Analysis of Water Absorption on the Young’s Modulus and Damping of Sponge Gourd (Luffa cylindrica) Composites

Composites reinforced with lignocellulosic fibers are attracting attention for use in several applications. This fact is directly linked to the advantages of using renewable lignocellulosic fibers. However, due to their cellulose-based structure, lignocellulosic fibers easily absorb water, which can affect the behavior of the composites. Surface treatments are used to reduce the hydrophilicity of fibers, but common surface treatments use chemicals, compromising the green approach of using lignocellulosic fibers. This work compares the water absorption behavior of sponge gourd-epoxy matrix composites with untreated and surface treated fibers. The effect of these treatments on the variation of the Young’s modulus and damping factor of the composites during the immersion time in distilled and salt water was also evaluated using the nondestructive impulse excitation test. In addition to the commonly used surface treatments (mercerization and acetylation), hornification has also been used to reduce the use of chemicals. The results obtained show that hornification is a competitive approach to reduce the water absorption of composites, being an interesting alternative to chemical surface treatments. A relationship was established between the amount of water absorbed and the variation in Young’s modulus and damping factor. Both properties stabilized when the water absorption saturation value was reached.