Adsorption Modification of Fillers and Structure Formation in Solutions of Polymers

On addition of a solid disperse phase to a polymer one requisite for its effectiveness as an active filler is close similarity of the molecular properties of the surface of the particles and the polymer. This along with high “dispersity” (specific surface area) is mainly responsible for the high effectiveness of various types of carbon black—a hydrophobic filler of organic origin. For the same reason the majority of mineral fillers, which are usually of hydrophilic character, have relatively low capacity for the active filling of polymers, which is made evident in improvement in the mechanical and other properties of the filled material. As a consequence particular importance attaches to processes of adsorption modification, i.e., the alteration of the molecular properties of the surface of particles of hydrophilic fillers by orientated adsorption of surface-active substances (SAS). The hydrophobicization of the surface of the particles of filler which takes place here increases their “wettability” by the polymer phase and enhances the strength of its bond to the polymer, as has been investigated in detail in the work of P. A. Rebinder et al.. In this case modification leads to activation of the filler; in a number of cases however activation does not take place. As models for filled systems we may take concentrated suspensions of particles of the fillers in solutions of polymers containing additions of surface-active substances, which depending upon the concentration in the solution and proportionally to its increase, at first peptize the particles, lyophilizing them, and then stabilize them as a result of lyophobicization. This causes in sequence coagulation structure-formation in the system and then destruction of the resulting structures. A number of investigations have been devoted to the influence of fillers and pigments on the properties of polymers in the presence of surface active substances —in rubbers, and in lacquers and paints based on drying oils, but the laws of adsorption modification of mineral disperse phases and its influence on the filling effect in connection with the composition and molecular properties of the complex system: polymer-solvent/filler (or pigment)/surface-active substance have not been systematically studied. The present paper aims to investigate this question.