Emulsifiers for Explosives

What Are Emulsifiers for Explosives?

Emulsifiers for explosives are specialized surfactants that create and stabilize water-in-oil (W/O) emulsions — the core structure of modern industrial emulsion explosives. In these formulations, microscopic droplets of an aqueous oxidizer solution (typically ammonium nitrate at 70–85% concentration) are dispersed as the internal phase within a continuous fuel oil phase. Without an effective emulsifier, the two immiscible phases would separate within hours — the ammonium nitrate would crystallize, the fuel would pool, and the explosive would lose sensitivity and become a safety hazard.

The emulsifier molecule sits at the oil-water interface, wrapping each oxidizer droplet in a molecular shell — the same fundamental emulsifier mechanism that operates in lubricants, but optimized for the extreme oxidizer loads and safety requirements of explosive formulations. This arrangement lowers interfacial tension, prevents droplet coalescence, and creates a durable structural matrix that can survive transport, borehole loading, and weeks of underground storage. Industry shorthand includes "explosive emulsifiers," "emulsion explosive surfactants," and "ANFO emulsion stabilizers." The products on this page supply the mining, tunneling, quarrying, and construction blasting industries — anywhere controlled, high-energy detonation is required.

How Do Explosive Emulsifiers Work?

The mechanism is fundamentally about interfacial stabilization. When an emulsifier is dissolved in the oil phase and mixed with the aqueous oxidizer under high shear, the molecules migrate to the newly formed oil-water interfaces. Their polar head groups (the succinic anhydride ring in PIBSA, or the sorbitan/sorbide ester group in S80) orient toward the water droplet surface via hydrogen bonding and dipole interactions. The non-polar hydrocarbon tail — a polyisobutylene chain in PIBSA, or a fatty acid chain in sorbitan esters — extends into the surrounding oil phase, creating a steric barrier that prevents adjacent droplets from touching and merging.

The quality of the emulsion depends on three factors the emulsifier directly controls: droplet size distribution (the finer and more uniform the droplets, the more stable the emulsion — PIBSA typically produces 1–5 μm droplets); interfacial film strength (the molecular film must resist thermal expansion, mechanical vibration, and the osmotic pressure that drives water across the oil membrane); and compatibility with the fuel phase (the emulsifier must fully dissolve in the chosen oil — mineral oil, diesel, recycled oil, or wax — without precipitating at storage temperatures). A well-formulated PIBSA-based emulsion can maintain droplet integrity for over 12 months; a poorly stabilized one can crystallize within 48 hours.

Key performance indicators include sleep time — how long the emulsified explosive can sit in a borehole before detonation without losing sensitivity; shear stability — resistance to emulsion breakdown during pumping through long hose lines in bulk delivery trucks; and water resistance — the continuous oil phase acts as a natural moisture barrier, critical for wet boreholes and underwater blasting. These are measured through rheology (viscosity vs. shear rate), droplet size analysis (optical microscopy or laser diffraction), and thermal cycling tests (cycling between -20°C and 50°C to simulate field conditions).

Explosive Emulsifier Chemistry Types

Two chemistry types dominate commercial emulsion explosive formulations: polymeric PIBSA-based emulsifiers and monomeric sorbitan ester-based emulsifiers. They are not interchangeable — each has a distinct molecular architecture, performance window, and cost position. Many large-scale mining operations use both in combination: PIBSA as the primary emulsifier for long-term stability, sorbitan ester as a co-emulsifier to fine-tune viscosity build and gas bubble retention. CheMost manufactures both types at the Jinzhou factory, produced through thermal adduction (PIBSA — zero chlorine) and esterification (S80) respectively.

PIBSA vs. Sorbitan Ester — Synergy, Not Competition

In practice, these two chemistries are not either/or — the best-performing bulk emulsion formulations use PIBSA as the primary emulsifier (0.5–1.5%) and sorbitan ester as the co-emulsifier (0.2–0.8%) to create a mixed interfacial film. The PIBSA provides the long-term steric barrier through its bulky polyisobutylene chains; the sorbitan ester packs into the gaps between PIBSA molecules, densifying the film and enabling faster initial viscosity build for gas bubble entrapment. This synergistic effect is well-documented in the patent literature — WO2017103635A1 describes PIBSA + sorbitan ester systems that outperform either chemistry used alone. CheMost's PIBSA and S80 grades are designed to be compatible co-emulsifiers in the same formulation. Beyond explosives, PIBSA is also the key precursor for ashless dispersants (PIBSI) and serves as a tackiness agent in industrial lubricants — learn more about PIBSA chemistry.

How to Select an Explosive Emulsifier

• Emulsion type: packaged vs. bulk. Packaged explosives (cartridges) need emulsifiers that deliver maximum shelf stability — PIBSA alone at 1.0–1.5% is the standard choice, often with wax in the fuel phase for additional structure. Bulk explosives (pumped from truck into borehole) need emulsifiers that build viscosity quickly to trap gas bubbles for sensitization — this is where S80 co-emulsifier (0.3–0.8%) makes the difference. Bulk formulations also demand higher shear stability to survive pumping through 50–100 meters of hose at 200–400 L/min.
• Sleep time requirements. If the explosive sits in the borehole for hours before firing (typical quarry blast), sorbitan ester-only formulations are adequate. If it sits for days or weeks (underground mining with sequential blasting schedules), PIBSA's long-term stability is essential. PIBSA-based emulsions routinely achieve sleep times of 7–30 days; S80-only formulations typically deliver 1–3 days before sensitivity loss begins.
• Oil phase composition. PIBSA dissolves readily in a wide range of fuel oils — mineral oil, diesel, paraffinic oil, and increasingly recycled oils (used engine oil, waste oil) as sustainability requirements grow. Sorbitan esters have narrower compatibility: they perform well in diesel and mineral oil but can precipitate in highly paraffinic or recycled oil blends. If your fuel phase includes recycled oil, PIBSA is the safer choice. Clariant's PIBSA line (ARKOMON) specifically markets compatibility with recycled oil formulations.
• Chlorine content — a hard pass/fail. PIBSA manufactured via the traditional chlorination route contains residual chlorine that can corrode equipment and interfere with emulsion stability. CheMost's thermal process uses no chlorine — the PIBSA activity is ≥99% with residual maleic anhydride below 0.5% and zero halogen content. This matters for mining companies with environmental discharge permits that monitor halogenated compounds. Always verify the manufacturing route — thermal adduction PIBSA commands a premium over chlorinated PIBSA for good reason.
• Temperature conditions at the mine site. PIBSA is a viscous liquid (650 mm²/s at 100°C) that requires heated storage (40–60°C) and heated pumping. In cold climates or remote sites without reliable heating infrastructure, S80's lower viscosity and easier handling become operational advantages. Conversely, in hot climates (Australian outback, South American desert mines) where emulsion temperatures can exceed 40°C in the borehole, PIBSA's thermal stability is non-negotiable — S80-only emulsions weaken and collapse under these conditions.
• Regulatory and safety compliance. Emulsion explosives are classified as Class 5.1 (oxidizing substances) during transport. The emulsifier itself is not classified as dangerous goods, but the finished emulsion's classification depends on the ammonium nitrate content and sensitization method. CheMost provides full MSDS and TDS documentation for both PIBSA and S80 grades. For mining operations subject to the Global Industry Standard on Tailings Management (GISTM) or similar ESG frameworks, the chlorine-free manufacturing route and the ability to formulate with recycled oils are documented points of differentiation in sustainability audits.

Applications of Explosive Emulsifiers