Développement de compositions polymères biosourcées sur base PLA pour des applications automobiles

National audiencePLA is a bio-based and biodegradable polymer with high tensile strength and rigidity. Nevertheless, its low impact toughness and its brittleness are obstacles for a use in highly loaded parts. To overcome these drawbacks, the influence of several additives is studied. First of all, PLA plasticization by TBC leads to a marked increase of ductility, however counterbalanced by a drop of tensile strength and rigidity. The formation of copolymers PLA-impact modifier (BS) allows to increase impact toughness but not ductility. Finally, quaternary compositions PLA-BS-TBC-clay nano-reinforcements have interesting tensile and impact properties compared to a mineral filled PP frequently used for automotive applications.Le PLA est un polymère biosourcé, biodégradable et à hautes rigidité et résistance en traction. Toutefois, sa faible résilience et sa fragilité sont des obstacles à son utilisation pour des pièces fortement sollicitées. Pour y remédier, cette étude s'intéresse à l'enrichissement progressif de compositions à base de PLA. Dans un premier temps, l'ajout de plastifiant (TBC) permet une nette augmentation de la ductilité du matériau, mais dégrade les autres propriétés en traction. La formation de copolymères PLA-modificateur d'impact (BS) permet un fort accroissement de la résilience, mais pas de la ductilité. Enfin, les compositions quaternaires PLA-BS-TBC-nanocharges d'argile constituent une piste viable pour une utilisation sous fortes sollicitations, grâce à des propriétés mécaniques en traction et à l'impact prometteuses, comparées à celles d'un PP chargé, classiquement utilisé dans l'automobile

Peculiar effect of stereocomplexes on the photochemical ageing of PLA/PMMA blends

International audienceThe effect of UV light on polylactide/poly(methyl methacrylate) (PLA/PMMA) blends produced by melt-extrusion with a special emphasis on the peculiar influence of PLA stereocomplexes on the photochemical behavior of the blends is the focus of this paper. Stereocomplexable PLA have been prepared by melt-blending of high-molecular-weight poly(l-lactide) (PLLA), poly(d-lactide) (PDLA) and PMMA. The photochemical behavior of resulting PLA/PMMA blends was studied by irradiation under photooxidative conditions (λ > 300 nm, temperature of 70 °C and in the presence of oxygen). The chemical modifications induced by UV light irradiation were analyzed using infrared spectroscopy (IR) and size exclusion chromatography (SEC). Morphological changes were studied by differential scanning calorimetry (DSC) and atomic force microscopy (AFM). It was shown that PDLA and PMMA don't affect the rate of photooxidation of PLLA. However, PLA stereocomplexes have a strong impact on the morphology of the blends during photochemical ageing

Interfacial Compatibilization into PLA/Mg Composites for Improved In Vitro Bioactivity and Stem Cell Adhesion

The present work highlights the crucial role of the interfacial compatibilization on the design of polylactic acid (PLA)/Magnesium (Mg) composites for bone regeneration applications. In this regard, an amphiphilic poly(ethylene oxide-b-L,L-lactide) diblock copolymer with predefined composition was synthesised and used as a new interface to provide physical interactions between the metallic filler and the biopolymer matrix. This strategy allowed (i) overcoming the PLA/Mg interfacial adhesion weakness and (ii) modulating the composite hydrophilicity, bioactivity and biological behaviour. First, a full study of the influence of the copolymer incorporation on the morphological, wettability, thermal, thermo-mechanical and mechanical properties of PLA/Mg was investigated. Subsequently, the bioactivity was assessed during an in vitro degradation in simulated body fluid (SBF). Finally, biological studies with stem cells were carried out. The results showed an increase of the interfacial adhesion by the formation of a new interphase between the hydrophobic PLA matrix and the hydrophilic Mg filler. This interface stabilization was confirmed by a decrease in the damping factor (tanδ) following the copolymer addition. The latter also proves the beneficial effect of the composite hydrophilicity by selective surface localization of the hydrophilic PEO leading to a significant increase in the protein adsorption. Furthermore, hydroxyapatite was formed in bulk after 8 weeks of immersion in the SBF, suggesting that the bioactivity will be noticeably improved by the addition of the diblock copolymer. This ceramic could react as a natural bonding junction between the designed implant and the fractured bone during osteoregeneration. On the other hand, a slight decrease of the composite mechanical performances was noted

Mechanistic insights on nanosilica self-networking inducing ultra-toughness of rubber-modified polylactide-based materials

<p>Developing novel strategies to improve the impact strength of PLA-based materials is gaining a significant importance in order to enlarge the range of applications for this renewable polymer. Recently, the authors have designed ultra-tough polylactide (PLA)-based materials through co-addition of rubber-like poly(ϵ-caprolactone-<i>co</i>-d,l-lactide) (P[CL-<i>co</i>-LA]) impact modifier and silica nanoparticles (SiO₂) using extrusion techniques. The addition of silica nanoparticles into these immiscible PLA/P[CL-<i>co</i>-LA] blends altered their final morphology, changing it from rubbery spherical inclusions to almost oblong structures. A synergistic toughening effect of the combination of P[CL-<i>co</i>-LA] copolymer and silica nanoparticles on the resulting PLA-based materials therefore occurred. To explain this particular behavior, the present work hence aims at establishing the mechanistic features about the nanoparticle-induced impact enhancement in these immiscible PLA/impact modifier blends. Incorporation of silica nanoparticles of different surface treatments and sizes was thereby investigated by means of rheological, mechanical and morphological methods in order to highlight the key parameters responsible for the final impact performances of the as-produced PLA-based materials. Relying on video-controlled tensile testing experiments, a toughening mechanism was finally proposed to account for the impact behavior of resulting nanocomposites.</p