The influence of structural and morphological changes on the electrokinetic properties of PA 6 fibres

A two-phase model composed of alternating crystalline and amorphous regions is usually used to describe the structure of fibre-forming polymers. Different changes in fibre fine structure influence the entire morphological character of the polymer. The ratio between the fibres crystalline and amorphous area (accessible part of the polymer) defines their adsorption character. In the present paper, we tried to analyse the interdependence between fibre structure and their electrokinetic character. The structure and the adsorption abilities of PA 6 fibres were modified by thermal treatment. The accessibility of free adsorption places in the amorphous part of PA 6 polymers was investigated by the determination of electrokinetic properties, which were analysed by ζ-potential determination. It was determined by streaming-potential measurements as a function of the pH and the surfactant concentration in the liquid phase. From the ζ-pH functions the adsorption potential for all ionic species Φ(i) (i.e. Φ(K+), Φ(H+), Φ(Cl-), Φ(OH-), in the case of potassium chloride solutions), the charge densities σ(k) and the pK values were calculated according to the Borner and Jacobasch model. From the ζ-surfactant concentration functions the adsorption isotherms were calculated. The results show that the modifications to the polymer structure cause different electrokinetic properties that correlate with the changes in the fine structure and morphology. After thermal treatments the crystallinity of the samples increases, which causes the increase in negativity of ZP(plateau) (pH=9).