Some starch-graft-polyacrylamide copolymers were prepared by the polymerization of corn starch with acrylamide in aqueous medium using a complex initiation system consisting of ceric ammonium sulphate and ammonium persulphate. The copolymers were applied to water-based drilling fluid as filtration control agents. Their grafting parameters such as percentage of grafting, grafting efficiency, and solution viscosity (η) were investigated by using elemental analyzer and rotational viscometer. The results showed that increases in initiator concentration and reaction temperature first favored and then impeded the grafting reaction. Grafting of acrylamide onto starch increased with the increase of monomer concentration. It also increased with increasing reaction time up to a certain degree and then leveled off. For the graft copolymers, a higher percentage of grafting and higher η were beneficial in decreasing the filtrate volume of water-based drilling fluid, even under an operating environments of 147°C and saturated salinity. A possible mechanism is proposed to interpret the improvement of fluid loss properties. J. VINYL ADDIT. TECHNOL., 2012. © 2012 Society of Plastics Engineers
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