Cellulose initiation

Recently, Li et al. [30], Yu et al. [31] reinvestigated the mechanism of graft copolymerization of vinyl monomers onto carbohydrates such as starch and cellulose initiated by the Ce(IV) ion with some new results as mentioned in Section II. Furthermore, they investigated the mechanism of model graft copolymerization of vinyl monomers onto chitosan [51]. They chose the compounds containing adjacent hydroxyl-amine structures, such as D-glucosamine, /mn5-2-amino-cyclohexanol, 2-... 

Additives in Grafting Styrene to Polyethylene and Cellulose Initiated by UVa... 

Components adsorbed on cellulose Initial rate of MV+ accumulation... 

Guzman, G. M. Graft reactions of vinyl monomers to cellulose, initiated by ceric ions. Anales Real Soc. Espan. Fiz. Quim. Ser. B 58, 193 (1962). 

The modification of the properties of cotton cellulosic textile products, through free radical-initiated graft copolymerization reactions with vinyl monomers, has been investigated at the Southern Laboratory for a number of years (6, 9). In this chapter, we summarize the basic mechanisms and principles involved in free radical reactions of cellulose, initiated by high energy radiation, ceric ion in acidic solution, and aqueous solutions of ferrous ion and hydrogen peroxide. Some of the properties of fibrous cotton cellulose graft copolymers are also presented. 

The hydroxyl radicals can react with cellulose, initiating graft copolymerization, or react with monomer, resulting in homopolymerization. A similar redox system is based on the use of ceric ions, which produce radicals by direct oxidation of the cellulose chains and thus initiate graft polymerization ... 

Monofunctional 1-hydroxycellulose triesters, such as tributyrate and propionate acetate derivatives, have been coupled to bis(4-isocyanotophenyl)disul-flde to obtain macroinitiators for the radical syntheses of three block copolymers of the type cellulose-initiator-initiator-cellulose [140]. 

These considerations reveal that three stages are involved in the low temperature pathway of cellulose initiation of pyrolysis, propagation, and product formation. The initiation period apparently in-... 

J.C. Artur, 0. Hinojosa, Oxidative reactions of cellulose initiated by free radicalsZZ J. Polym. Sci. part C (1971), No 36, 53-71. 

Barsbay, M. Gueven, O. Davis, T.P. Bamer-Kowollik, C. Barner, L. RAFT-mediated polymerization and grafting of sodium 4-styienesulfonate from cellulose initiated via y-radiation. Polymer 2009, 50 (4), 973-982. 

Some polymers already contain reactive groups that can initiate a graft polymerization. The hydroxyl groups in cellulose initiate the polymerization of ethylene imine ... 

Scheme 21 Synthesis of PROZO-grafted cellulose initiated from tosylated cellulose.

The fast pyrolysis decomposition of cellulose starts at temperatures as low as 150°C. Pyrolysis of cellulose below 300°C results in the formation of carboxyl, carbonyl, and hydro peroxide groups, elimination of water and production of carbon monoxide and carbon dioxide as well as char residue (Evans and Milne, 1987). Therefore low pyrolysis temperatures will produce low yields of organic liquid yields. Fast pyrolysis of cellulose, above 300°C, results in liquid yields up to 80 wt.%. Cellulose initially decomposes to form activated cellulose (Bradbury et al., 1979). Activated cellulose has two parallel reaction pathways, depolymerization and fragmentation (ring scission). The main products from each reaction pathway are rather different as ring scission produces hydroxyacetaldehyde, linear carbonyls, linear alcohols, esters, and other related products (Bradbury et al., 1979 Zhu and Lu, 2010 Lin et al., 2009) and depolymerization produces monomeric anhydrosugars, furans, cyclopentanones, and pyrans and other related products (Bradbury et al., 1979 Zhu and Lu, 2010 Lin et al., 2009). Each reaction pathway is independent and is influenced by pyrolysis temperature and residence time (Bradbury et al., 1979). 

