Stiffness cellulose

These cellulose esters form tough, strong, stiff, hard plastics with almost unlimited color possibilities. Articles made from these plastics have a high gloss and are suitable for use in contact with food. 

Air and Oil Filters. Liquid resole resins are used to coat and penetrate the cellulose fibers of filters and separators in order to increase strength and stiffness and protect against attack by the environment. The type of phenoHc to be used depends on both the final property requirements and the papermaking process. 

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...

The solvation by plasticiser also gives celluloid thermoplastic properties owing to the reduction in interchain forces. On the other hand since the cellulose molecule is somewhat rigid the product itself is stiff and does not show rubbery properties at room temperature, cf. plasticised PVC. 

The angle of the fibrils and the content of cellulose determine the properties of the plant fibers. The Hearle et al. s model [19] considers only these two structure parameters. For the description of stiffness, solely, the St layers were considered because the properties of these fibers were decisively dominated by the amount of these layers. 

Tests by Gatenholm et al. [8,10] on PHB-HV copolymers containing cellulose fibers (for example, the tradenamed Biopol) show that the mechanical properties of these systems are determined by the fiber and the fiber matrix interface on the one hand, and on the other hand by the composition of the matrix, that is, of HV proportion in the matrix. At an increased proportion of HV, the stiffness of the composite is reduced up to 30%, whereas elongation at break increases until about 60%. 

When used as substitutes for asbestos fibers, plant fibers and manmade cellulose fibers show comparable characteristic values in a cement matrix, but at lower costs. As with plastic composites, these values are essentially dependent on the properties of the fiber and the adhesion between fiber and matrix. Distinctly higher values for strength and. stiffness of the composites can be achieved by a chemical modification of the fiber surface (acrylic and polystyrene treatment [74]), usually produced by the Hatschek-process 75-77J. Tests by Coutts et al. [76] and Coutts [77,78] on wood fiber cement (soft-, and hardwood fibers) show that already at a fiber content of 8-10 wt%, a maximum of strengthening is achieved (Fig. 22). 

Glucose molecules can link together into chains, with each ring tethered to the next by a bridging oxygen atom. In one form, this is cellulose, the stiff material that gives the stalks of plants and the trunks of trees their structural strength. Chitin, a variation on cellulose, is an even stiffen material that forms the exoskeletons of crustaceans such as crabs and lobsters. 

Both polysaccharide molecules are relatively stiff, stiffer even than simple cellulosics such as HEC, and have a molecular masses in excess of two million. Recent work by Rinaudo and coworkers (Personal communication) and Crecenzi and colleagues (Int. J. Biol. Macromol., submitted) has shown that succinoglycan molecules are also stiffer than those of xanthan. 

Linear polymers, polystyrene and cellulose triacetate exhibit differences in hydrodynamic behavior in solution. Cellulose and its derivatives are known to have highly extended and stiff chain molecules below a Dp of about 300, but as the Dp Increases above 300 the chain tends to assume the character of a random coll (27,28). The assumption that hydrodynamic volume control fractionation in GPC may not be true for polystyrene and cellulose triacetate, though it has been found satisfactory for non-polar polymers in good solvents (29). 

The freedom to vary < ) and i so extensively—even if exaggerated here owing to the absence of other molecules—renders cellulose fragments such as an octamer, surprisingly flexible. Cellulose is generally considered to be a stiff molecule, but at least single-molecule simulations in vacuum at 400 K show it to have considerable internal mobility. The range of conformations that result from this mobility are quite apparent when the molecular shape is... 

Macromolecules with polar and stiff main chains (e.g., cellulose, polyara-mides) are often only soluble via complexation. 

Since Robinson [1] discovered cholesteric liquid-crystal phases in concentrated a-helical polypeptide solutions, lyotropic liquid crystallinity has been reported for such polymers as aromatic polyamides, heterocyclic polymers, DNA, cellulose and its derivatives, and some helical polysaccharides. These polymers have a structural feature in common, which is elongated (or asymmetric) shape or chain stiffness characterized by a relatively large persistence length. The minimum persistence length required for lyotropic liquid crystallinity is several nanometers1. 

Then there are flexible linear polymers which curl up in solution to give a random cell. If the chain is stiff, such as in cellulose or in DNA, the coil becomes highly expanded. 

All of the likely conformations of cellobiose, cellulose, and xylan are explored systematically assuming the ring conformations and IC-D-O-IC-4 ) angle for each pair of residues to be fixed and derivable from known crystal structures. The absolute van der Waals energies, but not the relative energies of different conformations, are sensitive to the choice of energy functions and atomic coordinates. The results lead to possible explanations of the known conformational stiffness of cellulose and Its solubility properties in alkali. The characteristics of xylan conformations are compared with cellulose. 

For these measurements, temperature has been varied between 55 and 110° C. In this temperature range, the solvent viscosity changes by a factor three 4.7 to 1.5 cps). It is very improbable that a noticeable internal friction factor would change just by the same factor. Moreover, as has already been pointed out at the end of Section 5.2.2, the curves obtained by plotting cot2 c vs reduced shear stress fjN are practically coinciding for dilute solutions of cellulose tricarbanilate fractions with M S 500,000 and for anionic polystyrenes. So one can conclude that the internal friction of the thermodynamically stiff molecules of cellulose tricarbanilate must be rather low. 

Landells, G., and C. S. Whewell Preparation and properties of regenerated cellulose containing vinyl polymers. I. Internal deposition of polymers. J. Soc. Dyers Colourists 67, 338 (1951). II. Staining, swelling, and stiffness characteristics. J. Soc. Dyers Colorists 71, 171 (195S). III. Moisture relations. J. Soc. Dyers Colorists 73, 496 (1957). 

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