Derivatization of cellulose

Commercial Derivatization of Cellulose. Cellulose, the world s most abundant polymer, is derivatized for use in a variety of markets. 

Commercial derivatization of cellulose begins with the addition of sodium hydroxide to form alkaH cellulose (AC) (eq. 1, R = carbohydrate). 

Commercial Derivatization of Cellulose. Cellulose, the world s most abundant polymer, is derivatized for use in a variety of markets. Two important classes are cellulose esters (qv) and cellulose ethers (qv). Cellulose esters are not water soluble and are not discussed here cellulose ethers are an important segment of water-soluble polymers. 

In another oudine, cellulose was complexed with cuprammonium ions (Nicoll and Conaway, 1943). Lately, laboratory-scale isolation has relied on polar aprotic solvents and solvent systems, e.g., dimethylsulfoxide, pyridine, Af,7V-dimethylacetamide-lithium chloride, and l-methyl-2-pyrrolidinone-lithium chloride (Baker et al., 1978 McCormick and Shen, 1982 Seymour et al., 1982 Arnold et al., 1994). These solvents have enabled such homogeneous17 reactions as O- and N-derivatization of cellulose and chitin (Williamson and McCormick, 1994) and selective site chlorination (Ball et al., 1994). Dimethylsulfoxide was the solvent in a homogeneous reaction of cellulose and paraformaldehyde, prior to isolation of purified cellulose (Johnson et al., 1975). In yet another outline, paraformaldehyde enabled superior quality extracts when the parent tissues were presoaked in this solution (Fasihuddin et al., 1988). 

Cellulose is an old polymer with new industrial applications. The derivatization of cellulose has opened up tremendous production and marketing possibilities for the adhesives industry. Various important adhesives have been derived from cellulose ethers. The structure and molecular size of cellulose and their influence on swelling and solubility are important considerations in the preparation of cellulose derivatives for adhesive applications. Modern cellulosic adhesives derived from grafted copolymers and polyblends are also proving very useful. 

Only a relatively small amount of information is available on the effect of substitution or derivatization of cellulose on its enzymatic degradation [3]. However, it has been suggested that if at least one hydroxyl group in each repeating units is substituted, the modified cellulose is not degraded by microorganisms [4]. 

Because of the strong intermolecular bonds, cellulose does not melt and does not dissolve readily in ordinarily available solvents chemists have resorted to the derivatization of cellulose to render it soluble and processable. Specifically, the viscose process was developed. It converted cellulose into sodium cellulose xanthate, which was soluble in a caustic solution, making it possible to wet-spin the polymer into a fiber or film. This technique was accepted worldwide and has prospered. The process, however, consists of multiple steps and causes pollution. As a result, end users have looked for alternate methods of processing cellulose. 

In this chapter we will elaborate on recent advances in dissolution and derivatization of cellulose and follow up with a description of new processes that lead to regenerated cellulose fibers. Finally, we will describe viscose processes and rayon fiber properties. 

Gericke M, Fardim P, Heinze T (2012) Ionic liquids - promising but challenging solvents for homogeneous derivatization of cellulose. Molecules 17 7458-7502... 

Recently (in the past two decades) there have been a number of new solvents developed for cellulose which yield true cellulose solutions. This in turn has led to homogeneous reaction conditions for the derivatization of cellulose. 

Researchers (39,41) have investigated the addition of various amines to the carbanilation reaction mixtures to decrease the reaction time needed for derivatization of cellulose, especially the reaction time required for a sample with high molecular weight. In DMSO and DMF, the amines catalyzed the conversion of the phenylisocyanate to its trimer phenylisocyanurate. In addition, several amines actually retarded the carbanilation reaction. Most significant was that the presence of several amines in the DMSO-phenylisocyanate reaction mixture caused depolymerization of the cellulose, especially high-molecular-weight cellulose. In some cases, the depolymerization was severe. All three components (amine, phenylisocyanate, and DMSO) were required for depolymerization to take place. 

In comparison with the nitrate, acetate, and carbanilate, very little is available in the literature that describes the systematic investigation of other cellulose derivatives by SEC analysis. This is surprising, given the number of cellulose derivatives that are available both commercially and experimentally. This may be because these derivatives are often incomplete derivatizations of cellulose, with DS ranging from less than 1 to near 3. Thus, suitable standards are even less readily available than those for the completely derivatized (e.g., DS about 3) cellulose nitrate and tricarbanilate. 

Dawsey X.R., Application and limitations of lithium chlotide/iVjV-dimethylacetamide in the homogeneous derivatization of cellulose, in Cellulosic Polymers, Blends and Composite, Ed. Gilbert R.D., Hanser, Munich, 1994, pp. 157-171. 

Mann G., Kunze J., Loth F., Fink H.-P., Cellulose ethers with a block-Uke distribution of substituents by structure-selective derivatization of cellulose. Polymer, 39,1998,3155-3165. 

Fischer S., Thiimmler K., Pfeiffer K., Liebert T, Heinze T, Evaluation of molten inorgairic hydrates as reaction medium for the derivatization of cellulose. Cellulose, 9, 2002, 293-300. 

Schnabelrauch M., Vogt S., Klemm D., Nehls 1., Philipp B., Readily hydrolyzable cellulose esters as intermediates for the regioselective derivatization of cellulose. 1. Synthesis and characterization of soluble, low-substituted cellulose formats, Angew. Makromol. Chem., 198, 1992,155-164. 

A few alternatives for the derivatization of cellulose have been found recently direct dissolution of cellulose has been developed. For textile filament yams, dissolution in N-methylmorpholine oxide (NMMO) is possible. The process is applied by Courtaulds and Lenzing. A solution in formic acid/phosphoric acid was found to have lyotropic behavior and tire yarns with very interesting properties could be produced (patented by Michelin). It even proved possible to use phosphoric acid alone (patented by AKZO), but the process was never commercialized. 

This emphasizes the need for suitable modification or derivatization of cellulose for its versatile and widespread use as a membrane material. Chemical modification alters cellulose properties with respect to elasticity, hydrophilicity, ion exchange or adsorption capacity, water uptake capacity, thermal, and microbial resistance. The reactive primary and secondary hydroxyl groups in its backbone structure serve as potential sites for the introduction of different functional groups. The possible modifications include etherification, esterification (Marchetti et al. 2000), oxidation,... 

One of the unexpected outcomes of the investigations was the surprisingly small change in the calculated solubility parameters upon derivatization of cellulose, which is performed precisely to increase solubility. Future studies in this area will improve the theoretical model used by including higher degrees of substitution, structural... 

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