ABSTRACT
When compounds based on nitrile rubber (NBR) are vulcanised in a mould a complex interfacial layer is formed at the surface of the mould. The components of the layer include vulcanisation and processing aids as well as residues of the NBR manufacturing process. When the moulding is removed parting occurs within the inter-layer; its constituents exert a dominant effect on the adhesion.
Rubber-mould adhesion has been studied by measuring the mould sticking index with a TMS rheom-eter and investigating the surfaces formed by X-ray photoelectron spectroscopy. This paper is concerned with the effects of organic sulphonate or sulphate emulsifier residues, which are common constituents of the interphase.
The adhesion has been measured of rubber compounds prepared with differing concentrations of sulphates or sulphates included, and by use of rubber coagulated from latices stabilised with different emulsifiers. The presence of these residues generally increases adhesion, probably because of strong adsorption of the polar sulphoxy groups on the surface of the mould steel, producing an interfacial layer which is not easily sheared. In’sle experiments a tendency was observed for adhesion to fall off at high sulphoxy residue concentration; this could be associated with weakness in shear of thicker layers of these compounds.
