Effect of High Pressure on Self Adhesion (Autohesion) of High Polymers

Abstract

Abstract The phenomenon of self adhesion of high polymers is one of the very important but little studied properties of these materials. Self adhesion of rubberlike polymers has been studied, but there is little work reported on the self adhesion of thermoplastics. There is, however, no doubt about the importance of the role of this phenomenon in the process of producing products from powdered and granular thermoplastics. The influence of temperature and pressure on the self adhesion of some thermoplastic powders was studied in the present work. The conditions for the formation of a transparent sample were found by pressing the powdered material in a heated cylindrical press. The samples pressed were 10 mm in diameter and 4–5 mm thick. The temperature and pressure were varied over a wide range. The samples were pressed in the following manner: The polymer sample was placed in the cold press and a given pressure was applied; the temperature was then raised to a given value and the sample was held at this temperature for 15 minutes; after cooling the press to 50–60° the pressure was released, the sample was removed from the press and the density to visible light was evaluated visually. When a transparent sample is obtained by pressing the thermoplastic polymer, partial or complete coalescence of the grains of the material takes place with a disappearance of grain boundaries. Under these conditions the strength of the sample may not reach the cohesive strength of the material as has sometimes been assumed.