ARS | Publication request: Biocomposites: The natural fiber contribution from bast and woody plants

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: May 1, 2011
Publication Date: September 6, 2011
Citation: D'Souza, N.A., Allen, M.S., Stevens, K., Ayre, B., Visi, D.K., Vidhate, S., Ghamarian, I., Webber III, C.L. 2011. Biocomposites: The natural fiber contribution from bast and woody plants. In: Webber, C.L. III, Liu, A., editors. Plant Fibers as Renewable Feedstocks for Biofuel and Bio-based Products. CCG International, Incorporated. p. 75-95.

Interpretive Summary: A composite material is generally described as a combination of two or more phases at the macroscopic level which results in an improved system with superior characteristics than that of its individual components alone. Extensive research has shown that plants are a value fiber source for use in composites (biocomposites). Often a plant tissue must be processed to gain access to the plant fibers suitable for composite materials. The process of separating the plant fibers from the extraneous plant material is called retting. Research was conducted to determine the impact of retting treatments (chemical retting, enzymatic retting, and traditional retting) on kenaf (Hibiscus cannabinus L.) and sebania [Sesbania herbacea (Mill.) McVaugh] fiber quality used in biocomposites. The NaOH retted kenaf fiber became more brittle, fractured, and the porosity was decreased, compared to the enzymatic retted kenaf fibers which had had a smooth fiber surface and increased porosity. Seven retting treatments were used on sesbania fibers, which included 3 NaOH treatments (2, 5, and 10% NaOH retted for 1 hr), 3 pectinolytic bacteria treatments (4, 8, and 12 hr retting), and traditional retting (pond water for 336 hr). Sesbania fiber quality decreased (surface texture and porosity) as the NaOH concentration increased. Increasing NaOH concentration increased the separation of individual fiber cells leading to the destruction of the honeycomb structure and an increased loss of cell wall integrity. Enzymatic treatments produced fibers similar to the traditional retting process, but in a much quicker time. There were no discernable differences in fibers retted for increasing durations in pectinolytic bacteria retting over the relatively short time durations tested. Fiber composite characteristics were also significantly impacted by the retting processed used on the sesbania fibers. Both yield stress and peak strain of the biocomposites decreased with the increase in NaOH retting concentration. One possible reason for these reductions in composite mechanical properties may be the development of local stress concentrations at the fiber and soft PVA matrix interface, due to stiffer sesbania fibers produced by the NaOH retting process. The results indicate care and caution must be employed when pairing the polymer and the natural fiber, as well as the impact of retting on the final composites.

Technical Abstract: A composite material is generally described as a combination of two or more phases at the macroscopic level which results in an improved system with superior characteristics than that of its individual components alone. Research was conducted to determine the impact of retting treatments (chemical retting, enzymatic retting, and traditional retting) on kenaf (Hibiscus cannabinus L.) and sebania [Sesbania herbacea (Mill.) McVaugh] fiber quality used in biocomposites. The NaOH retted kenaf fiber became more brittle, fractured, and the porosity was decreased, compared to the enzymatic retted kenaf fibers which had had a smooth fiber surface and increased porosity. Seven retting treatments were used on sesbania fibers, which included 3 NaOH treatments (2, 5, and 10% NaOH retted for 1 hr), 3 pectinolytic bacteria treatments (4, 8, and 12 hr retting), and traditional retting (pond water for 336 hr). Sesbania fiber quality decreased (surface texture and porosity) as the NaOH concentration increased. Increasing NaOH concentration increased the separation of individual fiber cells leading to the destruction of the honeycomb structure and an increased loss of cell wall integrity. Enzymatic treatments produced fibers similar to the traditional retting process, but in a much quicker time. There were no discernable differences in fibers retted for increasing durations in pectinolytic bacteria retting over the relatively short time durations tested. Fiber composite characteristics were also significantly impacted by the retting processed used on the sesbania fibers. Both yield stress and peak strain of the biocomposites decreased with the increase in NaOH retting concentration. One possible reason for these reductions in composite mechanical properties may be the development of local stress concentrations at the fiber and soft PVA matrix interface, due to stiffer sesbania fibers produced by the NaOH retting process. The results indicate care and caution must be employed when pairing the polymer and the natural fiber, as well as the impact of retting on the final composites.