Alkaline Degradation Of Cellulose Research Articles

Efficient Swelling and Mercerization of Bagasse Fiber by Freeze-Thaw-Assisted Alkali Treatment

The mercerization of fiber is an important method for the high-value utilization of cellulose. In this study, the bagasse fiber was mercerized by freeze–thaw-assisted alkali treatment (FT/AT). The effects of freezing temperature, freezing time, alkali concentration, and thawing temperature on cellulose and hemicellulose removal were studied. The optimal freezing temperature was −40°C, freezing time was 8.0 h, alkali concentration was 5.0%, and thawing temperature was 30°C. The highest removal rate of hemicellulose was 75.64%. It was 5.80% higher than that of alkali treatment (AT). The alkaline degradation of cellulose was inhibited. The penetration of alkaline solution to fiber was promoted by the assistance of freeze-thaw pretreatment. The effective alkali concentration (5.0%) of cellulose I completely transformed into cellulose II decreased by 66.67% compared with traditional alkaline mercerization (15.0%). The high-efficiency mercerization of fiber was achieved by FT/AT. It provides theoretical support for promoting the high-value utilization of lignocellulosic biomass.

Alkaline Degradation of Cellulose: Mechanisms and Kinetics

Cellulose powder and softwood sawdust were subjected to alkaline degradation under conditions representative of a cementitious environment for periods of 7 and 3 years, respectively. During the fir ...

Degradation of cellulose under alkaline conditions

A review of the important area of cellulose degradation under alkaline conditions is presented; it focuses on its relevance to the possible disposal of radioactive wastes in an underground repository in which cement-based waste encapsulation grouts and backfill may be employed. An overview of the alkaline degradation pathways of monosaccharides and substituted monosaccharides is initially presented, before progressing to the reactions involved in the alkaline degradation of cellulose, namely end-wise degradation, termination, alkaline scission, and oxidative alkaline degradation. Physical factors affecting reaction rates and the alkaline degradation of hemicellulose are also discussed. A review of the identity of the commonly detected alkaline degradation products (and their numerous synonyms) is presented, along with discussion of the rates of degradation of cellulose.

Degradation of Cellulosic Materials Under the Alkaline Conditions of a Cementitious Repository for Low- and Intermediate-Level Radioactive Waste. II. Degradation Kinetics

The degradation of cellulosic materials, differing mainly in the degree of polymerization and the number of reducing end groups, was studied under the alkaline conditions similar to those existing in a cementitious repository for low- and intermediate-level radioactive waste (pH 13.3, T = 25°C). The kinetics of alkaline degradation (peeling-off reaction) were studied and the data analyzed by the model of Haas et al. [13]. The observed kinetic parameters for the propagation reaction and overall stopping reaction were compared with literature data. Although measured under different experimental conditions, literature data and data from this study show a consistent picture. Differences in the extent of degradation observed for the different cellulosic materials could be satisfactorily explained by differences in reducing end group content and, consequently, by differences in the degrees of polymerization. Besides the number of reducing end groups, the degree of amorphousness also plays an important role. The main degradation products formed under the experimental conditions used are α- and β-(gluco)isosaccharinic acid. This is in agreement with many other studies on alkaline degradation of cellulose. The two isomers are formed in roughly equal amounts.

Alkaline Degradation of Cellulose: Estimation of the Concentration of Isosaccharinic Acid in Cement Porewater

