Caprolactam
A seven-membered ring with an amide in it, and essentially one job. More than 90% of the world's caprolactam is opened up and polymerised into Nylon 6.
Molecular Structure
What is Caprolactam?
Caprolactam is the cyclic amide of 6-aminohexanoic acid — a seven-membered ring holding one nitrogen and one carbonyl, with five methylene groups making up the rest. Seven-membered rings carry enough strain that ring-opening is thermodynamically favourable, and that is the whole basis of Nylon 6. Hydrolytic polymerisation opens the ring and links the units head to tail into a linear polyamide, with no second monomer and no salt formation step required.
The conventional route takes cyclohexanone through oximation with hydroxylamine and then a Beckmann rearrangement in oleum. It works well, but it produces large quantities of ammonium sulphate as a by-product — historically up to four tonnes per tonne of lactam — and the fertiliser value of that sulphate has a material effect on producer economics. Newer routes using ammoximation over titanium silicalite followed by a vapour-phase Beckmann rearrangement cut the sulphate co-product almost entirely.
Purity requirements are unusually strict, and not for the reasons that usually drive purity. Nylon 6 is polymerised to high molecular weight and then spun at high speed, so trace impurities that terminate chains, absorb ultraviolet light or catalyse degradation show up as filament breaks, dye faults and yellowing. That is why the specification is dominated by permanganate number, volatile bases and UV extinction rather than by assay.
Caprolactam is bought on its trace specification, not its assay. Two lots can both read 99.9% and behave completely differently in a spinning line — permanganate absorbing number, volatile bases and extinction at 290 nm are the figures that actually predict how the material will polymerise and spin.
Quick Reference
Key Physical & Chemical Properties
Structure & Bonding
A seven-membered lactam — one nitrogen, one carbonyl and five methylenes. The ring carries enough strain that the amide bond can be opened under hydrolytic conditions, which is precisely what Nylon 6 polymerisation exploits.
Skeletal structure — a seven-membered cyclic amide
Structural Identity
- IUPAC NameAzepan-2-one
- Common namesε-Caprolactam, 6-hexanelactam, CPL
- Molecular FormulaC₆H₁₁NO
- Molecular Weight113.16 g/mol
- Functional groupCyclic secondary amide
- Ring sizeSeven — strained enough to open
- Polymerises toNylon 6 (polyamide 6)
- Made fromCyclohexanone oxime, Beckmann route
- By-productAmmonium sulphate (oleum route)
- CAS Number105-60-2
- InChI KeyJBKVHLHDHHXQEQ-UHFFFAOYSA-N
Product Specifications
Chelora supplies Caprolactam in standard and custom grades. Contact us for specification sheets tailored to your process.
| Chemical name | ε-Caprolactam |
|---|---|
| CAS Number | 105-60-2 |
| Molecular formula | C₆H₁₁NO |
| Molecular weight | 113.16 g/mol |
| Purity (min) | ≥ 99.90 wt% |
| Crystallisation point (min) | ≥ 68.8 °C |
| Permanganate absorbing number (max) | ≤ 5 |
| Volatile bases (max) | ≤ 0.60 meq/kg |
| Free acid or alkali (max) | ≤ 0.10 meq/kg |
| Extinction at 290 nm (max) | ≤ 0.05 |
| Colour, 50% aqueous (max) | ≤ 5 APHA |
| Water — flake (max) | ≤ 0.05 wt% |
| Water — molten (max) | ≤ 0.10 wt% |
| Cyclohexanone oxime (max) | ≤ 5 ppm wt |
| Aniline (max) | ≤ 1.0 ppm wt |
| Iron (max) | ≤ 0.30 ppm wt |
| Ash (max) | ≤ 10 ppm wt |
| Flash point | 125 °C (closed cup) |
| Autoignition temperature | 375 °C |
| Transport classification | Not regulated as dangerous goods |
Downstream Applications & Derivatives
Key derivative chains and industrial uses of Caprolactam.
