Developing biodegradable menstrual products using co-stream proteins as a material alternative to fossil counterparts presents a significant environmental advantage across their entire value chain. The intrinsic properties of wheat gluten foams derived from wheat starch production have been validated with respect to their potential as absorbent core layers in disposable sanitary pads, which is relevant to the rising demand for eco-friendly disposable sanitary pad alternatives. Here, we report the fabrication of a gluten-porous absorbent layer and evaluate its liquid absorption properties and mechanical stability under relevant operating conditions compared to a commercial absorbent foam layer used in sanitary pads. The porosity was achieved using sodium and ammonium bicarbonate, which are non-toxic and food-grade blowing agents, and the materials were shaped/foamed using a conventional oven. The use of sodium bicarbonate resulted in a more homogeneous and lower-density foam with smaller pores than with ammonium bicarbonate. The developed prototypes show comparable mechanical properties under compression to foams used in commercial pads, retaining up to 95% of their initial shape after 3 h of compression. Moreover, the foamed structure permitted a liquid uptake of saline and blood of 4.5 g g−1 and 1 g g−1, respectively, with the possibility to absorb up to 1.5 g g−1 of saline under load. The results indicate that the choice of blowing agent has a large impact on the performance of gluten pads under constant pressure. It is thereby demonstrated here that protein-based foams have adequate mechanical and absorption properties that make them interesting for their future use as the absorbent layer in sanitary products following a circular economy model.

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 beta-sheet protein structures degraded more slowly than disordered/alpha-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.

In this thesis, the production of bio-based and biodegradable foams from wheat proteins (wheat gluten) is presented. Wheat gluten, a side stream from the ethanol/starch industry, was processed using both batch and continuous foaming methods. To produce the foams, glycerol, an effective protein plasticiser, was used, with two foaming agents common in food: sodium bicarbonate (SBC) and ammonium bicarbonate (ABC), to generate soft foams with both closed-and open-cell structures. ABC proved to be a better foaming agent in foam extrusion than SBC, but SBC performed well in the batch methods. Due to ABC’s low decomposition temperature, extrusion could take place at a temperature as low as 70 °C.

     Three different multifunctional additives (citric acid, gallic acid and genipin) were also used to influence and improve the foam properties. The mechanical properties showed that some of the materials could be potentially useful in cushioning and sealing applications. The foams also showed a high absorption of saline (model substance for body fluid) and blood (in the form of sheep’s blood), even under mechanical pressure. Based on these results, a wheat gluten-based product was manufactured as a proof-of-concept.

     The degradability of the foam in various relevant environments was studied. It was found that some foams degraded almost completely in soil after 8 weeks and in alkaline water after 5 weeks. It was also demonstrated that the foam also worked as a good fertilizer. As an alternative to direct composting when the foam is no longer used, the possibility of reusing the foam in a different form was evaluated. In this context, it was possible to produce plastic films from the foam.

I denna avhandling presenteras produktion av biobaserade och biologiskt nedbrytbara skum från veteproteiner (vetegluten). Vetegluten, en biprodukt från etanol-/stärkelseindustrin, bearbetades med både batch-metoder och kontinuerliga skummetoder. För att producera skummet användes glycerol, en effektiv proteinmjukgörare, tillsammans med två skumningsmedel som är vanliga inom livsmedelsindustrin: natriumbikarbonat (SBC) och ammoniumbikarbonat (ABC), för att skapa mjuka skum med både slutna och öppna cellstrukturer. ABC visade sig vara ett bättre skumningsmedel vid skumextrudering än SBC, men SBC presterade väl i batchmetoderna. Genom ABC’s låga sönderdelningstemperatur kunde extruderingen ske vid en så låg temperatur som 70 °C.

     Tre olika multifunktionella tillsatser (citronsyra, gallusyra och genipin) användes också för att påverka och förbättra skummets egenskaper. De mekaniska egenskaperna visade att vissa av materialen potentiellt kunde vara användbara i stötdämpande och tätande applikationer. Skummet visade också hög absorption av saltlösning (modellsustans för kroppsvätska) och blod (i form av fårblod), även under mekaniskt tryck. Baserat på dessa resultat tillverkades en veteglutenbaserad produkt som ett konceptbevis.

