# FOIM: Thermal Foaming of Shape Memory Polyurethane Foil

## TL;DR

FOIM is a shape memory polyurethane foil that can transform into a foam when heated to 60°C, useful for applications needing compact transport and shape change.

## Contribution

A new semi-finished shape memory polyurethane product (FOIM) with unique thermal foaming properties is introduced.

## Key findings

- FOIM exhibits a melting peak at 45°C and crystallization at 14°C, indicating soft segment phase transitions.
- The material can switch back to foam when reheated to 60°C after being compressed into a foil at that temperature.
- The structure remains stable despite significant deformation, as shown by buoyancy and heat transmission measurements.

## Abstract

This work introduces the semi‐finished product FOIM, a neologism from FOIl and foaM, a phase segregated polyester urethane urea (PEUU) foam, which is synthesized from poly(1,6‐hexylene adipate) diol, 4,4’‐methylene diphenyl diisocyanate, polyethylene glycol and water as blowing agent. The PEUU is obtained by following a one‐shot synthesis and is characterized by a hard/soft segment ratio of 1.06 and an open pore content of 78%. Differential scanning calorimetry reveals a melting peak at 45 °C and a crystallization signal at 14 °C, both of which are associated with the phase transitions of the soft segment. The glass transition temperature, which is determined as a local maximum within the tan δ using dynamic mechanical analysis, is 1 °C. During programming, the foam is heavily compressed at 60 °C. Once unloaded at 23 °C, a translucent foil, the FOIM, is obtained. When reheated to 60 °C, the foil switches back to the foam due to its pronounced shape memory properties. Intriguingly, the structure remains largely unaffected by the drastic deformation as indicated by buoyancy and heat transmission measurements. The ease of manufacture and functionality makes the technology attractive for applications, in which both low transport volumes and drastic shape changes are desired.

This study introduces FOIM, a polyester urea urethane foil that can be foamed once if it is heated to 60 °C because of its pronounced shape memory properties. The ease of manufacture and functionality makes the technology attractive for applications, in which both low transport volumes and drastic shape changes are desired.