Scientists Develop Self-Foaming Non-Isocyanate Polyurethanes Using Biowaste Fillers

Regulatory constraints have led to a growing interest in non-isocyanate polyurethanes, while the push for sustainability means there is a desire to increase the renewable content of plastics, including PU. Now, scientists in Italy, Belgium and France have developed isocyanate-free liquid formulations containing biofillers that can self-foam.

They investigated the potential of a variety of different biofillers sourced from waste streams, including lignin derivatives, proteins and polysaccharides. These were incorporated into isocyanate-free PU formulations, comprising CO2-based poly(cyclic carbonate)s, diamines and a catalyst.

The systems contained up to 30% by weight of biofillers. They were foamed at 100°C with no external foaming agent being added. They found that the moisture that is naturally present in the biofillers was able to partially hydrolyse the cyclic carbonates, creating CO2 as a blowing agent. Even at 1% by weight, the biofiller was able to stabilise the cells as they grew, leading to homogeneous foams.

They discovered that the nature of the biofiller had no significant effect on the density or morphology of the foam. However, there was a substantial difference in mechanical properties. For example, 10% keratin gave a rigid foam with a compression modulus of 21.9%, while including chitosan resulted in a much more flexible foam, with compression modulus of 0.2MPa.

Furthermore, initial investigations showed that the presence of biofiller did not prevent the foams being recycled into films via hot pressing. The researchers also suggested that any biowaste containing a degree of moisture can act as moisture reservoirs to initiate the foaming.

Source: Urethanes Technology