Packaging Temperature-Sensitive Products

Chromogenic materials change color or transparency depending on temperature, electrical voltage, pressure or exposure to light. In thermochromic materials, a pre-determined temperature change triggers this change in color. For example, in the food industry, thermochromic packaging can reveal whether the refrigeration chain has been interrupted. The temperature-sensitive additives used in this application are currently only available on the market as oil-based pigments.

The Chromogenic Polymers department at the Fraunhofer Institute for Applied Polymer Research IAP, Potsdam-Golm, Germany, is currently focusing research on the development of bio-based thermochromic plastics. These materials have a high market potential when used in films for packaging temperature-sensitive products in the medical, pharmaceutical and food industries.

"In particular bioplastics – which will play a major role in day-to-day life in the future – lose their bio-based status when commercially available thermochromic dyes are added. Our department has already demonstrated that the idea of thermochromic bioplastics can work. This is why we would like to use renewable raw materials when developing these materials for various applications," explains Department head Dr. Christian Rabe.

The introduction of thermochromic properties into commodity polymers – thermoplastics, thermosets, elastomers, lacquers and coatings – is one feature of the current work. In this context, it is the researchers' goal to retain the material properties relevant to the application. This requires thermochromic additives which are stable in the polymer matrix as well as during the manufacturing processes with their strongly differing demands:
heat and mechanical impact during the extrusion of plastics,
thermal and chemical impact during the curing of thermosets or crosslinking of elastomers, and
attack of solvents and other chemicals during the drying and curing of lacquers and coatings.

A further functionalization of polymeric materials will enhance their use and broaden their range of possible applications. The R&D work of the Fraunhofer IAP meets the growing interest of industrial applicants in the field of chromogenic materials.