Gluten Protein-Based Microcellular Foams and Composites: Development and Functional Properties

Sammanfattning: Most common foams are produced from non-renewable resources (e.g., synthetic plastics),with a number of environmental concerns, hence there is a demand for alternative bio-derivedfoam materials. Wheat gluten protein is widely known to have excellent foaming properties(e.g., in bread making) and is a possible alternative resource for making foam products.Gluten foams were produced using a lyophilization process (freeze-drying) and variousgluten/water-based mixtures were studied. Foams with varying properties were obtained bymixing various amounts of wheat gluten with glycerol (plasticizer) and bacterial cellulosefibers (reinforcement). The gluten foams looked like bread with a beige color and few visuallydetectable surface pores. They were generally characterized as having an open cell structurewith a porosity in the range 75-85% and pore sizes ranging between 20 and 73 ?m. Differentmechanical properties were obtained by using varying gluten concentrations and the differentadditives. Plasticizing with glycerol lead to increased flexibility of the foams, with the abilityto recover up to 95% after being compressed by 80%. By reinforcing with bacterial cellulosefibers the material became stiffer, with an increased elastic modulus. Confocal lasermicroscopy revealed that the fibers and gluten interacted. Analyzing the protein structure ofthe foams revealed that the different additives resulted in structures with different proteinpatterns. The samples containing glycerol were more polymerized and less extractable in SDS,whereas the fiber containing samples were only polymerized in small regions and easilyextracted in SDS. Generally the gluten foams had low conductivity values, with some valuesbelow 0.05 W/(m K), which was found to be dependant on density and pore structure. Glutenfoams were also shown to be more difficult to ignite when compared to other conventionalfoams. It was further observed that the foams did not drip making it increasingly difficult forthe fire to spread.