Slack Wax DAO (Deasphalting Oil) — Frequently Asked Questions

Slack Wax DAO (Deasphalting Oil) is the heaviest and most complex grade within the commercial slack wax family, produced from the deasphalting oil fraction of lubricating oil refining. It is classified under CAS No. 5 cSt at 100°C, and an oil content of 5–20% in Bio Green Wax's customised specification.

DAO is primarily sought as feedstock for microcrystalline wax production and for demanding industrial applications in rubber, construction, and anti-corrosion.

DAO stands for Deasphalting Oil — the specific process stream from which this slack wax grade originates. In lubricating oil refining, the deasphalting process uses light hydrocarbon solvents (typically propane or butane) to extract a high-quality, asphaltene-free oil fraction from heavy vacuum residue. This deasphalted oil is then subject to further processing including solvent dewaxing, from which the heavy wax fraction — Slack Wax DAO — is separated.

Slack Wax DAO originates from one of the most complex processes in lubricating oil refining. First, vacuum residue (the heaviest fraction from atmospheric crude oil distillation) undergoes propane or butane deasphalting, which removes asphaltenic compounds and produces a cleaner, heavy oil stream called deasphalted oil (DAO).

This DAO stream is then processed through solvent dewaxing — chilling in the presence of a solvent to crystallise the wax fraction — and the separated wax is Slack Wax DAO. Its heavy molecular weight, high viscosity, and dark colour are direct consequences of originating from the heaviest feedstock in the refinery.

0) is due to the heavy molecular weight aromatic and naphthenic compounds present in the deasphalting oil distillate. However, these colour-imparting components are removed during the further refining steps (hydrofinishing and deoiling) that convert DAO into microcrystalline wax.

The finished microcrystalline wax produced from DAO is a light-coloured, fine-crystalline product meeting pharmaceutical and cosmetic purity standards — demonstrating that raw material colour at the slack wax stage does not determine the quality of the refined end product.

Slack Wax DAO is distinguished from LMO, SPO, and MMO in several ways: it has the highest melting point (69–74°C vs 47–53°C for LMO); the highest viscosity at 100°C (18.5–22.5 cSt — approximately five times that of LMO); the darkest colour (ASTM ≤5.0 vs ≤L1.0 for LMO); and the heaviest molecular weight. Its oil content in Bio Green Wax's specification (5–20%) overlaps with SPO's range but its other properties are in a class of their own. DAO's extreme properties make it suitable for the most demanding industrial applications and for the production of premium refined wax products.

The melting point of Slack Wax DAO is 69–74°C as measured by ASTM D-87 — the highest of all four slack wax grades. The congealing point (ASTM D-938) is identically 69–74°C. This high melting point reflects DAO's long-chain, high-molecular-weight hydrocarbon composition. In practical terms, it means DAO requires significantly more heat to process than lighter grades — heated storage tanks, insulated pipework, and higher-powered heating systems are typically required in industrial DAO handling facilities.

Bio Green Wax Ltd supplies Slack Wax DAO with an oil content range of 5–20% as measured by ASTM D-721. This range reflects actual supplied product characteristics. For buyers using DAO as feedstock for microcrystalline wax production, the oil content of the incoming slack wax affects the deoiling process efficiency and the yield of finished microcrystalline wax — buyers with specific oil content requirements within the 5–20% range should discuss batch specifications with the sales team.

4 cSt). This extreme viscosity is a direct consequence of DAO's origin from the heaviest refinery distillate fraction. The very long hydrocarbon chains and complex molecular architecture of DAO create far greater intermolecular friction and resistance to flow than lighter grades.

For buyers, this has significant implications for handling infrastructure: DAO requires substantially higher operating temperatures for pumping, larger pump capacities, and well-insulated heated piping and tank systems.

The minimum flash point of Slack Wax DAO is 240°C as measured by ASTM D-93 (Pensky-Martens Closed Cup). This is the highest flash point of all four slack wax grades (LMO 145°C, SPO 200°C, MMO 220°C, DAO 240°C), reflecting the low volatility of DAO's heavy molecular components. The high flash point provides a generous safety margin during heated processing. While DAO is classified as a combustible material, its high flash point makes it one of the safer grades to handle from an ignition risk perspective, provided standard heated wax precautions are maintained.

The specific gravity of Slack Wax DAO at 70°C is 0.825–0.875 (ASTM D-1298) — the highest of all four slack wax grades (LMO: 0.770–0.830, SPO: 0.795–0.850, MMO: 0.785–0.845). This higher density reflects DAO's heavier molecular weight and more compact molecular packing. For buyers handling bulk liquid DAO, the specific gravity is essential for accurate volume-to-weight conversion when calculating tank fills, transport costs, and invoicing from liquid volume measurements.

