Biosourced spherical microbeads from brewer's spent grain for sustainable personal hygiene products

Abstract Many countries have recently banned the production and importation of petrochemical plastic microbeads for use as exfoliating agents in personal care products. Plastic particles in products of this nature are too small to be retrieved during wastewater treatment and they accumulate in the environment, negatively impacting living organisms and ecosystems. Sustainable alternatives that offer comparable mechanical properties to synthetic plastic microbeads could be developed using biowaste material. Brewer's spent grain (BSG), the primary residue of the brewery industry, is shown herein to be a promising starting material in the development of biodegradable, nontoxic microbeads. After dilute acid hydrolysis, pretreated lignocellulosic pulp from BSG is solubilized using an aqueous system of NaOH and ZnO. Solid microbeads may then be formed by dropping the resulting solution into an acid bath, filtering, and drying. The conditions of each step required optimization to successfully produce spherical microbeads with a mean diameter as small as 1.25 mm, a homogeneous size distribution, and an average hardness of 199 MPa. The beads also demonstrated superior cleansing abilities to commercially available natural exfoliating particles. BSG microbeads are therefore a promising option for use as a physical exfoliating agent in various personal hygiene products.