Abstract
Natural cork stopper manufacturing produces a significant amount of cork waste, which is granulated and combined with synthetic glues for use in a wide range of applications. There is a high demand for using biosourced polymers in these composite materials. In this study, xanthan gum (XG) and chitosan (CS) were investigated as possible natural binders for cork. Xanthan gum was oxidized at two different aldehyde contents as a strategy to improve its water resistance. This modification was studied in detail by 1H and 13C nuclear magnetic resonance (NMR), and the degree of oxidation was determined by the hydroxylamine hydrochloride titration method. The performance of the adhesives was studied by tensile tests and total soluble matter (TSM) determinations. Xanthan gum showed no water resistance, contrary to oxidized xanthan gum and chitosan. It is hypothesized that the good performance of oxidized xanthan gum is due to the reaction of aldehyde groups—formed in the oxidation process—with hydroxyl groups on the cork surface during the high temperature drying. Combining oxidized xanthan gum with chitosan did not yield significant improvements.
Highlights
Cork is a natural and renewable material with a unique combination of properties, such as elasticity, resilience, impermeability, low density, and very low conductivity of heat, sound and vibration [1]
Xanthan gum (XG) from Xanthomonas campestris was purchased from Sigma Aldrich, St
After periodate oxidation and dialysis, the product was subject to hydroxylamine hydrochloride
Summary
Cork (bark of Quercus suber L.) is a natural and renewable material with a unique combination of properties, such as elasticity, resilience, impermeability, low density, and very low conductivity of heat, sound and vibration [1]. Most of these properties arise from its distinctive structure. Cork waste from wine bottle stopper manufacturing is granulated and combined with a polyurethane adhesive to form an agglomerated material with many uses. These include the so-called technical cork stoppers and agglomerated cork panels for insulation or decorative uses. Cork granules can be used in other types of composite materials; for instance, as fillers in epoxy adhesives, allowing for density reduction and impact energy absorption [7,8]
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