Effect of alkali agents on molecular structure of PAC and drilling-mud fluid loss

During the polyanionic cellulose (PAC) manufacturing in slurry process, the influence of alkali agent on the structure and characterization of PAC was studied by producing PAC with NaOH, KOH and mixture thereof. The cellulose fibre swelling ratio in different alkali systems decreases in the order as follows: NaOH/KOH (molar ratio 9/1), NaOH, NaOH/KOH (molar ratio 1/1), NaOH/KOH (molar ratio 1/9), KOH. Crystalline grade of cellulose is in the reverse order. These results were obtained by means of X-ray diffraction and microscope. The degree of substitution of PAC and substituent distribution within anhydroglucose unit (AGU) were determined by means of ¹H NMR spectrum. The results show that the degree of substitution of PAC is higher and the distribution of the substituents in the anhydroglucose unit of PAC is more even in the presence of a little KOH. These made PAC have an excellent viscosity stability in salt and lactic acid and fluid loss resistance. When KOH was a major alkali agent, solubility of PAC in salt and lactic acid became worse and fluid loss increased.