A plastic that remembers

A new thermoplastic polyurethane (TPU) developed by Bayer MaterialScience together with the BAM Federal Institute for Materials Research and Testing in Berlin, Germany, shows that plastics can also have a memory.

Parts made of such a plastic can be temporarily reshaped and fixed in this shape. When heated to a certain temperature known as the switching temperature, they ‘remember’ their original shape and return to it virtually unchanged. In the case of the new product Desmopan® DP 2795A SMP, the switching temperature is approximately 40°C. The abbreviation SMP stands for the English designation for such plastics: Shape Memory Plastics.

"Given this special property, there are virtually no limits to the potential applications for the plastic," says Jürgen Hättig, Head of Business Development for TPU at Bayer MaterialScience. "We can imagine applications in areas ranging from mechanical engineering and the automotive, textile, sports and leisure industries to toy manufacturing and aerospace engineering." Possible applications include the easy repair of damaged bodywork parts using a hair dryer, remote temperature sensors, artificial muscles, hinges, self-loosening screws, packaging and shrink tubing.

Self-erecting film tunnels for agriculture
The two partners recently submitted a patent application for a possible application in the area of functional film tunnels and self-erecting structures. Film tunnels in a field act like greenhouses and accelerate the growth of lettuces and vegetables so that these can be harvested sooner than is possible if allowed to mature in the ‘classic’ manner under the open sky. While it is easy to lay flat films on a field, erecting a permanent tunnel with films can be a time-consuming and costly operation.

This is an opportunity for the new shape memory polymer. Profiles made of the new TPU plastic that have temporarily been brought into a flat shape are fastened to the transparent film. After the film has been laid on the bed, all that’s left to do is to heat the profiles to the switching temperature. They ‘remember’ their bent, permanent shape and pop up to form a half-tunnel, lifting the films with them. The mini-greenhouses are then ready for use.

Counterfeit-proof labels with QR codes
The new material could also prove useful in product and brand protection applications. The BAM has used the TPU product to develop labels with engraved and colored quick response (QR) codes. The codes can only be read if the labels are in their permanent shape. "The labels are thus very well suited as a means of storing information to mark and identify products in a way that is very difficult to counterfeit," says Dr Thorsten Pretsch, Head of the BAM department for the investigation of shape memory polymers. The project for labels with switchable readability is funded by the German Ministry of Education and Research.

Because the TPU material is free from plasticizers and antihydrolysis agents, it is also suitable for food contact applications. It also boasts all the typical advantages of TPU, such as high abrasion resistance, flexibility and good chemical resistance.