Starch benzoylation in supercritical CO2. A novel sustainable route towards biodegradable hydrophobic polymeric materials

Abstract

Starch is one of the best candidates to replace non-renewable plastics thanks to its plentiful availability in nature, and low cost. Food industry produces large amount of starch-containing waste, which are not utilizable as nutrients, therefore have potential for non-food applications. However, some of the physicochemical characteristics of starch, such as low thermal stability and high hydrophilicity are undesirable for many applications. Supercritical CO2 is an attractive alternative media for the chemical modification of starch due to its unique tuneable properties, non-toxicity and reduced cost. In this study we performed the benzoylation of starch using vinyl benzoate via a base-catalysed transesterification reaction in supercritical CO2 employing different reaction conditions (temperature, pressure, reaction time, reagents feed) obtaining a wide range of degrees of substitution (0.01-3.00), as determined via elemental analysis and NMR. The modified starches were fully characterized (FT-IR, TGA, DSC, SEM, contact angle, rheology), revealing an overall increased hydrophobicity and improved thermal stability while retaining most of their biodegradability potential. To the best of our knowledge, this is the first report of benzoylation of starch in supercritical CO2 (scCO2), paving the way for the industrial application of this novel solvent in the hydrophobization of starches.