Viscoelastic Properties of Kenaf Bast Fiber in Relation to Stem Age

Kenaf (Hibiscus cannabinus L., Malvaceae) is a high-yielding tropical plant traditionally grown for the long, strong bast fibers that develop in the bark layer of the stem. Cultivation spread internationally in the early to mid-twentieth century, but interest waned, particularly in developed counties, as raw materials for cordage and related products shifted from biological to petrochemical sources [1]. Concerns over rising costs, unstable supply, and negative environmental impact of fossil fuels are promoting renewed interest in traditional fiber crops [2]. Kenaf is a multipurpose crop with various harvestable components: leaves and tender shoots are suitable for forage; the woody core has attributes for forest-product substitutes, absorbents, and structural materials; and seeds have an oil and protein composition similar to cotton seed [3]. The bast fibers, however, remain the primary economic incentive to grow kenaf. Beyond cordage, bast fibers are expanding into new markets of moldable, nonwoven fabrics, and reinforced composite materials in automotive, aerospace, packaging and other industrial applications [4, 5]. This trend is in part due to the fiber’s physical properties of light weight, competitive tensile strength and stiffness, and vibration damping properties, and also due to the fiber being a renewable and biodegradable resource [2, 4]. Nonwoven materials made of kenaf or other natural fibers blended with polyester or polypropylene are efficient sound absorbers and can meet industry specifications of Abstract Natural fibers traditionally used for cordage are proving valuable for advanced industrial applications due in part to beneficial physical and chemical properties, but also because they are a renewable and biodegradable resource. Kenaf (Hibiscus cannabinus L., Malvaceae) produces high yields of lignocellulosic bast fibers in the bark layer, and is a promising crop for supplying emerging fiber markets. Bast fibers are bundles of cells that undergo extensive cell-wall thickening during maturation. Bundle maturity is therefore an important determinant of the fibers’ mechanical properties and ultimately contributes to their quality in specific applications. Fiber bundles in stem sections of progressive age were analyzed by epifluorescence microscopy, and viscoelastic properties determined by dynamic mechanical thermal analysis. Earlyforming primary fibers were larger than later-forming secondary fibers, but cell-wall thickening contributed most to elastic and viscous response of the fiber.