Polyamide 6 is the most widespread engineering polyamide in the world and the base material from which most «nylon» parts start. We break down what defines its properties, why it is so sensitive to moisture, and how to run it correctly through processing.
Definition and nomenclature
Polyamide 6 (PA6; colloquially — nylon-6, kapron, kaprolon) is a semi-crystalline thermoplastic polymer of the aliphatic polyamide class. It is obtained by ring-opening polymerization of ε-caprolactam. Unlike PA66, which requires two monomers, PA6 is synthesized from just one — this simplifies control of molecular weight and makes the process cheaper on an industrial scale. By industry estimates, PA6 is one of the most produced engineering polyamides on the planet.
| Parameter | Designation |
|---|---|
| Abbreviation per ISO 1043-1 | PA6 |
| Systematic name | poly(ε-caprolactam) |
| CAS Number | 25038-54-4 |
| Repeating unit | –[NH–(CH₂)₅–CO]– |
| Traditional names | kapron, nylon 6, polyamide 6 |
A little history
The first industrial PA6 was synthesized by Paul Schlack in Germany in 1938 under the trade name «Perlon» — at roughly the same period when DuPont were finishing their work on PA66. The two monomer routes turned out to be competing solutions to a single problem: creating a synthetic fibre. PA6 has been processed in Ukraine for decades, yet primary caprolactam today is predominantly imported — the domestic market runs on imported feedstock and European and Asian compounds.
Chemistry and structure: why PA6 is sensitive to moisture
The PA6 molecule is a long linear chain in which the amide groups –CO–NH– are separated by segments of five methylene (–CH₂–) links. Picture «street lamps» (the amide groups) along a road: in PA6 they stand close together. It is precisely between them that interchain hydrogen bonds N–H···O=C arise — the «glue» that gives dry PA6 a modulus of around 3 GPa without any reinforcement.
These same hydrogen bonds are the reason for its high water absorption. Water molecules readily embed themselves between the amide groups, breaking the bridges and acting as a plasticizer. That is why, in a humid environment, PA6 typically takes up to 9–10% water by mass, and its modulus in the conditioned state drops roughly by half. This is not a defect but a feature of the class, one that simply has to be designed in.
PA6 is a semi-crystalline polymer: in a moulded part the more stable α-form and the metastable γ-form coexist, and the base degree of crystallinity is typically 30–45%. It depends on the cooling rate, the mould temperature, and the presence of nucleating agents and fillers — hence the noticeable influence of the moulding regime on the final properties.
Properties
The values below are typical for the class of unfilled PA6, not the data sheet of a specific grade. Note the two columns: dry state and conditioned (50% relative humidity) — the difference illustrates the moisture dependence.
| Parameter | Dry | Cond. (50% RH) | Method |
|---|---|---|---|
| Density | 1,14 g/cm³ | 1,14 g/cm³ | ISO 1183 |
| Tensile modulus | ≈3,0 GPa | 1,5–1,7 GPa | ISO 527 |
| Tensile strength | ≈80 MPa | 55–65 MPa | ISO 527 |
| Elongation at break | 50–70% | 150–300% | ISO 527 |
| Charpy notched impact strength | 5–8 kJ/m² | 12–25 kJ/m² | ISO 179 |
| Melting temperature | ≈220 °C | ISO 11357 | |
| Glass transition (Tg), dry | 50–60 °C | ISO 11357 | |
| HDT at 1,82 MPa | ≈70 °C | ISO 75 | |
| Water absorption to saturation | 8,5–9,5% | ISO 62 | |
Drying and processing
The main processing method for PA6 is injection moulding. A typical barrel temperature profile is roughly 240→270 °C, with a mould temperature of 60–90 °C (higher for glass-filled grades). For profiles, pipes, films, and monofilament, extrusion of grades with higher melt viscosity is used.
The most critical step is drying. PA6 absorbs moisture from the air very quickly, and moulding «wet» pellets produces scrap: silver streaks, bubbles, a drop in mechanical performance. That is why the pellets are dried to a residual moisture typically ≤0,2% and processed immediately. Examid® PA6 leaves the MW warehouse with controlled moisture — for small runs from a freshly opened bag you can often go straight to processing without additional drying, but for series production a dryer is put in line.
PA6 modifications and the Material Wizard range
«Pure» PA6 is only a starting point. Real engineering tasks are covered by its modifications, and it is precisely these that make up the Material Wizard range. We manufacture PA6 grades to our own formulation; each is comparable in characteristics to well-known European analogues and is shipped with a batch certificate.
| Modification | What it delivers | Approximate modulus |
|---|---|---|
| Glass-filled (GF15…GF50) | stiffness, heat resistance, dimensional stability | 5–16 GPa |
| Carbon fibre (CF) — carbon-nylon | maximum specific stiffness, ESD/antistatic | 16–30 GPa |
| Impact-modified (HI) | high impact strength, cold resistance | 2,0–2,3 GPa |
| Self-extinguishing (FR) | UL94 V-0 flammability, halogen-free | depends on the base |
| Special (P1136, N6005, LM) | cable ties, thin-walled products, laser marking | close to the base |
CF is shown here only as one of the reinforcement directions for stiffness comparison. Below are the base grades most often requested by Ukrainian process engineers.
