In gypsum board (plasterboard) production, sodium lignosulfonate is used as a water reducer for the stucco slurry. It disperses the calcined gypsum particles so the slurry stays fluid with less water. Less water means less to evaporate in the drying kiln, which lowers drying energy or allows higher line speed. Because lignosulfonates and their sugars can retard gypsum setting, the dose is balanced with the accelerator.
How It Works in the Stucco Slurry
- Dispersion: lignosulfonate adsorbs on stucco particles and gives them a negative charge, breaking up flocs and releasing trapped water.
- Water reduction: the same flow is reached at a lower water-to-stucco ratio.
- Drying energy: every kilogram of water not added is a kilogram not evaporated in the kiln.
- Setting: sugars and low-molecular-weight fractions slow gypsum hydration; plants compensate with accelerator dose and by choosing low-sugar grades.
Plasterboard Grade Specification
| Parameter | Sodium Lignosulfonate Plasterboard Grade (GAC-NaLS-Plasterboard) |
|---|---|
| Appearance | Yellow-brown powder |
| Lignosulphonate content | 55% min (dry basis) |
| Water reducing capacity | 8% min |
| Reducing sugar | 7% max |
| Calcium & magnesium | 0.5% max |
| Sulphate (SO42-) | 2–5% |
| pH | 7.0–9.5 |
| Water-insoluble matter | 1.5% max |
| Moisture | 5% max |
Lignosulfonate vs Naphthalene Sulfonate in Gypsum Board
| Point | Sodium lignosulfonate | Naphthalene sulfonate (SNF/NNO) |
|---|---|---|
| Water reduction | Moderate | Higher at equal dose |
| Effect on setting | Some retardation (sugars) | Less retardation |
| Cost | Lower | Higher |
| Typical use | Alone or blended to reduce cost | Main dispersant on many high-speed lines |
Plant Trial Procedure
- In the lab, measure slurry flow (e.g. patty or slump test) at fixed water/stucco ratio for several doses.
- Find the water reduction at equal flow compared with the current dispersant.
- Measure setting time (e.g. Vicat or temperature rise) and adjust accelerator.
- On the line, reduce water stepwise, monitor board weight, core-paper bond and kiln energy.
- Check board properties: nail pull, flexural strength and humidified bond.
Frequently Asked Questions
Why is lignosulfonate used in gypsum board?
As a water reducer: it disperses the stucco so less water is needed, which reduces drying energy in the kiln.
Does lignosulfonate slow the setting of gypsum?
It can, mainly because of residual sugars. Low-sugar grades and accelerator adjustment control this.
Can lignosulfonate replace naphthalene sulfonate in plasterboard?
Partly or fully on some lines. It gives less water reduction per kilogram, so it is often blended with naphthalene sulfonate to balance cost and performance.
Related Pages
Questions about a specification, a test method or a trial: contact us or email info@greenagrochem.com.
