Cellulose and its Derivatives

Cellulose primarily undergoes chain cleavage under irradiation. Destruction of the glucose units occurs parallel to cleavage, so that total degradation into water soluble products will occur at radiation doses above 5,000 kGy [724]. 

Left ultimate tensile strength Right yield strain 

Polyphenylene sulfide is resistant to ionizing radiation. Measurements on molded parts made from glass fiber-reinforced polyphenylene sulfide have shown that neither flexural strength nor Young s modulus change under y- (50,000 kGy) or neutron radiation (10,000 kGy) [572]. Polyphenylene sulfide can be repeatedly sterilized. 

Polyphenylene sulfide also exhibits very good resistance to microwave radiation, especially at the frequencies used for food preparation (2.45 GHz) [572]. 

Polysulfone exhibits remarkably high resistance to y-radiation and, in the typical thickness for service applications, is largely permeable to X-rays used in medical diagnostics and therapy [572]. 

Hemicellulose is the second most familiar polysaccharide next to cellulose comprising one-fourth to one-third of most plant materials, and in the past twenty years hemicellu-loses have been used as feedstock for producing sugars. Hemicelluloses are mostly hetero-polysaccharides classified according to the sugar residues present, namely xylans, mannans, arabinans and galactans, which are either linear or branched polymers. The most abundant hemicellulose is (3-l- 4-D-xylan, which is built from p-l- 4-linked D-xylopyranosyl residue, which forms the linear backbone of the polymer. 

Pectin is a family of complex polysaccharides present in the walls that surround growing and dividing plant cells. It is also present in the junction zone between cells within secondary cell walls, including xylem and fiber cells in woody tissue. Pectin is an essential 

Poiymers from agro resources (By extraction and separation) 

Threshold volume fractions observed for cellulose acetate (CA and CTA), ethyl cellulose (EC) and hydroxypropyl cellulose (HPC), each in various solvents, are presented in Table 3. The results depend to some extent on the solventThe data included are not exhaustive. Other cellulose esters exhibit mesomorphic behavior Chanzy et al. observed mesomorphic behavior in solutions of cellulose itself when dissolved in N-methylmorpholine N-oxide containing water at concentrations of cellulose in the range 20-55 % w/v, depending on the temperature, the water content of the solvent and the degree of polymerization of the cellulose. Solutions of cellulose in mixtures of trifluoroacetic acid with 1,2-dichloroethane or with chloroform are hkewise lyotropic at concentrations of 20% (w/v) and above according to Patel and Gilbert 

The cellulose derivatives chosen for inclusion in Table 3 are those for which the required data for comparison with the theory as outhned above are available. For cellulose acetate, r o/n 1100 200 in the limit n oo Taking 

Maissa, Vellutini and Sixou Bh a, Fellers and White Werbowyj and Gray Conio, Bianchi, Ciferri, Tealdi and Aden 

6 Tanner and Berry obtained r o/n = 1080 for a secondary acetate (CA) of degree of substitution 2.45 dissolved in trifluoroacetic acid or in a mixture of methylene chloride and methanol. They found larger values of 1350 or greater for the triacetate (CTA) Kamide, Miyazaki and Abe on the other hand, report lower values of ca. 600 for CTA. The disparity may reflect the difficulties caused by aggregation of CTA Hence, we adopt the same value for CTA as for CA, on the plausible grounds that they should be similar in this respect 

lu = 5.2 A and M = 265 (for CA), one obtains = 26 according to Eq. (13), and, from Eq. (11), Vp = 0.284 at incipience of a nematic (or cholesteric) phase. The experimental values in Table 3 are generally somewhat greater than this result, but the differences are not beyond the uncertainty in the characteristic chain dimension, here represented by r o/n. Inasmuch as this ratio depends on the solvent, as is well known, dependence of the threshold Vp on the solvent is to be expected. Available data do not permit a definitive correlation, however, between Vp at incipience of the mesomorphic phase and the influence of the solvent on chain flexibility. 

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The polydispersity of softwood milled wood lignin, as measured by M /M = 2.5, is high compared with that of cellulose and its derivatives. 

The pyrophosphate complex of Mn(II) ion was found to initiate grafting of acrylonitrile onto cellulose and its derivatives [36,37],... 

The photo-induced process of modification of cellulose and its derivatives was reported by Geacintov and coworkers [67,68]. Thus, acrylonitrile, vinyl acetate, styrene, MMA, and the binary system of styrene and AN were grafted onto cellulose and cellulose derivatives. In... 

There are a number of naturally occurring polymers which find technical application, including cellulose and its derivatives, starch, and rubber. In addition, a number of important biological materials, most notably the proteins, are made up of macromolecules. These will be considered briefly in the sections which follow. 

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. 

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). 

While most CA s of disaccharides have depended only on intrinsic characteristics of the molecule, experimental results depend strongly on the environment. By experiment, Kamide and Saito ( ) have shown that the degree of flexibility of cellulose and its derivatives is strongly dependent on the dielectric constant of the solvent as well as the exact type and degree of substitution. Since a substantial portion of the polymer flexibility depends on the extent of variability of the torsion angles at the intermonomer linkage, the dependence of polymer flexibility on type of solvent and substitution means that the disaccharide flexibility also should depend on those factors. Non-polar solvents allowed the molecules to have greater flexibility than did polar solvents (35). 

The rigidity of cellulose and its derivatives are affected by the solvent and by the type and degree of substitution ( ) and thus V2 is... 

Arthur, J. C., Jr., Chemical Modification of Cellulose and its Derivatives, Chap. 2 in Comprehensive Polymer Science, Vol. 6, G. C. Eastmond, A. Ledwith, S. Russo, and P. Sigwalt, eds., Pergamon Press, Oxford, 1989. 

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. 

Significant advances to this end have been made using primarily liquid crystal copolyesters as the rigid-rod chain in various matrix polymers (2,3). Surprisingly, while cellulose and its derivatives also exhibit LC phenomena... 

Dor4e, Charles (1875- ). A Brit scientist specializing in Cellulose and its derivatives. Author of the books The Methods of Cellulose Chemistry , Chapman Hall, London, 2nd ed (1947), 543pp and. Les Methodes de la Chimie de la Cellulose Comprenant des Methodes de Recberches sur les Celluloses Composees , Dunod, Paris (1949), 578pp and many other publications NOTE No biographical info was in the literarure thru Dec 1966... 

The affinity of cellulose and its derivatives for water can be explained by the existence of hydrogen bonds that bind the molecules of the cellulose chain either directly or with the help of water molecules, as outlined in Fig. 82. The existence of hydrogen bonds has been confirmed experimentally by studies of the infra-red absorption spectra of cellulose and its derivatives (the subject will be discussed later, on p. 287). 

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. 

Formerly it was believed that in their physical properties, as for instance no increase in boiling point and in osmotic pressure, colloidal solutions of cellulose derivatives were radically different from solutions of crystalline substances having small molecules. Now, however it is clear that the difference is not so considerable and that a close analogy exists between solutions of cellulose and its derivatives and those of substances of low molecular weight. 

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