ISSN:
0022-3832
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Nitrocellulose prepared from heterogeneously degraded cotton and technical rayon pulp has been divided into different fractions by adding water to the acetone solution. The osmotic pressure and the viscosity of each acetone solution at various concentrations have been measured. Within a range of concentration of 1.5 to 10 grams per liter the reduced osmotic pressure shows a linear dependence on the concentration. The molecular weight values obtained are in the range 26,000 to 2,500,000. The value of the virial coefficient B in the osmotic pressure equation depends on the molecular weight. With increased molecular weight the value of B decreases, at first strongly, later more slowly. This fact, which has also been observed on polystyrenes by Outer, Carr, and Zimm (measurements of light scattering), cannot be explained by the Flory-Huggins theory. It depends on the flexibility of the threadlike molecules. An equation is given showing the relationship between B and M in satisfactory agreement with the experimental data. This equation contains as a parameter the length of a statistical chain element (Kuhn's theory), as obtained by viscosity measurements. Schulz stated that the entropy of dilution of the system nitrocellulose-acetone differs but little from the ideal value. Consequently the positive excess term calculated for the athermal solution has to be compensated by a further negative term deriving from the solvation. Until now calculations of the solvation only supplied positive terms. Yet, a negative term is obtained, considering the fact that the bond of the acetone molecules with the nitrocellulose is fixing the orientation of the acetone molecule in a much stronger way than it would be in pure acetone. The statistical mechanical calculation shows that this model gives satisfactory results. The measurements of the viscosity cannot be represented by the Huggins theory. The plotting of ηsp./c against c gives curves the slope of which strongly increases with the molecular weight. The molecular weight being rather high, no linear relationship can be reached in plotting ηsp./c against ηsp. The intrinsic viscosity therefore had to be determined by graphic extrapolating. These values are used to find the relationship between intrinsic viscosity and molecular weight, and for the quantitative testing of the Kirkwood-Riseman theory. The Staudinger formula cannot be applied for higher degrees of polymerization. The Kirkwood-Riseman theory is confirmed for degrees of polymerization down to n ≈ 200. Below this value systematic discrepancies occur, the reasons for which are discussed. The measurements seem to demonstrate that there are small but characteristic differences between the molecular parameters of cotton cellulose and wood pulp.
Additional Material:
15 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1952.120080608
