Sustainable Wheat Protein Biofoams: Dry Upscalable Extrusion at Low Temperature

Biodegradation, Bioassimilation and Recycling Properties of Wheat Gluten Foams

Protein-based foams are potential sustainable alternatives to petroleum-based polymer foams in e.g. single-use products. In this work, the biodegradation, bioassimilation, and recycling properties of glycerol-plasticized wheat gluten foams (using a foaming agent and gallic acid, citric acid, or genipin) were determined. The degradation was investigated at different pH levels in soil and high humidity. The fastest degradation occurred in an aqueous alkaline condition with complete degradation within 5 weeks. The foams exhibited excellent bioassimilation, comparable to or better than industrial fertilizers, particularly in promoting coriander plant growth. The additives provided specific effects: gallic acid offered antifungal properties, citric acid provided the fastest degradation at high pH, and genipin contributed with cross-linking. All three additives also contributed to antioxidant properties. Dense β-sheet protein structures degraded more slowly than disordered/α-helix structures. WG foams showed only a small global warming potential and lower fossil carbon emissions than synthetic foams on a mass basis, as illustrated with a nitrile-butadiene rubber (NBR) foam. Unlike NBR, the protein foams could be recycled into films, offering an alternative to immediate composting.

Genipap Oil as a Natural Cross-Linker for Biodegradable and Low-Ecotoxicity Porous Absorbents via Reactive Extrusion

Proteins derived from agroindustrial coproducts and a natural cross-linking agent (genipap oil containing genipin) were used to develop porous materials by reactive extrusion for replacing fossil-based absorbents. Incorporating genipap oil allowed the production of lightweight structures with high saline uptake (above 1000%) and competing retention capacity despite their porous nature. The mechanical response of the genipap-cross-linked materials was superior to that of the noncross-linked ones and comparable to those cross-linked using commercial genipin. The extruded products were hemocompatible and soil-biodegradable in less than 6 weeks. The compounds generated by the degradation process were not found to be toxic to the soil, showing a high bioassimilation capacity by promoting grass growth. The results demonstrate the potential of biopolymers and new green cross-linkers to produce fully renewable-based superabsorbents in hygiene products with low ecotoxicity. The study further promotes the production of these absorbents using low-cost proteins and continuous processing such as reactive extrusion.

Proteins for Applied and Functional Materials

Shifting from a petroleum-based plastic society to a newer one built on circular economy principles requires maximizing the use of renewable resources and resolving the challenges that come with their use. Biopolymers have taken an important role in the design of biobased materials with functional properties, especially those derived from biomass available at a large scale. A number of recent studies have shown how proteins have a new dimension in developing functional materials, taking a step forward from their traditional use in food and biomedicine. Correlating the amino acidic profile of proteins at the nanoscale with their thermomechanical properties at the macroscale enables us to translate these precision polymers into a versatile design of materials, targeting large-scale applications such as foams and food packaging. Moreover, the advances in understanding proteins from a bottom-up perspective reached promising achievements for their use in applications that were not foreseen before, including biosensors, optoelectronics, and semiconductors.

Effects of multi-functional additives during foam extrusion of wheat gluten materials

To broaden the range in structures and properties, and therefore the applicability of sustainable foams based on wheat gluten expanded with ammonium-bicarbonate, we show here how three naturally ocurring multifunctional additives affect their properties. Citric acid yields foams with the lowest density (porosity of ~50%) with mainly closed cells. Gallic acid acts as a radical scavenger, yielding the least crosslinked/ aggregated foam. The use of a low amount of this acid yields foams with the highest uptake of the body-fluid model substance (saline, ~130% after 24 hours). However, foams with genipin show a large and rapid capillary uptake (50% in one second), due to their high content of open cells. The most dense and stiff foam is obtained with one weight percent genipin, which is also the most crosslinked. Overall, the foams show a high energy loss-rate under cyclic compression (84-92% at 50% strain), indicating promising cushioning behaviour. They also show a low compression set, indicating promising sealability. Overall, the work here provides a step towards using protein biofoams as a sustainable alternative to fossil-based plastic/rubber foams in applications where absorbent and/or mechanical properties play a key role.

Porous Thermoformed Protein Bioblends as Degradable Absorbent Alternatives in Sanitary Materials

Protein-based porous absorbent structures can be processed and assembled into configurations suitable for single-use, biodegradable sanitary materials. In this work, a formulation based on a mixture of proteins available as industrial coproducts is processed into continuous porous structures using extrusion and assembled using conventional thermal methods. The experimental design led to formulations solely based on zein-gluten protein bioblends that could be manufactured as liquid absorbent pellets, compressed pads, and/or porous films. The processing versatility is attributed to the synergistic effect of zein as a low viscosity thermoformable protein with gluten as a readily cross-linkable high molecular weight protein. The capillary-driven sorption, the biodegradability of the materials, and the possibility to assemble the products as multilayer components provide excellent performance indicators for their use as microplastic-free absorbents. This work shows the potential of biopolymers for manufacturing sustainable alternatives to current nonbiodegradable and highly polluting disposable items such as pads and diapers.

Thermomechanical Stress Analysis of Hydrated Vital Gluten with Large Amplitude Oscillatory Shear Rheology

Vital gluten is increasingly researched as a non-food product for biodegradable materials. During processing, the protein network is confronted with increased thermal and mechanical stress, altering the network characteristics. With the prospect of using the protein for materials beyond food, it is important to understand the mechanical properties at various processing temperatures. To achieve this, the study investigates hydrated vital gluten under thermomechanical stress based on large amplitude oscillatory shear (LAOS) rheology. LAOS rheology was conducted at increasing shear strains (0.01-100%), various frequencies (5-20 rad/s) and temperatures of 25, 45, 55, 65, 70 and 85 °C. With elevating temperatures up to 55 °C, the linear viscoelastic moduli decrease, indicating material softening. Then, protein polymerization and the formation of new cross-links due to thermal denaturation cause more network connectivity, resulting in significantly higher elastic moduli. Beyond the linear viscoelastic regime, the strain-stiffening ratio rises disproportionately. This effect becomes even more evident at higher temperatures. Lacking a viscous contribution, the highly elastic but also stiff network shows less mechanical resilience. Additionally, at these elevated temperatures, structural changes during the protein's denaturation and network shrinkage due to water evaporation could be visualized with confocal laser scanning microscopy (CLSM).

Functionalization Routes for Keratin from Poultry Industry Side-Streams-Towards Bio-Based Absorbent Polymers

Keratin is a largely available protein that can be obtained from the ca. 3 million tons of feathers that the European poultry industry produces as a side-stream. Here, the functionalization of keratin from poultry feathers was evaluated using a one- versus two-stage process using two functionalization agents (succinic anhydride-SA and ethylene dianhydride-EDTAD). The functionalization resulted in the keratin having improved liquid swelling capacities, reaching up to 400%, 300%, and 85% increase in water, saline, and blood, respectively, compared to non-functionalized keratin. The highest swelling was obtained for samples functionalized with EDTAD (one-stage process), while the highest saline uptake was noted for samples processed with 25 wt% SA (two-stage process). Swelling kinetics modeling indicated that the water uptake by the functionalized samples takes place in two steps, and the EDTAD samples showed the highest diffusivity. It is demonstrated that the one-stage functionalization of keratin utilizing EDTAD results in better performance than two-stages, which allows for resource-saving and, thereby, protecting the environment. The results show some potential for the keratin to be utilized as liquid absorbent materials in water, saline, and blood uptake applications. Using keratin from side-streams is an advantage from a sustainability perspective over biomacromolecules that need to be extracted from virgin biomass.