Long-term water aging effects on the durability of alkali-treated bamboo fiber reinforced composite

This paper investigates the degradation mechanisms and mechanical properties of alkali-modified bamboo fiber composites under long-term water aging (up to 120 days) at 25 °C. The main findings show that alkali-treatment reduces the equilibrium moisture content of composites to 12.01 ± 0.04% after a treatment duration of 48 h. At dry conditions, the tensile strength and modulus of composites reach their maximum values of 290 ± 11.2 MPa and 11.5 ± 0.61 GPa for a soaking time of 4 h, then, gradually drop to smaller values, respectively. Beyond 120 aging-days, the tensile strength of 4, 24 and 48 h-modified fiber composites considerably decreases by 66.32 ± 0.33%, 60.99 ± 0.26% and 81.68 ± 0.41%, respectively. Similarly, their Young’s modulus falls by 39.72 ± 0.25%, 49.04 ± 0.19% and 41.71 ± 0.37%, respectively. As confirmed by SEM, this significant drop is attributed to the severe microstructural damage of fibers and matrix which is a result of the prominent differential swelling between the internal cell wall layers. However, the findings attractively reveal a slight decline of about 18.15 ± 0.34% and 15.79 ± 0.33% in the tensile strength of raw and 0.5-h-modified fiber composites after 120 aging-days, respectively. Likewise, their Young’s modulus decreases by 18.55 ± 0.4% and 14.47 ± 0.28%, respectively. This good aging resistance of the raw and 0.5-h-modified fiber composites suggests that the matrix plasticization, physical expansion of fibers as well as hydrolysis reaction are the main aging mechanisms.