Effect of zirconates and silanes treatments on the physical and mechanical properties of flax fibers for applications in cementitious composites
The advantage of natural fiber reinforced cement composites (NFRC), especially flax fibers based composites, lies in the improvement of mechanical and thermal properties of the matrix, and in the reasonable cost. However, the wide use of these materials is hampered by their low stability. The natural fiber in the porous alkaline matrix is slowly damaged and the reinforcing effect of the fiber decreases. Fiber treatment can be used to improve aging of the NFRC. This approach can have the advantage of improving the fiber–matrix interface and the hydrophobicity of the fiber. Chemical grafting of functional groups at the surface of fibers is a promising process for improving durability and adhesion of flax fibers used as reinforcement material in a cementitious matrix. This research gives an insight into the effect of chemical modification of flax fibers by two different sizings: (1) alkyltrialkoxysilane (RSi(OR′)3) and (2) zirconium butoxide (Zr(OCH2CH2CH2CH3)4). Chemical treatments at the fiber surface were characterized by Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Moisture absorption measurements at room temperature and 80% of relative humidity were carried out in order to study the hydrophobicity of the modified fibers. Tensile tests were performed on fibers to determine the sizing effects on mechanical properties of the treated flax fibers. Fibers degradation was evaluated by measuring the variations in tensile strength after exposing them to alkaline solutions. The results show significant effects of the surface treatments on the hydrophobicity of the flax fibers and the prevention of their degradation in a cementitious simulated environment. In particular, surface treatment with zirconates significantly improves the water resistance of the fibers, while silane efficiently improves the resistance of the fibers against degradation when immersed in an alkaline solution.