METHOD FOR PREPARING HYDROXYALKYL STARCH

1 . A method for preparing hydroxyalkyl starch comprising the steps of:

hydrolyzing a starch;

reducing the hydrolyzed starch; and

substituting the reduced starch with hydroxyalkyl group in a dry process.

2 . The method for preparing hydroxyalkyl starch according to claim 1 , wherein the hydrolysis is carried out by an acid treatment.

3 . The method for preparing hydroxyalkyl starch according to claim 2 , wherein the acid is selected from hydrochloric acid, sulfuric acid, oxalic acid and a mixture thereof; and the acid amount of the treatment is 0.1-1 part by weight based on 100 parts by weight of the dry weight of the starch.

4 . The method for preparing hydroxyalkyl starch according to claim 1 , which further comprises the step of bleaching the hydrolyzed starch prior to the reduction step.

5 . The method for preparing hydroxyalkyl starch according to claim 4 , wherein the bleaching is carried out by treatment with one or more selected from the group consisting of sodium metabisulfite, hydrogen peroxide and sodium hypochlorite.

6 . The method for preparing hydroxyalkyl starch according to claim 1 , wherein the reduction is carried out by adding a hydrogen gas generated from a reducing agent to the starch.

7 . The method for preparing hydroxyalkyl starch according to claim 6 , wherein the reducing agent is selected from sodium borohydride, hydrogen, sulfur dioxide and a mixture thereof; and the amount of reducing agent is 0.1-1 part by weight based on 100 parts by weight of the dry weight of the starch.

8 . The method for preparing hydroxyalkyl starch according to claim 1 , wherein the substitution in the dry process is carried out by drying the reduced starch, treating the dried starch with an alkaline catalyst, and etherifying the alkaline catalyst-treated starch.

9 . The method for preparing hydroxyalkyl starch according to claim 8 , wherein the alkaline catalyst is prepared by mixing an aliphatic glycol and an alkaline solution in a weight ratio of 1:1 to 5:1.

10 . The method for preparing hydroxyalkyl starch according to claim 9 , wherein the aliphatic glycol is selected from propylene glycol, ethylene glycol, butylene glycol, diethylene glycol and dipropylene glycol, and the alkaline solution is 50% sodium hydroxide solution or potassium hydroxide solution.