Effect of graft-copolymer on the structure and behaviour of solid mixtures of cellulose acetate and polyacrylonitrile

Abstract

Mixtures of polymers may be used effectively to modify the properties of high molecular weight materials. This method is based on the theoretical possibility of controlling the properties of these materials by modifying their chemical compositions and molecular structures by means of the appropriate selection of miscible polymers. The properties of polymer mixtures largely depend on the effect of the components on one another, i.e. on their compatibility [1–3]. Molecular mixtures of compatible polymers are really materials with completely new properties, and articles made from them may possess good mechanical properties. However, compatible polymer systems are by no means commonly found. Mixtures of incompatible polymers generally have a coarse type of structure which is reflected in poor mechanical properties. If on the other hand it is somehow found possible to obtain a highly dispersed mixture from incompatible polymers, the fabricated articles may combine the properties of the miscible components so that the strength properties will be superior to those of any of the components taken separately. One method of increasing the homogeneity and stability of mixtures of incompatible polymers is by introducing a graft-copolymer into the system [1, 4]. In previous investigations [4, 5] we showed that if we take a mixture of cellulose acetate (CA) and polyacrylonitrile (PAN), which are incompatible, and then add CA-PAN graft-copolymer to this mixture, considerable improvements in the homogeneity and stability of mixtures of the solutions are obtainable, although the introduction of the graft-copolymer does not prevent the separation of CA and PAN, i.e. it creates kinetic compatibility. This tends to enhance the mechanical properties of the fibre obtained from the mixture. It may be assumed that the condition of the initial solution that is to be modified by the graft-copolymer will largely be reflected in the structure of the resulting fibre, and this will provide the possibility of modifying the mechanical properties of the material. In this paper we are reporting on a study of the structure of mixtures of CA and PAN in the condensed state to determine the particular changes it may undergo owing to the introduction of the graft-copolymer. The structure is investigated in relation to certain mechanical properties of the products.