Influence of various retting methods on properties of kenaf fiber

Gum, as the important noncellulosic tissue present in kenaf fiber, has a close relation with downstream processing and product properties, so the predominant task in pretreatment of kenaf fiber for textile application, retting, is to remove gum including pectin, hemicellulose, lignin, and other impurities without damage to cellulose fiber. The traditional retting method is water retting; that is, the harvested kenaf bast is soaked in natural water (rivers or tanks) in which indigenous bacteria attack the gum in an anaerobic process, yielding much water pollution. Currently, much interest has been focused on various retting methods in order to seek one environmentally-friendly method. Therefore, microbe, chemical, water, and microbe–chemical rettings are performed in this experiment. Retted kenaf fibers at optimal conditions of various retting methods are then characterized and compared by light microscopy and indices consisting of residual gum content, fineness, tenacity, elongation, and softness. In addition, chemical oxygen demand (COD) is also tested. The results indicate that microbe retting induces higher residual gum content and lower elongation but better tenacity and softness and finer fiber; chemical retting gives lower tenacity and thicker fiber; water retting produces weak, poor quality fiber; and microbe–chemical retting produces moderate indices.