R. M. Gohil

Solution properties of cellulose triacetate—I. Method of fractionation and light scattering, osmometry, viscometry on dilute solutions

Abstract Cellulose triacetate prepared from Egyptian cotton was fractionated by the adsorption technique using porous adsorbent calcium silicate. Chloroform-acetone mixture is suitable for preferential adsorption of CTA on calcium silicate while chloroform-ethanol is adequate for desorption of the polymer from the adsorbent. Light scattering and osmotic pressure measurements for various fractions reveal that fractions are monodisperse. The viscosity measurements along with light scattering give the Mark-Houwink constants in chloroform at 30° as v = 0.800 and K′ = 1.396 × 10−4. Studies showed negligible partial draining character and therefore the higher value of v seems to be mainly due to solvent-polymer interaction, which is common for many stiff chain polymers like cellulose and amylose derivatives. Other parameters, e.g. second virial coefficient, radius of gyration and unperturbed dimension, have also been evaluated.

Crystallization of polyacrylonitrile: Growth mechanisms for various growth features

SummaryCrystallization of polyacrylonitrile has been carried out at different temperatures from fractionated sample, and different morphological growth features obtained are compared with those observed previously from unfractionated sample. Several new growth features like rectangular single crystals, twinned crystals, ovals and spherulites have been observed. The role of different typical growth features for the development of spherulites has been studied. It seems that the proposed growth mechanism for the development of spherulite grown either from the melt or concentrated solution is the same for different polymers. From the observed growth features of dendritic nature in different conditions, a mechanism of development of dendritic spherulite is discussed.ZusammenfassungDie Kristallisation von Polyacrylnitril und anderen Polymeren wird nach der Methode der Filmbildung ausgeführt. Das Polyacrylnitril war hergestellt durch Polymerisation von Acrylnitril initiiert mit einem Cer-Ionen-Redoxsystem. Die Fraktionierung des Polyacrylnitrils wurde mit der Methode, dieKobayashi undFujisaki beschrieben haben, durchgeführt. Die vorliegende Studie für die Untersuchung der wachsenden Kristalle wurde an einer Probe mit dem mittleren Molekulargewicht

Rectangular single crystals of polyacrylonitrile

\bar M_w = 1,2 \times 10^5

A source of screw dislocation in polyoxymethylene crystals

durchgeführt. Cellulosetriacetat (CTA) mit dem Molekulargewicht

Slip-step on polyoxymethylene crystals

\bar M_n = 3,5 \times 10^5

Morphology of polyacrylonitrile

, bestimmt aus Viskositätsmessungen in Chloroform bei 25 °C nach Haward und Parikh, wurde ebenso wie Polydthylen (PE), mit