Cellulose acylation properties

The present paper reports novel methods to prepare thermally meltable cellulose and wood-based materials and their properties. Two methods are emphasized (a) a grafting and (b) acylation combined with grafting. 

Extensive research into the thermal properties of long-chain cellulose esters (LCCE) has produced an understanding of the melt- and flow properties of fully as well as partially substituted derivatives. It is apparent that Tg declines quickly to between 50 and 150 C as acyl chain length exceeds that of butyrate (O Fig. 21). 

Considerable interest has been expressed in benzoylated derivatives of 2-diethylaminoethylated polysaccharides, the acylated derivative being produced by the action of benzoyl chloride on, for example, 0-(2-di-ethylaminoethyl)cellulose. Naphthoylated and benzoylated, naphtho-ylated 0-(2-diethylaminoethyl) celluloses may be similarly produced, and these substitutions of the free hydroxyl groups in the 0-(2-diethyl-aminoethyl)celluose increase the non-ionic attractions between the polysaccharide and polynucleotides. This phenomenon has been exploited in the synthesis and separation of soluble ribonucleic acids. " Some difficulties have been experienced in producing sizable quantities of benzoylated 0-(2-diethylaminoethyl)cellulose, but the analogous preparation of benzoylated O-(2-diethylaminoethyl) cross-linked dextran was more successful, the product having properties similar to those of the corresponding cellulose derivative. 

The most prominent cellulose ester produced on the industrial scale is cellulose acetate. The reaction is usually performed with acetic anhydride and with sulfuric acid as a catalyst. To minimize heterogeneities, acetylation is allowed to run nearly to completion, and subsequently partial ester hydrolysis is initiated by the addition of water until a desirable solubility is achieved that corresponds to a DS of about 2.5. Such higher acyl homologues as propanoyl or butanoyl exhibit more thermoplastic properties. Many specialized esters such as chiral (-)-menthyloxyacetates, furan-2-carboxylates, or crown-ether-containing acylates have been prepared on the laboratory scale and characterized by NMR spectroscopy. Various procedures have been applied, using anhydrides and acyl chlorides as acylating agents in combination with such bases as pyridine, 4-dimethylaminopyridine (DMAP), or iV,iV -carbonyldi-imidazole. The substitution pattern of cellulose acetates has also been modified by postchemical enzymatic deacetylation. Cellulose 6-tosylates have been used as activated intermediates for nucleophihc substitution to afford 6-amino-6-deoxy, 6-deoxy, or 6-deoxy-6-halo-celluloses. ... 

Esters of cellulose with interesting properties such as bioactivity and thermal and dissolution behavior can be obtained by esterification of cellulose with nitric acid in the presence of sulfuric acid, phosphoric acid, or acetic acid. Commercially important cellulose esters are cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate. Cellulose esters of aliphatic, aromatic, bulky, and functionalized carboxylic acids can be synthesized through the activation of free acids in situ with tosyl chloride, iV,iV -carbonyldiimidazole, and iminium chloride under homogeneous acylation with DMA/LiCl or DMSO/TBAF. A wide range of cellulose esters that vary in their DS, various substituent distributions, and several desirable properties can be obtained through these reactions. Recently, a number of enzymes that degrade cellulose esters have been reported. Some of them are acetyl esterases, carbohydrate esterase (CE) family 1, and esterases of the CE 5 [169-172] family. 

The hydrophilic surface of the cellulose-based nanoreinforcements leads to poor interaction between matrix and the filler [29]. Furthermore, the chemical compatibility is very important in controlling the dispersion and the adhesion among them. Therefore, it is common to see weak filler-matrix interactions when hydrophilic whiskers were added to hydrophobic matrices [4]. The miscibility of cellulose nanofillers with hydro-phobic matrices can be improved by various surface modifications, for example, esterification and acylation. The increment in the filler/matrlx compatibility produces the enhancement of mechanical and thermal properties but also enhances the barrier properties [30]. 

C. S. R. Freire, A. J. D. Silvestre, C. P. Neto, A. Gandini, L. Martin, and I. Mondragon, Composites based on acylated cellulose fibers and low-density polyethylene Effect of the fiber content, degree of substitution and fatty acid chain length on final properties. Compos. Sci. Technol. 68(15-16), 3358-3364 (2008). 

Cellulose esters of carboxylic acids with 7c-electron structures, e.g. where R in the acyl chloride is a benzoyl, cinnamoyl, furoyl or thenoyl group, have been prepared. " The effects of these groups on the properties of cellulose, particularly on the absorption, transfer and localization of energy from ionizing radiations in cellulose, have been reported. Dependent on mechanical restrictions of the fibers during chemical modification and the DS of the products, many of the initial mechanical properties of the fibers are retained. 

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