Zinc isooctanoate reacts rapidly with liberated HCl, neutralising it before it can catalyse further PVC degradation. The products are zinc chloride (ZnCl₂) and free isooctanoic acid. This reaction is fast and efficient - zinc isooctanoate is the primary first-response scavenger. Problem: ZnCl₂ is a Lewis acid that accelerates PVC degradation at elevated concentrations - this is called "zinc burning" and causes rapid discolouration if zinc is not replenished.

Calcium isooctanoate reacts with the ZnCl₂ product of Step 1 to regenerate zinc isooctanoate and form harmless calcium chloride (CaCl₂). This metathesis reaction (ligand exchange) effectively replenishes the zinc stabiliser capacity and prevents ZnCl₂ build-up. Calcium acts as a sacrificial co-stabiliser - it is consumed but in doing so maintains the active zinc isooctanoate pool throughout the processing window.

Zinc isooctanoate's reaction with HCl generates ZnCl₂ as a byproduct. ZnCl₂ is a Lewis acid that coordinates with the PVC backbone and catalyses dehydrochlorination - the very process the stabiliser is supposed to prevent. If too much zinc is used relative to calcium (high Zn/Ca ratio), ZnCl₂ accumulates faster than calcium can convert it back to zinc isooctanoate, causing a sudden rapid degradation (known as "zinc burn" or "zinc kick") characterised by an abrupt colour change from yellow to black.

Zinc can form soaps with many fatty acids. The isooctanoate is preferred in liquid Ca/Zn one-pack systems for the following reasons:

• Liquid at RT → compatible with liquid one-pack formulation philosophy
• High Zn% per gram (MW 144, AV ~385) → efficient metal loading in stabiliser
• Oil-soluble → compatible with liquid paraffin and plasticiser-based stabiliser systems
• Good hydrolytic stability (α-ethyl branch) → shelf life of stabiliser solution

Note: Zinc stearate is used in solid Ca/Zn stabiliser systems (powder/flake form); zinc isooctanoate is specifically for liquid stabiliser formulations.

• Secondary HCl scavenger: Ca(isooctanoate)₂ + 2HCl → CaCl₂ + 2 IOA - slower than zinc reaction, serves as backup
• Zinc replenisher: Key function - converts ZnCl₂ back to Zn(isooctanoate)₂ via metathesis
• Thermal buffer: Calcium salts moderate the temperature profile during extrusion, reducing hot spots
• Lubrication: As a soap, calcium isooctanoate contributes mild external lubrication to PVC melt, reducing friction on processing equipment surfaces
• Compatibility: Good compatibility with plasticisers (DOTP, DINCH), epoxidised soybean oil (ESBO), and antioxidants in the one-pack formulation

PVC wire and cable insulation and jacket compounds use Ca/Zn stabilisers for low-voltage electrical cables, data cables, and building wires. This is one of the largest PVC stabiliser markets globally. The RoHS Directive in the EU specifically prohibits lead in electrical and electronic equipment, accelerating the Ca/Zn transition in this sector. Ca/Zn one-packs are added at 2–4 phr in flexible PVC cable compounds.

Rigid PVC window profiles require stabilisers with outstanding long-term heat and UV stability - profiles must maintain whiteness and dimensional stability for 25–40 years in outdoor exposure. While Ca/Zn stabilisers are used in profiles, organotin (for EU premium products) and calcium/zinc mixed-metal systems compete here. IOA-based Ca/Zn one-packs are particularly used in Asian and emerging-market profile production where cost efficiency is important.

Flexible PVC flooring (LVT, homogeneous vinyl), decorative film, and packaging film rely on Ca/Zn stabilisers. The flexible nature of these products (high plasticiser content, 30–50 phr DOTP) means the stabiliser must be compatible with the plasticiser system and must not cause plasticiser interaction or bloom. Isooctanoate-based Ca/Zn systems are preferred in these applications because of their good plasticiser compatibility.

PVC plastisol (a paste-form PVC compound) for coated fabrics, gloves, and automotive underseal requires liquid stabiliser systems that disperse uniformly in the plastisol without affecting viscosity unduly. Ca/Zn liquid one-packs are ideal for plastisol stabilisation - the oil-soluble isooctanoate metal soaps disperse readily in the plasticiser-rich plastisol medium without creating lumps or gel particles.

Isooctanoic acid adsorbs onto ferrous and non-ferrous metal surfaces via the carboxylate group, forming a protective monolayer that displaces water and oxygen from the metal surface. This surface-active corrosion inhibition mechanism is particularly effective in water-containing metalworking fluid systems where metal surfaces are continuously exposed to aqueous environments.

