A novel polyurethane microcapsule coated with polyacrylamide using D-sorbitol as chain extender for enhanced oil recovery

Polyacrylamide (PAM) serves as an effective thickening agent for oil recovery. However, its viscosity loss during underground transport significantly reduces oil recovery efficiency in reservoir applications. To solve this problem, polyurethane was selected for microencapsulation of PAM through a simple emulsion polymerization method in this work. It is worth mentioning that non-toxic and renewable D-sorbitol was used as a chain extender in the synthesis of polyurethane microcapsules instead of the commonly used diols or diamines obtained from non-renewable petroleum resources, which has not been reported in previous reports. Mechanical stirring was used to simulate the state of polymer subjected to shear during stratigraphic transport. The releasing performance of the microcapsules was characterized by measuring the change of viscosity with time. Meanwhile, we optimized the ratio of D-sorbitol to achieve the longest release time. Experiments showed that D-sorbitol was feasible as a chain extender for the preparation of microcapsules of polyurethane, and the microcapsules prepared at a concentration of 8% D-sorbitol solution had the longest slow-release time of 75 h at 25 °C and 500 rpm. We also prepared samples with BDO as a chain extender for comparison, and the experiments showed that SO8 has a longer slow-release time and can better meet the demand. The prepared microcapsules SO8 exhibited excellent shear resistance and heat resistance, which was attributed to the rigidity and high cross-linking density brought about by D-sorbitol as a hard chain segment of polyurethane. These PAM-containing microcapsules had a promising application in enhancing oil recovery.