Cellulose physical properties

Tables 1 and 2 Hst the important physical properties of formamide. Form amide is more highly hydrogen bonded than water at temperatures below 80°C but the degree of molecular association decreases rapidly with increa sing temperature. Because of its high dielectric constant, formamide is an excellent ionizing solvent for many inorganic salts and also for peptides, proteias (eg, keratin), polysaccharides (eg, cellulose [9004-34-6] starch [9005-25-8]) and resias.

Other fibrous and porous materials used for sound-absorbing treatments include wood, cellulose, and metal fibers foamed gypsum or Pordand cement combined with other materials and sintered metals. Wood fibers can be combined with binders and dame-retardent chemicals. Metal fibers and sintered metals can be manufactured with finely controlled physical properties. They usually are made for appHcations involving severe chemical or physical environments, although some sintered metal materials have found their way into architectural appHcations. Prior to concerns regarding its carcinogenic properties, asbestos fiber had been used extensively in spray-on acoustical treatments. 

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. 

Fig. 3. Effects of composition on physical properties. A, acetyl B, butyryl C, cellulose. 1, increased tensile strength, stiffness 2, decreased moisture sorption 3, increased melting point 4, increased plasticizer compatibiUty 5, increased solubiUties in polar solvents 6, increased solubiUties in nonpolar...

Production of cellulose esters from aromatic acids has not been commercialized because of unfavorable economics. These esters are usually prepared from highly reactive regenerated cellulose, and their physical properties do not differ markedly from cellulose esters prepared from the more readily available aHphatic acids. Benzoate esters have been prepared from regenerated cellulose with benzoyl chloride in pyridine—nitrobenzene (27) or benzene (28). These benzoate esters are soluble in common organic solvents such as acetone or chloroform. Benzoate esters, as well as the nitrochloro-, and methoxy-substituted benzoates, have been prepared from cellulose with the appropriate aromatic acid and chloroacetic anhydride as the impelling agent and magnesium perchlorate as the catalyst (29). 

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). 

Cellulose Derivatives. Chemical modification markedly alters the physical properties of ceUulose. Common derivatives iaclude methylceUulose ethylceUulose [9004-57-3] ptopylceUulose /7(9(93 -/ -7/, hydroxyethjlceUulose /7(9(94- 52-(97, hydtoxyptopylceUulose [9004-64-2],... 

Bacterial Cellulose. Development of a new strain of Acetobacter may lead to economical production of another novel ceUulose. CeUulon fiber has a very fine fiber diameter and therefore a much larger surface area, which makes it physicaUy distinct from wood ceUulose. Its physical properties mote closely resemble those of the microcrystalline ceUuloses thus it feels smooth ia the mouth, has a high water-binding capacity, and provides viscous aqueous dispersions at low concentration. It iateracts synergisticaUy with xanthan and CMC for enhanced viscosity and stabUity. 

The important features of rigidity and transparency make the material competitive with polystyrene, cellulose acetate and poly(methyl methacrylate) for a number of applications. In general the copolymer is cheaper than poly(methyl methacrylate) and cellulose acetate, tougher than poly(methyl methacrylate) and polystyrene and superior in chemical and most physical properties to polystyrene and cellulose acetate. It does not have such a high transparency or such food weathering properties as poly(methyl methacrylate). As a result of these considerations the styrene-acrylonitrile copolymers have found applications for dials, knobs and covers for domestic appliances, electrical equipment and car equipment, for picnic ware and housewares, and a number of other industrial and domestic applications with requirements somewhat more stringent than can be met by polystyrene. 

Typical physical properties of celluloid are compared with other cellulose plastics in Table 22.2. 

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)...

Although the prime function of plasticisers in cellulose acetate is to bring the processing temperature of the compound below the polymer decomposition temperature, it has additional values. An increase in the plasticiser content will reduce the melt viscosity at a given temperature and simplify processing. The physical properties of the finished product will be modified, increasing toughness... 

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. 

Weathering. This generally occurs as a result of the combined effect of water absorption and exposure to ultra-violet radiation (u-v). Absorption of water can have a plasticizing action on plastics which increases flexibility but ultimately (on elimination of the water) results in embrittlement, while u-v causes breakdown of the bonds in the polymer chain. The result is general deterioration of physical properties. A loss of colour or clarity (or both) may also occur. Absorption of water reduces dimensional stability of moulded articles. Most thermoplastics, in particular cellulose derivatives, are affected, and also polyethylene, PVC, and nylons. 

Since the changes in physical properties are often the impetus for grafting, it is necessary to briefly touch on this, in this section. A number of general reviews on grafting have also included some discussion on the changes in physical properties [126-129] that usually determine the field of applications. Some other reviews deal with certain properties and applications, such as sorbency [70] and ion exchange properties [130] of cellulose. 

The mechanical and physical properties of natural fibers vary considerably, as it is with all natural products. These properties are determined by the chemical and structural composition, which depend on the fiber type and growth circumstances. With this cellulose, the main component of all natural fibers varies from fiber to fiber. 

A surprisingly low concentration of water can reduce the viscosity such that reclaimed PET cannot be used for the blow molding of bottles with acceptable physical properties. The established solution to the moisture problem is to dry the recycled PET in special dryers prior to use. However, the drying process is both time and energy intensive. Paper labels can cause problems in PET recycling if they decompose during washing and removal. The paper fibers formed can produce cellulose fibers that are difficult to remove from the reprocessed PET.1... 

Wood is a composite material that is made, up basically of a mixture of three main constituents, cellulose, hemicellulose, and lignin (see Textbox 54), all of them biopolymers synthesized by the plants, which differ from one another in composition and structure (see Textbox 58). The physical properties of any type of wood are determined by the nature of the tree in which the wood grows, as well as on the environmental conditions in which the tree grows. Some of the properties, such as the density of wood from different types of trees, are extremely variable, as can be appreciated from the values listed in Table 71. No distinctions as to the nature of a wood, whether it is a hardwood or a softwood, for example, can be drawn from the value of its specific gravity. 

See also Carboxymethyl celluloses applications, 5 452t in paper manufacture, 18 115 physical properties, 5 450t production from chloroacetic acid,... 

Dimethylacetamide (DMAc), cellulose solvent (with lithium chloride), 5 384 N, N-Dimethylacetamide (DMAc), 23 703 extractive distillation solvent, 8 802 solvent for cotton, 8 21 N, AA-Dimethylacrylamide (DMA), 20 487 P,P-Dimethyl acrylic acid, physical properties, 5 35t Dimethylallylamine, 2 247... 

Inorganic bismuth compounds, 4 17—26 Inorganic bromamines, 13 101—104 Inorganic bromine compounds, 4 318-339 Inorganic cellulose esters, 5 394-412 physical properties, 5 402 103 preparation, 5 396-402 uses of, 5 402 08... 

Organic cellulose esters, 5 412—439 analysis, 5 430—434 economic aspects, 5 427—430 health and safety factors, 5 434—435 liquid crystalline, 5 418 manufacture and processing, 5 418—427 physical properties, 5 415—418, 416t, 417t... 

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