Polydispersity of Cellulose

Highly degraded cellulosic materials, such as viscose rayon, D.P. 250 to 350, may be dispersed in 8-12 % caustic at low temperatures. Upon increasing the temperature in a stepwise manner, the dispersed material may be fractionally precipitated. This method of fractionation is of particular interest since viscosity data indicate that the state of dispersion of degraded cellulosic materials in caustic solution and in cuprammonium solution is similar.  

The fractionation of cellulosic materials dispersed in cuprammonium solution has usually been accompanied by an amount of degradation sufficient to render the results questionable. However, Battista and Sisson, using acetone and n-propyl alcohol as precipitants, were able to resolve viscose rayon yam (D.P. 490) dispersed in cuprammonium solution into fractions varying in average degree of polymerization from 535 to 142, and from 615 to 132, respectively. 

The fractionation of cellulosic materials dispersed in aqueous solutions of ethylenediamine saturated with cupric hydroxide has been achieved by the stepwise addition of sulfuric acid, according to Straus and Levy.  

By careful nitration of cellulosic materials with nitric acid in the presence of phosphoric acid and phosphoric anhydride, a minimum of degradation occurs. According to Schieber, the resulting cellulose nitrate may be separated by stepwise dispersion with successively richer solvent mixtures into a series of fractions of var3dng chain lengths. 

Further studies by Badgley and Mark on relatively homogeneous fractions of a secondary cellulose acetate obtained by controlled precipitation from acetone and methylcellosolve solutions (with methyl alcohol), showed that equations 9, 10 and 11, above, apply over relatively narrow ranges of DP. Above a DP. of about 380, equation 9 gave D.P. values higher than those obtained by osmotic pressure measurements. Modification of equation 11, to the form 

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From another point of view, it can be seen that approximate conformity of cellulose nitrates to both of the asymptotic relations (63) and (89) for [ /] and (SF), respectively, implies that the number 0 should remain essentially constant at its asymptotic value 0, given by Eq. (57). Since it is difficult to assess the polydispersity of cellulose nitrate fractions, the constancy of 0, rather than its numerical value, should be of prime importance in testing the consistency of our conclusions. Doty, Schneider and Holtzer (59) and Newman and Flory (198) both originally reported, that 0 decreased systematically with decreasing molecular weight. Later Holtzer, Benoit and Doty (726) preferred to regard 0 as essentially constant at about 1.9 1021, somewhat smedler... 

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

History. Starting from the ID point statistics of Zernike and Prins [116] J. J. Hermans [128] designs various ID statistics of black and white rods. He applies these models to the SAXS curves of cellulose. Polydispersity of rod lengths is introduced by distribution functions, / , (,r)108. Hermans describes the loss of correlation along the series of rods by a convolution polynomial . One of Hermans lattice statistics is namedparacrystalby Hosemann [5,117]. Hosemann shows that the field of distorted structure is concisely treated by the methods of complex analysis. A controversial subject is Hosemann s extension of ID statistics to 3D [63,131,227,228],... 

Although the chemical structure of cellulose is understood in detail, its supermolecular state, including its crystalline and fibrillar structure is still open to debate. Examples of incompletely solved problem areas are the exact molecular weight and polydispersity of native cellulose and the dimensions of the microfibrils. 

The polymer properties of cellulose are usually studied in solution, using solvents, such as CED or Cadoxen (see Section 9.2). On the basis of the solution properties, conclusions can be drawn concerning the average molecular weight, polydispersity, and chain configuration. However, the... 

The polydispersity of the cellulosic material may be readily determined by the sedimentation equilibrium procedure from the relative distribution of the dispersed particles from the axis of rotation. The... 

History. Starting from the ID point statistics of Zernike and Prins [116] J. J. Hermans [128] designs various ID statistics of black and white rods. He applies these models to the SAXS curves of cellulose. Polydispersity of rod lengths is introduced by distribution functions, Hermans describes the loss of corre-... 

Chain length and molecular mass distribution have of course also strong implications for the performance of modified cellulose. For ethers, the degree of polymerization, DP, is usually between 50 and 2000 (300 for esters), as compared with 100 to 3000 for cotton cellulose and 600 to 1000 for wood cellulose. The relatively high polydispersity of the molecular mass originates from the starting material. 

