Thermoformability analysis of TPO sheets blended with postindustrial secondary feedstock

Abstract

Production scrap is a significant cost for automotive thermoforming due to the expensive resin costs and large part sizes. Manufacturers strive to regrind and reprocess sheet cutouts from production runs, however, the utilization of a secondary feedstock can be limited by its impact on the sheet processing behavior. To mitigate the economic impact of production scrap, the thermoformability of a blend needs to be predicted at the material development stage. In this work, a test mold is designed to assess the thermoformability of blended TPO sheets. The mold design is developed to evaluate the effects of different geometries. Regrind content is introduced in the blend before extrusion to compare the sheet properties to those of a virgin material configuration. The statistical analysis of the thermoforming experiments shows that the sheet thickness reduction is affected by the draw ratio and sheet temperature. Multivariate regression modeling allows for predicting the thermoformed part thickness as a function of the sheet configuration, draw ratio, and processing conditions. However, the introduction of regrind content, below 50%, did not affect thermoformability. The stretchability of the sheets was also characterized by uniaxial tensile testing and dynamic mechanical analysis, confirming the absence of negligible differences when regrind content is introduced in the blend.

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