Exfoliating agents for skincare soaps obtained from the crabwood waste bagasse, a natural abrasive from Amazonia

Abstract

Many personal cleansing products contain microplastics threatening coastal habitats, deep sea, as well as freshwater lakes. Non-pollutant biomasses with natural abrasiveness are potential substitutes for scrub-type cosmetics. This study sought to explore the potential of applying crabwood seed bagasse from Amazonia as an exfoliating agent of skincare soaps. The raw feedstock was characterized by chemical composition and particle size distribution. The morphologies of the crabwood particles and commercial exfoliating agents were compared. Thermal pretreatments were carried out in an attempt to make the particles inert. It was verified that crabwood particles contain above 50% of non-structural organic components in their mass. The high heterogeneity of particle size allowed selecting portions with dimensions comparable to commercial products, between 0.3 and 0.4 mm. The rough surface of crabwood particles was similar to those of other natural plant exfoliating agents suitable for intense skin exfoliation. Thermal pretreatments only partially volatilized non-structural components. The release of oil traces, which contains mainly palmitic and oleic acids, led the pH of the water to an unacceptable level (≤ 5.0), discouraging the direct application of crabwood bagasse in the skin. Nevertheless, when added to non-ionic surfactant based-soaps, pH remains adequate for skincare (≈ 6.0). The smaller particles (average diameter of 0.3 mm) submitted to the most drastic thermal pretreatment, 140 °C for 48 h of exposure, resulted in liquid skincare soaps with better properties. The crabwood particles’ potential to be added as an exfoliating agent in skincare soaps was confirmed.