Cellulose density

Fig. 9 Active cellulose density vs. time (10mm particle)...

Only cellulose is the feedstock of pyrolysis process treated in the model. Cellulose mass consunq>tion represents the degree of the pyrolytic conversion. Figures 10 and 11 show the mass losing curves as pyrolysis proceeds for 2 ram and 10 mm particles respectively. As can be seen that cellulose density decreases all the way down to zero. The density in the outside surface layer decreases much faster than the center. It takes about 5s for the 2 mm cellulose particle to be devolatilized completely, and 60s for the 10mm particle. It also shown that devolatilization of cellulose particles proceeds layer by layer, which is more obvious for the outside layers and for the large particle. 

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. 

Among the bast textile fibers, the density is close to 1.5 g/cm, or that of cellulose itself, and they are denser than polyester, as shown iu Table 5. Moisture regain (absorbency) is highest iu jute at 14%, whereas that of polyester is below 1%. The bast fibers are typically low iu elongation and recovery from stretch. Ramie fiber has a particularly high fiber length/width ratio. 

Refining and Fractionation. These processes are used to alter and select cellulose properties so the final sheet has the desired properties (51). Properties of recycled fibers differ from those of fibers prepared directly from wood. For example, recovered chemical fibers have lower freeness, an apparent viscosity leading to different water drainage characteristics on paper machines. Recovered fibers also have iacreased apparent density, lower sheet strength, iacreased sheet opacity, inferior fiber—fiber bonding properties, lower fiber sweUiag, lower fiber flexibiUty, lower water reteatioa, reduced fiber fibrillatioa, and much lower internal fiber delamination. 

EthylceUulose [9004-57-3], a cellulose either (qv), as prepared commercially, ie, of high DS, is thermoplastic and has alow density (1.14 g/cm ). It forms films of good thermostabiUty and excellent flexibiUty and toughness. EthylceUulose is used in lacquers, inks, and adhesives and is combined with waxes and resins in the preparation of hot-melt plastics. It is also used as a pharmaceutical tablet binder. 

Cellulose ester Shrinking point, °C Mp °C Water tolerance value 50% di 75% di 95% di Density, g/mL Tensile strengtl MPa ... 

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. 

Another method for direct precipitation of cellulose acetate powder suitable for extmsion into plastics is described (90). The reaction solution is precipitated with dilute aqueous acetic acid at 80—85°C in the presence of a coagulant such as isopropyl acetate. The resulting powder particles have a higher bulk density and absorb plasticizers more readily than powders obtained by the usual methods. 

Filter aids should have low bulk density to minimize settling and aid good distribution on a filter-medium surface that may not be horizontal. They should also be porous and capable of forming a porous cake to minimize flow resistance, and they must be chemically inert to the filtrate. These characteristics are all found in the two most popular commercial filter aids diatomaceous silica (also called diatomite, or diatomaceous earth), which is an almost pure silica prepared from deposits of diatom skeletons and expanded perhte, particles of puffed lava that are principally aluminum alkali siheate. Cellulosic fibers (ground wood pulp) are sometimes used when siliceous materials cannot be used but are much more compressible. The use of other less effective aids (e.g., carbon and gypsum) may be justified in special cases. Sometimes a combination or carbon and diatomaceous silica permits adsorption in addition to filter-aid performance. Various other materials, such as salt, fine sand, starch, and precipitated calcium carbonate, are employed in specific industries where they represent either waste material or inexpensive alternatives to conventional filter aids. 

Wood, then, is a foamed fibrous composite. Both the foam cells and the cellulose fibres in the cell wall are aligned predominantly along the grain of the wood (i.e. parallel to the axis of the trunk). Not surprisingly, wood is mechanically very anisotropic the properties along the grain are quite different from those across it. But if all woods are made of the same stuff, why do the properties range so widely from one sort of wood to another The differences between woods are primarily due to the differences in their relative densities (see Table 26.1). This we now examine more closely. 

Around Izod notch Low-density polyethylene Ethylene-propylene block copolymers Cellulose nitrate and propionate ABS and high-impact polystyrene Bis-phenol A polycarbonate... 

Figure 8 Optical density (280 nm) versus irradiation time (hours) for cellulose triacetate films 0-2,4-DHB D-2H-4BB DHBP-F A-2H-4MB A-HMBP-F and B-HBBP-F.

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