Moisture Content in Expanded Perlite — Hygroscopic Behavior & Storage Stability:
Moisture content refers to the percentage of water retained in expanded perlite after production. Typical values range from 0.1–1.0%. Moisture affects flowability, bulk density, thermal conductivity, and storage stability.
Moisture content represents the amount of water physically adsorbed on the surface of expanded perlite particles.
It is not chemically bound water and does not contribute to expansion.
1.1 Free Moisture
• Adsorbed on particle surfaces
• Removed at 105°C
• Affected by humidity and storage conditions
1.2 Residual Process Moisture
• Remains after expansion
• Depends on cooling and handling
Moisture content is a post expansion property.
High quality expanded perlite typically contains 0.1–0.3% moisture.
High quality expanded perlite typically shows WI 75–90.
3.1 Standard Method: Oven Drying at 105°C
Procedure:
1. Weigh sample
2. Dry at 105°C for 24 hours
3. Re weigh
4. Moisture (%) = (Mass loss / Dry mass) × 100
3.2 Importance of Controlled Drying
• Prevents thermal alteration
• Ensures accurate measurement
3.3 Moisture vs. LOI
Moisture is removed at 105°C. LOI is measured at 900–1,000°C.
4.1 Ambient Humidity
Perlite is mildly hygroscopic.
4.2 Storage Conditions
Open storage → higher moisture.
4.3 Particle Size
Fine grades absorb more moisture.
4.4 Cooling Process
Insufficient cooling → higher residual moisture.
5.1 Bulk Density
Higher moisture → higher bulk density.
5.2 Flowability
Moisture increases cohesion → reduced flow.
5.3 Thermal Conductivity
Moisture increases thermal conductivity.
5.4 Filtration
Moisture reduces permeability.
5.5 Horticulture
Moisture affects substrate water balance.
• Surface chemistry
• Natural porosity
• Hydration history
Some deposits absorb moisture more readily.
Q: Does moisture affect expansion?
No — expansion occurs before moisture measurement.
Q: Can moisture be reduced artificially?
Yes — through controlled drying.
Q: Why does moisture vary?
Storage, climate, and particle size.
