Cellulose hydrolytic degradation

Cellulose may be degraded by a number of environments. For example, acid-catalysed hydrolytic degradation will eventually lead to glucose by rupture of the l,4-(3-glucosidic linkages. Intermediate products may also be obtained for which the general term hydrocellulose has been given. 

Desizing by chemical decomposition is applicable to starch-based sizes. Since starch and its hydrophilic derivatives are soluble in water, it might be assumed that a simple alkaline rinse with surfactant would be sufficient to effect removal from the fibre. As is also the case with some other size polymers, however, once the starch solution has dried to a film on the fibre surface it is much more difficult to effect rehydration and dissolution. Thus controlled chemical degradation is required to disintegrate and solubilise the size film without damaging the cellulosic fibre. Enzymatic, oxidative and hydrolytic degradation methods can be used. 

Scheme 12 Hydrolytic degradation preceding free radical oxidation of cellulose macromolecules.

Hydrolytic degradation is especially important in polymers with hydrolyzable links between the CRUs. Thus, polyesters can be saponified to yield the starting materials from which they were formed. Acetal links in synthetic polymers such as polyoxymethylene, or in natural polymers such as cellulose, can be hydrolyzed with acids. However, the resistance to hydrolysis depends very much on the structure of the polymer for example, polyesters of terephthalic acid are very difficult to hydrolyze while aliphatic polyesters are generally easily hydro-... 

Hydrolytic Degradation of Cellulose and Separation of the Hydrolysis Products by Chromatography... 

Deters, and Huang (129) describe the formation of graft copolymers of cellulose triacetate and vinyl chloride in vibratory mill treatments. Through hydrolytic degradation of the triacetate backbone, they isolated the polyvinyl chloride side chains and characterized them by infrared spectroscopy and cryoscopic molecular weight determination. The length of the side chains has been found to be between 15 and 30 vinyl chloride units. 

The relevance of the question discussed above to the problem of hydrolytic degradation of cellulose arises from both stereochemical and electronic factors associated with the difference in conformation of the glycosidic linkage as well as with the participation of the C6 oxygen in the bifurcated intramolecular hydrogen bond. The implications of these factors will now be considered. 

Our experimental work started from the following original cellulose samples (a) acetate-grade, bleached cotton linters, DP 1800 (b) hot, refined, spruce, sulphite-dissolving pulp, machine dried, ca. 93% a-cellulose, DP — 750 (c) never-dried, normal, rayon-grade, beech sulphite pulp, ca. 90% a-cellulose, DP = 825 (d) commercial cellulose powders obtained by hydrolytic degradation and/or mechanical disintegration of cotton linters or spruce sulphite pulp. 

A common feature of vapor-phase thermohydrolysis, liquid-phase acid hydrolysis, and enzymatic hydrolysis of cellulose is a significant influence of lateral order on the rate of chain cleavage, the DP finally reached, and weight loss. But with regard to this influence of the physical structure of cellulose, there also exist remarkable differences between these three modes of hydrolytic degradation. 

Fungal cellulase enzyme systems capable of efficiently catalyzing the hydrolytic degradation of crystalline cellulose are typically composed of endo-acting cellulases (EGs), exo-acting cellulases (CBHs), and at least one cellobiase (1-6). The CBHs are typically the predominant enzymes, on a mole fraction basis, in such systems (7). Consequently, the CBHs have been the focus of many studies (8). The three-dimensional structure of prototypical CBHs is known (9-12) and their specificities are, in general, well characterized (13,14). However, mechanism-based kinetic analyses of CBH-catalyzed cellulose saccharification are rather limited (15,16). Studies of this latter type are particularly difficult owing to the inherent complexity of native cellulose substrates. 

Acid-catalyzed hydrolytic degradation of cellulose proceeds according to the principles of chemical kinetics. Nonetheless, concepts of kinetics have not been widely applied in the literature concerning the conservation of cellulosic materials. Thirty years ago, McBurney (I) provided an excellent exposition of this subject. We will review the subject in the light of developments since that time (2) and will present examples from the literature and from our own work to illustrate ways in which an analysis of the kinetics of chain scission can help conservators better understand the deterioration of cellulose-based materials. 

B. G. Ranby, Inst. Phys. Chem., Univ. Uppsala, Arkiv Kemi, 4, 241 (1952). Fine structure and reactions of native cellulose. Electron microscope study of morphology of celluloses from wood, cotton, bacteria, tunicates, and algae behavior of samples on swelling in sodium hydroxide and hydrolytic degradation. 

The section on degradation of organics deals with paints, plastics, nylon, wood, and architectural organics. The effects of acid deposition on wood and other cellulosic materials are described. Strength losses in wood may be caused by hydrolytic degradation of the hemicelluloses and a sulfonation reaction of the lignin. Thus, the fibrils and matrix structure is affected. Cotton materials can be affected similarly, and soiling will result. The effect of acid deposition of nylon is indicative of a potentially shorter serviceable lifetime for outdoor fabrics. 

Several observations related to this phenomenon have been made on the cellulase of Ruminococcus albus strain 7. Crystalline cellulose is degraded by this organism. Cell-free preparations are active in decreasing the turbidity of cellulose suspensions. The amount of hydrolytic activity against soluble cellulose derivatives is not different for the three variants. Two major cellulolytic components have been separated by... 

The fraction consisting of cellulose and hemicellulose or, in other words, the set of all carbohydrates in a lignocellulosic material, is also called holocellulose. Thus, holocellulose is the product obtained after selective removal of lignin, with very low residual-lignin content, minimal loss of polysaccharide, and minimal oxidative and hydrolytic degradation of cellulose. The a-cellulose is the part of material that is insoluble in strong NaOH (17.5%) and may also be designated by crystalline cellulose [5]. In this work, the values of holocellulose and a-cellulose are also shown in Table 1. 

Hydrocelluloses are produced by the hydrolytic degradation of celluloses. They are similar to )8-celluloses and are also referred to as microcrystalline celluloses. If 5% of these degraded celluloses (degree of polymerization 100-200) is beaten into water with rapid stirring, a creamy substance is produced that is used in the foodstuff industry as a nondigestable thickener. The creamy consistency arises because of physical cross-linking of cellulose crystallites. 

These treatments are usually made using diluted solutions of NaOH (1-10%) at low or high temperature and concentrated NaOH solutions over 10% only at low temperatures. NH OH and anhydrous NH (gas or liquid) are also used to activate the organic materials, particularly in cases where increased hydrolytic degradation is concentrated upon. In cases of isolation of cellulose nanofibers, treatments with peroxide alkaline solution, peroxide alkaline-hydrochloric acid, 5 wt% potassium hydroxide and 18 wt% potassiimi hydroxide generate cellulose fibers with average diameters between 3 nm to 5 nm [30]. 

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