EXPERIMENTAL-STUDY OF THE THERMOFORMING OF A BLEND OF STYRENE-BUTADIENE COPOLYMER WITH POLYSTYRENE

Material characterization and thermoforming studies were completed usi ng a blend of a styrene-butadiene copolymer with polystyrene used comm ercially for the production of cups and dishes. This composition was t hermoformed between 135 and 152 degrees C. Studies consisted of formin g 30-mil and 46-mil sheets at 130, 140, and 150 degrees C at three eva cuation rates in an aluminum cylindrical mold. The mold was instrument ed with a pressure transducer to follow the change in pressure during forming and two Linear Voltage Displacement Transducers, which served as mold wall contact sensors, The results indicated that the process i s extremely rapid (0.25-0.60 sec) for the high and medium evacuation r ates. The process was found to require a low pressure differential for forming (typically <4 psi). The final part thickness distribution and extension ratio data indicated that Me material stretches into the ap proximate shape of a spherical segment, contacts the bottom/center of the mold, contacts the sides, and finally stretches into the corners. The tensile strength and modulus of elasticity measurements of the fin al part were slightly less than the original sheet properties for samp les measured in the machine direction but slightly greater for samples taken in the transverse direction. However, the percent elongation at break increased significantly in both the machine and transverse dire ctions.