Abstract
In this work, bamboo fibers are chemically modified with NaOH solution of 1, 4, and 7 wt% concentrations at room temperature, respectively, and subsequently the untreated and treated fibers are prepared with epoxy resin for unidirectional composites by hot pressing molding technique. Tensile and micro-bond tests are conducted on the composite specimens to obtain mechanical properties, such as tensile strength and modulus, elongation at break, and interfacial strength. Besides, scanning electron microscopy (SEM) is employed to perform morphological observations for constituent damages. In addition, the influence of alkali concentration on the thermal performance of epoxy-based composites is examined by using differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. It is found that composite tensile strength reaches the maximum when the alkali concentration is 4%, increased by 45.24% compared with untreated composites. The composite elongation at break increases on increasing the concentration. Inversely, the composite modulus decreases as the concentration increases. Besides, the results demonstrate that the chemical treatment on the fiber surface could improve interface adhesion, as observed from its topography by SEM. Micro-bond test reveals that there is maximum interfacial shear strength when the alkali concentration is 4%, which increases by 100.30% in comparison with the untreated samples. In case of thermal properties, the DSC analysis indicates that the glass transition temperature is maximized at 4% alkali concentration, which is increased by 12.95%, compared to those from unmodified fibers. In addition, TG results show that the 4% concentration also facilitates thermal stability improvement, indicative of superior interfacial bonding.
Highlights
In recent years, natural fiber composites as a class of environmentally friendly materials possess excellent mechanical properties being in favor of engineering plastics, and have attracted increasing attention in the fields of construction, transportation, aerospace, and new energy vehicles [1]
Ren et al [21] employed a single fiber pull-out test to determine the interfacial shear strength (IFSS) of bamboo fibers/PP; the results show that this value was dominated by several factors, such as fiber structure, embedded length, and fiber diameter
17.78%, 45.24%, and 28.92%, respectively, as compared with 0%. This is attributed to the fact that hemicellulose, pectin, and part of lignin of bamboo fibers are effectively removed by the NaOH
Summary
Natural fiber composites as a class of environmentally friendly materials possess excellent mechanical properties being in favor of engineering plastics, and have attracted increasing attention in the fields of construction, transportation, aerospace, and new energy vehicles [1]. Such composites have replaced traditional wood in terms of furniture products. As one of the most commonly-used thermosets, is Molecules 2019, 24, 2682; doi:10.3390/molecules24152682 www.mdpi.com/journal/molecules. In view of high modulus and high temperature performance, the epoxy has been widely used in various engineering applications
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