Slack Wax is a semi-refined petroleum wax obtained as a by-product during the solvent de-oiling process of lubricating oil base stocks in petroleum refineries. It serves as the primary intermediate raw material for producing fully refined paraffin wax, semi-refined paraffin wax, and microcrystalline wax.
Slack wax consists of a mixture of solid paraffinic wax crystals and entrained mineral oil, giving it a soft, greasy, and plastic texture. Depending on crude source and refining severity, slack wax typically contains 5% to 35% oil, which directly affects hardness, melting point, color, and industrial usability.
Chemical Composition & Structure
✔ Predominantly long-chain paraffinic hydrocarbons (C20–C40+)
✔ Entrained lubricating oil fractions
✔ Minor iso-paraffins and naphthenic hydrocarbons
✔ Chemically inert and non-reactive
This structure makes slack wax hydrophobic, chemically stable, and highly compatible with other waxes, oils, polymers, and additives.
Key Characteristics
High Oil Content (5%–35%)
Controls softness, penetration, and flexibility. Higher oil content produces softer wax with lower melting point, while lower oil content yields harder wax with higher refining yield.
Soft, Plastic Texture
Semi-solid consistency allows easy processing, blending, coating, and impregnation.
Moderate Melting Range (45°C – 65°C)
Allows low-energy melting and easy temperature control in industrial operations.
Oxidation & Chemical Stability
Resistant to oxidation, non-corrosive, and stable during storage and transport.
Moisture & Water Resistance
Hydrophobic nature makes slack wax an excellent moisture barrier.
Typical Physical & Mechanical Properties
| Property | Typical Range | Industrial Significance |
|---|---|---|
| Melting Point | 45°C – 65°C | Processing temperature |
| Oil Content | 5% – 35% | Softness & application range |
| Penetration @ 25°C | High | Plasticity indicator |
| Flash Point | 150°C – 200°C | Safe handling |
| Density | 0.78 – 0.88 g/cm³ | Coating thickness |
| Viscosity (molten) | Higher than paraffin | Lubrication & adhesion |
| Color (ASTM) | 2 – 5 | Refinery quality |
Refining & Production Process
Vacuum Distillation
Separation of heavy lubricating fractions.
Solvent Dewaxing
Wax removed from base oil using MEK / Toluene solvents.
Slack Wax Separation
Wax–oil mixture filtered and recovered.
De-Solventizing & Solidification
Solvent removed and wax cast into slabs, blocks, or pellets.
Further Processing (Optional)
Used as feedstock for paraffin wax and microcrystalline wax production.
Classification of Slack Wax (By Oil Content)
| Type | Oil Content | Characteristics |
|---|---|---|
| Low Oil Slack Wax | 5% – 10% | Harder, higher wax yield |
| Medium Oil Slack Wax | 10% – 20% | Balanced properties |
| High Oil Slack Wax | 20% – 35% | Very soft, high plasticity |
Available Forms & Packaging
Physical Forms
✔ Solid slabs / blocks
✔ Granules / pellets
✔ Molten bulk supply
Packaging Options
✔ Poly-lined bags
✔ Carton boxes
✔ HDPE / MS drums
✔ Bulk tanker supply
✔ Export-grade customized packing
Applications of Slack Wax
Wax Refining Industry
Feedstock for paraffin and microcrystalline wax.
Candle Manufacturing
Improves flexibility, mold release, and reduces brittleness.
Rubber & Tire Industry
Processing aid and anti-ozonant wax for surface protection.
Matchstick Industry
Stick impregnation for moisture resistance and controlled burning.
PVC & Plastics
Lubricant and processing aid.
Textiles, Cables, Plywood & Construction
Lubrication, waterproofing, corrosion protection.
Leather, Shoe & Floor Polishes
Enhances gloss, flexibility, and water resistance.
Advantages of Slack Wax
✔ Low-cost wax raw material
✔ Highly versatile industrial feedstock
✔ Easy to blend and process
✔ Excellent moisture barrier
✔ Stable during storage and transport
✔ Adjustable properties by oil content
Limitations
⚠ Not suitable for food or cosmetic use without refining
⚠ High oil grades may bleed in some applications
⚠ Requires controlled heating for bulk handling
Slack Wax vs Paraffin Wax
| Property | Slack Wax | Paraffin Wax |
|---|---|---|
| Refining Level | Semi-refined | Fully refined |
| Oil Content | 5% – 35% | < 0.5% – 1% |
| Texture | Soft, greasy | Hard, crystalline |
| Cost | Lower | Higher |
| Direct End Use | Industrial | Consumer & industrial |
| Odor | Mild petroleum | Odorless |
Slack Wax is a critical petroleum wax intermediate bridging crude oil refining and finished wax products. Its adjustable oil content, plastic texture, moisture resistance, and blending flexibility make it indispensable across wax refining, rubber, plastics, packaging, agriculture, and construction industries.