A Comparison of Ester- and Ether-Based Bio-TPUs With Regard to Their Resistance to Environmental Influences in Terms of Their Mechanical and Adhesive Properties

The demand for bio-based alternatives to fossil-based plastics is growing rapidly due to the increasing environmental awareness of consumers and manufacturers, as well as the goal of carbon-neutral production. There are many promising alternatives that can be obtained from various renewable resources, but their use in series production, especially of technical components, is often hampered by doubts about their usability and, above all, their resistance to environmental influences. The present study is intended to help overcome these obstacles and demonstrate the applicability of bio-based TPUs in multi-component technical parts with high bonding requirements. Different polyester and polyether TPUs were used, and their resistance to elevated temperatures and humidity was compared. Both the mechanical properties and the bond strength in bio-based hard-soft composites were investigated. It was shown that good to very good bond strengths of approximately 2.5–8 N/mm could be achieved depending on the Shore hardness. The formation of adhesive forces depends on both the type of polyol and its proportion in the TPU. While ether-based TPU exhibited higher adhesive bond strengths, the strength increases with a higher proportion of soft segments. After storage tests, a decrease in bond strength was observed, mainly due to thermal aging effects and absorption of water molecules, correlating with the change in mechanical properties.