Alkaline pre-extraction
The pre-extraction was carried out in an autoclave. The extraction conditions were as follows: alkaline charge 10, 12 and 18%, temperature 50, 60 and 70 °C and hold time 60, 70 and 90 min after the set temperature was reached. The solid to liquor (S:L) ratio was fixed at 1:4 (w:w) and held constant in all experiments. The rice straw used for each experiment was 50 g based on oven dry (OD) weight. At the end of treatment, the solid residue was recovered by filtration and washed with distilled water. The solid fraction was used for soda–AQ pulping process. Soluble hemicelluloses liquor was precipitated by adding ethanol and collected after centrifugation.