Optimization of Alkaline Treatment Conditions of Flax Fiber Using Box–Behnken Method

Abstract

Flax fibers, along with a number of other plant fibers, are rich in cellulose, are relatively cheap, have low density, are highly biodegradable, and are easily renewable with the potential for many composites' reinforcement. However, natural fibers are hydrophilic in nature and covered with waxy substances and pectin, which obstruct the hydroxyl groups from reacting with most binder materials, making it less attractive for reinforcement in polymer composites. Natural fibers are, therefore, usually subjected to alkaline treatment to bleach the fiber surface, swell the cell wall to enable large chemical molecules to penetrate the crystalline region, stop the moisture absorption, and increase the surface roughness. The main goal of this work is to study the effect of the alkaline treatment conditions on the mechanical properties of flax fiber. The effect of treatment parameters such as NaOH concentration, soaking time, and treatment temperature on single fiber tensile strength (TS) and Youn's Modulus (YM) was investigated. In order to optimize the properties of flax fiber, Design-Expert software was used to establish the design matrix and to analyze the experimental data. Numerical and graphical optimization techniques were used. Furthermore, the effect of alkaline treatment on surface morphology, crystallinity, and thermal properties of flax fiber was investigated. The results were processed using the analysis of variance (ANOVA) technique, namely the Box–Behnken method. The results indicated that within the limits of treatment conditions used in this study, the proposed models predicted single fiber TS and YM adequately. In addition, DTA/TGA results showed that alkaline treatment improved thermal stability of flax fibers.