4. Conclusion
The rice straws were treated by two different treatments, NaOH solution and thermal steam explosion, to extract fibers. For the chemical treatment, higher NaOH concentration results in extensive chemical extraction with lower fiber yielding and shorter fiber diameter and length, yet the fiber aspect ratio increases with increasing concentration. The steam explosion appeared to break down the fibers more than the chemical treatment with shorter length and larger aspect ratio. However, the visual inspection and the FTIR analyses show that the steam-exploded fibers contain larger proportions of remaining lignin and hemicelluloses than those from the chemical treatments. The steam-exploded treatment shows higher fiber yielding than the chemical treatment. The extracted fibers, from chemically treatment and steam-exploded treatment, were used to form thermal insulation pads. The thermal conductivity coefficients of the straw-fiber insulation pads are in the range of 0.11–0.14 W/m-K, which are similar to those of gypsum boards and bricks but much higher than that of the EPS foam. The aspect ratio of the extracted fibers minimally affects the insulation property. The steam-exploded fiber insulation exhibits lower thermal conductivity than the chemically-treated fiber insulation, which may be due to different chemical and molecular structures of the fibers. The life cycle assessment indicated that the thermal steam explosion is shown to be a more environmental-friendly method than the NaOH treatment. The steam exploded treatment obviously reduced environmental impacts in the category of freshwater eutrophication, human toxicity, terrestrial ecotoxicity and marine ecotoxicity due to the avoided NaOH usage and higher fiber yielding.