The objective of this study was to develop a hermetical alkali digestion process to obtain single cellulosic fibers from kenaf bast. Kenaf bast were hermetically digested into single fiber using a 5% sodium hydroxide solution for one hour at four different temperatures (80°C, 110°C, 130°C, and 160°C). The hermetical digestion process used in this study produced fibers with high cellulose content (84.2–92.3%) due to the removal of lignin and hemicelluloses. The surface hardness and elastic modulus of the fibers digested at 130°C and 160°C were improved significantly compared with those digested at 80°C. The tensile modulus and tensile strength of the individual fibers reduced as the digestion temperature increased from 110°C to 160°C. Micropores were generated in fiber cell wall when the fibers were digested at 130°C and 160°C. The studies on the composites that were made from polypropylene reinforced with the digested fibers indicated that the compatibility between the digested fibers and polypropylene matrix was poor. 1. Introduction Kenaf (Hibiscus cannabinus) an agricultural crop, is in the Malvaceae family, belonging to the division of Magnoliophyta. The history of kenaf cultivation can be traced back to ancient Africa [1]. Kenaf grows very quickly, rising to the heights of 12 to 14 feet in 4 to 5 months. In the United States, kenaf is mainly cultivated in Mississippi, Texas, and California, and so forth. Kenaf yields six to eight metric tons of bast and core per acre annually [1]. Kenaf bast fiber is a lignocellulosic fiber that has been used for pulp, paper, and textiles [2]. It is a good potential reinforcement material for polymer composites [3–8]. The lignocellulosic fiber mainly consists of cellulose, hemicelluloses, and lignin. Noncellulosic substances such as lignin, hemicelluloses, and pectins hold the cellulose fibrils together. The reinforcement effect for the lignocellulosic fiber is influenced by its cellulose content. Usually, high cellulose content can be obtained from the chemical retting [2, 9–14]. Retting is a term to describe a process to digest wood and agricultural stalks, especially bast crop stalks, into fibers. Alkali treatment is a standard procedure used in pulp and paper industries to remove lignin [15]. Through the alkali digestion process, individual fibers can be obtained by separating the fiber bundles. A uniform fiber distribution in the polymer composites may be easily achieved by using the individual fibers as reinforcements. In addition, micropores in the fiber can be created [16], which provide spaces for
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