Nylon 6 Textile Filament
The largest outlet. Partially and fully drawn yarn for apparel, hosiery, swimwear and technical fabrics, where PA6 offers better dyeability and softer handle than PA66.
BCF & Carpet Fibre
Bulked continuous filament for residential and contract carpet. Solution-dyed PA6 gives colourfastness and stain resistance that piece-dyed alternatives struggle to match.
Industrial & Tyre Cord Yarn
High-tenacity yarn for tyre carcass cord, conveyor belting, ropes, webbing and airbag fabric, where fatigue resistance under repeated flexing matters more than absolute modulus.
Engineering Plastics
Glass-filled and mineral-filled PA6 compounds for automotive under-bonnet components, electrical housings, power tool bodies and structural brackets replacing metal.
Nylon 6 Barrier Film
Biaxially oriented PA6 film for vacuum and modified-atmosphere food packaging — oxygen barrier, puncture resistance and thermoformability in a single layer.
Specialities
Lysine synthesis, crosslinking agents, polymer plasticisers and a solvent role in selected coating and pharmaceutical applications.
Why source Caprolactam through Chelora Petrochem?
Verified Origin
Full origin certification and asset-backed supply chain documentation — no grey-market supply.
Grade Flexibility
Fibre and resin grades supplied, in flake or molten form. We specify against permanganate number, volatile bases and UV extinction because those are what your polymerisation and spinning line actually respond to.
Full Documentation
CoA, SDS, REACH compliance, transport documentation, and food-contact or destination-market certificates with every shipment.
Logistics Support
Experienced in both bagged and heated bulk logistics — 25 kg bags and jumbo bags of flake, and insulated, nitrogen-blanketed ISO tanks for molten delivery, Indian and international.
Storage & Handling Guidelines
Always refer to the full SDS before handling. The following is a summary of key requirements.
- Keep dry. Caprolactam is strongly hygroscopic, and moisture pickup is the single most common reason an on-spec lot goes off-spec in the buyer's own warehouse.
- Store flake in sealed, moisture-proof packaging in a cool, dry, ventilated store out of direct sunlight, and rotate stock rather than holding it long.
- Hold molten material at 75–85 °C under a dry nitrogen pad. Above roughly 90 °C in the presence of air, colour and permanganate number degrade measurably within days.
- Minimise time in the molten state altogether. Molten caprolactam is a transfer condition, not a storage form, and every extra day at temperature costs quality.
- Use stainless steel throughout for molten service. Iron pickup shows up as colour and as a UV extinction failure long before it shows up as an assay problem.
- Trace-heat and insulate all lines, valves and pumps. Caprolactam solidifies at about 69 °C and frozen lines are the standard failure mode in molten handling.
- Treat molten material as a thermal burn hazard as well as a chemical one, and provide eyewash and washing facilities at every transfer point.
- Control dust on flake handling and mist at heated transfer points with local extraction — caprolactam vapour and mist are respiratory irritants.
- Segregate from oxidising agents, strong acids and strong bases, and label every container clearly.
Hazard Summary
Classification: Acute Tox. 4 oral (H302), Skin Irrit. 2 (H315), Eye Irrit. 2 (H319), STOT SE 3 respiratory irritation (H335). Caprolactam is moderately hazardous rather than acutely dangerous, and is not classified as a carcinogen.
Respiratory irritation is the main occupational issue: caprolactam dust, vapour and mist irritate the nose, throat and airways at low airborne concentrations. ACGIH lists a TLV-TWA of 5 mg/m³ for the inhalable fraction; apply whichever limit is in force at your site, and control by extraction rather than by respirators alone.
Molten handling: material held at 75–85 °C presents a thermal burn risk in addition to skin and eye irritancy. Splash protection at connections should be specified for hot liquid, not just for chemical contact.