Slack Wax DAO's most strategically important application is as primary feedstock for microcrystalline wax production — a high-value, fine-crystalline refined wax used in pharmaceuticals (tablet coatings, ointment bases), food coatings, cosmetics, and precision adhesive applications.

Beyond microcrystalline wax production, DAO is used in: heavy rubber compounding and tyre manufacturing; construction waterproofing membranes and dampproofing compounds; pipeline coating and anti-corrosion wax formulations; bitumen and road asphalt modification; heavy-duty corrugated board moisture barriers; electrical cable insulation and jacketing compounds; and industrial adhesives and sealants.

Converting Slack Wax DAO into microcrystalline wax involves two main processing stages. 5–3% depending on the target microcrystalline specification. Second, hydrofinishing (catalytic hydrogen treatment) removes the aromatic and naphthenic colour bodies responsible for DAO's dark amber colour, producing a light-coloured, fine-crystalline finished product.

The resulting microcrystalline wax has a much finer crystal structure than paraffin wax, giving it superior adhesion, flexibility, and moisture barrier properties.

In construction applications, Slack Wax DAO is used in waterproofing membrane formulations and dampproofing compounds applied to foundations, below-grade structures, and roofing systems. Its high melting point (69–74°C) and heavy molecular weight provide excellent thermal stability and durability in membrane applications that may be exposed to elevated temperatures — such as flat roof waterproofing systems subject to summer solar heating. DAO is typically blended with bitumen, polymers, and other modifiers to achieve the desired membrane flexibility and adhesion properties.

Slack Wax DAO is used as a base component in heavy-duty anti-corrosion wax formulations applied to steel pipelines, offshore structures, bridge components, and industrial equipment. Its high melting point ensures the wax film remains intact at elevated service temperatures.

The heavy wax is applied either as a hot melt, as a wax-solvent blend, or as a petrolatum-type compound, forming a thick, durable moisture and oxygen barrier that prevents rust and corrosion on metal surfaces. DAO-based anti-corrosion compounds are particularly valued in aggressive environments such as coastal, marine, and industrial chemical exposure.

Yes, Slack Wax DAO is used as a bitumen modifier and extender in road asphalt and roofing bitumen applications. Adding heavy wax to bitumen can modify its rheological properties — affecting stiffness, viscosity, and temperature susceptibility — to improve road performance at extreme temperatures.

Wax-modified bitumens can show improved rutting resistance at high temperatures and better low-temperature cracking resistance, depending on the specific formulation. DAO's high melting point and heavy molecular weight make it suitable for bitumen modification where a thermally stable modifier is required.

To source Slack Wax DAO from Bio Green Wax Ltd, please submit a product enquiry via biogreenwax.com or contact us at info@biogreenwax.com or +44 20 7101 3847. Please provide your destination country, required monthly volume, preferred Incoterm (FOB, CIF, or DDP), and any specific technical requirements such as oil content range or additional documentation. Our sales team will provide a quotation with pricing, lead time, and available documentation details.

Slack Wax DAO's high melting point (69–74°C) and very high viscosity (18.5–22.5 cSt at 100°C) mean it requires heated infrastructure for liquid handling. Buyers receiving DAO in bulk liquid form need: heated storage tanks capable of maintaining temperature above 74°C; heated and insulated pipework to prevent solidification during transfer; and appropriately rated pumps for high-viscosity fluids. For solid-form deliveries (drums or bags), a heated melting tank is required before processing. These infrastructure requirements should be assessed before placing a first order.

Bio Green Wax Ltd provides full documentation with every Slack Wax DAO shipment, including: Certificate of Analysis (CoA) covering 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, and D-1552 sulphur content; Safety Data Sheet (SDS/MSDS); commercial invoice; packing list; and bill of lading. Certificate of Origin, customs documentation, and any destination-specific regulatory compliance certificates can be arranged on request.

Yes, Bio Green Wax Ltd welcomes long-term supply arrangements for Slack Wax DAO. Contract supply provides buyers with price stability, guaranteed volume allocation, and priority order fulfilment — particularly valuable for processors and manufacturers requiring consistent monthly volumes for continuous production processes such as microcrystalline wax manufacturing or heavy rubber compounding. Contact our sales team at info@biogreenwax.com to discuss contract terms, pricing structures, and supply schedules that match your production requirements.