ABSTRACTThe sorption of radionuclides on repository components (e.g. cement) is an important process since it controls the release of radionuclides from the repository [1]. A strong sorption of radionuclides is desirable since it will allow only a small release of radionuclides to the geo-and biosphere. The strong sorption behaviour of radionuclides, however, could possibly be decreased by several orders of magnitude by the presence of organic ligands. Ligands such as EDTA, NTA, citric acid etc. are inherent components of radioactive waste since these complexing agents are used in nuclear power stations for decontaminating purposes. Other ligands might be formed by degrading organic polymers present in low and intermediate level radioactive waste [2, 3]. Cellulose materials such as cotton, paper and wood form a substantial part (ca. 50 %) of the organic waste [1]. The use of large amounts of cement for constructing a repository causes alkaline environments in which the pH of the pore solution will remain above 12.5 for periods of the order of 105years [4]. It is well known from the literature that cellulose is unstable under alkaline conditions and will degrade to water soluble, low molecular weight compounds by the peeling-off reaction [5]. The main degradation product of cellulose is isosaccharinic acid (ISA), which is stable under alkaline conditions [5-10]. ISA enhances the solubility of Pu(IV) [7, 8] and has an adverse effect on the sorption of Eu(III), Th(IV) and Ni(II) [6]. For instance, in a solution of 10-3M ISA, the solubility of Pu(IV) at pH 12 increases by a factor of 20000 [11]. The sorption of Pu(IV) [8], Eu(III), Th(IV) and Ni(II) [6], however, was affected to only a minor extent. The observed effects were - by analogy with gluconic acid [12] - interpreted to be due to a strong complexation of these metals. The concentration of ISA in the pore water is the key parameter for evaluating its effect on radionuclide sorption [13].A full assessment of the effect of cellulose degradation on the sorption requires a detailed understanding of the mechanisms involved. The present study gives an overview of the different processes involved and describes how to quantify the concentration of isosaccharinic acid in the pore water of a repository.

Importance of the Alkaline Degradation of Cellulose in Performance Assessment of a Cementitious Radioactive Waste Repository

It is the aim of the present poster to show two approaches for assessing the influence of the alkaline degradation of cellulose on the sorption of tri- and tetravalent radionuclides. The two approaches differ in their degree of conservativity, one is a conservative, the other a realistic model case. The result of both examinations is expressed in terms of sorption reduction factors, valid for a situation where cellulose degradation products are influencing the sorption of radionuclides on cement.

Studies on the alkaline degradation of cellulose. III. Alkaline treatment in presence of anthraquinone

Anthraquinone (AQ) reduces the rate of alkaline degradation of cotton and bagasse celluloses. This is due to the stabilization effect of AQ on the cellulose macromolecules. The D.P. values for the resulting oxycelluloses were in the order: alkali-AQ-treated cotton > alkali-AQ-treated bagasse > alkali-treated bagasse > alkali treated cotton. Thus, intracrystalline linkage with AQ is more efficient in chain stabilization in the alkaline degradation of cellulose than the intercrystalline linkages. This is because the latter is usually followed by intracrystalline degradation of decrystallized cellulose chains without AQ links. Furthermore, the bulky units of AQ penetrate within the cellulose chanis, separate them further apart and thus enhance decrystallization and accessibility. Also, many factors were found to affect the reactivity of the oxycelluloses obtained, namely, the chain length, availability of active groups and the extents of decrystallization and oxidation.

Studies on the alkaline degradation of cellulose: Part II effect of the supermolecular structure of the pulp

The supermolecular structure of cellulosic pulp plays an important role in its alkaline degradation behaviour. In spite of the well-known compact, ordered and less accessible supermolecular structure of cotton cellulose, it has greater susceptibility to alkaline oxidative degradation than bagasse cellulose. Bagasse kraft pulp undergoes inter-crystalline swelling followed by oxidative degradation which is mostly restricted to the amorphous domains of the fibre. However, in the case of cotton linter the degradation takes place through intracrystalline swelling. In this case the reactant penetrates the crystallites and stronger degradation takes place. The extent of degradation depends upon the structure of the original cellulose. Intracrystalline degradation is more efficient than the intercrystalline degradation in cellulose decrystallization. The purity of the pulp and good hydrolytic attack affect the fibril structure which strongly influences its reactivity towards xanthation.

