The Compound · Materials
When Standard Nylon Isn’t Enough: PA6T and PPA Compounds
Glass-filled PA66 covers a remarkable share of engineering parts. Two things eventually beat it: sustained heat close to its limits, and the stiffness it loses once it has absorbed water. Semi-aromatic polyamides answer both. The price is paid partly in the resin and partly on the shop floor, and it is worth understanding both before a drawing calls for a PA6T compound.
What "semi-aromatic" means
PA6 and PA66 are aliphatic: their backbones are flexible chains of CH₂ groups between amide links. Replace the adipic acid in PA66 with terephthalic acid and you get PA6T, with a rigid benzene ring in every repeat unit. Pure PA6T melts at 371 °C, too high to process without degrading it. Commercial grades are therefore copolymers, most commonly PA6T/6I, PA6T/66 and PA6T/DT.
ASTM D5336 defines a polyphthalamide as a polyamide in which terephthalic acid, isophthalic acid or a combination makes up at least 55 mol% of the diacid portion. The ratio matters. More terephthalic acid raises the glass transition temperature, and if more than 55% of the acid is isophthalic, the copolymer becomes amorphous.
PA6/6T (also written PA6T/6) combines caprolactam-based PA6 units with 6T units. It melts lower than PA6T/6I and processes much more like a conventional nylon. "HTN", short for high-temperature nylon, is a commercial label rather than a chemical class, so always ask for the ISO 1043 designation.
How they compare
| Property | PA66 GF30 | PA6/6T GF35 | PA6T/6I GF35 |
|---|---|---|---|
| Melting point (DSC) | 260 °C | 295 °C | 320 °C |
| HDT A at 1.8 MPa | 250 °C | 245 °C | above 280 °C |
| Tensile modulus, dry / conditioned | 10,000 / 7,200 MPa | 12,000 / 12,000 MPa | 14,000 / 14,000 MPa |
| Moisture at 23 °C / 50% RH | 1.5–1.9% | 0.8–1.2% | 1.6% |
| Water absorption at saturation | 5.2–5.8% | 4.3–5.3% | 3.8% |
| CTE along / across flow (10⁻⁶/K) | 28 / 88 | 15 / 65 | 22 / 51–53 |
| Melt temperature | 280–300 °C | 310–330 °C | 335–355 °C |
| Mould temperature | 80–90 °C | 80–120 °C | 140–170 °C |
Typical values from BASF datasheets: Ultramid A3EG6, Ultramid T KR 4355 G7 and Ultramid Advanced T1000HG7. Glass contents differ (30% against 35%), so compare trends rather than decimals.
Two results deserve a second look. The PA6/6T grade does not beat PA66 GF30 on HDT. Its case is stiffness that ignores moisture, and creep: a 1,000-hour creep modulus of 8,700 MPa (conditioned), against 5,300 MPa for the PA66 grade. Second, the PA6T/6I grade takes up about as much moisture at 50% RH as PA66 GF30, yet its modulus does not change. The water is still there. Its high glass transition means the absorbed water no longer softens the material at room temperature. Hot data confirm it: 12,500 MPa at 80 °C and 10,000 MPa at 120 °C, dry.
Where PPA earns its place
- Coolant and thermal management. Thermostat housings, pumps and cooling-system parts appear among the listed applications for the PA6T/6I grade above, alongside fuel systems and fuel cells.
- Electronics assembled by reflow. A high melting point allows surface-mount parts to be soldered with lead-free processes; connectors and sensors are typical.
- Lighting. LED headlight components are an established use.
- High-glass metal replacement. Where 50–70% glass is needed for rigidity, see our note on metal replacement.
- Electric vehicles. Covered in plastics in electric vehicles.
What changes on the shop floor
Tool heating. The PA6T/6I GF35 grade lists a mould temperature of 140–170 °C, and a 50% glass grade 150–180 °C, with at least 150 °C recommended. That means oil or high-pressure water units, insulating plates between mould and platen, and insulation on the outside of large tools. A cold tool leaves the polymer under-crystallised: poor surface, and parts that keep shrinking the first time they see heat in service.
Melt and residence time. Melt temperatures run around 335–355 °C. The 50% glass grade allows a maximum residence time of five minutes, so match the barrel to the shot weight.
Drying. The same 50% glass grade asks for 0.03% moisture, 0.05% at most, reached at 120 °C for eight hours in a dry-air dryer. DuPont's limit for standard nylon is below 0.2%. Our guide to drying nylon before moulding covers dryer practice.
Wear. High glass loadings are abrasive. Hardened screws, barrels and cavity steels pay for themselves.
The PA6/6T bridge. The PA6/6T grade runs at 310–330 °C melt with an 80–120 °C mould, within reach of water-heated tools. For moulders without oil-heated tooling, it is often the practical first step up from PA66.
OSAMIDE semi-aromatic grades
Our OSAMIDE range includes five semi-aromatic grades:
- RAG 7 — PA6T/6I, 35% glass fibre.
- RAG 10 — PA6T/6I, 50% glass fibre, heat-stabilised.
- RAG 12 — PA6T/6I, 60% glass fibre, heat-stabilised.
- RAG 14 — PA6T/6I, 70% glass fibre, heat-stabilised.
- CG10 H — PA6/6T, 50% glass fibre, heat-stabilised.
Flame-retardant, UV-stabilised and coloured versions can be developed on request. If you are deciding whether you need PPA at all, start with PA66 GF30 vs PA6 GF30, or browse the material finder.
FAQ
Can I mould PPA in a tool built for PA66?
The geometry often transfers; the heating often does not. Check that the tool can hold 140–170 °C evenly, that sliding fits and ejectors allow for steel expansion at that temperature, and that the steel is hardened for high glass content. Shrinkage also differs, so plan a trial.
Does PPA absorb water?
Yes, though less at saturation: 3.8% for the PA6T/6I GF35 grade against 5.2–5.8% for PA66 GF30 in the reference data. The more important difference is that its modulus is unchanged after conditioning.
Is "HTN" the same as PPA?
Not necessarily. "HTN" is a commercial label used for several high-temperature polyamides. Ask for the ISO 1043 designation, such as PA6T/6I-GF35, and compare grades on that basis.
Weighing PA66 against a semi-aromatic grade? Send your temperature profile and environment through our contact page and we will send TDS and samples of OSAMIDE RAG 7, RAG 10 or CG10 H for your trials.
Sources
- ASTM D5336-22, classification for polyphthalamide injection moulding materials (preview)
- Wikipedia: Polyphthalamide
- BASF: Ultramid Advanced T1000HG7 LS BK23593 product information (PA6T/6I GF35)
- BASF: Ultramid Advanced T1000HG10 UN processing data sheet (PA6T/6I GF50)
- BASF: Ultramid T KR 4355 G7 product information (PA6T/6 GF35)
- BASF: Ultramid A3EG6 product information (PA66-GF30)
- DuPont: Zytel and Minlon nylon resins molding guide
