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United States Department of Agriculture

Agricultural Research Service

Research Project: Integrated Crop, Soil, and Water Management Systems for Sustainable Production of Sugarcane for Bioenergy Feedstock

Location: Sugarcane Research Unit

Title: The effect of retting on mechanical properties, surface chemistry and morphology of kenaf fibers

Authors
item Ramesh, Dinesh -
item Ayre, Brian -
item Webber, Charles
item D'Souza, Nandika -

Submitted to: Journal of Industrial Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 15, 2012
Publication Date: N/A

Interpretive Summary: Kenaf plants (Hibiscus cannabinus L.) are fast-growing and can reach maturity in 6 months, yielding 18 dry metric tons per hectare annually. The fibers from the kenaf bark and inter core can be used for many industrial purposes including absorbents, reinforcing fibers for plastics, for paper pulp, textiles, and cordage. The long bast fibers which grow in the bark portion of the plant have been used for textiles and cordage for over 6000 years. Retting is used to separate the bast fiber strands within the kenaf bark from the surrounding non-fibrous tissues. Historically, a natural retting process was used which involved striping the bark of the kenaf stalks, tying the bark strips into bundles, and placing the bark bundles in ponds or slow moving streams. Indigenous microbes in the water would slowly break down and dissolve the chemical bonds between the bast fiber strands and the non-fibrous materials. The water would not only provide a suitable environment to support the microbes, but also serve as a means to help wash away the non-fibrous material. After months of microbial breakdown, long bundles of bast fiber strands would remain where there were once bark bundles. Although the natural retting method was very effective in producing excellent fiber strands for making textiles and cordage, the process was very time consuming. The modern interest in using kenaf bast fibers for reinforcing plastics and in nanotechnology applications has generated motivation to develop faster methods of retting kenaf bast fiber strands. Three retting processes were investigated to produce kenaf fiber strands: 1) alkali retting with 2% sodium hydroxide, 2) enzymatic retting with pectinase, and 3) natural retting with microbial populations originating from pond water. It was determined that the pectinase treatment effectively removed hemicelluloses and lignin from the kenaf fiber surface and produced kenaf fibers with superior mechanical properties. The pectinase retting process yielded more consistent and superior quality fibers than the alkali retting process, producing quality fibers equal to microbe retted fibers in a shorter time, which would be more suitable for large scale production.

Technical Abstract: Bast fibers grow in the bark layer of many plants, and have been used for textiles and cordage for over 6000 years. Bast fibers of kenaf (Hibiscus cannabinus L.) are retted by three methods and a comparative assessment of available reactive groups on the fiber surface and mechanical properties are of value. Three retting processes were investigated to produce kenaf fiber strands: 1) alkali retting with 2% sodium hydroxide, 2) enzymatic retting with pectinase, and 3) natural retting with microbial populations originating from pond water. The resulting kenaf fibers were characterized by dynamic mechanical analysis (DMA), Raman spectroscopy (FT-Raman), polarized optical microscopy (POM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and optical fluorescence microscopy. DMA determined that pectinase and microbe treated fibers had superior viscoelastic properties compared to alkali retting. XPS and Raman studies indicated that the pectinase retting was effective in removing pectin, hemicellulose, and lignin. SEM and optical microscopy showed the surface morphology and cross sectional architecture were preserved in pectinase retting. The pectinase retting process yielded more consistent and superior quality fibers than the alkali retting process, producing quality fibers equal to microbe retted fibers in a shorter time, which would be more suitable for large scale production.

Last Modified: 12/18/2014
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