Sodium Silicate in Paper Production — Filler & Adhesive | Lộc Thiên
Sodium silicate (Na₂SiO₃, CAS 1344-09-8) — also known as water glass — is a versatile inorganic chemical in the paper and packaging industry. It plays three main roles: filler to increase stiffness, binder between kraft paper layers, and surface adhesive for corrugated carton. No single sodium silicate grade fits all stages — choosing the right module (SiO₂:Na₂O ratio) determines output quality.
1. Role of Sodium Silicate in Paper Production
In the paper and packaging production line, sodium silicate appears at various stages thanks to its mild alkalinity (pH 11–13), film-forming ability, and lower cost compared to organic adhesives.
1.1. Reinforcing Filler for Kraft Paper
When added to the pulp at the wet-end stage, sodium silicate acts as an active filler — not only filling gaps between cellulose fibers but also forming chemical bonds with the fibers. The mechanism: silicate ions (SiO₃²⁻) react with metal cations (Ca²⁺, Al³⁺) in the pulp system to form calcium silicate hydrate (C-S-H) gel that attaches to fiber surfaces, increasing tensile strength and stiffness of the final product.
According to research from US Patent 10041211, a blend of sodium silicate and precipitated calcium carbonate (PCC) increases filler content by an additional 5% (from 20% to 25%) without compromising paper strength, while also reducing dusting on printing surfaces. Typical dosage: 0.5–2% sodium silicate by dry weight of PCC, combined with PAC (poly-aluminum chloride) at 1–5 kg per ton of paper.
1.2. Adhesive in Corrugated Carton and Paper Tube Production
In carton box production, sodium silicate replaces starch adhesive in applications requiring moisture and heat resistance. Water glass adhesive penetrates deeply into the paper fiber structure, forming a hard inorganic bond after drying. Module 2.8–3.0 provides the best adhesion for corrugated carton production — this ratio balances sufficient viscosity for even coating on corrugated flutes with fast enough setting time to hold the fold.
For industrial paper tube production (core-board), cores, and cardboard tubes, sodium silicate module 3.0–3.3 is preferred because it forms a hard, compression-resistant film, especially when tubes must bear the weight of heavy paper rolls.
1.3. Stabilizer in Pulp Bleaching
In H₂O₂ pulp bleaching processes, sodium silicate acts as a stabilizer — preventing H₂O₂ from decomposing too rapidly due to catalysis by metal ions (Fe²⁺, Mn²⁺) in the water. Module 2.0–2.5 (high alkalinity, low viscosity) suits this role because of its stronger complexing ability with heavy metals, keeping H₂O₂ stable throughout the bleaching process.
2. Module 2.0 vs 3.3 Comparison — Choosing the Right One for the Application
Module = molar ratio SiO₂/Na₂O. This parameter determines almost all properties of sodium silicate.
Module 2.0–2.5 (low ratio):
- Low viscosity (~60–200 cP), easy to pump and dilute
- High alkalinity (pH ~12–13) — suitable as bleaching stabilizer, wastewater treatment
- Dry film is brittle, moderate adhesion
- Lower cost — used for applications not requiring high mechanical strength
Module 3.0–3.3 (high ratio):
- High viscosity (~1,500–9,600 cP), forms thicker film
- Lower alkalinity (pH ~11) — safer for paper fibers
- Hard dry film, good compression resistance
- Fast setting time — ideal for paper tube and load-bearing carton adhesives
Quick comparison table:
| Parameter | Module 2.0–2.5 | Module 3.0–3.3 |
|---|---|---|
| Main application | Bleaching stabilizer, recycled pulp | Paper tube adhesive, carton, heat-resistant |
| Viscosity (20°C) | 60–800 cP | 900–9,600 cP |
| pH | 12–13 | 11–12 |
| Dry film hardness | Low–medium | High |
| Setting time | Slow | Fast |
| Cost | Lower | Higher |
Module selection conclusion: Carton and paper tube adhesive → choose module 2.8–3.3. Bleaching aid → choose module 2.0–2.5. Lộc Thiên delivers with batch COA — confirm module when ordering.
3. Actual COA — Lộc Thiên Sodium Silicate
Each Lộc Thiên sodium silicate shipment comes with a COA (Certificate of Analysis) with the following specifications. Below are the product parameter ranges — exact values on each batch COA:
Technical specifications table:
| Item | Parameter | Test Method |
|---|---|---|
| Formula | Na₂SiO₃ / Na₂O·nSiO₂ | — |
| CAS | 1344-09-8 | — |
| Product form | Liquid solution, clear to slightly turbid | Visual |
| Module (SiO₂:Na₂O) | 2.0–3.3 (per batch COA) | Titration HCl 0.5N + KF |
| Density (20°C) | 1.35–1.55 g/mL | Hydrometer |
| Solids content | 35–45% | Drying at 105°C to constant weight |
| pH (1% solution) | 11–13 | pH meter |
| Na₂O | 9–12% (w/w) | Titration HCl 0.5N, bromthymol blue indicator |
| SiO₂ | 26–31% (w/w) | Gravimetric / KF titration |
| Insoluble residue | ≤0.5% (w/w) | G4 filter, drying at 105°C |
Packaging specifications:
- 30L jerrycans, 200L drums (steel or plastic), 1000L IBC totes
- Dedicated 5–30 ton tankers for bulk volumes
- Documentation: MSDS/SDS + COA as required
Note: For high module (3.0–3.3), solution viscosity may increase if stored beyond 12 months or at low ambient temperature. Check flowability before feeding into dosing pumps.
