cellulosic chains. Graftability of the samples treated with 100% ethylene diamine is lower that of the sample treated with 75%. This is due to the dissolution of low DP chains and some of the hemicelluloses, which is detectable by the increase in DP of the sample teated with 100% ethylene diamine. 

Chemical reaction methods are effective in destroying the crystallinity of cellulose. For example, xanthation can decrystallize cellulose (34), but such elaborate processes appear much too costly unless cellophane or rayon fibers are the objectives. One route that might be effective and economical would be treatment of crystalline cellulose with alcohol in the presence of acid catalysts. Low-molecular-weight acetals may be formed, which could plasticize the cellulose at the same time that the degree of polymerization is reduced. 

Thermoplasticization of Wood by Graft Copolymerization in De-crystallized State. We have reported that wood can effectively be decrystallized without a weight-loss by treating with a non-aqueous cellulose solvent, the SO2-DEA-DMSO solution (11). Thus, use of the non-aqueous cellulose solvent as a reaction medium for the graft-copolymerization of monomers to wood was expected to result in products with branch polymers more uniformly distributed. The results obtained by the homogeneous grafting of cellulose (10) were expected to support this idea. 

The most important alternative crystalline form is cellulose II. This form can result from treatment of cellulose in concentrated alkali, such as 23% NaOH, followed by rinsing in water. This is also the main form that results from crystallization of dissolved cellulose, such as regeneration of rayon. Supercritical water can also effect the transformation [216]. The treatment of cotton in milder alkali, for industrial mercerization, amounts mainly to disruption and decrystallization rather than transformation to crystalline II. Cellulose II can occur as the native state when the normal biosynthesis and subsequent crystallization is disrupted [217-219]. 

Decrystallization. The crystallinity of cellulose is an inherent property that is an important determinant of its mechanical properties, affinity for water, and accessibility to chemical reagents. Because cellulose comprises almost 50% of the wood, its crystallinity is a determinant of the behavior of the wood as well. Any disruption or change in the crystallinity of the cellulose will cause significant changes in properties and, thus by our definition, degradation. 

Methods for increasing the accessibility and, hence, the reactivity of cellulose continue to receive attention. These methods are based on the fact that swelling agents can bring about some decrystallization of the structure and this, in turn, increases the extent by which it can be penetrated by chemical reagents. 

There have been many research projects over the years studying ways to thermoform ligno-cellulosics. Most of the efforts have concentrated on film formation and thermoplastic composites. The approach most often used involves the ehemieal modification of cellulose, lignin, and the hemicelluloses to decrystallize and modify the eellulose and to thermoplastieize the lignin and hemicellulose matrix to mold the entire lignoeellulosic resource into films or thermoplastic composites [92 97]. 

The anhydride functionality in the compatibilization research described before may react with the lignocellulosic, but there is no evidence to support that at this time. A higher level of grafted anhydride on the polypropylene would be required for the alloy reactions, and it would be expected that the reaction between grafted thermoplastic and jute or kenaf would take place both on the matrix polymers (lignin and hemicelluloses) and in the cellulose backbone. Some decrystallization of the cellulose may be desired to give more thermoplastic character to the entire composite. 

According to the results of X-ray investigations, in the range of SA concentration from 50 to 60 wt% the degree of crystallinity (Cr) of obtained particles increased slightly. On the other hand, when SA concentration was more than 60 wt% the decrystallization of the particles occurred due to increased solubility of the cellulose in a sufficiently concentrated sulfuric acid as a result the low-crystalline particles are formed. 

On a commercial scale the reactions are heterogeneous in nature. That is, the cellulose remains in a fibrous or particulate state throughout the reactions. The cellulose is activated (swollen) by water, alkali metal hydroxides, liquid ammonia, dimethyl formamide, dimethyl sulfoxide, acetic acid or quaternary ammonium hydroxides. However, aqueous NaOH is most commonly used as it promotes decrystallization of the cellulose and functions as a catalyst for the ether formation. Usually ca. 18% by... 

It should be born in mind, however, that the activation parameters calculated refer to the sum of several reactions, whose enthalpy and/or entropy changes may have different signs from those of the decrystallization proper. Specifically, the contribution to the activation parameters of the interactions that occur in the solvent system should be taken into account. Consider the energetics of association of the solvated ions with the AGU. We may employ the extra-thermodynamic quantities of transfer of single ions from aprotic to protic solvents as a model for the reaction under consideration. This use is appropriate because recent measurements (using solvatochromic indicators) have indicated that the polarity at the surface of cellulose is akin to that of aliphatic alcohols [99]. Single-ion enthalpies of transfer indicate that Li+ is more efficiently solvated by DMAc than by alcohols, hence by cellulose. That is, the equilibrium shown in Eq. 7 is endothermic ... 

Concentrated sulfuric acid has been used to dissolve and hydrolyse native cellulose (see Figure 7.6). The concentrated acid can disrupt hydrogen bonding between the cellulose chains and thus decrystallize the cellulose. Then, water is added to rapidly hydrolyse cellulose into glucose. The diluted sulfuric acid is re-concentrated for the next cycle of decrystallization and hydrolysis steps. The final products include a mixture of C5 and C6 sugars. The hydrolysis process is generally more complex than pyrolysis or liquefaction. However, hydrolysis enables selective decomposition of the biomass polymers and thus provides access to useful platform chemicals that are unavailable from pyrolysis or liquefaction techniques. 

Figure 7.28 Scheme of structural transformation of cellulose as a result of physico-chemical decrystallization. 

In order to improve the accessibility of crystalline cellulose [24], the swelling of cellulose in ammonia or in molecules such as amines is a simple and classical way. This procedure leads to cellulose IIIi from cellulose I (native cellulose) and has been frequently used to improve the reactivity of crystalline cellulose for the preparation of derivatives in better yields [25-26], Indeed, this conversion carried out essentially at a solid-state process that keeps the integrity of the cellulose microfibrils while achieving a substantial decrystallization and a reorganization of the intra-crystalline hydrogen bond pattern of cellulose [27-28],... 

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