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In this paper, the potential of soda cooking to extract fibrous residues from rice
hulls was investigated. Soda cooking was carried out at 170°C for 60 minutes
using 5 to 13% NaOH. The goal was to selectively degrade silica and lignin from
the structure of the rice hulls and produce fibrous carbohydrates that could be
used as fillers in polymer biocomposites. This was studied by characterizing the
physical and chemical properties of the fibrous residues and the spent liquor
products. Results of scanning electron microscopy have revealed a substantial
fragmentation of rice hulls above 7.5% NaOH charge. The fragmentation was
accompanied with a significant removal of silica and lignin and the reduction of
fibrous residues yield to 57% at 13%NaOH. Wet chemical composition analyses,
infrared spectroscopy and x-ray spectroscopy have also revealed that lignin and
silica were partly retained in the fibrous residue while the carbohydrates content
were not affected. It is therefore concluded that soda cooking could be among
the best processes for dissolving lignin and silica from rice hulls if the cooking
conditions are optimized.