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.