What is polyanionic cellulose (PAC)?

Polyanionic cellulose (PAC) is a water-soluble polymer derived from chemically modified natural cellulose. It is an anionic cellulose ether. As an upgraded product of sodium carboxymethyl cellulose (CMC), it offers superior solubility, salt and alkali resistance, and thickening properties. It is widely used in a variety of industries, including oil drilling, papermaking, coatings, ceramics, pharmaceuticals, and food. Due to its excellent chemical stability and environmental friendliness, PAC has become an important functional additive in various industrial systems.

Chemical Structure and Properties of PAC

PAC is derived from natural cellulose. Through an etherification reaction, carboxymethyl groups and anionic groups (–CH₂–COONa) are introduced to the hydroxyl groups on the cellulose molecule, resulting in anionic derivatives. Its molecular chain contains numerous hydrophilic groups that can form hydrogen bonds with water molecules, resulting in excellent water solubility.

PAC has a high molecular weight. Its degree of substitution (DS, generally between 0.8 and 1.2) and degree of polymerization (DP) are key parameters determining its performance. A higher DS indicates improved water solubility and salt tolerance, broadening its application range. Based on molecular weight and DS, PAC is generally classified into two types:

PAC-LV (Low Viscosity): A low-viscosity type primarily used to control fluid loss in drilling fluids;

PAC-HV (High Viscosity): A high-viscosity type that reduces fluid loss while increasing system viscosity and carrying capacity.

PAC dissolves in both cold and hot water, forming a transparent, stable, viscous solution with excellent film-forming, suspending, and emulsifying properties. It is also highly adaptable to pH fluctuations, remains stable in alkaline and high-salt environments, and resists degradation.

Key Performance Characteristics of PAC

2.1. Excellent Thickening and Suspending Properties

PAC's long, flexible molecular chains result in high solution viscosity, effectively improving the rheological properties of the system. In drilling fluids, coatings, and slurry systems, PAC stabilizes suspended solid particles, preventing sedimentation and stratification.

2.2. Excellent Filtration Control Performance

In oil drilling fluids, PAC forms a dense filter cake layer on the wellbore, significantly reducing fluid loss and preventing wellbore collapse and formation fluid infiltration. Compared to CMC, PAC maintains stable fluid loss control even in high-temperature, high-salt environments.

2.3. Excellent Salt and Alkali Resistance and Thermal Stability

Due to the presence of anionic groups, PAC maintains excellent solubility and viscosity stability in electrolyte solutions containing NaCl, CaCl₂, and MgCl₂, making it suitable for offshore drilling and highly saline environments.

2.4. Environmentally Friendly and Non-Toxic

Derived from natural cellulose, PAC is biodegradable and contains no harmful ions or heavy metals, making its use safe for both the environment and humans.

Main Applications of PAC

3.1. Oil Drilling Industry

PAC is the most important high-efficiency fluid loss additive and rheology modifier in drilling fluids.

PAC-LV is used in freshwater, seawater, and brine drilling fluids, effectively reducing fluid loss and stabilizing the wellbore.

PAC-HV is used to increase drilling fluid viscosity and improve cuttings-carrying capacity.

Its salt and high-temperature resistance make it irreplaceable in complex geological conditions.

3.2. Papermaking Industry

In the papermaking process, PAC can be used as a surface sizing agent and water-retention aid, improving the oil and water resistance and smoothness of paper. It also improves the uniformity and flow of coating fluids, enhancing printing results.

3.3. Daily Chemicals and Coatings Industry

In detergents, toothpastes, and emulsion coatings, PAC acts as a thickener, dispersant, and stabilizer, preventing particle settling and enhancing product texture and storage stability.

3.4. Ceramics and Building Materials

PAC can be used as a dispersant and binder in ceramic slurries, improving fluidity and reducing cracking. In cement mortars, it can enhance water retention and workability.

3.5. Food and Pharmaceuticals

Food-grade PAC exhibits excellent thickening, emulsification, and stabilization properties. It is commonly used in systems such as juices, sauces, and pharmaceutical suspensions. It is safe and non-toxic, meeting FDA and EU standards.

PAC, with its excellent water solubility, salt tolerance, and filterability, has become an indispensable high-performance additive in industries such as oil drilling, papermaking, daily chemicals, and coatings. It not only improves the rheological behavior and stability of systems but also adheres to the development of green and environmentally friendly practices. With the continuous advancement of chemical materials technology, the modification possibilities of PAC will become more diverse, and its application areas will further expand, providing more efficient and sustainable solutions for industrial production.