Physical Constants of Cellulose

V/146 PHYSICAL CONSTANTS OF CELLULOSE TABLE 14. OTHER ELECTRICAL PROPERTIES... 

V/148 PHYSICAL CONSTANTS OF CELLULOSE TABLE 18. OTHER SOLVENTS"... 

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.

The bulk density of cellulose acetate varies with physical form from 160 kg/m (10 lb /ft ) for soft dakes to 481 kg/m (30 lb /fT) for hammer-milled powder, whereas the specific gravity (1.29—1.30), refractive index (1.48), and dielectric constant of most commercial cellulose acetates are similar. 

The influence of the polarity of solvents on their ability to dissolve nitrocellulose has been also demonstrated by Wo. Ostwald [50], who has introduced the value fi2/e as an expression characterizing the strength of solvent ( —dipole moment, e-dielectric constant). Good solvents of acetyl celluloses are characterized by a high iM2/s value. The physical significance of /i2/e is not clear, however, and its introduction has not helped to clarify the process of dissolution. 

Proof of grafting was presented through comparison of the solubilities of their saponified vinyl acetate and cellulose grafts and of the physical mixtures of the corresponding homopolymers. While from a cupriethyl-enediamin solution of the physical mixture pure cellulose is precipitated on acidification, the precipitate from the graft solution always contains constant amounts of polyvinyl alcohol, as proven by infrared spectroscopy. 

The reason is that the minerals serve as a shield physically protecting cellulose fibers from cellulolytic enzymes diffusing into the matrix. At pH 7.5-9, the enzymes have 10-1000 times lower activity, depending on the types of the enzymes, pH, and the dissociation constants of catalytically active groups in the enzyme active center. 

The role of inherent polarization and ionic transport effects in actuation mechanism of EAPap actuators are investigated. To physically investigate the actuation mechanism, several tests are performed. X-ray diffraction (XRD) spectra are compared before and after electrical activation and the possibility of crystalline structure change is observed. Dielectric property measurement indicates a dependence of the dielectric constant on fiber direction, as well as on frequency, humidity, and temperature. Thus, we conclude that piezoelectric effect and ionic migration effect are in the EAPap at the same time associated with dipole moment of cellulose paper ingredients. The amount of these effects may depend on environmental condition. 

It is also known that chemical and physical abnormalities in the cellulose molecule can produce weak bonds (30,31) thus, structural abnormalities may set up strain at localized points. At such positions, the rate constants for hydrolysis may be increased by as much as 10,000 (31). In the presence of acid, these properties would be enhanced and would assist UV grafting. Such a mechanism may even be the predominant process by which acid accelerates UV grafting. 

These studies were later extended to the ignition of specially prepared cellulose sheets" as a model for the broad class of kindling fuels. These sheets were made from a single batch of wood a-cellu-lose, with various proportions of carbon black added to provide a variation in optical properties from white to black. The thickness of the sheet varied within the range of 0.002 to 0.03". Furthermore, the samples were prepared in two densities, which gave two different sets of heat-conduction properties. Thus, the experimental samples had the same chemical properties but a considerable latitude for variation in physical properties. The samples were exposed to constant thermal radiation at levels of 2—23 cal.cm. sec. , to establish the relationship between the threshold of ignition (with the exposure parameter) and the fuel properties. 

Recently, in a similar vein, Macedo et al. [31] also compared bacterial cellulose and polytetrafluoroethylene (PTFE) as physical barriers used to treat bone defects in guided tissue regeneration. In this study, two osseous defects (8 mm in diameter) were performed in each hind-foot of four adult rahhits, using surgical burs with constant... 

The mechanical properties of protein-based materials closely depend on the plasticizer content, temperature and ambient relative humidity (16,34,35). At constant temperature and composition, an increase in relative humidity leads to a major change in the material properties, with a sharp drop in mechanical strength and a concomitant sharp rise in distortion. These modifications occur when the Tg of the material is surpassed (Figure 1). These variations can be reduced by implementing crosslinking treatments (physical or chemical) or using high cellulose or mineral loads (22). 

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