Structure-property relationships of thermoformed products based on recyclates

Thermoforming is very sensitive regarding the used material especially when it comes to recycled materials. With the “design from recycling” approach and the consideration of a multilayer structure, post-consumer polypropylene recyclates (rPP) could be used for thermoformed cups/containers. Due to insufficient sorting techniques, the problem of cross-contamination with the respective other polyolefin polyethylene (PE) occurs in rPP. It has been evaluated that the remaining PE content is strongly influencing the properties of thermoformed products. While it can be assumed that there is a positive impact on toughness, properties like the stackability or the shrinkage of the cups will be negatively affected. Therefore, methods for characterization of the PE content have been used for developing correlations allowing for quality control in the production. Several correlations have been found which enable the prediction of product properties by only testing input material properties. Thermal characterization methods are sensitive to the PE content and were hence used to predict the shrinkage profile of the thermoformed product. The results show the importance of structure-property relationships and illustrate the possibility of process adjustments based on a profound material understanding.