In which process stages of the papermaking industry can calcium formate be utilized?

Within the complex and intricate production processes of the papermaking industry, numerous chemical auxiliaries play pivotal roles; calcium formate stands out as one such auxiliary of unique value, demonstrating positive impacts across multiple process stages and contributing to improvements in both paper quality and production efficiency.

Calcium formate demonstrates significant efficacy during the paper sizing stage. The objective of sizing is to impart water resistance to the paper, thereby ensuring that ink does not bleed or feather during writing and printing. Traditional sizing agents often require specific conditions to ensure their effective reaction and fixation. Calcium formate acts as a reaction promoter by regulating the pH of the sizing system, thereby creating an environment more conducive to the bonding of the sizing agent with the paper fibers. Taking alkyl ketene dimer (AKD) sizing as an example: AKD sizing requires a weakly alkaline environment to facilitate its hydrolysis and subsequent esterification reaction with the fibers. To a certain extent, calcium formate can slowly release calcium ions; by working synergistically with other components in the system, it helps maintain the appropriate alkaline range. This allows the AKD sizing agent to function more effectively—thereby enhancing the paper's water resistance—without negatively impacting other critical parameters such as paper brightness or strength.

Calcium formate also plays a crucial role in the fiber treatment process. Raw papermaking fibers often contain impurities—such as lignin—which must be removed during the pulping process to enhance fiber quality. In chemical pulping processes, the addition of calcium formate helps optimize cooking conditions. It interacts with the chemical agents present in the cooking liquor to accelerate the rate at which lignin dissolves, while simultaneously minimizing damage to the fibers. For instance, during the sulfate pulping process, calcium formate facilitates the nucleophilic attack of sodium hydroxide and sodium sulfide—present in the cooking liquor—upon the lignin molecules. This results in the faster and more thorough separation of lignin from the raw fiber material, thereby reducing energy consumption during cooking, shortening cooking times, and increasing pulping yields. Furthermore, the resulting fibers are softer and finer, laying a solid foundation for the subsequent paper formation stage.

Wastewater treatment represents another critical challenge facing the papermaking industry, and here, too, calcium formate proves to be a valuable asset. Papermaking wastewater is rich in organic matter, and its direct discharge causes severe environmental pollution. During the biological treatment stage of wastewater, calcium formate serves as a supplementary carbon source for microorganisms. As microorganisms decompose pollutants within the wastewater, they require an adequate carbon source to sustain their growth and metabolic activities. The formate ions present in calcium formate can be rapidly utilized by microorganisms to provide energy, thereby stimulating microbial proliferation and enhancing their activity. This, in turn, accelerates the decomposition and transformation of organic matter in the wastewater, improves its biodegradability, optimizes treatment efficiency, and assists papermaking enterprises in achieving compliance with environmental discharge standards.