Carboxymethyl cellulose (CMC), scientifically known as sodium carboxymethyl cellulose, is a versatile surface-active colloid with a polymer structure. Its extensive applications span various industries, including papermaking, textiles, coatings, oil fields, rubber, ceramics, medicine, and mineral processing. In the production lines of high-end whiteboard paper and coated cardboard paper, a crucial coating bonding additive is utilized - CMC for coated paper. This high-grade fine chemical exhibits specialized technical indicators, advanced performance, and notable specificity.

The unique characteristics of Special CMC for coated paper make it irreplaceable by modified starch and PVA in the manufacturing of medium and high-speed coated paper, thanks to its outstanding performance and robust hydrophobicity. Consequently, the development of Special CMC for coated paper holds significant importance in meeting the evolving needs of the papermaking industry, especially in the production of medium- and high-speed coated white cardboard and high-grade whiteboard paper.

Raw Materials and Reagents

The raw materials and reagents employed in the production process include wood pulp, refined cotton, sodium hydroxide, chloroacetic acid, ethanol, isopropyl alcohol, methanol, nitric acid, hydrogen peroxide, ammonia, glacial acetic acid, tetramethylammonium chloride, etc. All these materials are of industrial-grade quality.

Preparation Methods

1) Kneading Method:

Utilizing short cotton linters as raw materials, the kneading method involves degreasing, immersion in caustic soda solution, and pressing to create alkali cellulose. Subsequently, a kneader is used, employing alcohol (methanol, ethanol, isopropyl alcohol) as a solvent for the etherification reaction with chloroacetic acid, followed by neutralization and washing. While this method is widely adopted domestically, it presents challenges such as unstable product viscosity, low purity, and difficulty in dissolution.

2) Slurry Method:

In the slurry method, wood pulp (paper pulp) is soaked in a high-expansion solution composed of water, isopropyl alcohol, and caustic soda. After suitable treatment at a specific temperature and duration, chloroacetic acid is added, and the reaction is heated. The addition of caustic soda neutralizes the reaction, followed by filtration, washing, and drying. This method, predominantly employed by foreign production companies, boasts high product purity, excellent quality, stable performance, and suitability for large-scale production. However, drawbacks include high initial investment and elevated energy consumption for solvent recovery.

3) Modification for Coated Paper:

The special requirements for CMC in coated paper production include lower viscosity, moderate degree of substitution, higher purity, good viscosity stability, and excellent instant solubility. The CMC produced solely through the slurry process falls short of meeting these requirements for white cardboard and high-grade whiteboard paper production. Therefore, modifications to the slurry process or CMC itself are necessary.

CMC modification methods encompass pre-treatment, intermediate treatment, and post-treatment. Pre-treatment involves treating cellulose with substances like ammonia, liquid alkali, or borax before alkali cellulose formation. Intermediate treatment incorporates additional modifiers, such as sodium hypochlorite and phase transfer catalysts, during the carboxymethylation reaction. Post-treatment involves the addition of high-concentration hydrogen peroxide or nitric acid after the etherification reaction to produce CMC.

Preparation Example:

To illustrate, immerse 200g of wood pulp in a solution containing 125g of caustic soda, 600mL of isopropyl alcohol, 10g of composite catalyst, and water. Stir the mixture for 2.5 hours at room temperature, then add 96g of chloroacetic acid, 110g of isopropyl alcohol, and 5g of phase transfer catalyst (tetramethylammonium chloride). Heat to 67°C, hold for 1.5 hours, cool down, and neutralize. Introduce 20g of hydrogen peroxide and 5g of stabilizer, then filter, dry, and pulverize to obtain a slightly yellow granular product.