The performance requirements for sodium carboxymethyl cellulose (CMC) in various papermaking processes vary significantly depending on the process's function.
The core focus is on matching performance indicators with demand, such as adsorption retention, film-forming and water-resistant properties, and dispersion compatibility.
First, let's clarify the meaning of key indicators: degree of substitution (DS, affecting water solubility and adsorption, range 0.2-1.5); viscosity (2% aqueous solution viscosity, affecting flowability and film-forming properties); purity (ash and salt content, affecting compatibility); whiteness (affecting paper appearance); and pH (affecting equipment and pulp stability, typically 6-8).
The pulping process focuses on fiber bonding and filler retention. The required DS is 0.6-0.9 (medium-low, strong adsorption, easy bonding of fibers and fillers), viscosity is 500-1500 mPa·s (medium-low, balanced adsorption and pulp dehydration), ash content is ≤ 8% (loose, impurities do not affect internal performance), and whiteness is ≥ 80% (low requirement, does not affect the finished product appearance).
The papermaking process focuses on paper stock rheology and dehydration. The DS is 0.7-1.0 (medium, balanced adsorption of fine fibers and paper stock flow), viscosity is 300-1000 mPa·s (low-medium, optimized flow and anti-flocculation), pH is 6.5-7.5 (neutral, prevents equipment corrosion and pulp instability), and dispersibility is medium (quick dissolution without agglomeration to avoid paper sheet defects). The core of the surface sizing process is film formation, water resistance, and surface strength. DS values of 0.8-1.2 (medium-high, good water solubility, dense film formation) are recommended, along with a viscosity of 1000-3000 mPa·s (medium to prevent sizing solution penetration and uneven coating). Whiteness should be ≥90% (high requirement, directly impacting the paper's surface appearance), and ash content should be ≤5% (low to prevent film spotting). The film should be continuous and flexible to prevent folding and cracking and resist water penetration.
The coating process focuses on pigment dispersion and coating adhesion. DS values of 0.9-1.4 (high, optimal dispersion, preventing pigment agglomeration) are recommended, along with a viscosity of 100-800 mPa·s (low to ensure coating fluidity and facilitate uniform coating). Ash content should be ≤3% (very low to prevent degradation of coating gloss and printing), and salt content should be ≤1% (low to prevent disruption of dispersion and adhesion). Compatibility with adhesives such as PVA is also required to prevent delamination.
The core differences can be summarized in three points:
DS ranges from medium-low (0.6-1.0) in pulping/papermaking to medium-high (0.8-1.4) in surface sizing/coating.
Viscosity is adjusted as needed, with the lowest requirements for coating (100-800 mPa・s), medium for surface sizing (1000-3000 mPa・s), and medium-low for pulping/papermaking (300-1500 mPa・s).
In terms of purity, the surface process (sizing/coating) has much higher requirements for whiteness (≥90%) and ash content (≤5%/≤3%) than the internal process (whiteness ≥80% and ash content ≤8%). When selecting CMC, for pulping/papermaking, priority should be given to products with medium-low DS, medium-low viscosity, and normal purity; for surface sizing, focus on medium-high DS, medium viscosity, high whiteness, and low ash content; for coating, choose products with high DS, low viscosity, very low ash content, low salt, and compatibility with adhesives.
