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In this study, modified TiO2 grafted flax fibers were used to reinforce PLA composites. The fibers were oxidized in order to improve the interfacial adhesion of the fibers to TiO2 film. The TiO2 film was created on the flax fiber by a Sol-Gel dip-coating technique. The interfacial adhesion of the fibers to the matrix was investigated qualitatively by microscopy, and quantitatively by measuring inter-laminar shear strength. Impact and tensile tests characterized the mechanical properties of the modified TiO2 grafted flax fiber reinforced composites. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Dynamic mechanical analysis (DMA) were used to reveal the thermal and thermo-mechanical behavior of the composites. The hygroscopic behaviors of the composites were determined by the water uptake assessment. The results showed statistically significant increase in adhesion bonding of the modified fibers to the matrix. The modified TiO2 grafted flax fibers increased the impact resistance of pure PLA by three times. The microscopic observations verified the modifications in the mechanical and physical properties of the composites. Moreover, the amount of water sorption decreased by 18% in the modified TiO2 grafted fiber reinforced composite. Keywords: PLA composite, Flax fiber, TiO2 coating, Interfacial adhesion, Physico-mechanical properties, Moisture absorption

This study aims at functionalizing flax fibers by grafting an amphiphilic TiO2 thin film. The film was created on the fiber by the Sol–Gel technique. The fibers were firstly primed to reach a minimum possible roughness, and then were coated using the dip-coat method. The crystalline structure and the morphology of the TiO2 particles, and, the TiO2-grafted film were determined using X-ray diffraction, and Transmission Electron Microscopy. Mechanical properties of the TiO2-grafted flax strands were investigated by a tensile test. Dynamic contact angle tensiometer was used to probe the differences between wettability of the TiO2-grafted and non-grafted flax strands. The results show that the particles obtained from the Sol–Gel technique created a 100 nm-thick film of TiO2 in the anatase form. The statistical evaluation of the tensile tests exhibits a significant improvement in mechanical properties of the TiO2-grafted flax strands. Moreover, the TiO2 coated flax fibers show a wide range of wetting angles in comparison with the other samples. Keywords: Natural fibers, Surface modification, Grafting, TiO2 thin film, Wettability, Mechanical properties