Clay‐filled starch films. Part I: Effect of clay kind and glycerol concentration on functional properties of composites

Abstract

The aim of this work was to improve the mechanical and water barrier properties of composite films prepared from starch and clays, plasticized with glycerol at different concentrations. The effects of hydrophilic Closite Na+ and Nanomer PGV were compared with that exerted by organically modified more hydrophobic Nanofil 2 and NanoBent ZR‐1. The antimicrobial activity of composites containing hydrophobic clays was also investigated. The hydrophilic Nanomer PGV at concentrations of 5–10% increased the tensile strength (TS) of unplasticized composites, but starch‐Closite Na+ composites were too brittle to measure their mechanical properties. The hydrophobic clays did not improve the mechanical properties of the unplasticized composites. In the presence of glycerol at concentrations of 20–30%, TS of composites containing hydrophilic clays and even hydrophobic NanoBent ZR‐1 increased in comparison to plasticized films without clay. None of the clays improved the water barrier properties of the unplasticized composites, while in the plasticized composites all the clays decreased the water vapor permeability to an extent dependent on the kind and concentration of clay and glycerol concentration. Starch‐NanoBentZR‐1 composite showed very high activity against gram‐positive Staphylococcus aureus and Listeria innocua. Starch‐Nanofil 2 composites were characterized by smaller activity. Neither composite showed any antimicrobial activity, or their activity against gram‐negative bacteria was low.