Lead azide is not readily dead-pressed, ie, pressed to a point where it can no longer be initiated. However, this condition is somewhat dependent on the output of the mixture used to ignite the lead azide and the degree of confinement of the system. Because lead azide is a nonconductor, it may be mixed with flaked graphite to form a conductive mix for use in low energy electric detonators. A number of different types of lead azide have been prepared to improve its handling characteristics and performance and to decrease sensitivity. In addition to the dextrinated lead azide commonly used in the United States, service lead azide, which contains a minimum of 97% lead azide and no protective colloid, is used in the United Kingdom. Other varieties include colloidal lead azide (3—4 pm), poly(vinyl alcohol)-coated lead azide, and British RE) 1333 and RE) 1343 lead azide which is precipitated in the presence of carboxymethyl cellulose (88—92). 

Many ceUulosic derivatives form anisotropic, ie, Hquid crystalline, solutions, and cellulose acetate and triacetate are no exception. Various cellulose acetate anisotropic solutions have been made using a variety of solvents (56,57). The nature of the polymer—solvent interaction determines the concentration at which hquid crystalline behavior is initiated. The better the interaction, the lower the concentration needed to form the anisotropic, birefringent polymer solution. Strong organic acids, eg, trifluoroacetic acid are most effective and can produce an anisotropic phase with concentrations as low as 28% (58). Trifluoroacetic acid has been studied with cellulose triacetate alone or in combination with other solvents (59—64) concentrations of 30—42% (wt vol) triacetate were common. 

Suspension polymerization of VDE in water are batch processes in autoclaves designed to limit scale formation (91). Most systems operate from 30 to 100°C and are initiated with monomer-soluble organic free-radical initiators such as diisopropyl peroxydicarbonate (92—96), tert-huty peroxypivalate (97), or / fZ-amyl peroxypivalate (98). Usually water-soluble polymers, eg, cellulose derivatives or poly(vinyl alcohol), are used as suspending agents to reduce coalescence of polymer particles. Organic solvents that may act as a reaction accelerator or chain-transfer agent are often employed. The reactor product is a slurry of suspended polymer particles, usually spheres of 30—100 pm in diameter they are separated from the water phase thoroughly washed and dried. Size and internal stmcture of beads, ie, porosity, and dispersant residues affect how the resin performs in appHcations. 

There are many chemical methods for generating radicals reported in the hterature that do not involve conventional initiators. Specific examples are included in References 64—79. Most of these radical-generating systems carmot broadly compete with the use of conventional initiators in industrial polymer apphcations owing to cost or efficiency considerations. However, some systems may be weU-suited for initiating specific radical reactions or polymerizations, eg, grafting of monomers to cellulose using ceric ion (80). 

For ink vehicles based on hydroxyl group containing binders such as nitrocellulose and cellulose acetate, the tetraalkyl titanates cross-link the binder prematurely, limiting the storage stabiUty of the printing ink. Chelated organic titanates such as TYZOR AA and TYZOR TE are preferred for use in these cases because they only initiate cross-linking when the ink is heated to temperatures above 80°C (503). 

Dispersion Technology. Substantial advancements in dispersion technology have been made since the initial introduction in 1923 of disperse dyes in paste form for cellulose acetate. Dyes were dissolved in sulfonated fatty acids such as sulforicinoleic acid [36634-48-7] (SRA),... 

Treatment of the algal cellulose (mixture of la—IP) from Valonia in ethylenediamine to give Cellulose IIIj simultaneously induced sub fibrillation in the initial microfihril (75). Thus crystallites 20 nm wide were spHt into subunits only 3—5 nm wide, even though the length was retained. Conversion of this IIIj back to I gave a material with an electron diffraction pattern and nmr spectmm similar to that of cotton Cellulose ip. 

Stabilization and Digestion. Following the initial washing steps, the stabilization of CN occurs. This involves removal of any remaining sulfuric acid since it would catalyze the decomposition of CN. The sulfuric acid present is both physically entrained in the product and chemically bonded to the cellulose chain. CN can contain 0.2—3% esterified H2SO4, depending on the DS of nitration. The sulfonate ester can be easily removed by... 

Class B direct dyes have poor leveling power and exhaustion must be brought about by controlled salt addition. If these dyes are not taken up uniformly in the initial stages it is extremely difficult to correct the urdevelness. They are dyes that have medium—high affinity and poor diffusion. In their apphcation the cellulose is entered into a dyebath containing ordy dye. The salt is added gradually and portionwise as the temperature is increased and possibly the final additions made after the dyebath has come to the bod. 

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