• Effective on steel, cast iron, aluminium, and copper alloys
• Used alone or in amine salt form (amine isooctanoate) for better water compatibility in semi-synthetic MWF
• Typical treat rate: 0.5–2.0 wt% in metalworking concentrate

Molybdenum isooctanoate and antimony isooctanoate are oil-soluble EP additives used in gear oils, cutting fluids, and industrial lubricants operating under high-load/high-temperature conditions. Under EP conditions, the metal soap thermally decomposes at the tribological contact zone, forming a protective sacrificial film (MoS₂, Sb compounds) that prevents metal-to-metal contact and scuffing.

• Mo isooctanoate (1–3% Mo): gear oils, engine oils (friction modifier + EP)
• Sb isooctanoate: cutting fluids; lower-cost EP alternative to Mo
• Zinc isooctanoate (ZDTP alternative): anti-wear in low-zinc lubricant systems

Isooctanoic acid and its amine salts are used directly in metalworking fluid (MWF) concentrates for:

• Neat cutting oils (straight oils): IOA contributes lubricity to the hydrocarbon base; metal soaps improve boundary lubrication
• Soluble (emulsion) oils: amine salt of IOA acts as emulsifier + corrosion inhibitor in the water-diluted cutting fluid
• Semi-synthetic fluids: IOA derivatives bridge the oil and water phases, providing both lubricity and corrosion protection
• Aluminium processing: IOA-based corrosion inhibitors are particularly effective for aluminium alloys, which are sensitive to many conventional inhibitors

Lithium, calcium, and aluminium soaps of isooctanoic acid can be used as minor components in grease formulations. Calcium isooctanoate contributes mild thickening and water resistance in complex-grease systems. In industrial gear oils, zinc isooctanoate serves as a mild anti-wear additive that is more environmentally acceptable than conventional zinc dialkyldithiophosphate (ZDDP) in applications requiring low-ash lubricants.

• Acid value: 375–395 mg KOH/g - must be consistent batch-to-batch for reproducible metal soap synthesis stoichiometry
• APHA colour: ≤ 30 (lower colour → paler Ca/Zn stabiliser → better PVC appearance)
• Water content: ≤ 0.05% - critical; water causes cloudiness in metal salt solutions and side reactions in synthesis
• Acidity consistency: Variance in AV between batches < ±5 mg KOH/g - for batch-to-batch stabiliser quality control
• Iron content: ≤ 5 ppm - iron contamination causes discolouration of PVC; specify and test

• Acid value: 375–395 mg KOH/g - controls metal salt conversion in Mo/Zn soap synthesis
• APHA colour: ≤ 50 - some discolouration tolerated in lubricant applications
• Water content: ≤ 0.1% - lower water reduces foaming in MWF systems and improves stability of organometallic synthesis
• Sulphur content: Specify if low-sulphur lubricant application; some synthesis routes may introduce trace sulphur
• Chloride content: ≤ 10 ppm - chloride causes corrosion of metal workpieces and equipment in MWF application

Q1: Why do Ca/Zn stabilisers need both calcium and zinc isooctanoate? Can zinc alone stabilise PVC?

Zinc isooctanoate alone cannot provide sustained PVC stabilisation because of the "zinc burning" problem. When zinc isooctanoate reacts with HCl (Step 1 of the mechanism), it produces zinc chloride (ZnCl₂). At even moderate concentrations, ZnCl₂ is a Lewis acid that dramatically accelerates PVC dehydrochlorination - the exact process the stabiliser is supposed to prevent. So zinc-only systems work very briefly and then cause catastrophic rapid degradation. Calcium isooctanoate is essential as the zinc replenisher (Step 2): it converts ZnCl₂ back to zinc isooctanoate, keeping the active zinc pool available throughout the processing window. The Ca:Zn ratio (typically 3:1 to 8:1 by metal) must be maintained - too little calcium and zinc burning occurs; too much zinc and the calcium is consumed too quickly. This is why both metal soaps, at the right ratio, are required in every Ca/Zn stabiliser system.

Q2: How do Ca/Zn stabilisers compare to organotin stabilisers for PVC?

