(pressebox) (Würzburg, 14.01.2026) Polypropylene recyclates are becoming increasingly important, especially in long-lasting applications. To ensure their reliability, the SKZ Plastics Center is working on a new testing method based on the Strain Hardening Test (SHT).

A quantitative assessment of material quality is crucial for the use of polypropylene recyclates. In particular, the failure mechanisms relevant to polyolefins must be taken into account—above all, stress crack resistance, i.e., a material's ability to resist slow crack growth. The strain hardening test (ISO 18488) is already established for virgin polyethylene in pipe applications.

On this basis, the SKZ is launching a two-year research project to develop a comparable, easy-to-use method for polypropylene recyclates. Initially, recyclates will be simulated by mixtures of materials with known properties. “Our main focus is on the dependence of the test results on mixture proportions and ratios,” explains Britta Gerets, Senior Engineer at SKZ.

The method will then be validated on post-industrial (PIR) and post-consumer (PCR) recyclates. In addition, the extent to which stress crack resistance can be improved by the targeted addition of virgin material will be investigated.

Interested parties can contact the research team via the SHT_PP-Rezyklate project page or by email.

The IGF project “SHT_PP-Rezyklate” of the research association FSKZ e. V. is funded by the German Federal Ministry for Economic Affairs and Energy (BMWE) as part of the program for the promotion of industrial joint research (IGF) on the basis of a resolution of the German Bundestag (FKZ: 01IF24200N).

Über SKZ - Das Kunststoff-Zentrum: The SKZ is climate protection company and a member of the Zuse Association. This is an association of independent, industry-related research institutions that pursue the goal of improving the performance and competitiveness of industry, especially SMEs, through innovation and networking.