Cellulose reactive sizes

Retention aids are necessary to coagulate and flocculate the pulp and to avoid losses due to fibers, fillers and additives passing through the mesh of the forming screen. ->Cationic starches are the only RR-based polymers used to retain mineral fillers and cellulose-reactive sizes. The market is dominated by polyacrylamide, which is applied as W/O emulsion. The aqueous polymer solution is dispersed in kerosene, the substitution of which by RR-based oils (e. g., rape seed oil) is subject of intensive investigations. 

Another group of effective sizes include alkyl ke-tene dimers (- fatty diketenes) and alkenylsucci-nic anhydrides. These products react with the OH-groups of the cellulose fiber. While rosin-based sizes can only by used in acid paper making processes, the cellulose-reactive sizes are used in neutral and alkaline paper making. The result is better sheet strength, reduced corrosion on the equipment, less salt in the effluent and better stability of the paper towards aging (archival paper). 

Lewin and coworkers [255-260] developed an accessibility system based on equilibrium sorption of bromine, from its water solution at pH below 2 and at room temperature, on the glycosidic oxygens of the cellulose. The size of the bromine molecule, its simple structure, hydrophobicity, nonswelling, and very slow reactivity with cellulose in acidic solutions, contribute to the accuracy and reproducibility of the data obtained. The cellulose (10 g/1) is suspended in aqueous bromine solutions of 0.01-0.02 mol/1 for 1-3 h, depending on the nature of the cellulose, to reach sorption equilibrium. The diffusion coefficients of bromine in cotton and rayon are 4.6 and 0.37 x 10 cm /min, respectively. The sorption was found to strictly obey the Langmuir isotherm, which enables the calculation of the accessibility of the cellulose as follows ... 

In view of the immense commercial importance of phthalocyanines as pigments, it is perhaps surprising that only a few are of importance as textile dyes. This is primarily due to the size of the molecules they are too large to allow penetration into many fibres, especially the synthetic fibres polyester and polyacrylonitrile. An example of a phthalocyanine dye which may be used to dye cellulosic substrates such as cotton and paper is C. I. Direct Blue 86 (96), a disulfonated copper phthalocyanine. In addition, a few blue reactive dyes for cotton incorporate the copper phthalocyanine system as the chromophoric unit (Chapter 8). 

Raw wood contains 45-60% of cellulose. Morphologically this kind of cellulose is distinguished from cotton cellulose by the smaller size of its fibres. Chemically it is more reactive. 

In dyeing PES-CEL mixtures, disperse dyes are used for the PES component. The CEL portion can be dyed with practically all classes of dyes suited to cellulose (see Sections 4.2-4.8). The selection of suitable dyes depends not only on the equipment available, the desired shade, and the batch size, but also on economic factors, with the required fastness taken into account. Thus, reactive dyes (see Section 4.2) are used preferentially for all types of clothing textiles, but vat dyes (see Section 4.4) are employed where extreme demands are made on washfastness or weatherproofness. 

Two main criteria for the membrane selection are pore size and material. As peroxidases usually have sizes in the range of 10-80 kDa, ultrafiltration membranes with a molecular cutoff between 1 and 50 kDa are the most adequate to prevent enzyme leakage [99]. The materials commonly applied to ultrafiltration membranes are synthetic polymers (nylon, polypropylene, polyamide, polysulfone, cellulose and ceramic materials [101]. The adequate material depends on a great number of variables. When enzyme is immobilized into the matrix, this must be prepared at mild conditions to preserve the enzymatic activity. In the case of enzyme immobilization onto the membrane, this should be activated with the reactive groups necessary to interact with the functional groups of the enzyme. If an extractive system is considered, the selection of the hydrophilicity or hydro-phobicity of the membrane should be performed according to the features of reactants, products, and solvents. In any case, the membrane should not interfere with the catalytic integrity of the enzyme. 

Cellulosic substrates contain pores or voids of different sizes [10,12,13]. Pore structure determines the internal accessible surface area of a cellulose substrate and thus affects its accessibility or reactivity. 

A study of the effect of the structure and size of the amine radical (butylamine, dibutylamine, hexylamine, piperidine, aniline) on its reactivity in the nucleophilic replacement of tosyloxy groups in cellulose tosylate has shown (29) that this reactivity depends primarily on the basicity of the amine. TTiis assumption was confirmed by a study of the interaction of cellulose toxylates of different degrees of substitution (DS from 0.3-1.7) wit iminodiacetic and anthranilic acids 30, 31). TTie degree of substitution of the reaction products with respect to the N-carboxyalkyl(aryl)amino groups was found to be lower than that of the corresponding N-alkyl(aryl)araino derivatives. 

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