Poly(lactic acid)/clay nanocomposites: effect of nature and content of clay on morphology, thermal and thermo-mechanical properties.

Nanocomposites were prepared by melt blending Poly(lactic acid) with 5 and 7wt% of an organically modified montmorillonite or an organically modified magnesium sodium fluoro-hectorite or unmodified sepiolite. All nanocomposites show a good level of clay dispersion into the polymer matrix as well as a considerable thermal and thermo-mechanical properties improvement. According to thermal analysis, the clays seem to act as nucleating agents inducing a higher degree of crystallinity of the polymer and rate of crystallization. Similar increases in the thermal stability of Poly(lactic acid) were obtained for all clays. Concerning layered silicate nanocomposites, it was found that the main influencing factors on the thermo-mechanical properties appear to be the aspect ratio and dispersion of clay nanoplatelets, rather than polymer/clay chemical compatibility. Needle like sepiolite shows thermo-mechanical improvements comparable to some layered silicates and an interesting ability to maintain high storage modulus values at increasing temperatures, due to its good dispersion within the polymer without the need of organic modifiers as instead necessary for layered clays used in this work.

PBAT based nanocomposites for medical and industrial applications.

Poly(butylene adipate-co-terephthalate) (PBAT) based nanocomposites were prepared by melt blending PBAT with 5 and 10 wt.% of clay nanoparticles (unmodified and modified montmorillonites, unmodified and modified fluoro-hectorites, and unmodified sepiolites). All nanocomposites showed a good level of clay distribution and dispersion into PBAT, especially nanocomposites with high clay chemical affinity with the polymer matrix. DSC results showed that addition of layered silicates slightly hindered kinetics and extent of crystallization of PBAT; however, sepiolite particles were able to promote polymer crystallization kinetics and the transformation of the PBAT crystal structure to a more ordered form. Similar increases in the thermal stability of PBAT in nitrogen and air were obtained upon addition of all clays, due to a barrier effect of the clays toward polymer decomposition product ablation. Preliminary biocompatibility tests indicated that PBAT based materials with 10% clay content have good biological safety and display almost no cytotoxicity. The addition of all nanofillers increased the hardness of PBAT matrix. The DMA analysis showed that all nanocomposites presented higher E' values than neat PBAT, indicating that addition of clays improved the mechanical properties of PBAT. For layered silicate nanocomposites, the main influencing factors on the thermo-mechanical properties appeared to be the aspect ratio and dispersion of clay nanoplatelets, rather than polymer/clay chemical affinity. The highest E' values of sepiolite based nanocomposites make this nanoparticle the most attractive material for tissue engineering and environmental industrial applications.

Degradation of poly (lactic acid) and nanocomposites by Bacillus licheniformis.

BACKGROUND, AIM, AND SCOPE: The disposal problem due to non-degradable petroleum-based plastics has raised the demand for biodegradable polymers. The degradation of poly (lactic acid) (PLA) has been studied for several years, but the understanding of involved mechanisms is still incomplete. Based on our previous studies, and it is hypothesized an enzymatic involvement, the aim of this study was to continue investigations on the degradation of PLA and its nanocomposites by Bacillus licheniformis. MATERIALS AND METHODS: Biodegradation of PLA and its nanocomposites (CLOISITE 30B and SOMASIF MEE) was performed on compression-molded, 25 × 25 × 0.6-mm films. Firstly, two plastic films were dipped into sterile nutrient broth inoculated with B. licheniformis and incubated at 32°C. Then, to verify if biodegradation was due to extracellular esterase, the culture broth was filtered to remove B. licheniformis cells, and the plastic materials were put into this broth. RESULTS AND DISCUSSION: PLA degradation by B. licheniformis was accelerated by the presence of organoclays. After 5 months in liquid culture, nanocomposites showed only the 10% of residual mass, compared with the 60% of pure PLA. Extracellular esterase activity was detected in the filtered culture broth confirming that PLA biodegradation was probably due to this enzyme action.

Polylactic acid and polylactic acid-based nanocomposite photooxidation.

The importance of photooxidation in promoting formation of anhydride functional groups and thus promoting hydrolysis/biodegradation of polylactic acid and PLA nanocomposites were elucidated. PLA-based nanocomposites were prepared by adding 5% wt filler content of sodium montmorillonite (ClNa), sodium montmorillonite partially exchanged with Fe(III) (ClFe), organically modified montmorillonite (Cl20A), unmodified sepiolite (SEP), and fumed silica (SiO2). The pure PLA and nanocomposites were UV-light irradiated in artificial accelerated conditions representative of solar irradiation (λ > 300 nm) at 60 °C in air. The chemical modifications resulting from photooxidation were followed by IR and UV-visible spectroscopies. The infrared analyses of PLA photooxidation show the formation of a band at 1845 cm(-1) due to the formation of anhydrides. A photooxidation mechanism based on hydroperoxide decomposition is proposed. The mechanism proposed is confirmed by an increase in anhydride formation rate: the main responsible for this acceleration was identified as transition metals contained in the nanofillers as impurities and involved in the catalytic hydroperoxide decomposition.