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The hydroxypropylation reaction was carried out in three different media viz., water, water in presence of a phase transfer catalyst (PTC), tetrabutylammonium bromide (TBAB) and 2-propanol. A weighed quantity (20g) of finely powdered dry cassava starch was made into a slurry by adding distilled water / 2-propanol (40mL) to adjust a solid concentration of 500 g/kg and stirred using a mechanical stirrer. To this suspension, anhydrous sodium sulphate (100 g/kg based on starch dry weight) was added with mild stirring to protect the starch from swelling. Sodium hydroxide (10 g/kg of the starch by weight) was then added as a 50 g/kg aqueous solution with rapid agitation of the slurry, followed by the required amount of propylene oxide and the reaction was carried out in a closed vessel at 30 ± 2 °C for 24 h. Propylene oxide was added to give 50, 100, 150 and 200 g/kg final concentrations based on the starch dry weight. Upon completion of reaction, the pH of the slurry was adjusted to 6.0 using 50 g/kg aqueous hydrochloric acid, filtered and washed several times with distilled water. The product was finally washed with 2-propanol and was dried overnight in an air oven at 45°C. In one set of experiments, TBAB (100 g/kg based on starch dry weight) was added before the addition of propylene oxide and all other steps were performed in the same manner as described above. The products synthesised in aqueous medium using the four different concentrations of propylene oxide were denoted from S1 to S4 and those prepared in presence of PTC were denoted as to S5 to S8. The samples synthesised in 2-propanol were labeled from S9 to S12.


Central Tuber Crops Research Institute
Sreekariyam, Thiruvananthapuram, Kerala - 17