Properties And Sizing Performance Of ASA Emulsion Stabilized By Laponite With The Presence Of Urea

Alkenyl succinic anhydride (ASA) is a common sizing agent. It is usually added topapermaking system as ASA-in-water (O/W) emulsion. To get a satisfactory sizingeffect, a large amount of emulsifiers have to be employed to stabilize the ASA emulsionin the traditional method. What’s worse that it has to input high energy, but theproduction efficiency is low. In order to make up for the above defects and avoid theadverse impact of emulsifiers in the same time, in this paper Laponite modified by ureaor urea synergism with Laponite were used to stabilize ASA, respectively. to investigatethe reaction between urea and Laponite, the preparation conditions and sizingperformance of the ASA emulsions. Meanwhile the relationship between emulsionvolume fraction and the emulsion properties and sizing performance also wereinvestgated.According to the experiment, urea can adsorbe on the surface of Laponite, reducethe extent of hydration and the negative surface charge density, change the turbidity ofLaponite aqueous dispersion, and enlarge the interlamellar spacing (001) of Laponiteafter being cured as well. However, it has almost no effect on the interface betweenLaponite aqueous dispersion and ASA. When using Laponite modified by urea tostabilize ASA emulsion, it was found that the presence of urea can reduce the chargelevel of Laponite in the preparation of ASA emulsion. When the water-oil ratio is1:3,the charge level of Laponite is only0.4wt%, and the charge level of urea is2.5wt%based on the Laponite, ASA-in-water emulsion could be prepared with smaller diameterof droplets, narrower droplet size distribution, higher sizing perfomance and betterstability.When using urea synergism with Laponite to stabilize ASA emulsion, theintroduction of urea can decrease the droplet sizie, enhance the uniformity of drplet sizedistribution, improve the stability of ASA emulsions and improve the sizingperformance. In addition, when the charge level of urea based on Laponite is50wt%, itmeans that the negative charge density reaches its minimum and the maximum turbity isobtained, the ASA emulsion with the best stability, smallest average drop diameter,narrowest droplet distribution and the highest sizing performance. To stabilize ASAemulsion with urea and Laponite, it can also reduce the hydrolysis of ASA. What ismore, even if the emulsion is storaged as long as120min, the sizing performance of ASA emulsion stabilized by Laponite and urea is hardly changed. However, when ASAemulsion stabilized by Laponite alone, the sizing performance is decreased remarkablyafter the storage exceeds30min.When the ASA volume fraction is from10%to50%, the emulsion isASA-in-water, the sizing performance is almost the same. What is more, only a littleASA occurres hydrolysis after the storage exceeds12h. However, when the ASAvolume fraction is50%, the sizing performance decreased sharply as the srorage timeprolonged. While when the ASA volume fraction is10%,20%,30%or40%, the sizingperformance changed not obviously. When ASA volume fraction is greater than80%,water-in-ASA emulsion is obtained; when the ASA volume fraction is between60%and70%, catastrophic phase inversion is occurs, along with the conductivity and theviscosity of ASA emulsion increases sharply and decreases rapidly, respectively.Either Laponite alone or urea synergism with Laponite to stabilize ASA emulsion,the sizing performance is significantly improved after addition of aluminum sulfate. Inaddition, the sizing performance is the best when the pulp pH is6-6.5. The retentionsystem has particular influence on the sizing performance of ASA emulsion. It could begreatly improved by adopting the cationic Polyacrylamide (CPAM)/Laponite anionicmicroparticle retention system to the ASA emulsion sizing performance.