Stearate intercalated layered double hydroxides: effect on the physical properties of dextrin-alginate films

Glycerol-plasticized dextrin-alginate films were prepared by solution casting. They contained a fixed amount (16.6% mass/dry film mass) of functional filler based on the reaction products of the LDH, Mg₄Al₂(OH)₁₂CO₃·3H₂O, and stearic acid (SA). The films were characterized using infrared (IR) spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effect of filler composition on water vapour permeability and film stiffness was determined. The ratio of stearic acid (SA) to the LDH (Mg₄Al₂(OH)₁₂CO₃·3H₂O) was varied over the full composition range. Infrared spectroscopy and X-ray diffraction studies confirmed that the SA intercalated into the LDH. The Young’s modulus of films attained a maximum value (more than double the value for the neat film) at a filler composition of 60% SA. The water vapour permeability showed a broad minimum at filler compositions of 50–80% SA. Scanning electron microscopy revealed that in this composition range the filler assumes a high-aspect-ratio platelet morphology. This contrasts with the sand rose morphology of the LDH starting material and the globular dispersion of 100% SA in the film.