4. ZDHC Level 1 — MRSL Compliance
Sodium silicate (CAS 1344-09-8) is listed in ZDHC (Zero Discharge of Hazardous Chemicals) at Level 1 — it does not contain hazardous chemicals from the MRSL V3.1 list above threshold levels. This is an input condition for textile dyeing and paper mills requiring ZDHC certification for export.
Lộc Thiên provides batch-specific COA — plants can use this documentation to cross-check against ZDHC MRSL Level 1 requirements before introducing the chemical into production processes.
5. Reference Mixing Ratios
Carton adhesive formula (module 2.8–3.2):
- Sodium silicate as supplied — 70–80% by volume
- Water — 20–30% by volume (adjust viscosity to 800–1,200 cP)
- Optionally add 0.5% nanoclay to increase toughness by 25% (per Faria et al., 2025 — article in Cellulose journal)
Bleaching aid formula (module 2.0–2.5):
- Sodium silicate — 1–3% by dry pulp weight
- H₂O₂ — 2–5% by dry pulp weight
- NaOH — adjust pH to 10.5–11
- Bleaching temperature: 60–80°C, time 45–90 minutes
6. Operational Notes
- Do not mix sodium silicate with strong acids (HCl, H₂SO₄) outside the process — the reaction instantaneously forms silica gel, clogging pipes.
- Equipment cleaning: After using water glass adhesive, rinse immediately with hot water (>60°C) before the film hardens.
- Storage: Keep lid tightly sealed after use — avoid absorbing CO₂ from air, which forms silica precipitate. Shelf life: 6–12 months from manufacturing date.
- PPE: Alkali-resistant gloves, safety goggles — sodium silicate at pH 11–13 causes skin and eye irritation.
Frequently Asked Questions about Sodium Silicate in Paper Production
What dosage of sodium silicate is used in paper production?
The dosage depends on the purpose: as kraft paper filler: 2–5% of dry pulp weight; as carton adhesive: 10–15% (diluted with water at 1:1 to 1:3 ratio); as pulp preservation aid: 0.5–1%. Consult the batch COA and perform a jar test before application. Lộc Thiên supplies various module grades — call 0979 891 929.
Which Na₂SiO₃ module is suitable for carton adhesive?
Module 3.2–3.3 (high SiO₂:Na₂O) is most suitable for carton adhesive due to high viscosity, fast drying time, and strong bonding strength. Module 2.0–2.5 is more suitable for paper filler and preservation aids. Lộc Thién supplies all modules — contact 0979 891 929 for advice on selecting the right grade.
Does silicate affect paper whiteness?
No. Sodium silicate at recommended dosage (2–5%) does not reduce paper whiteness. When used as a filler, silicate is a clear, colorless liquid — it does not affect the finished paper color. In paper bleaching processes, silicate also helps stabilize H₂O₂, reducing bleaching agent consumption and maintaining more stable whiteness.
Can silicate be replaced by other chemicals in paper production?
Silicate can be replaced by kaolin or CaCO₃ as a filler, but silicate has the advantage of being a liquid that is easy to dose, generates no dust, and has lower cost. As a carton adhesive, starch can substitute but requires cooking and longer drying time. Silicate remains the most economical choice for most paper mills in Vietnam.
Where to buy sodium silicate for paper mills?
Hóa Chất Lộc Thiên — supplies bulk sodium silicate module 2.0–3.3, batch COA, ZDHC Level 1. 6 warehouses nationwide, 20 tankers of 5–30 tons. Same-day delivery to industrial parks. Call 0979 891 929 for a quote and advice on the right module for your paper production line.
7. Buy Bulk Sodium Silicate for Paper Mills
Lộc Thiên supplies liquid sodium silicate in bulk by drum, IBC, or tanker. Delivery from 6 nationwide warehouses — Ho Chi Minh City, Bình Dương, Đồng Nai, Hanoi, Đà Nẵng, Cần Thơ — to all industrial parks within the day.
Paper mills can source Na₂SiO₃ + NaOH (liquid caustic soda) + H₂O₂ from a single source — optimizing logistics and ensuring consistent quality. Contact hotline 0979 891 929 — quote within 15 minutes, batch COA/MSDS.
--- References ---
- US Patent 10041211 — Method of increasing filler content in paper or paperboard
- Faria et al. (2025). Multilayer paper composites. Cellulose 32(7): 4525–4552
Quality control: QC Phan Cẩm Thủy inspects and Võ Thị Như Hòa approves each batch of Sodium Silicate. Batch COA — precise module ratio and density.
- ZDHC MRSL V3.1 Conformance Guidance V2.0
- TCVN / Liquid sodium silicate standard — physical and chemical specifications