     Skummets nedbrytbarhet i olika relevanta miljöer studerades. Det visade sig att vissa skum nästan fullständigt bröts ner i jord efter 8 veckor och i alkalisk vattenlösning efter 5 veckor. Det demonstrerades också att skummet fungerade bra som gödningsmedel. Som ett alternativ till direkt kompostering när skummet inte längre används, utvärderades möjligheten att återanvända skummet i en annan form. I detta sammanhang var det möjligt att producera plastfilmer från skummet.

The production of biodegradable gluten-based protein foams showing complete natural degradation in soil after 26 days is reported, as an alternative to commercial foams in disposable sanitary articles that rely on non-biodegradable materials. The foams were developed from an extensive evaluation of different foaming methodologies (oven expansion, compression moulding, and extrusion), resulting in low-density foams (ca. 400 kg/m3) with homogenous pore size distributions. The products showed the ability to absorb 3–4 times their weight, reaching ranges for their use as absorbents in single-use disposable sanitary articles. An additional innovative contribution is that these gluten foams were made from natural and non-toxic wheat protein, glycerol, sodium and ammonium bicarbonate, making them useful as fossil-plastic-free replacements for commercial products without the risk of having micro-plastic and chemical pollution. The impact of different processing conditions on forming the porous biopolymer network is explained, i.e., temperature, pressure, and extensive shear forces, which were also investigated for different pH/chemical conditions. The development of micro-plastic-free foams mitigating environmental pollution and waste while using industrial co-products is fundamental for developing large-scale production of single-use items. A sanitary pad prototype is demonstrated as an eco-friendly material alternative that paves the way for sustainable practices in manufacturing, and contributes to the global effort in combating plastic pollution and waste management challenges, Sustainable Development Goals: 12, 13, 14, and 15.

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.

Biocomposites based on wheat gluten and reinforced with carbon fibers were produced in line with the strive to replace fossil-based plastics with microplastic-free alternatives with competing mechanical properties. The materials were first extruded/compounded and then successfully injection molded, making the setup adequate for the current industrial processing of composite plastics. Furthermore, the materials were manufactured at very low extrusion and injection temperatures (70 and 140 degrees C, respectively), saving energy compared to the compounding of commodity plastics. The sole addition of 10 vol % fibers increased yield strength and stiffness by a factor of 2-4 with good adhesion to the protein. The biocomposites were also shown to be biodegradable, lixiviating into innocuous molecules for nature, which is the next step in the development of sustainable bioplastics. The results show that an industrial protein coproduct reinforced with strong fibers can be processed using common plastic processing techniques. The enhanced mechanical performance of the reinforced protein-based matrix herein also contributes to research addressing the production of safe materials with properties matching those of traditional fossil-based plastics.

Hygroscopic biopolymers like proteins and polysaccharides suffer from humidity-dependent mechanical properties. Because humidity can vary significantly over the year, or even within a day, these polymers will not generally have stable properties during their lifetimes. On wheat gluten, a model highly hygroscopic biopolymer material, it is observed that larger/thicker samples can be significantly more mechanically stable than thinner samples. It is shown here that this is due to slow water diffusion, which, in turn, is due to the rigid polymer structure caused by the double-bond character of the peptide bond, the many bulky peptide side groups, and the hydrogen bond network. More than a year is required to reach complete moisture saturation (≈10 wt.%) in a 1 cm thick plate of glycerol-plasticized wheat gluten, whereas this process takes only one day for a 0.5 mm thick plate. The overall moisture uptake is also retarded by swelling-induced mechanical effects. Hence, hygroscopic biopolymers are better suited for larger/thicker products, where the moisture-induced changes in mechanical properties are smeared out over time, to the extent that the product remains sufficiently tough over climate changes, for example, throughout the course of a year.

Glycerol-plasticized wheat gluten was explored for producing soft high-density biofoams using dry upscalable extrusion (avoiding purposely added water). The largest pore size was obtained when using the food grade ammonium bicarbonate (ABC) as blowing agent, also resulting in the highest saline liquid uptake. Foams were, however, also obtained without adding a blowing agent, possibly due to a rapid moisture uptake by the dried protein powder when fed to the extruder. ABC's low decomposition temperature enabled extrusion of the material at a temperature as low as 70 °C, well below the protein aggregation temperature. Sodium bicarbonate (SBC), the most common food-grade blowing agent, did not yield the same high foam qualities. SBC's alkalinity, and the need to use a higher processing temperature (120 °C), resulted in high protein cross-linking and aggregation. The results show the potential of an energy-efficient and industrially upscalable low-temperature foam extrusion process for competitive production of sustainable biofoams using inexpensive and readily available protein obtained from industrial biomass (wheat gluten).