Insights on the properties of physically and chemically treated grape stalks

Abstract

This study evaluated the effects of heat treatment and mercerization on the properties of grape stalks, a residue of the wine industry. Stalks were submitted to six different treatment combinations and evaluated. It was observed an increase in cellulose and ash contents and a decrease in lipids and lignin contents for the mercerized samples. Although these samples have not presented pronounced chemical composition changes, significant water absorption capacity differences of stalks physically treated were observed. Mercerization increased the fiber surface roughness and damaged the central lumen of the stalks, as shown by SEM images. Chemical treatments decreased the thermal stability of stalks once the accentuated degradation started in lower temperatures; physical treatment increased stalks' thermal stability. The antimicrobial activity of grape stalks against Staphylococcus aureus was proved once inhibition halos were observed, especially for the stalks physically treated without water immersion, not mercerized. The opposite behavior was registered against the Escherichia coli, for which none of the samples showed inhibition halo. From the results, the incorporation of modified stalks in polymeric, geopolymeric, and water-based matrices could be considered a promising proposal to improve the properties of the biocomposites, generating new and sustainable materials with daily life applications in packaging, aerospace, automotive, and construction industries.