Mechanism of the anisotropic dimensional change of the wax pattern prepared by the softened wax technique. (1) Relationship between recovery and crystal orientation.

In order to obtain information on the behavior of wax pattern distortion and to reveal its mechanism, the following experiments have been conducted: measurements of fundamental properties including distribution of molecular weight, crystal structure, phase transition, and viscosity, and investigation of the crystal orientation and recovery phenomena. If the wax is deformed plastically at higher temperatures, transformation appears to be a smooth transition from an isotropic distribution of the crystal orientation to an arranged structure. In the case of uniaxial compression, the c-axes are rearranged parallel to the compressed direction and the b-axes and a-axes are randomly oriented in the plane normal to the c-axes. This preferred orientation is due to the crystal rotation. The degree of preferred orientation increases with the increase in compression ratio over all temperatures between 35 degrees C and 55 degrees C. Above 45 degrees C, the degree of orientation decreases with an increase in temperature despite the equal compression ratio. From this fact, the degree of orientation is associated with the crystallinity at deformation temperatures as well as the degree of deformation. The preferentially oriented specimen expands greatly in the direction parallel to the molecular chain axis and shrinks to a great extent in the direction perpendicular to the chain axis. This anisotropy is caused mainly by the recovery. Moreover, the extent of recovery is associated closely with the degree of the preferred orientation. The dimensional change due to the recovery is extraordinarily large (30 to 40%) in comparison with the normal thermal expansion from room temperature to 45 degrees C (approximately 1.2%). This large extent of recovery is explained by the rubber-like deformation in the amorphous region.