• Coronavirus pandemic have made facemasks worldwide healthcare essentials • Shortage of masks exposes medical personnel and the public to the risk of infection • Utilisation of sustainable raw materials to develop bio-based masks is needed • Electrospun and compression moulded gluten can be used to develop biobased masks • Gluten masks can be made flame retardant by adding b10 wt% of lanosol.

Superabsorbent polymers (SAPs) are important in the health-care and personal care industries. Products like bed pads and diapers improve the comfort and sanitary conditions for people all over the world, with SAPs reaching yearly production volumes of ca. 2 million tons. However, recent sustainability issues have questioned the high negative footprint of polymers from nonrenewable resources. Biomacromolecules, especially when functionalized, have properties that make them an attractive alternative for the production of biobased SAPs. Proteins are a particularly interesting alternative due to their high variability and because of their relatively low price, being available as side streams from the agricultural industries. Due to the harsh extraction conditions, these side stream proteins are not competing with the food industry and alternative source-effective uses are advantageous in a circular bioeconomy. As the properties of a SAP material come from a combination of neutralized functional groups to promote polar liquid uptake and intermolecular cross-links to prevent dissolution, proteins offer unique opportunities due to their variability in polymerization. An increased understanding of the protein characteristics and how these can be tuned through functionalization is therefore a prerequisite for the successful development of a commercial biobased SAP that utilizes industrial and nontoxic wastes toward more sustainable products. This review focuses on proteins as biomacromolecules with relevant characteristics for superabsorbent functions, and discusses the opportunities that they may offer toward sustainable SAPs utilizing nontoxic chemicals and following the green chemistry principles.

The development of fully natural wheat gluten foams showing rapid and high uptake of water, sheep blood, and saline solution, while maintaining high mechanical stability in the swollen state, is presented. Genipin was added as a natural and polar cross-linker to increase the polarity of the protein chains, whereas cellulose nanofibers (CNFs) were added as a reinforcement/stiffener of the foams, alone or in combination with the genipin. The presence of only genipin resulted in a foam that absorbed up to 25 g of water per gram of foam and a more than 15 g uptake in only 8 min. In contrast, with CNF alone, it was not possible to maintain the mechanical stability of the foam during the water uptake and the protein foam disintegrated. The combination of CNF and genipin yielded a material with the best mechanical stability of the tested samples. In the latter case, the foam could be compressed repeatedly more than 80% without displaying any structural damage. The results revealed that a strong network had formed between the wheat gluten matrix, genipin, and cellulose in the foam structure. A unique feature of the absorbent/foam, in contrast to commercial superabsorbents, was that it was able to rapidly absorb nonpolar liquids (here, n-heptane) due to the open-cell structure. The capillary-driven absorption due to the open-cell structure, the high liquid absorption in the cell walls, and the mechanical properties (both in dry and swollen states) of these natural foams make them interesting as a sustainable replacement for a range of petroleum-based foam materials, including absorbent hygiene products such as sanitary pads.

Functionalized wheat gluten (WG) protein particles with the ability to absorb fluids within the superabsorbent range are presented. Ethyleneditetraacetic dianhydride (EDTAD), a nontoxic acylation agent, was used for the functionalization of the WG protein at higher protein content than previously reported and no additional chemical cross-linking. The 150−550 μm protein particles had 50−150 nm nanopores induced by drying. The EDTAD treated WG were able to absorb 22, 5, and 3 times of, respectively, water, saline and blood, per gram of dry material (g/g), corresponding to 1000, 150 and 100% higher values than for the as-received WG powder. The liquid retention capacity after centrifugation revealed that almost 50% of the saline liquid was retained within the protein network, which is similar to that for petroleum-based superabsorbent polymers (SAPs). An advantageous feature of these biobased particulate materials is that the maximum swelling is obtained within the first 10 min of exposure, that is, in contrast to many commercial SAP alternatives. The large swelling in a denaturation agent (6 M urea) solution (about 32 g/g) suggests that the secondary entangled/folded structure of the protein restricts protein network expansion and when disrupted allows the absorption of even higher amounts of liquid. The increased liquid uptake, utilization of inexpensive protein coproducts, easy scalable protocols, and absence of any toxic chemicals make these new WG-based SAP particles an interesting alternative to petroleum-based SAP in, for example, absorbent disposable hygiene products.

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Protein nanofibrils (PNFs) have been prepared by whey protein fibrillation at low pH and in the presence of different metal ions. The effect of the metal ions was systematically studied both in terms of PNF suspension gelation behavior and fibrillation kinetics. A high valence state and a small ionic radius ( e.g ., Sn 4+ ) of the metal ion resulted in the formation of hydrogels already at a metal ion concentration of 30 mM, whereas an intermediate valence state and larger ionic radius (Co 2+ , Ni 2+ , Al 3+ ) resulted in the hydrogel formation occurring at 60 mM. A concentration of 120 mM of Na + was needed to form a PNF hydrogel, while lower concentrations showed liquid behaviors similar to the reference PNF solution where no metal ions had been introduced. The hydrogel mechanics were investigated at steady-state conditions after 24 h of incubation/gelation, revealing that more acidic (smaller and more charged) metal ions induced ca . 2 orders of magnitude higher storage modulus as compared to the less acidic metal ions (with smaller charge and larger radius) for the same concentration of metal ions. The viscoelastic nature of the hydrogels was attributed to the ability of the metal ions to coordinate water molecules in the vicinity of the PNFs. The presence of metal ions in the solutions during the growth of the PNFs typically resulted in curved fibrils, whereas an upper limit of the concentration existed when oxides/hydroxides were formed, and the hydrogels lost their gel properties due to phase separation. Thioflavin T (ThT) fluorescence was used to determine the rate of the fibrillation to form 50% of the total PNFs ( t 1/2 ), which decreased from 2.3 to ca . 0.5 h depending on the specific metal ions added.

The functionalization of inexpensive potato protein concentrate (PPC) is presented as a simple and easily scalable method to produce bio-based superabsorbent powders. Five nontoxic acylating agents were evaluated at different reaction temperatures for solvent-free acylation of the protein. The best results were obtained for succinic anhydride (SA) and a reaction temperature of 140 °C. These conditions resulted in efficient functionalization that provided formation of a useful network, which allowed high uptake of fluids and little material disintegration during the uptake, that is, due to protein hydrolysis during the functionalization. The SA-acylated PPC showed increased water and saline swelling capacities of 600 and 60%, respectively, as compared to untreated PPC. The acylated potato protein also showed a saline liquid holding capacity of approximately 50% after centrifugation at 1230 rpm for 3 min, as well as a significant blood swelling capacity of 530%. This blood swelling represents more than 50% of that of a commercial fossil-based superabsorbent (SAP) used for blood absorption in sanitary health products. The swelling properties of these inexpensive protein-based acylated materials highlight their potential as sustainable SAP materials (from industrial side-streams) in applications such as daily care products that are currently dominated by fossil-based SAPs.