Characterization of the Effect of Clay on Morphological Evaluations of PLA/Biodegradable Polymer Blends by FT-Rheology

다국어 초록 (Multilingual Abstract)

<P>The effects of Cloisite nanoparticulate clays on the morphologies of three biodegradable polymer blends, that is, poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL), PLA/poly(butylene adipate-<I>co</I>-terephthalate) (PBAT), and PLA/poly(butylene succinate-<I>co</I>-adipate) (PBSA), were investigated by linear and nonlinear rheological analysis. All three polymer blends, PLA/PCL, PLA/PBAT, and PLA/PBSA, were blended at a ratio of 80/20 wt %. Three different clays, C20A, C30B, and CNa+, were used as compatibilizers. Two organically modified clays, C30B and C20A, were located at interfaces between the matrix and dispersed phases. Of these two clays, C30B showed the best compatibilizing effect in all three polymer blends. This was attributed to the presence of hydroxyl groups on its attached surfactant, which also promoted the insertion of polymer chains into clay galleries. C20A also exhibited good compatibilization because of its large interlayer spacing. Exfoliated clay enhanced the compatibilizing effect, whereas the unmodified clay CNa+ was located in the disperse phase in all three blends, and this was considered to be due to its small interlayer distance and poor intercalation, as confirmed by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. Wetting coefficient calculations predicted clay locations well. Nonlinear-linear viscoelastic ratios (NLR ≡ normalized nonlinear viscoelastic properties/normalized linear viscoelastic properties) were used to quantify droplet size and to assess the compatibilizing effects of the three clays in PLA/PCL, PLA/PBAT, and PLA/PBSA blends. NLR values were consistent with morphological results, which are found to be inversely related to droplet size. Blends containing C30B or C20A showed higher NLR values, whereas the values of blends containing CNa+ remained almost constant (≈1). The effect of C30B concentrations on PLA/PCL, PLA/PBAT, and PLA/PBSA blends was also investigated. Interestingly, PLA/PCL and PLA/PBSA containing C30B showed maximum NLR values at critical C30B concentrations. The decrease in NLR values after critical C30B concentration was probably due to a lack of further droplet stabilization beyond the critical concentration because droplet interfaces were fully covered with exfoliated clay. On the other hand, the NLR values of the three blends containing C20A increased with increasing C20A concentration. C20A displayed less exfoliation than C30B, and as a result, C20A further stabilized droplets at high concentrations.</P>
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