Solid sodium silicate (Na₂O·nSiO₂), also known as water glass, is widely used in the paper industry due to its binding properties, alkalinity, and surface activity. It plays a critical role in pulp treatment, wet-end chemistry, and paper performance enhancement. Below is a detailed analysis of its core applications and technical mechanisms.
1. Key Application Areas
(1) Pulp Fiber Dispersion and Drainage Aid
Function:
Sodium silicate dissociates in water to form colloidal SiO₃²⁻, which adsorbs onto fiber surfaces, reducing fiber flocculation and improving pulp uniformity.
Neutralizes charges to enhance fines and filler retention, increasing drainage speed (beating degree reduced by 10-15%).
Process Parameters:
Dosage: 0.1–0.5% (based on dry pulp weight).
Modulus (n) selection: n=2.0–2.5 (balances dispersion and viscosity).
(2) Key Component in Deinking Agents for Recycled Paper
Mechanism:
Creates an alkaline environment (pH 9–11) to soften ink, while silicate colloids encapsulate ink particles for removal.
Synergizes with H₂O₂ to prevent decomposition and improve bleaching efficiency.
Typical Formula:
Sodium silicate (3–5%) + surfactant (e.g., fatty acid soap) + H₂O₂ (1–2%).
(3) Paper Strengthening Agent (Partial Starch Replacement)
Advantages:
Forms -Si-O-C- bonds with fibers, enhancing dry/wet strength (dry strength increases by 5–8%).
Cost-effective alternative to cationic starch, suitable for low-grade packaging paper (e.g., corrugated board).
Limitation: Excessive use may reduce paper flexibility (recommended dosage <1%).
(4) Flame-Retardant Paper Production
Synergistic System:
Sodium silicate (20–30%) + borates (e.g., borax) → Coated paper forms an insulating silicate glass layer when exposed to fire.
Applications: Fireproof boards, flame-retardant cable wrapping paper.
2. Synergistic Effects with Other Paper Chemicals
Combination Effect
Sodium silicate + Cationic starch Improves fiber bonding, mitigates negative impact on Zeta potential.
Sodium silicate + Bentonite Enhances filler retention (especially CaCO₃), reduces white water turbidity.
Sodium silicate + H₂O₂ Optimizes deinking efficiency, minimizes fiber damage (pH buffered to 9–10).
3. Process Optimization and Considerations
(1) Optimal Addition Points
Best location: Pulper or refiner inlet (ensures thorough mixing).
Avoid direct contact with acidic chemicals (e.g., alum) to prevent Al-silicate precipitation, which clogs fabrics.
(2) Impact of Modulus (n)
Low modulus (n=1.6–2.0): Fast dissolution, ideal for dispersion and deinking.
High modulus (n=2.5–3.0): Strong binding, suitable for strengthening or flame retardancy.
(3) Environmental and Cost Balance
Advantages: Non-toxic, biodegradable, aligns with sustainable papermaking.
Challenge: High dosages may cause silica buildup in white water systems (requires periodic cleaning).
4. Industry Cases and Data
Case Study (Corrugated Paper Mill):
Adding 0.3% sodium silicate (n=2.2) increased tensile strength by 6% and reduced production costs by $2–3/ton.
Deinking Line Data:
Sodium silicate + H₂O₂ improved deinking efficiency from 78% to 92%, reducing residual ink area by 40%.
5. Future Trends
Nano-sodium silicate: Enhances specialty papers (e.g., battery separator paper) via nano-SiO₂ fiber reinforcement.
Smart-responsive silicates: pH/temperature-sensitive formulations for precise process control.
Post time: Jun-28-2025