The physicochemical properties of alkylated polysaccharides have received some attention, and details of the structures and conformations of 0-methylcelluloses, and their interaction in micelle junctions, have been included in a thorough discussion of polysaccharide gels and networks. Information on the polydispersity of samples of partially methylated cellulose may be obtained from column fractionation and by fractional precipitation from a solvent-nonsolvent system, but, for a more complete characterization of polydispersity, fractionation with a series of solvent-nonsolvent systems is necessary. The solubility, in water, of polysaccharides that are mainly methylated may be considerably improved by introduction of a few suitable ionizing groups, for example, by reaction with monochloroacetic acid to introduce carboxymethyl ether groups. The general sorption and diflFusion features of hydrocarbons and other... 

There is no specific mechanism incorporated into the model to determine the size of cellulose chains or the means of their termination and so to predict the inbuilt degree of polydispersity. Again, such addenda are not difficult to contrive. It could well be, for example, that the ratio between the rate of membrane flow from the Golgi apparatus to the vicinity of the plasmalemma and the turnover number of the GDPGlc-cellulose glucosyltransferase determines chain size and that there is no specific code for terminating the chains. 

Cellulose is insoluble in water and common organic solvents. This leads to the formation of colloidal suspension when cellulose whiskers are suspended in water. The stability of these suspensions depends on the dimensions of the dispersed particles, their size polydispersity and surface charge. Different acids have been used as solvents for dissolution of cellulose. Sulfuric and hydrochloric acids have been extensively used for whisker preparation, but phosphoric [68] and hydro-bromic acids [69] have also been reported for such purposes. When whiskers are... 

By gamma ray irradiation of cellulose fibers, it was noticed that a separation of a gas mixture (25-30% H 13-18% CO 45-58% CO and 2-3% CH ) occurs due to the dehydrogenation, depolymerization and glucoside chain destruction. By analyzing the molar mass and polydispersity of the irradiated cellulose fibers with gel permeation chromatography technique, it was concluded that cellulose destruction by high energy radiation profoundly affects the molecular structure on both a primary and supramo-lecular level [34]. 

Cellulose, a polydisperse linear 1,4-p-glucan, is part of a renewable resource which is the most abundant natural polymer on earth. It has been estimated that the global production of cellulose is 1.5 trillion tons each year, and is considered an almost inexhaustible source of raw material for environmentally friendly and biocompatible products. Cellulose is widely used for coatings, membranes, pharmaceuticals, and foodstuffs. ... 

Gu [9] applied the diluted assumption theory to the concentrated cellulose in N-methlymorpholine-N-oxide monohydrate (NMMOH2O) solution. He got relative differential MIVD curves of three kinds of cellulose pulps from the dynamic data of cellulose/NMMQH2O solution in 2000. But the results were not compared with the results reported by GPC. In 2004, the relative differential MIVD curves of four kinds of cellulose pulps were calculated on the basis of that method and the calculated results were compared with the non-calibrated GPC results by Zhang [10]. In their rheology experiments, the cellulose concentration in NMMO-H20 solution was fixed (9%, wt), and the polydispersity index (PDI) of cellulose was not calculated. 

The natural biopolymers, to which HA belongs, are not polydispersed polymers due to the matrix nature of their synthesis. The nature of the biochemical synthesis is determined by the matrix the enzyme upon which the triopolymer is synthesized. Nevertheless, during biopolymer extraction and purification processes they degrade in one way or another. For example, polygalactomannan, different types of cellulose (wood or cotton), chitosan and hyaluronan are isolated as a wide range of the relatively narrow dispersed macromolecule fractions. 

Copolymerization of methyl methacrylate with cellulose has also been initiated by the decomposition of peroxide groups formed on ozonolysis of cellulose. An examination of the polydispersity of poly(methyl methacrylate) chains... 

The DLS is one of the most popular techniques for light scattering, as it allows particles smaller than 1 nm to be analyzed. In the analysis of cellulose whiskers DSL is a complementary technique, since it provides a particles size frequency distribution and the polydispersity index of the sample [76]. 

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