The microbiology programme for UK Nirex

The Nirex Safety Assessment Research Programme (NSARP) considers the effect of microbial action on the repository near field. The upper limit of growth for natural soil organisms appears to be pH 12.25. Environmental conditions in the repository will probably allow slow growth particularly on damp wastes. Experiments using packed columns of waste and concrete have shown that an extremely high pH is not conducive to rapid microbial growth. However, viable populations can exist within regions adjacent to the concrete, e.g. where a surface film coats the concrete. Carbon dioxide and methane will be produced by microbial action within the repository but actual rates of production will be lower than that in a domestic landfill. The cellulosic fraction of waste is the main determinant of cell growth. It appears to be the sugar acids arising from alkaline degradation of cellulose which cause enhanced plutonium solubility. The potentially beneficial reduction of chemically derived polyhydroxy acids by the microorganisms is possible. A mathematical model has been constructed to describe the main features of biological action in the repository.

The Effects of the Degradation of Organic Materials in the Near Field of a Radioactive Waste Repository

ABSTRACTUK Nirex Ltd are seeking to develop a deep underground repository for the disposal of solid ILW and LLW in the UK. The formation of water-soluble complexants from the degradation of the solid organic polymers and cellulosic materials present in such wastes may influence the solubility and sorption properties of a number of radioelements. A number of materials have been chemically degraded under alkaline, anaerobic conditions representative of the near field of the repository. Measurements of plutonium solubility in the leachates obtained show that the degradation of cellulose is of particular concern; the effects on the solubility can be several orders of magnitude greater than those of other organic materials. Products formed from the degradation of ion-exchange resins were found to have little effect. Solubilities of a number of other radioelements in aerobically degraded cellulose leachates are also given. The effect of reducing the ratio of celluloseto cement in the degradation experiments results in a decrease in plutonium solubility in the corresponding leachate. Several of the likely degradation products of cellulose have been individually synthesised including isosaccharinic acid, a key degradation product of cellulose. Enhanced plutonium solubilities have been measured in 10-3M solutions of these compounds. Sorption of plutonium onto cement from leachates obtained by the degradation of 10% cellulose in cement is reduced by about two orders of magnitude. Interaction with cement removes significant concentrations of complexants from solution. Thermodynamic modelling studies show that hydroxyl groups present in the compounds which result from the alkaline degradation of cellulose can strongly complex with plutonium.

Non-oxidative and oxidative alkaline degradation of pectic acid

As alkaline degradation products of pectic acid, 6 hydroxymonocarboxylic, 16 dicarboxylic, and 2 tricarboxylic acids were identified by g.l.c.-m.s. as their trimethylsilyl derivatives. In the absence of oxygen, the most abundant degradation products are 3-deoxy-2- C-(hydroxymethyl)pentaric, 2,3-dideoxypentaric, 2-deoxy-3- C-methyltetraric, malic, and 2 1,4-anhydro-3-deoxy-2- C-(hydroxymethyl)pentaric acids, whereas, in the presence of oxygen, glycolic, oxalic, malic, 3-deoxypentaric, and 2- C-carboxy-3-deoxypentaric acids preponderate. The routes of formation of these acids show many similarities with those encountered in the alkaline degradation of cellulose.

Formation of 1,4-Anhydro-3-deoxypentitol-2-carboxylic Acids by Alkaline Degradation of Cellulose.

An anhydroisosaccharinic acid obtained in large amounts by end-wise degradation of cellulose in alkaline media, and in small amounts in hydrolysates of cellulose, has been identified as a 1,4-anhydro-3-deoxypentitol-2-carboxylic acid (3-hydroxy-5-(hydroxymethyl)oxolane-3-carboxylic acid). Structural evidence was obtained by GC-MS studies of the compounds (as Me3Si derivatives) obtained on degradation of the acid to 1,4-anhydro-3-deoxypentitol by reduction of the methyl ester followed by periodate oxidation and borohydride reduction. In aqueous alkali, the acid is likely to be formed from a dicarbonyl precursor by benzilic acid rearrangement.

The Chemistry of Alkaline Degradation of Cellulose and Oxidized Celluloses II

The Chemistry of Alkaline Degradation of Cellulose and Oxidized Celluloses II

The Chemistry of Alkaline Degradation of Cellulose and Oxidized Celluloses I

The Chemistry of Alkaline Degradation of Cellulose and Oxidized Celluloses I