Preparation of sodium alginate encapsulated anionic polyacrylamide microcapsules with delayed thickening performance

Polyacrylamide (PAM) is a polymer compound that is widely used in oil extraction, wastewater treatment, food processing and other fields. As a typical polymer flooding agent, PAM has received much attention in the field of oil extraction due to its unique of viscoelastic properties. However, polymer flooding faces several challenges in oil reservoirs, including high injection pressure, high shear loss and crossflow. In an effort to overcome this challenge, we designed a method of coating Ca2+ cross-linked sodium alginate onto the core structure of polyacrylamide, providing shear resistance and sustained release performance for the polymer. The important role of the shell material was indirectly demonstrated by measuring its apparent viscosity using digital rotary viscometer. Moreover, the swelling behavior of microcapsules in water was observed using an optical microscope. The protective shell made the slow release of anionic PAM into water under stirring at 500 rpm, maintaining the viscosity of the fluid below 10 mPa·s within 2 h, and the viscosity increased from 1.8 mPa·s to 30 mPa·s after 35 h. In addition, this work revealed the importance of effective encapsulation by emulsification/external gelation method and a facile shell modification by the layer-by-layer self-assembly method.