Revealing the Foaming Process of Gluten-Based Materials by Extrusion—Towards the Production of Sustainable Porous Plastics

Polymer foams have an important role in society due to their wide range of densities, and they are extensively used as cushioning, damping, thermal, and sound insulation materials. In 2021, ca. 29.357 thousand tons of polymeric foams were consumed, of which most is used in the packaging, building and construction industry¹. However, foams are mainly obtained from petroleum-based recourses and are not biodegradable. Thus, there is a strong motivation to develop foams using biopolymers from renewable resources for combating their environmental impact. Here, wheat Gluten proteins (WG) is an interesting biopolymer candidate due to their elasticity and foaming properties. The recently demonstrated possibility to develop WG-based foam materials using traditional polymer processing techniques (e.g. extrusion) paves an avenue to substitute conventional petrochemical foams with biopolymers.² However, challenges have raised when extruding WG, primarily because of the protein's sensibility to the high shearing forces and high temperatures, which can impact the protein network structure. Previous work has shown that extruded WG protein foams have resulted in foams having cushioning properties in a similar range as synthetic polyethylene foams².<br/>This project's main objective is to study the effect of different formulations during the extrusion of WG materials towards forming porous materials. An advantage of WG protein concentrate used is that they are obtained as co-streams from the agricultural and food industries. Sodium bicarbonate (NaHCO₃) and ammonium bicarbonate (NH₄)HCO₃ have been used as chemical blowing agents, which provided the extruded material with different foam morphologies. The effect of having glycerol as a plasticizer of the WG has also been studied. Scanning Electron Microscopy has revealed that the most optimal formulation resulting in extruded WG foam structure is based on the use of ammonium bicarbonate (5 wt%). The possibility of producing porous materials using biodegradable and renewable resources is foreseen as an important environmental contribution to replacing petroleum-based foams.<br/>¹Smithers (2021). The future of polymer foams to 2026. Retrieved from https://www.smithers.com/services/market-reports/materials/the-future-of-polymer-foams-to-2025<br/>²George. A; Lacoste. C.; Damien. E . (2018). Effect of formulation and process on the extrudability of starch-based foam cushions. Industrial Crops & Products, 306-314.