Experimental study of the thermoforming of a blend of styrene‐butadiene copolymer with polystyrene

Abstract

AbstractMaterial characterization and thermoforming studies were completed using a blend of a styrene‐butadiene copolymer with polystyrene used commercially for the production of cups and dishes. This composition was thermoformed between 135 and 152°C. Studies consisted of forming 30‐mil and 46‐mil sheets at 130, 140, and 150°C at three evacuation rates in an aluminum cylindrical mold. The mold was instrumented 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 is extremely rapid (0.25–0.60 sec) for the high and medium evacuation rates. 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 the material stretches into the approximate 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 final part were slightly less than the original sheet properties for samples 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 directions.