Blends of thermoplastic starch (TPS) and poly(lactic acid) (PLA) (70/30 TPS/PLA wt/wt)
were thermopressed to produce biodegradable sheets. These sheets were coated with
cross-linked chitosan by two different methods: spraying and immersion. The coated
sheets presented a more irregular surface than uncoated samples, which was associated
with the chitosan reticulation. The chitosan coating reduced the water solubility and the
water vapor permeability of the sheets due to being less hygroscopic. Coated sheets were
more rigid and had higher tensile strength than uncoated sheets, because the cross-linking
joins the macromolecules covalently, reducing the mobility of the chains. Higher glycerol
concentration in the TPS increased the elongation at break due to the glycerol plasticizing
effect. Coating by spraying was more effective at changing the sheet properties than
coating by immersion, and this technique can be used to reduce the hydrophilic character
of biodegradable
fi
lms, allowing their use as packaging materials.