Isolation of cellulose fibers from kenaf using electron beam

Abstract

Cellulose fibers were isolated from a kenaf bast fiber using a electron beam irradiation (EBI) treatment. The methods of isolation were based on a hot water treatment after EBI and two-step bleaching processes. FT-IR spectroscopy demonstrated that the content of lignin and hemicellulose in the bleached cellulose fibers treated with various EBI doses decreased with increasing doses of EBI. Specifically, the lignin in the bleached cellulose fibers treated at 300 kGy, was almost completely removed. Moreover, XRD analyses showed that the bleached cellulose fibers treated at 300 kGy presented the highest crystallinity of all the samples treated with EBI. Finally, the morphology of the bleached fiber was characterized by SEM imagery, and the studies showed that the separated degree of bleached cellulose fibers treated with various EBI doses increased with an increase of EBI dose, and the bleached cellulose fibers obtained by EBI treatment at 300 kGy was separated more uniformly than the bleached cellulose fiber obtained by alkali cooking with non-irradiated kenaf fiber.

Introduction

Kenaf (Hibiscus cannabinus) is one of the non-wood fibers that grow in tropical and sub-tropical areas. Recently, kenaf has drawn much attention as a replacement wood because it grows rapidly, reaching 12–18 feet in just five months, and also has good fiber quality (Seo et al., 2008, Nishino et al., 2003, Adamson and Bagby, 1975).

Kenaf cell walls in common with wood consist of stiff fillers, called cellulose fibers, embedded into soft matrix substances such as hemicellulose and lignin. Cellulose fibers of semicrystalline is a linear polymer with high aspect ratio and excellent mechanical properties including a high Young`s modulus and a very great potential for use as reinforcement in composite, pulps for producing paper, and converting into a wide variety of derivative products such as rayon and an alternative fuel source. On the other hand, lignin and hemicellulose of a perfectly amorphous structure are softer than cellulose and act as glue between celluloses fibers by virtue of the interaction or linkages between the cellulose and the matrix (Yang et al., 2007). And then, in order to efficiently isolate cellulose fibers, it is essential to remove the lignin and hemicellulose as much as possible. Cooking process is done to remove the lignin and hemicellulose in the chip. This process use a combination of high temperature and chemicals such as alkaline sulfate and acid sulfite to break or weaken the chemical bonds by chemical action so that the cellulose fibers can be separated (Turbak et al., 1983, Charkraborty et al., 2005). However, the chemical cooking processes are still encountered with a large amount of high-efficiency, cost-effective, and environment-friendly problems (Dey and Gupta, 1992).

Electron beam irradiation (EBI), without adverse effects, has been used to decrease cell wall constituents, or degrade and delignify cellulose based fibers. The basic advantages of EBI includes the ability to promote changes in reproducibly and quantitatively, without the introduction of chemical reagents and without the need for special equipment to control temperature, environment, and additives (Van Soest et al., 1984, Mason et al., 1988, Masri and Zarkawi, 1994, Sandev and Karaivanov, 1977).

The aim of this study was to provide a progressive and convenient process for cellulose isolation from EBI kenaf bast fiber using only water without chemicals during cooking treatment. The obtained cellulose fibers were characterized using a chemical composition, FT-IR, SEM, and XRD.