PRESSURE BONDING AND COHERENCY OF PLASTIC AND FRAGMENTARY MATERIALS

The manufacture of plastics, now in particulate or granulated forms, for subsequent densification into geometrical shapes by pressure has necessitated the exploration of the physicomechanical behavioral effects of compression. Two categories of powders (plastic and fragmentary) were uniaxially compressed in a cylindrical mold, and the mechanisms of pressure bonding and volume reduction were continuously monitored in terms of volume change with axial stress. Two plastic powders (polypropylene and polystyrene) under high axial stress (450 MPa) did not produce coherent compacts. Polyethylene and sodium chloride (which has plastic properties) readily formed compacts in the stress range 30-250 MPa. The variation of stress with time and the degree of compact coherency of these plastics were compared with the physicomechanical properties, surface hardness, and diametral strength of fragmentary materials (dicalcium phosphate and sugar) to predict the pressure bonding and strength of various densified plastic polymers.