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Poly(lactic acid) (PLA)/halloysite nanotubes (HNT) nanocomposites were prepared by melt extrusion using a masterbatch dilution process. Effect of addition of both unmodified halloysites (HNT) and quaternary ammonium salt treated halloysites (m-HNT) was investigated at different nanofiller contents. A homogeneous distribution/dispersion of halloysites in the PLA matrix is obtained for both unmodified and modified nanotubes within the studied composition range. The nucleating effect of halloysites, resulting in a limited increase of degree of crystallinity, is more pronounced in the case of m-HNT. Besides, the rigidity, tensile, flexural, and impact resistances of PLA significantly increase on addition of halloysites, the property improvement being higher for m-HNT than for HNT. Interestingly, there is no significant embrittlement (almost constant elongation at break). Based on micromechanical models, this superior reinforcement efficiency of m-HNT was ascribed to the better interfacial compatibility induced by the modification of the nanotube surface.

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This study shows the interest of elaborating polylactide/halloysite nanocomposites by means of water assisted extrusion (WAE). Besides, WAE gives access to materials with improved fire properties and prevents molecular degradation.

This work reports measurements of the elastic modulus of halloysite nanotubes. Nanoscale three-point bending tests were performed on individual nanotubes using an atomic force microscope. Nanotubes exhibit elastic behaviour at small deformations. The stiffness of the tubes, and hence their elastic modulus, was deduced from force curve measurements using an appropriate mechanical model. The boundary conditions were also identified by recording the stiffness profile of a tube along its suspended length. An average elastic modulus of 140 GPa is obtained for a set of tubes with outer diameters ranging between 50 and 160 nm. Moreover, the elastic modulus increases with decreasing outer diameter, with a steep jump below 50 nm. The size dependence of the elastic modulus may be attributed to: (i) surface tension effects for thinner tubes and (ii) a non-negligible contribution of shear deformations to the total deflection for larger tubes.

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In this study, polyamide 12 (PA12)/untreated halloysite nanotubes (HNTs) nanocomposites are prepared in a semiindustrial scale extruder using a non-traditional "one step" water-assisted extrusion process. A morphological study is carried out using a combination of scanning electron microscopy and transmission electron microscopy analyses to evaluate the influence of water injection and filler content on the quality of clay dispersion. The use of water injection slightly improves the nanoscale dispersion at low HNTs content (<8 wt.%), while this effect is more pronounced at higher filler loading (16 wt.%). A mechanism explaining the physico-chemical action of water during extrusion is proposed. The materials are characterized with respect to their mechanical, thermo-mechanical, thermal and fire properties. A strong correlation is found between nanostructure and physical properties; the more uniform dispersion of the clay nanotubes, the higher mechanical reinforcement, thermal stability and fire retardancy of PA12 nanocomposites. Tensile tests results are interpreted in terms of three mechanical models: the Halpin-Tsai's model for stiffness and the interfacial strength model and the Pukanszky's equation for yield strength. Linear fits of the experimental data confirm that the superior reinforcement of nanocomposites prepared using water injection results from improved clay dispersion and better interfacial adhesion between PA12 and HNTs. In view of these promising results, the proposed direct melt compounding method could be easily scaled-up towards the production of PA12-HNTs nanocomposites at an industrial scale.