• Grønborg, Frederik
• Spangenberg, Jon
• Daugaard, Anders Egede
• Susoff, Markus Lothar
• Pedersen, David Bue

Abstract

This study explores the influence of mold temperatures below 60°C on thermoplastic polyurethane (TPU) properties during injection molding, focusing on phase separation and its impact on mechanical, thermal, and viscoelastic properties. Using a combination of micro-indentation, temperature scanning stress relaxation, and conventional characterization methods, the research highlights how increased mold temperatures promote more distinct phase separation, enhancing mechanical stability and physical properties. The novel use of micro-indentation revealed a gradient in material stiffness from the surface to the core of injection-molded samples, attributed to differential cooling rates and shear forces, which affect phase separation and crystallinity of the hard domains. These insights are critical for applications requiring specific surface properties and underscore the importance of understanding the interplay between chemical composition and processing conditions for optimizing TPU properties. Furthermore, the paper shows that tensile testing, differential scanning calorimetry, and Shore hardness cannot quantify the effects of mold temperatures below 60°C. The research highlights the influence and importance of chemical composition, rheological history, and thermal history on the properties of TPU.

Topics

• surface
• phase
• chemical composition
• differential scanning calorimetry
• injection molding
• thermoplastic
• crystallinity
• shore hardness