Cellulose and Its Esters

Rogovin, Z. A., and U. Zhun-Zhui Structure and properties of cellulose and its esters. LXXXV. Synthesis of new derivatives of cellulose and other polysaccharides. IV. Synthesis of graft copolymers of carboxymethyl cellulose and caprolactam. Vysokomolekulyarnye Soedineniya 1, 1630 (1959). 

Cellulose and Its Esters(Except Cellulose Nitrate) Analytical Procedures. Tests for cellulose used in industries other than manuf of expls proplnts are described in Refs 1-6. 

A comprehensive account of the methods used in cellulose chemistry has been published. It includes the preparation and reactions of cellulose and its esters and ethers, chemical and physical anal3rsis, microscopy, and radioactive-tracer techniques. 

This class of compounds embraces different polymers in the backbone of which certain links are bound via an ether oxygen atom saturated and unsaturated aliphatic polyethers, polyphenylene oxides, polyacetals, epoxide polymers, cellulose and its esters, and so on. 

The macromolecular isolated state will presumably be met with only in a fraction of the cases considered, for example, in the paraffins, polystyrenes, polyoxymethylenes and possibly also in rubber. But for cellulose and its esters, particularly, a different state of solution is indicated. For and against these views we may mention the effect of temperature on relative viscosity which is found to be small by Staudinger and his collaborators, but considerable by others, for example, Danes, Ecken-stamm, McBain, K. H. Meyer,Philippoff and others. Lieser has recently adduced important reasons for the existence of micellar threadlike molecular aggregates in solutions of cellulose xanthate. 

The important feature is the formation of polyene sequences by successive eliminations. These absorb visible light, causing the polymer initially to become yellow and eventually black. Similar reactions can occur with many polymers, e.g. poly(vinyl alcohol), poly(vinyl acetate) and cellulose and its esters. If the elimination reactions are allowed to go to high conversions, the polymer is typically transformed into a carbonaceous char, which may be quite thermally stable. Much of fire retardant chemistry is aimed at increasing char yields in polymer thermolysis. 

In Table 3 are summarized the general structures and liquid crystal characteristics of hydroxypropyl cellulose and its ester derivatives. 

Cellulose and its derivatives are sensitive to solar radiation and degrade rapidly under weathering conditions. Cellulose itself is among the least weather resistant substances. Cellulose ethers are less resistant than cellulose esters [32]. 

Cellulose and its derivatives - esters and ethers - are not very resistant to aggressive media. They are severely attacked by acids and bases, some derivatives even by water. Appendix Table A.23 [32]. It should be noted that plasticizers are extracted in constant contact with solvents, causing embrittlement. Short-term contact (also with swelling solvents) does not cause stress-cracking. Once the solvents evaporate, the old property condition is reestablished [656]. 

Acetic anhydtide is a mature commodity chemical ia the United States and its growth rate in the 1970s and 1980s was negative until 1988 when foreign demand neatly doubled the exports of 1986. This increase in exports was almost certainly attributable to the decline in the value of the U.S. doUar. Over four-fifths of all anhydtide production is utilized in cellulose acetate [9004-35-7] manufacture (see Cellulose esters). Many anhydtide plants are integrated with cellulose acetate production and thus employ the acetic acid pyrolysis route. About 1.25 kg acetic acid is pyrolyzed to produce 1.0 kg anhydtide. 

The predominant cellulose ester fiber is cellulose acetate, a partially acetylated cellulose, also called acetate or secondary acetate. It is widely used in textiles because of its attractive economics, bright color, styling versatiUty, and other favorable aesthetic properties. However, its largest commercial appHcation is as the fibrous material in cigarette filters, where its smoke removal properties and contribution to taste make it the standard for the cigarette industry. Cellulose triacetate fiber, also known as primary cellulose acetate, is an almost completely acetylated cellulose. Although it has fiber properties that are different, and in many ways better than cellulose acetate, it is of lower commercial significance primarily because of environmental considerations in fiber preparation. 

From 1946 to mid-1987, Farbenfabriken Bayer AG in Germany was the European producer of cellulose acetate, cellulose acetate butyrate (CAB), and cellulose acetate propionate (CAP) before closing its faciUties. Bayer s exit from the cellulose acetate mixed esters business leaves Eastman Chemical Co. in the United States as the sole producer of CAB/CAP resins. 

Thermal Properties. The thermal stabiUty of cellulose esters is deterrnined by heating a known amount of ester in a test tube at a specific temperature a specified length of time, after which the sample is dissolved in a given amount of solvent and its intrinsic viscosity and solution color are deterrnined. Solution color is deterrnined spectroscopically and is compared to platinum—cobalt standards. Differential thermal analysis (dta) has also been reported as a method for determining the relative heat stabiUty of cellulose esters (127). 

The most important of the esters is cellulose acetate. This material has been extensively used in the manufacture of films, moulding and extrusion compounds, fibres and lacquers. As with all the other cellulose polymers it has, however, become of small importance to the plastics industry compared with the polyolefins, PVC and polystyrene. In spite of their higher cost cellulose acetate-butyrate and cellulose propionate appear to have retained their smaller market because of their excellent appearance and toughness. 

The difficulties in the extraction of XG from the cell walls as well as its separation from the other cell-wall polymers have been interpreted by various suggestions [260]. In addition to the existence of strong hydrogen bonds with cellulose and some hemicelluloses, various covalent bonds have been considered to fix the XG in the cell walls [261] such as esters with the COOH groups... 

At first glance, the HRC scheme appears simple the polymer is activated, dissolved, and then submitted to derivatization. hi a few cases, polymer activation and dissolution is achieved in a single step. This simplicity, however, is deceptive as can be deduced from the following experimental observations In many cases, provided that the ratio of derivatizing agent/AGU employed is stoichiometric, the targeted DS is not achieved the reaction conditions required (especially reaction temperature and time) depend on the structural characteristics of cellulose, especially its DP, purity (in terms of a-cellulose content), and Ic. Therefore, it is relevant to discuss the above-mentioned steps separately in order to understand their relative importance to ester formation, as well as the reasons for dependence of reaction conditions on cellulose structural features. 

The Fourier Trairsform Infrared (FTIR) spectrum obtained from non-adapted tomato cell walls is very similar to that from the onion parenchyma cell wall (both contain cellulose, xyloglucan and pectin) although there is more protein in the tomato walls (amide stretches at 1550 and 1650 cm-i) (Fig 4). In DCB-adapted tomato cell walls, the spectrum more closely resembles that of either purified pectins or of a commercial polygalacturonic acid sample from Sigma with peaks in common at 1140, 1095, 1070, 1015 and 950 cm-t in the carbohydrate region of the spectrum as well as the free acid stretches at 1600 and 1414 cm-i and an ester peak at 1725 cm-k An ester band at 1740 cm-i is evident in both onion parenchyma and non-adapted tomato cell wall samples. It is possible that this shift in the ester peak simply reflects the different local molecular environment of this bond, but it is also possible that a different ester is made in the DCB-adapted cell walls, as phenolic esters absorb around 1720 cm-i whilst carboxylic esters absorb at 1740 cm-k The... 

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