Using urea to improve stability, sizing performance and hydrolysis resistance of ASA emulsion stabilized by Laponite

As a paper sizing agent, alkenyl succinic anhydride (ASA) emulsion is generally stabilized by cationic starch or synthetic polymer. In this paper, Laponite and urea were employed as particle stabilizer and the modifier of Laponite particle, respectively, to stabilize the ASA emulsion. It is founded that the presence of urea enhances the stability of ASA emulsion, reduces the emulsion droplet size, resulting in improved sizing performance of the ASA emulsion. ASA emulsion with smallest droplet size and best sizing performance on BCTMP is obtained at the urea dosage of 50 wt% based on Laponite. The sizing test of ASA emulsion and the infrared spectrum analysis of ASA substances separated from ASA emulsions with different storage time indicate that the introduction of urea in emulsification process can restrain the hydrolytic action of ASA effectively and sustain the sizing performance of ASA emulsion even two hours after its preparation. This is a possible way to solve the problem that paper mills have always encountered: the too rapid hydrolysis of ASA emulsion.