Carboxymethyl cellulose (CMC) is primarily used as a functional additive in the papermaking process. Through its unique chemical properties, it plays a crucial role in multiple stages, including the pulp interior, paper surface, and coating preparation. Its core functions include enhancing the paper's physical strength, improving surface properties, and optimizing coating rheology. The Core Functions and Mechanisms of CMC in Papermaking

CMC is a water-soluble anionic polymer compound. The carboxymethyl and hydroxyl groups on its molecular chain can form numerous hydrogen bonds with the hydroxyl groups on the surface of pulp fibers. This mechanism allows it to play multiple roles in papermaking:

· Strengthening Agent: The viscous solution formed by CMC dissolving in water can coat the fibers. During paper drying, the "bridging" effect of hydrogen bonds significantly enhances the bonding force between fibers, thereby improving the dry strength, wet strength, burst strength, and stiffness of the paper.

· Sizing Agent: CMC has excellent film-forming properties. When its solution is coated onto the paper surface and dried, it can form a continuous, transparent film. This film fills fiber pores, preventing the penetration of water and ink, improving the paper's water resistance and surface strength, and reducing lint and dusting.

• Dispersion and stabilization: As a powerful dispersant, CMC optimizes fiber distribution in the network, promotes uniform weaving, and improves paper uniformity. Simultaneously, it increases the retention rate of fillers, fine fibers, and other chemical additives, stabilizing the entire papermaking system.

Specific applications of CMC in different papermaking processes

Depending on the addition location and process purpose, CMC applications are mainly divided into the following three aspects:

• Wet-end addition (in-pulp addition): CMC is added to the pulp during the pulping stage. Its main purpose is to shorten beating time, improve refining efficiency, and uniformly disperse fibers, improving paper uniformity. More importantly, it can act as a reinforcing agent, directly improving the internal physical strength of the paper and producing a synergistic effect with dry and wet strength agents.

• Surface sizing: CMC is formulated into a sizing solution and coated onto the surface of the formed paper. This is mainly used to improve the surface strength, smoothness, gloss, and oil resistance of paper while controlling paper curl. It is particularly suitable for cultural papers and packaging papers with high requirements for printability and surface performance.

· Coating Preparation (for Coated Paper): In the production of coated paper (such as art paper), CMC is added to the pigment coating. Its main role in this step is to enhance the water retention of the coating and prevent adhesive migration, thereby ensuring uniform coating quality. At the same time, it can improve the rheology and pseudoplasticity of the coating to adapt to high-speed coating equipment and increase the retention rate of brighteners, making the paper whiter and brighter.

Key Parameters and Selection in Practical Applications of CMC

In actual production, to achieve the best results, it is necessary to select the appropriate CMC product specifications according to the paper type and production process:

· Viscosity Selection: Viscosity directly affects the flowability and film-forming properties of the sizing solution. For example, for surface sizing of cultural paper, CMC with a viscosity of 800-1200 mPa·s is often selected to ensure good spreadability and film strength; while for packaging paper, products with lower viscosity (such as 500-800 mPa·s) may be selected to prioritize strength requirements. 

· Substitution Degree Selection: The degree of substitution (DS) reflects the degree of substitution of carboxymethyl groups in the CMC molecule, affecting its water solubility, viscosity, and reactivity. Generally, CMC with a substitution degree in the range of 0.6 to 0.8 is more commonly used in papermaking, balancing solubility, adhesion, and cost. 3

· Compound Use: CMC is often compounded with other additives to achieve synergistic effects. The most common application is compounding with oxidized starch for surface sizing, with a ratio typically between CMC: starch = 1:8 and 1:10. This comprehensively improves strength, water resistance, and cost-effectiveness. When added in the wet end, compounding with cationic additives can also improve single-pass retention.

Founded in 1994 and based in Luoyang, China, Luoyang Hengxin Polymer Material Co., Ltd. specializes in the production of Sodium Carboxymethyl Cellulose (CMC) and Polyanionic Cellulose (PAC), serving a wide range of industries including oil drilling, mining, ceramics, textiles, paper making, and construction. With a 25-acre facility, advanced production equipment, and an annual capacity of 20,000 metric tons, the company combines strong manufacturing capabilities with cost advantages and flexible operations. Its products have been widely recognized by major enterprises such as PetroChina and Sinopec, while its extensive experience and customer-focused approach enable it to meet diverse technical requirements across global markets.

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