Surface chemical modification of thermoplastic starch: reactions with isocyanates, epoxy functions and stearoyl chloride

Thermoplastic starch (TPS) films plasticized with 20 and 30 wt.% of glycerol were treated with various reagents in order to make their surface less sensitive to moisture. Phenyl isocyanate (PhNCO), a phenol blocked polyisocianate of trimethylol propane and toluene diisocyanate (TMP-TDI-Phenol), a styrene-co-glycidyl methacrylate (PS-GMA) co-polymer and stearoyl chloride (StCl) were used for these superficial chemical modifications. Two reaction procedures were adopted, viz., suspension at room temperature or under reflux and dipping in the reactant solution followed by heating. The treated films were characterized by contact angle measurements, from which the corresponding surface energies were calculated in terms of, polar and dispersive components. In all instances, the polar contribution was drastically reduced by the treatment, indicating that the surfaces had become more hydrophobic. The most effective treatment was achieved with phenyl isocyanate in xylene. The dipping + heating treatment seems to be the most appropriate procedure for practical applications.