Organotin stabilisers (dibutyltin maleate, DBTDL, methyltin, etc.) offer superior thermal stabilisation performance - higher initial colour, longer heat stability, and excellent lubrication - which is why they remain the dominant stabiliser for demanding applications like clear PVC bottles, thin-film extrusion, and premium window profiles in Europe. Ca/Zn stabilisers are generally less thermally efficient (shorter processing window before colour change) and require more complex formulation (ESBO synergist, β-diketone, phosphite co-stabiliser) to approach organotin performance. However, Ca/Zn systems have two decisive regulatory advantages: they contain no tin (organotin compounds are increasingly restricted due to toxicity); and they can be formulated completely without SVHC or CMR substances. For RoHS-compliant cables, food-contact flexible PVC, toys, and medical applications, Ca/Zn is the preferred or only compliant option. For cost-sensitive applications in Asia and emerging markets, Ca/Zn is also economically preferred.

Q3: What is the typical phr addition level for a Ca/Zn one-pack in PVC cable compound?

For PVC wire and cable compounds (flexible PVC for insulation and jacketing), a liquid Ca/Zn one-pack stabiliser is typically added at 2–4 phr (parts per hundred parts PVC resin). At 2 phr, the system provides acceptable thermal stability for standard low-voltage cables processed at 170–185°C. At 3–4 phr, extended processing windows and better long-term heat ageing performance are achieved for higher-specification cables or higher processing temperatures. The specific addition level depends on: the PVC formulation (degree of plasticisation, filler loading); processing temperature and residence time; service temperature requirements; and the specific one-pack's metal content (a one-pack with 1% total metal by weight will need a higher phr addition than one with 2% total metal to achieve the same effective metal concentration in the final compound). Always base addition levels on the one-pack supplier's technical data sheet, confirmed by your own processing trials.

Q4: Can isooctanoic acid be used as a corrosion inhibitor directly in metalworking fluids?

Yes - isooctanoic acid itself is surface-active and can adsorb onto metal surfaces to form a protective barrier layer, providing a degree of ferrous corrosion inhibition in neat and oil-soluble systems. However, free IOA has poor water solubility (~0.1 g/100 mL) and would not distribute effectively in the water phase of emulsion or semi-synthetic MWF. For water-containing MWF, the preferred form is an amine salt of isooctanoic acid (e.g., triethanolamine isooctanoate, monoethanolamine isooctanoate), which is water-compatible and provides both corrosion inhibition and mild emulsification. The amine neutralises the acid group, making the salt water-soluble while retaining the surface-active C8 chain for metal surface adsorption. Treat rates for amine isooctanoate in MWF concentrates are typically 1–3 wt%, with the diluted in-use fluid concentration at 0.02–0.06 wt% isooctanoate.

Q5: How does iron contamination in isooctanoic acid affect PVC stabiliser performance?

Iron contamination in isooctanoic acid is particularly detrimental in PVC stabiliser applications. Iron ions (Fe²⁺/Fe³⁺) are pro-oxidants that catalyse oxidative degradation reactions in PVC and in the stabiliser components, producing colour bodies and accelerating discolouration of the PVC compound. Even at trace levels (above ~10 ppm Fe in the IOA), iron contamination can cause: visible yellowing of white or light-coloured PVC products; reduction in the effective processing window (Fe accelerates the degradation reactions the stabiliser is trying to prevent); discolouration of the stabiliser solution itself (pale yellow to orange if Fe is high). Iron typically enters isooctanoic acid from contact with iron piping or storage vessels in the manufacturing or logistics chain. Specify Fe ≤ 5 ppm in your IOA purchase specification if it is destined for light-coloured PVC stabiliser applications, and use dedicated stainless steel storage to prevent re-contamination after delivery.

Q6: Is there a difference between isooctanoic acid grades for PVC stabiliser vs lubricant applications?

Yes - PVC stabiliser applications are more demanding on colour and iron content than most lubricant applications. For PVC stabiliser synthesis (Ca/Zn isooctanoate production), the ideal IOA specification is: APHA colour ≤ 30 (low colour gives pale stabiliser solutions, which is important for white PVC), iron ≤ 5 ppm (prevents catalytic yellowing), and water ≤ 0.05% (prevents cloudiness in the Ca/Zn solution). For lubricant applications (Mo, Zn, or Ca soap synthesis for MWF or gear oil additives), APHA ≤ 50 is typically acceptable and iron content is less critical (lubricant performance is not sensitive to iron at these trace levels). Both applications require similar acid value (375–395 mg KOH/g) and water content (≤ 0.1%). Sinolook Chemical can supply isooctanoic acid that meets both sets of requirements - contact us for your specific grade and volume needs.