Slack Wax SPO (Spindle Oil) — Frequently Asked Questions

Slack Wax SPO (Spindle Oil) is a semi-solid petroleum-derived wax produced as a byproduct of lubricating oil refining, specifically from the spindle oil distillate fraction. It is the second lightest grade in the commercial slack wax family (after LMO), classified under CAS No. 64742-61-6. SPO exhibits a pale to light yellow colour on the ASTM D-1500 scale (maximum 1.5), a melting point of 53–58°C, and an oil content of 5–20% in Bio Green Wax's customised specification. It is one of the most widely traded slack wax grades globally due to its versatile application profile.

SPO stands for Spindle Oil — the lubricating oil distillate fraction from which this slack wax grade is produced. Spindle oil historically referred to a light, low-viscosity lubricating oil used to lubricate textile mill spindles and precision machinery spindles. The wax fraction crystallised from this distillate during the solvent dewaxing process in refining is designated as Slack Wax SPO.

The primary differences between SPO and LMO are melting point, colour, and viscosity. SPO has a higher melting point (53–58°C vs 47–53°C for LMO), a slightly darker colour (ASTM ≤1.5 vs ≤L1.0), and a higher viscosity at 100°C (4.7–5.7 cSt vs 3.1–4.2 cSt). SPO's oil content in Bio Green Wax's specification is 5–20%, which overlaps with LMO's 10–25% but extends to a lower minimum. In practical terms, SPO is a slightly harder, more structured wax than LMO, making it more suitable for applications requiring better form stability such as polishes, particleboard coatings, and rubber processing.

Slack Wax SPO is the most widely traded grade globally because its balanced oil content and mid-range melting point make it compatible with the broadest range of industrial applications — from candle blending and matches to particleboard waterproofing, rubber processing, polishes, fertiliser coatings, and wax emulsions. Its versatility means it serves multiple industries simultaneously without requiring the more specialised handling of heavier grades like MMO or DAO, and it is available in significant volumes from major refinery sources including Pertamina's Cilacap facility.

No. Slack Wax SPO and paraffin wax are related but distinct products. Both are petroleum-derived hydrocarbon waxes from the same refining process, but paraffin wax has undergone additional deoiling and refining steps that reduce its oil content to below 0.5% (fully refined) or below 3% (semi refined). Slack Wax SPO retains 5–20% residual oil, giving it a softer, more pliable character and making it unsuitable for food, cosmetic, or pharmaceutical applications without further processing.

The melting point of Slack Wax SPO is 53–58°C as measured by ASTM D-87. This is higher than LMO (47–53°C) but lower than MMO (58–64°C) and DAO (69–74°C), placing SPO in the mid-light range of the slack wax spectrum. The congealing point (ASTM D-938) is also 53–58°C. This melting point range means SPO is a firm solid at room temperature and requires moderate heating to achieve a workable melt — typically achievable with standard industrial heating equipment.

Bio Green Wax Ltd supplies Slack Wax SPO with an oil content range of 5–20% as measured by ASTM D-721. This operational range reflects actual supplied product characteristics. The oil content affects the softness, adhesion properties, and processing behaviour of the wax in downstream applications. Buyers with specific oil content requirements within this range — for example, for polish formulations requiring a firmer texture — should discuss batch specification requirements with the sales team.

Slack Wax SPO has an ASTM D-1500 colour maximum of 1.5, placing it in the pale to light yellow range on the standardised glass comparator scale. This is a small but visible step darker than Slack Wax LMO (maximum L1.0), reflecting the slightly higher aromatic and naphthenic compound content of the spindle oil distillate fraction. For most industrial applications — particleboard, rubber, polishes, paper coatings — this colour level has no impact on end-product performance.

The minimum flash point of Slack Wax SPO is 200°C as measured by the Pensky-Martens Closed Cup (PMCC) method per ASTM D-93. This is significantly higher than Slack Wax LMO's 145°C minimum, providing a larger safety margin during heated processing and storage. SPO is classified as a combustible material and standard precautions for heated wax handling apply, including maintaining processing temperatures comfortably below the flash point and ensuring adequate ventilation in melting areas.

