Capillary Effect in the Layers of Rubber-Fabric Composites

Rubber-fabric composites belong to a class of anisotropic reinforced composite laminates intended for operation in contact with a liquid medium. Each layer of such composites performs a specific function in the operation of printing machines. The rubber layer is located on the surface of the material and is impenetrable with respect to hydrophilic liquids, but can swell to a limited extent in organic solvents. The fabric layers provide structural integrity and tension of the layered composite material; they are protected from the penetration of a liquid medium by layers of rubber in a plane perpendicular to the arrangement of the layers. In the plane parallel to the arrangement of the layers, the fabric is permeable with respect to aqueous solutions and organic solvents. This permeability is based on the capillary effect of absorption. In order to eliminate the anisotropy of the permeability of reinforced layered composite materials, it is proposed to apply additional layers on the end surface to block the access of liquid to the capillary space through the pores, gaps between the threads, and fibers of the fabric layers. The additional layers are applied by brushing or dipping into solutions of suspensions and emulsions of film-forming polymers such as polyvinyl alcohol, polytetrafluoroethylene, and acrylic polyester. Techniques for estimating the porosity experimentally and calculating the average radius of the capillaries based on a physical model of the composite porous structure are presented. The capillary pressure leading to absorption is described based on Laplace’s law. The laboratory testing bench represents an upgraded Klemm–Winkier device. The penetration of liquids into the porous structure of a rubber-fabric composite through the end surface is measured. The sizes of the pores in the structure of the composite and their number, volume, and the rate of pore filling with water through the end surface of the samples of anisotropic reinforced layered composites used in printing are calculated. A decrease in water permeability through the protective layers at the end surface is shown depending on the chemical and phase composition of the film-forming polymers. The diagrams of the permeability, absorption kinetics, and porosity parameters of the rubber-fabric composite are compared. The fractions of capillaries with different diameters and their distribution throughout the cross-sectional area are determined.