ISSN:
0022-3832
Schlagwort(e):
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
PartI. It was confirmed that certain cellulose nitrates in 1% solution in acetone become more viscous and finally gel on standing over CaO, PbO, the basic salts of weak acids and strong bases, and certain other materials. The gels, whose formation was facilitated by increased temperature, were broken by the addition of a small amount of acid. The rate of gelling increased with the nitrogen content of the cellulose nitrate, indicating that residual hydroxyl groups were not involved. Nor did gelling occur under the same conditions in 1% solutions of cellulose acetate and ethyl cellulose of comparable degree of substitution. The rate of gelling was enormously increased when COOH groups were artificially introduced into the cellulose before nitration. Gelation is most probably due, therefore, to the cross-linking of different cellulose nitrate chains through COOH or possibly SO3H groups.Part II. Dilute (〈 0.2%) cellulose nitrate solutions on standing over CaO show a fall in viscosity with time (contrast 1). By ultracentrifuge examination this was shown to be due (for CaO and PbO treated solutions), not to degradation of the cellulose nitrate chains, but to association processes leading to the formation of aggregates of higher sedimentation constant and molecular weight. Sedimentation constants corresponding to molecular weights of several millions were observed from a cellulose nitrate of initial molecular weight ca. 100,000. Untreated control solutions showed no change in the state of aggregation. The association processes followed an approximately first-order law at room temperature and were made more rapid by increase in temperature. After sedimentation, the association products could not be redispersed. Calcium introduced into cellulose nitrate before solution in acetone did not cause association or any other noticeable effect at low concentration.
Zusätzliches Material:
5 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pol.1948.120030514
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