Biodegradable Polymer/Halloysite Nanocomposites
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Biodegradable polymer/halloysite nanotube (HNT) nanocomposites have been found to have superior mechanical properties over that of the neat polymer. Two extremes of biodegradable polymers have been made into halloysite containing nanocomposites, from the very rigid, brittle poly(lactic acid) (PLA) to the very ductile poly(vinyl alcohol) (PVOH). Both nanocomposites utilized relatively low loadings of halloysite to realize improved mechanical properties over that of the neat polymer.
The Young’s modulus of PLA increased by 35% with a 10 wt.% loading of washed halloysite. Gains of 47% were seen at 5 wt.% loadings of sodium dodecyl sulfate (SDS) treated HNT. The incorporation of SDS treated HNTs into PLA nanocomposites showed increased tensile strength at yield and Young’s Modulus over that of the PLA/peroxide washed HNT nanocomposites. Almost no change in the thermal degradation was observed for any of the samples.
The PVOH/HNT/montmorillonite (MMT) nanocomposites showed increased tensile strength over that of the neat PVOH samples. The Young’s Modulus was improved by 71% with the addition of 9.0% HNT and 1.0% MMT, while maintaining transparency of the thin film. The decreased strain at break (40% lower than neat PVOH) was to be expected, as the addition of a very stiff nanoparticle to a very ductile material will reduce the elongation under tensile stresses. The addition of smectic clay (MMT) to a PVOH/HNT nanocomposite further improved the mechanical properties of the thin film, with no reduction in optical transparency.
The improvements in mechanical properties of PLA/HNT and PVOH/HNT/MMT will expand the usefulness of PLA and PVOH for new applications, especially where high mechanical performance and environmentally friendly biodegradable products are desired.