Examid® PA6 GF30Glass-filled polyamide 6 — the base grade for series mouldingModulus ≈9 GPa · HDT ≈215 °C · 30% glass fibreRequest supply terms → Examid® PA6 CF30Electrically conductive carbon-nylon for ESD/ATEXHigh specific stiffness · Antistatic · Low densityRequest supply terms → Examid® PA6 HIImpact-resistant, elastomer-modified polyamide 6Increased impact strength · Cold-resistant applicationsRequest supply terms → Examid® PA6 GF50 R10Maximum glass fibre with an impact modifierModulus ≈16 GPa · Metal replacement · Impact R10Request supply terms → Examid® PA6 P1136Special feedstock for cable tiesLubricant + nucleating agent · Stable geometryRequest supply terms → Examid® PA6 N6005High-flow polyamide 6 for thin-walled productsHigh flow · Fills thin wallsRequest supply terms →The base glass-filled grades are convenient to compare on the PA6 GF30 hub; the carbon-filled ones — on the PA-CF hub. If you need maximum stability in water or in the cold, look towards polyamide 12; we broke down the difference between the bases in the article PA66 versus PA6.
Designation and standards
The base format is PA6 or PA6-GF30 per ISO 1043-1; extended specifications — per ISO 1874. Ukrainian process engineers usually look for a grade by its ISO code rather than by a brand name, because switching between suppliers is common practice. For flammability under UL94, the base grade and most GF grades have a class of HB or V-2, while special halogen-free formulations reach V-0. Pure PA6 contains no substances from the SVHC list under REACH.
Recycling
PA6 is one of the best-recycled engineering polymers. Mechanical recycling (grinding, cleaning, re-granulation) yields a regranulate which, for demanding applications, is blended with virgin material. Chemical recycling also exists — depolymerization back to caprolactam. Material Wizard works with recycled polyamides in its compound development programme — details on the recycled polymers hub.
Limitations worth knowing in advance
PA6 is an all-rounder, but not a «material for everything». Its properties depend strongly on moisture, so for precision electronics or stable dimensions in a humid environment, PA12, PA610, or PPA are more often chosen. Strong concentrated acids (formic, sulfuric) dissolve it. Without a UV stabilizer, PA6 degrades in the sun. And unfilled PA6 warps in 3D printing due to high shrinkage — for printing, reinforced grades are almost always used.
What to check before a production run
- The residual moisture of the pellets before moulding/extrusion and the actual drying regime.
- The dimensional stability of the part after conditioning and «wet–dry» cycles.
- The impact strength on the actual part at the minimum service temperature.
- Ageing in contact with the working medium (lubricants, fuel, hot water, UV).
- For GF/CF grades — wear of the mould, screw, and hot runner, and anisotropy due to fibre orientation.
- Batch-to-batch consistency of characteristics and behaviour after reprocessing of scrap.
Expert breakdown: 5 questions worth asking before choosing PA6
1. In what state will the part work — dry or wet? Calculating «for stiffness» using the dry figures of PA6 in a humid assembly leads to underestimating deflections. Design in the conditioned values.
2. What is the real maximum temperature? Continuously above roughly 100–120 °C for base PA6 is a risk zone; look at heat-stabilized GF grades, PA66, or a higher class.
3. Is the stiffness needed from the material or from the geometry? Sometimes a stiffening rib is cheaper than switching to a GF/CF compound; if not — reinforcement gives a several-fold increase in modulus.
4. Are there flammability requirements in the specification? Base PA6 is HB; for electrical engineering, design in a self-extinguishing V-0 grade from the outset, rather than «we’ll sort it out later».
5. Is the drying logic accounted for in production? «Wet» pellets are the most common cause of PA6 scrap. A dryer and moisture control must be part of the technology, not an option.
FAQ
How does polyamide 6 differ from PA66 in simple terms?
PA6 is synthesized from one monomer (ε-caprolactam), PA66 — from two. In practice PA66 melts higher (around 260 versus 220 °C), takes up less water in the saturated state, and is a little more heat-stable, but more expensive. PA6 is more processable and more available — a rational choice for a wide range of parts with a service temperature of roughly up to 80–120 °C.
How long and under what conditions should PA6 be dried before processing?
Roughly 4–6 hours at 80 °C in a hot-air dryer with dehumidified air, or 2–4 hours in a vacuum pellet dryer; the target residual moisture is typically ≤0,2% (lower for reinforced grades). After drying, the pellets take up moisture from the air again within hours, so they are processed immediately or stored in a heated hopper.
Why does PA6 change its properties so strongly with moisture?
The strength of the polyamide is held by hydrogen bonds between the amide groups. Water molecules embed themselves between them and act as a plasticizer: the material becomes more flexible and tougher, but the modulus in the conditioned state can drop by roughly half compared with the dry state. This is only partially reversible — each «wet–dry» cycle leaves small losses.
Can PA6 be printed on a 3D printer?
Yes, but base unfilled PA6 warps strongly due to high shrinkage. In practice, for FDM one takes PA6 with reinforcement (glass or carbon fibre — carbon-nylon): it reduces warping and gives rigid functional parts. Dry pellets/filament, a high-temperature zone, and a heated bed and, ideally, an enclosure are required.
Can polyamide 6 be bought in Ukraine?
Yes. Material Wizard manufactures, to its own formulation, a range of PA6 grades — from base unreinforced to glass-filled, impact-resistant, and electrically conductive compounds — and ships pellets from warehouses in Derazhnia and Kharkiv. You can buy with delivery across Ukraine; check the availability of a specific grade and the terms with a specialist.
Material Wizard — a Ukrainian manufacturer and supplier of engineering polymers: technical grade selection, samples for testing, warehouses in Derazhnia and Kharkiv.