Expanding and recycling a water-resistant bioderived rigid foam using CO2-responsive amines and carbonated water

Abstract

Rigid foams such as expanded polystyrene (EPS) packing have become common when transporting or storing valuable items. EPS is an inexpensive, lightweight, and robust protective material that can be easily moulded into a desired shape. Economically, EPS is an excellent choice for packaging; however, it puts a significant strain on the environment. It is made from petrochemicals, uses smog-forming organic solvents as blowing agents, and is rarely recycled because it is expensive to recycle. Biobased foams have been developed to try and mitigate the environmental impacts of EPS production and end-of-life but have poor water resistance during use, which is a key feature in packaging. We have developed a rigid foam material from vanillin that addresses the environmental issues of EPS and the lack of water resistance of current biobased foams. Adding a tertiary amine group to a vanillin-derived polymer made it possible for the polymer to be CO₂-responsive, as polymers containing tertiary amines can alter their properties in the presence or absence of CO₂ and water. This CO₂-responsive feature allowed the polymer to be hydrophobic during use but dissolve in carbonated water at the end of life. The dissolved polymer in carbonated water can be re-expanded back into a foam by rapid heating, which allows the polymer to have improved recyclability compared to EPS and avoid organic solvent blowing agents. This bioderived CO₂-responsive rigid foam can be recycled back into new rigid foam materials with a 98% material recovery efficiency. Recycling had an impact on the foam mechanical properties but the foam maintained water resistance even after 5 recycling cycles. A bioderived CO₂-responsive rigid foam such as this may, after further development, be a greener substitute for EPS packing materials.