Polyanionic cellulose (PAC) and sodium carboxymethyl cellulose (CMC) are two types of cellulose ethers that have similar chemical structures and properties, but differ in some key aspects.

PAC is a water-soluble cellulose ether that has a high degree of substitution, meaning that a large number of carboxymethyl groups are attached to the cellulose backbone. PAC is commonly used as a viscosifier and fluid loss reducer in oil drilling fluids due to its excellent water retention, stability, and thickening properties.

CMC, on the other hand, is a water-soluble cellulose ether that is widely used as a thickener, binder, and stabilizer in various industries, including food, pharmaceuticals, cosmetics, and paper production. CMC is produced by the reaction of cellulose with monochloroacetic acid to introduce carboxymethyl groups into the cellulose backbone. The degree of substitution of CMC is lower than that of PAC, but it still provides good water retention, stability, and thickening properties.

Although both PAC and CMC are cellulose ethers with similar properties, they differ in some key aspects. For example, PAC is typically used in the oil drilling industry due to its high degree of substitution and excellent fluid loss reduction properties, while CMC is used in a wider range of industries due to its lower degree of substitution and versatility in various applications.

Overall, PAC and CMC are both important cellulose ethers with unique properties and applications. While PAC is mainly used in the oil drilling industry, CMC has a wider range of applications in various industries due to its versatility and lower degree of substitution.