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Flax fibers have found widespread use in eco-composite materials because of their remarkable mechanical properties compared to glass fibers. However, their low stability limits their use on a larger scale when employed in hot or humid environments. Therefore, the surfaces should be modified before the composite process to provide the best interfacial interactions and increase the dispersion of natural fibers. To tackle this problem, two kinds of modifications can be considered: wet and dry modifications. This research explores different methods to improve the adhesion between flax fibers and the poly lactic acid (PLA) polymer. Morphological and chemical modifications in the presence of acetone, alkali (as a wet modification), and with air atmospheric pressure plasma (as a dry modification) are compared in this research. The results revealed that altering the chemical characteristics on the surface significantly changed the mechanical properties of the final composite. More specifically, the Fourier transform infrared spectroscopy (FTIR) data indicate that wax-related peaks (2850 and 2920 cm−1) were eliminated by both wet and dry treatments. Dynamic mechanical analysis (DMA) results also highlighted that a better bond between the flax fibers and the PLA matrix is obtained with the plasma modification.

International audience

Ammonium polyphosphate (APP) was grafted onto the surface of exfoliated graphite nanoplatelet (GNP) to obtain a novel flame retardant, GNP-g-APP, and thereafter was incorporated into the ethylene vinyl acetate (EVA) to improve its flame retardancy. The chemical structures of the precursors and the target product were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and energy dispersive X-ray spectroscopy (EDS) techniques. FTIR spectra appeared at 1056 and 1103 cm−1 were attributed to P O C asymmetric stretching bond, that conformed formation of GNP-g-APP. Thermal stability behaviour and flame retardancy performance of the samples were evaluated by TGA, UL-94, micro-calorimetry, and cone calorimetry. TGA measurements revealed the superiority of GNP-g-APP over GNP. The micro-calorimetry analyses indicated a sharp fall in both the total heat release (THR) and the peak of heat release rate (pHRR) of EVA containing 30 wt.% GNP-g-APP, evidenced by a thick char layer formed as barrier. Cone calorimetry confirmed flame-retardant effect of GNP-g-APP featured by a reduction in pHRR (−63 %) and THR (−31.6 %) due to the formation of a cohesive char layer. Although GNP addition sharply decreased the elongation at break of 70/30 (w/w) composites from 500% for neat EVA to 71%, a very promising value of 364% for EVA/GNP-g-APP sample preserved superior flexibility.

International audience; A series of samples based on poly(3-hydroxybutyrate) (PHB) containing five different additives were prepared and their thermal stability and flammability were discussed. The samples were first underwent flammability screening of by using Pyrolysis Combustion Flow Calorimeter (PCFC) analyses. Then, four samples were selected for further investigations. PHB composites containing sepiolite (Sep.) inorganic nanofiller, and also organic ammonium polyphosphate (APP) were examined for flammability and thermal behavior using PCFC, thermogravimetric analysis (TGA), flame test, and Differential Scanning Calorimetry (DSC) analyses. Moreover, burning behavior of samples were captured on a digital camera to give a deeper sense of their flammability character for comparison. The results revealed a significant improvement of flammability and thermal stability of composites, particularly in the presence of sepiolite with respect to the value obtained for unfilled PHB. Regarding TGA results, the char residue yield was increased to ca. 20.0 wt.% in the presence of sepiolite, while 0.0 wt.% was observed for PHB. PCFC measurements uncovered higher performance of PHB-Sep. sample as signaled by 40% reduction in the peak of heat release rate with respect to PHB. According to observations, PHB-Sep. sample showed non-dripping behavior with high capacity of charring in the presence of Sep. in vertical flame test.