Carboxylic modification of welan gum

Welan gum has disadvantages such as poor solubility, low viscosity, and poor crosslinking property, when it is applied in petroleum industry, comparing to guar gum. Two methods for the carboxylic modification of welan gum were developed, carboxyethyl modification and citric acid modification, to improve the solubility in water, viscosity, and crosslinking ability of welan gum in the borax crosslinking system. The solubility time of carboxyethyl modified and citric acid modified welan gum were shortened to 30 and 90 min, respectively. The highest viscosity of citric acid modified product was 49.4 mPa s, the viscosity after crosslinking was raised at least 1.2 times to the highest four times than that before crosslinking. The results indicated three factors affecting the properties of modified products: (1) how many function groups in the modifying agent; (2) the way to connect the function group; and (3) the whole structure of the modifying agent.