Quality is the commercial risk: caprolactam's real exposure is not toxicological but economic. Moisture pickup, iron contamination and time at temperature will all take a compliant lot off specification, and the resulting yarn faults are usually discovered on the spinning line rather than in the warehouse.
Fire: a combustible solid with a flash point of 125 °C and autoignition at 375 °C. Thermal decomposition releases carbon monoxide, oxides of nitrogen and ammonia, so fire response should assume irritant and toxic combustion products.
Environmental: readily biodegradable and not classified as hazardous to the aquatic environment, but releases should still be contained. Large spills impose a significant oxygen demand on receiving water and on effluent plants.
PPE minimum: safety glasses or goggles, gloves and coveralls for flake handling; face shield, heat-resistant gloves and splash protection for molten service.
Consult the full SDS for exposure limits, spill containment, emergency response and disposal before any use.
Frequently Asked Questions
Technical and commercial questions about Caprolactam sourcing and specifications.
What is caprolactam used for?
Over 90% is polymerised into Nylon 6. Within that, the main outlets are textile filament yarn for apparel and technical fabrics, bulked continuous filament for carpet, high-tenacity industrial yarn for tyre cord and airbag fabric, glass-filled engineering resin for automotive and electrical parts, and biaxially oriented film for food packaging. The small remainder goes into lysine synthesis, crosslinkers and speciality applications.
Why does caprolactam purity matter so much for Nylon 6?
Because the polymer is built to very high molecular weight from a single monomer, so anything that interferes with chain growth has an outsized effect. Monofunctional impurities cap growing chains and cap molecular weight. Basic nitrogen compounds interfere with the polymerisation equilibrium. UV-absorbing species and iron promote yellowing and thermal degradation during spinning. The result is that impurities measured in parts per million determine whether yarn spins cleanly at speed or breaks repeatedly, which is a far tighter constraint than the assay figure suggests.
What is permanganate absorbing number and what does it tell you?
It measures how much permanganate the material consumes under standard conditions, which indicates the concentration of oxidisable impurities — chiefly unsaturated compounds and residual intermediates left over from the oximation and rearrangement steps. It is a broad-spectrum indicator rather than a specific assay, and that is exactly why it is useful: it catches degradation and contamination that no single targeted test would find. Along with volatile bases and extinction at 290 nm, it is the figure fibre producers look at first.
Should I buy flake or molten caprolactam?
It depends on volume and on what you have installed. Molten delivery avoids remelting entirely, which saves energy and avoids a thermal cycle that costs quality, so it suits large integrated polymerisation plants running continuously. It requires insulated, nitrogen-blanketed, trace-heated receiving facilities and a reliable offtake rate. Flake is more flexible, stores far better, and suits smaller or intermittent consumption — at the cost of a melting step and careful moisture control in the warehouse.
Why is ammonium sulphate relevant to caprolactam pricing?
Because the conventional oleum-based Beckmann route generates a great deal of it — historically up to four tonnes per tonne of caprolactam — and the producer has to sell it as fertiliser. When sulphate prices are strong, that credit meaningfully reduces the net cost of the lactam; when they are weak, it becomes a disposal problem instead. Producers running ammoximation and vapour-phase Beckmann routes generate little or none, so their cost position is insulated from the fertiliser market. It is worth knowing which route your supplier operates.
What documentation does Chelora provide?
Every shipment includes a Certificate of Analysis covering purity, crystallisation point, permanganate absorbing number, volatile bases, free acid or alkali, extinction at 290 nm, colour, water, cyclohexanone oxime, aniline, iron and ash; a Safety Data Sheet to GHS and REACH format; confirmation that the material is not regulated as dangerous goods; an origin certificate; and food-contact or destination-market certificates where the application requires them.
Request a quote or specification sheet
Talk to Chelora's sourcing team about Caprolactam grade, volume, logistics, documentation, and lead times. We respond within one business day.