Slack Wax SPO has a maximum sulphur content of 0.20%wt as measured by ASTM D-1552. This is lower than Slack Wax LMO's maximum of 0.30%wt and equal to the sulphur limits for MMO and DAO. For rubber and tyre applications where sulphur can influence vulcanisation chemistry, SPO's 0.20% maximum is preferable to LMO and should be confirmed against your formulation's sulphur tolerance with your technical team.

Slack Wax SPO is used across a wide range of industries. Key applications include: candle manufacturing as a base and blending wax; MDF, particleboard, and plywood waterproofing; shoe, floor, and furniture polish formulations; match head impregnation; laminate and paper moisture-barrier coatings; textile finishing and warp sizing lubrication; rubber processing as a compounding aid; fertiliser anti-caking agent coatings; and wax emulsion and dispersion production. Its broad compatibility makes it one of the most versatile petroleum wax raw materials available.

In the MDF (medium-density fibreboard), particleboard, and plywood manufacturing industries, Slack Wax SPO is used as a waterproofing and hydrophobisation agent. During board production, melted SPO is applied to wood fibres or chips before pressing — either by injection into the fibre mat, spray application, or wax emulsion addition — to impart moisture resistance to the finished panel. The wax migrates to the fibre surfaces and creates a hydrophobic barrier that reduces water absorption, improving the board's performance in humid environments.

Yes, Slack Wax SPO is a common raw material in shoe, floor, and furniture polish formulations. Its mid-range oil content (5–20%) and moderate hardness give polishes a balance of spreadability and film-forming properties that harder, more refined waxes cannot always achieve cost-effectively. SPO is typically blended with harder waxes (such as carnauba or fully refined paraffin) and solvents to achieve the desired gloss, rub resistance, and application characteristics for the specific polish type.

Yes, Slack Wax SPO is used as a processing aid and protective wax in rubber compounding and tyre manufacturing. In rubber formulations, it functions as an anti-ozonant by blooming (migrating) to the surface of the cured rubber article, creating a protective wax film against atmospheric ozone attack. SPO's slightly higher melting point compared to LMO means it offers better form stability during rubber mixing while still melting and dispersing effectively during the compounding process.

In fertiliser manufacturing, Slack Wax SPO is used as an anti-caking coating applied to granular fertiliser particles. The wax is melted and sprayed onto the fertiliser granules, forming a thin hydrophobic coating that prevents the particles from absorbing moisture and clumping together during storage and transport. This anti-caking function is critical for maintaining flowability and ease of application in the field. SPO's balanced oil content and melting point make it well-suited for this coating process.

Bio Green Wax Ltd supplies Slack Wax SPO in industrial bulk quantities to B2B buyers. Minimum order quantities depend on your destination, preferred logistics format (bulk tanker, flexitanks, drums), and specific grade requirements. Contact our sales team at info@biogreenwax.com or through biogreenwax.com to discuss your volume requirements and receive a tailored quotation.

Every shipment of Slack Wax SPO from Bio Green Wax Ltd is accompanied by a Certificate of Analysis (CoA) covering all ASTM-tested specification parameters (ASTM D-1500 colour, D-87 melting point, D-938 congealing point, D-721 oil content, D-445 viscosity, D-93 flash point, D-1298 specific gravity, D-1552 sulphur). A Safety Data Sheet (SDS) is also provided. Additional documentation including Certificate of Origin, customs documentation, and specific regulatory compliance certificates can be arranged based on your destination country requirements.

Slack Wax SPO is typically transported in solid form in lined jumbo bags, fibre drums, or as bulk loads in heated tankers depending on order volume. For large bulk orders, heated ISO tank containers or heated road tankers maintain the wax in a liquid state for direct unloading into recipient tanks. At ambient temperatures, SPO is solid and stable. It does not require refrigeration and is not classified as a dangerous good for transport purposes under standard conditions, though standard combustible material precautions apply for documentation and labelling.

Bio Green Wax Ltd maintains rigorous quality assurance for all products including Slack Wax SPO. Every batch is tested against the full specification before shipment and accompanied by a Certificate of Analysis confirming compliance. If product does not meet the agreed specification on arrival, we work directly with customers to resolve the issue. For buyers with specific tolerance requirements tighter than our standard specification range, please discuss your requirements with the sales team before placing an order.