Sustainable Sanitary Products from Cellulose/Protein Composites—Challenges and Approaches

The market for sanitary products is exponentially increasing, reaching over 130 billion USD in 2019. Despite the pandemic, the sanitary industry continued to grow and got net sales of around 7.8 % in the first quarter of 2020 compared with the corresponding period during 2019. About 50% of this market accounts for diapers (adults and babies), and a conservative estimate results in 20 million tons/year waste. A critical aspect is that these sanitary products are single-use and consist of &gt;70% non-biodegradable plastics. The non-biodegradable petroleum-based hygiene products consist of superabsorbent polymer SAP (30 % of the total dry weight) and nonwoven polyethylene/polypropylene (PE/PP) fibers. The material research has focused on decreasing the environmental impact of these products using bio-based PE/PP, which are still non-degradable. At the same time, the absorbent component polymer (SAP) still originates from fossil-based resources. The limited sustainability of the current sanitary products and the growing demand have promoted biobased and sustainable polymeric alternatives in these materials, including the SAP.<br/>We have established a protocol to produce an absorbent and porous sanitary pad article manufactured with protein as the primary protein matrix, using industrial processing techniques (e.g., extrusion + compression molding). The so far performed test at industrial partners has shown that the product resembles properties of a commercial reference product. The results revealed that the porosity and liquid performance were improved compared to techniques found in our previous related works. The bio-based product could even be colored using simple techniques, complying with industrial requirements to commercially such products. A conclusion reached is that the best performing protein matrix was gluten protein, while other protein matrixes (3 tested) showed slightly less mechanical performance. However, one limitation associated with the use of gluten is their amino-acidic profile, which is low lysine as charged amino acid residue, leading to a swelling performance of ca. 40 % compared to the synthetic absorbent core extracted from the commercial sanitary pad. At the same time, the product by itself cannot carry on enough liquid absorption (urine and blood) to compete with other critical hygienic articles in the market, e.g., incontinence/diaper products. An additional limitation of gluten matrixes is that their thermal processing is challenging, and the formation of the porous structure (responsible for the liquid uptake) is non-homogenous. Here, cellulose has been used as a bio-based filler to provide controlled formation of pores in the protein matrixes while increasing the product's mechanical properties and their liquid swelling performance. Our suggested sanitary article has shown biodegradation up to 50% in regular soil after 15 days, whereas the commercial material did not show biodegradability even after 95 days of soil exposure.<br/>Using renewable resources to mass-produce a sustainable thermal processed sanitary article is suggested as a potential alternative to commercial non-sustainable components for the future hygiene industry. Using raw materials based on industrial side-streams and fillers that are innocuous to the environment is currently the only way to promote a non-polluting hygiene industry, contributing to circular bioeconomic principles and the United Nations Sustainable Development Goals 2030.