Advances in the Use of Protein-Based Materials: Toward Sustainable Naturally Sourced Absorbent Materials

Abstract

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.

High Capacity Functionalized Protein Superabsorbents from an Agricultural Co‐Product: A Cradle‐to‐Cradle Approach

“…The average water uptake by the WG25ED4GEN sample was 24 and 36 g g −1 after 30 min and 24 h immersion, respectively (Figure 1a), representing the highest reported swelling for WG‐based superabsorbent materials. [ 1 ] In contrast, the addition of GEN before EDTAD (WG4GEN25ED) led to a material that reached only 8 g g −1 of water absorption (Figure 1a). The uptake was, however, slightly higher than that for WG4GEN (only 4 wt% GEN), which was expected as GEN will extensively cross‐link the protein molecules mainly through the lysine groups.…”

“…Proteins have been demonstrated as a natural raw material for the production of superabsorbent polymers (SAP). [ 1,2 ] The richness of different functional groups along the protein molecular chains and the fact that the proteins are available as co‐products from the agricultural industry make them attractive in SAP applications for replacing their petroleum‐based counterparts. The diversity of the protein constituents also makes them interesting as compared to other natural polymers such as polysaccharides.…”

“…[ 3–10 ] The chemical modification of proteins via acylation has here been acknowledged as one of the more promising techniques for the functionalization of proteins toward superabsorbency. [ 1,3,5,11–15 ] The derived charged carboxylic acid groups in the polypeptide chains, from the use of ethylenediaminetetraacetic dianhydride (EDTAD), has resulted in dried protein materials with a swelling capacity sufficient to replace petroleum‐based SAP. [ 3 ] EDTAD is used as an acylation agent due to its high reactivity from dilute aqueous solutions, in addition to its nontoxic nature.…”

“…[ 26 ] At the same time, it has however been demonstrated that the swelling kinetics of the WG system can be modified by the addition of protein cross‐linkers. [ 1,2,27 ] Here, aldehyde cross‐linking agents for proteins have been used although they are regarded as toxic, e.g. glutaraldehyde, which accordingly does not make them the preferred choice in the targeted application area for SAPs in human daily‐care products.…”

Gallic acid-functionalized graphene hydrogel as adsorbent for removal of chromium (iii) and organic dye pollutants from tannery wastewater

“…[18][19][20] For the removal of both Cr(III) ions and organic dyes from tannery wastewater, adsorption has proved to be an attractive disposal technique based on its low cost, simplicity of operation and recycling of the adsorbent. [21][22][23][24] However, most traditional adsorbents, including polymeric resins, 25 activated carbon, 26 silica, 27 and metal oxides, 28,29 usually suffer from either low adsorption capacity or low efficiency. Over the past decade, freestanding graphene hydrogel (GH), fabricated by self-assembly of reduced GO sheets through p-p interactions, has attracted much attention as a super adsorbent for wastewater treatment, due to its unique properties, such as three-dimensional (3D) porous network structure, large surface area, low density, chemical stability and aromaticity.…”