Title: Surface Characterization of Untreated and Solvent-Extracted Rice Straw Authors
Submitted to: Colloids and Surfaces B: Biointerfaces
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 10, 2004
Publication Date: March 10, 2005
Citation: Inglesby, M.K., Gray, G.M., Wood, D.F., Gregorski, K.S., Robertson, R.G., Sabellano, G.P. 2005. Surface characterization of untreated and solvent-extracted rice straw. Colloids and Surfaces B: Biointerfaces. 43:83-94. Interpretive Summary: Rice straw is a severely underutilized renewable resource. Its burning has been banned in California, resulting in the accumulation of over 1 million tons per annum. Rice straw utilization in conventional building materials, such as medium density fiberboard and particle board, is currently explored. While medium density fiberboard can successfully be produced, challenges have been encountered by the industry with the manufacture of particle board from rice straw. Factors proposed responsible included the high amounts of silicon dioxide, morphological characteristics, and surface characteristics, such as the presence of lipids. It is well established that a thorough understanding of the nature of fiber surfaces is critical because surfaces determine the interfacial properties in composites and ultimately the final product performance. Therefore, the focus of this study was to investigate the effects of plant lipid removal by solvent extraction on the the physico-chemical surface characteristics of rice straw.
Technical Abstract: Surface characteristics of untreated and solvent extracted rice straw and intact rice plant stem and sheath tissue have been investigated using reflectance Fourier Transform Infrared Spectroscopy (FTIR-ATR), electrokinetic analysis (EKA), and scanning electron microscopy (SEM). Klason lignin and Kappa numbers were determined according to TAPPI standard methods. Sohxlet extractions were performed with hexanes, ethyl acetate, chloroform, ethanol-toluene and benzene-ethanol azeotropes. The FTIR reflectance spectra showed differences between the untreated sheath and stem tissues. It was found that the functional groups of the stem interior tissues were masked by another substance, which is proposed to be potassium oxalate monohydrate. This mineral salt, readily removed by water-washing, was affected by the solvent extractions with varying results. The extracted amounts ranged from 1 to 7%. While lipid removal was detectable by the FTIR reflectance method, the streaming potential method showed only slight differences between the curves representing the zeta potential (mV) as a function of pH of the untreated versus extracted samples. Reduced values of the iso-electric points were observed for the extracted samples as compared to the untreated rice straw, indicative of more acidic surface characteristics.