Effect of fiber surface treatment on structure, moisture absorption and mechanical properties of luffa sponge fiber bundles

Luffa sponge (LS) is a resourceful natural plant fiber with polyporous structure, which can be effectively used for reinforcement of light weight composite materials. However, reduction in the moisture absorption tendency and enhancement in the mechanical properties of LS fiber bundles by chemical modifications are highly desirable in order to utilize LS as reinforcement material. In this study, three chemical treatments including the use of 5% sodium hydroxide and 5% hydrogen peroxide (5%NaOH-5%H2O2), 10% NaOH and 20% acetic acid (10%NaOH-20%CH3COOH), and 18% NaOH and 1.6% carbamide (18%NaOH-1.6%CO(NH2)2) were used to modify the LS fiber bundles. And the effect of the three chemical treatment methods on the micro/nano structures, moisture absorption and mechanical properties of LS fiber bundles was investigated by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), polarized light microscopy (PLM), fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis, moisture regain (MR) and tensile strength test. The results showed that the treatment with 10%NaOH-20%CH3COOH could significantly improve the mechanical properties of LS fiber bundles, the increase of the tensile strength was 121.3%. However, the treatment with 5%NaOH-5%H2O2 could sharply decrease the mechanical properties of fiber bundles, the reduction of the tensile strength was 75.0%. Furthermore, the treatment with all the three above mentioned chemical combinations could reduce the moisture absorption of LS fiber bundles. The decrease in the moisture regain was found to be 29.0, 16.9, and 12.4%, respectively.