Properties of Cellulose

Key properties of cellulose nitrate are good dimensional stability, low water absorption, and toughness. Its disadvantages are its flammability and lack of stability to heat and sunlight. 

The bulk properties of regenerated cellulose are the properties of Cellulose II which is created from Cellulose I by alkaline expansion of the crystal stmcture (97,101) (see Cellulose). The key textile fiber properties for the most important current varieties of regenerated cellulose are shown in Table 2. Fiber densities vary between 1.53 and 1.50. 

A. Grobe, Properties of Cellulose Materials, Polymer Handbook, 3rd ed., John Wiley Sons, Inc., New York, 1989, pp. 117—170. 

The chemical and physical properties of cellulose depend ia large measure on the spatial arrangements of the molecules. Therefore, cellulose stmctures have been studied iatensively, and the resulting information has been important ia helping to understand many other polymers. Despite the extent of work, however, there are stiU many controversies on the most important details. The source of the cellulose and its history of treatment both affect the stmcture at several levels. Much of the iadustrial processiag to which cellulose is subjected is iatended to alter the stmcture at various levels ia order to obtain desired properties. 

Standardized test methods for analyzing the chemical composition, viscosity, and physical properties of cellulose esters have been adopted by the ASTM and are described in substantial detail (110). 

The cellulose esters with the largest commercial consumption are cellulose acetate, including cellulose triacetate, cellulose acetate butyrate, and cellulose acetate propionate. Cellulose acetate is used in textile fibers, plastics, film, sheeting, and lacquers. The cellulose acetate used for photographic film base is almost exclusively triacetate some triacetate is also used for textile fibers because of its crystalline and heat-setting characteristics. The critical properties of cellulose acetate as related to appHcation are given in Table 10. 

Table 10. Uses and Critical Properties of Cellulose Acetate ...

Table 22.2 Typical physical properties of cellulosic plastics. (It is necessary to quote a range of figures in most instances since the value of a particular property is very dependent on formulation)...

Table 22.4 Influence of amount of plasticiser (dimethyl phthalate) on some physical properties of cellulose acetate compositions...

Typical values for the principal properties of cellulose acetate compounds are tabulated in Table 22.2 in comparison with other cellulosic plastics. Since cellulose acetate is seldom used today in applications where detailed knowledge of physical properties are required these are given without further comment. 

Grafting presents a means of modifying the cellulose molecule through the creation of branches of synthetic polymers, which impart to the cellulose certain desirable properties without destroying the properties of cellulose. The polymerization of vinyl monomers may be initiated by free radicals or by certain ions. Depending on the monomer, one or the other type of initiation may be preferred. The grafting process depends on the reactivity of the monomer used, the type of initiation, and cellulose accessibility [1,2]. 

Electric discharge methods are known [31] to be very effective for nonactive polymer substrates such as polystyrene, polyethylene, polypropylene, etc. They are successfully used for cellulose-fiber modification to decrease the melt viscosity of cellulose-polyethylene composites [32] and to improve the mechanical properties of cellulose-polypropylene composites [28]. 

Cellulose esters, properties of Cellulose, homogeneous reaction ... 

The oldest method of resolving enantiomers by TLC takes advantage of the natural chiral properties of cellulose and triacetylcellulose resulting from the helical structure of the polymers (98). Amino acid derivatives have been resolved on silica gel layers impregnated with chiral acids or bases, for example. 

L Westman, T Lindstrom. Swelling and mechanical properties of cellulose hydrogels. IV. Kinetics of swelling in liquid water. J Appl Polym Sci 26 2561-2572, 1981. 

Relative crystallinity undoubtedly influences such properties of cellulosic materials as rigidity, flexibility, plasticity and extensibility. Likewise the amount and reactivity of intercrystalline cellulose are major factors in common processing treatments such as bleaching, dyeing, pulping and wet finishing. Further refinement of measuring methods and the development of further correlations between crystallinity and fiber properties would contribute much to this important field. 

The remarkable property of cellulose fibres which gives rise to their widespread use in paper and board products is their ability, when dried in contact with each other from water, to form a strong bond. Perhaps more importantly, this bond can be completely disrupted by the re-addition of water and this is the essential property which allows cellulosic fibres to be relatively easily recycled. 

Their model, which became a standard, combined the important features of both concepts by proposing micelles of long, not short, molecules. The physical properties of cellulose were attributed to these forces, for example, tensile strength to the primary valence bonds and insolubility to the secondary forces. 

Close contact was maintained with the schools at Darmstadt where E. Berl was actively involved in the evaluation of the technical properties of cellulose and its derivatives, and Karlsruhe. Mark was an associate professor at Karlsruhe, and accordingly observed G. Bredig and A. Reis studies of the physical chemistry of colloids and crystals. 

Then, a few months afterward Meyer repeated and generalized the cellulose structure to include crystalline knots at regular intervals (28). This model was useful in explaining not only the properties of cellulose, but those of rubber as well. Staudinger called the concept unusable, incorrect, and dubbed it "the New Micelle Theory". 

Danko, T. Properties of cellulose separators for alkaline secondary batteries. Proceedings of the 10th Annual Battery Conference on Applications 8z Advances, IEEE New York, 1995 p 261. 

Permeability Properties of Cellulose Triacetate Hollow-Fiber Membranes for One-Pass Seawater Desalination... 

As the effects of an annealing step on the properties of cellulose acetate membranes, the increase of crystallinity by means of the X-ray diffraction method (12, 13) and the changes of pore sizes by the BET adsorption method l5) have been reported. 

The study of mesophases of cellulose and cellulose derivatives is an active field which has expanded rapidly since the initial observation of liquid crystms of hydroxy-propyl cellulose in 1976. There are two areas that warrant turther investigation recent observations regarding the influence of solvent and/or substituents on the cholesteric helicoidal twist await a theoretical explanation there is a lack of careful studies to permit a theoretical treatment of the behavior of ordered celltdose phases. To date, no applications have been developea where the unusual properties of cellulose derivatives are utilized. 

The water absorption properties of cellulose may be increased by grafting on polar groups, such as carboxyl groups, as in Super Slurpers, and this absorption may be decreased by the introduction of nonpolar moieties, such as ester groups, as in cellulose acetate. 

Another typical property of cellulose and its derivatives dependent on water sorption is the swelling of the fibre that occurs under the influence of certain solutions such as aqueous sodium hydroxide or an ammoniacal solution of cupric oxide, i.e. cuprammonium . The process of swelling does not start with sorption as in the instance of water. In the first stage of swelling the liquid penetrates the molecular chains of the cellulose, gradually coming in contact with all of them so that chemical combination takes place to form alkali celluloses, (C6H,0O5) NaOH and (C6H,0O5)2 NaOH. 

The properties of cellulosic graft copolymers have been studied to a considerable extent but mainly in the form of grafted fibers or films of ill-defined composition. However, a few properties have been measured on well defined grafts (147). It was found that solutions of cellulose acetate-polystyrene grafts in dimethyl formamide are less tolerant to the addition of polystyrene than cellulose acetate itself. This result was attributed to the greater coil expansion in the case of the graft copolymer. On the other hand, the tolerance of the grafts to each homo-... 

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). 

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