Neat resin: Hexcel HexPly 8552
Where to buy| Property | English | Metric (converted) |
|---|---|---|
| Density | 0.0470 lb/in³ | 1.30 g/cm³ |
| Glass transition, dry | 392 °F | 200 °C |
| Glass transition, wet | 309 °F | 154 °C |
| Tensile strength | 17.5 ksi | 121 MPa |
| Tensile modulus | 0.677 Msi | 4.67 GPa |
| Tensile strain | 1.7% | 1.7% |
| Gel time at 350 °F | 13 min | 13 min |
| Service temperature | up to 250 °F | up to 121 °C |
Hexcel HexPly 8552 sheet (2020), "amine cured, toughened epoxy". Wet and dry Tg are measured per the sheet; the gap between them is the moisture effect the FAA describes.
What the FAA handbook says (pp. 7-6 to 7-7)
Epoxies come in viscosities from liquid to solid, and the technician should use the maintenance manual to select the type. Used widely in prepreg resins and structural adhesives.
Advantages: high strength and modulus, low volatiles, excellent adhesion, low shrinkage, good chemical resistance, ease of processing. Disadvantages: brittleness and reduction of properties with moisture. Cure is slower than polyester. Cure temperatures run from room temperature to about 350 °F (180 °C); the most common are 250–350 °F (120–180 °C).
Mixing and pot life
Pot life is the time a resin stays workable after the hardener is added; once expired the batch is discarded and a new one mixed (FAA-H-8083-31B, glossary). It depends on temperature and quantity: use the pot life calculator and weigh the mix with the mix ratio calculator. AC 43.13-1B 3-2 says to mix with the manufacturer’s instructions.
Quick check
A mixed batch is past its pot life but still looks fluid. What do you do?
- Use it quickly, it still flows.
Not this one. Past pot life, the resin may not perform to specification.
- Discard it and mix a new batch.
Best fit. The FAA glossary says an expired catalyzed resin must be discarded and a new batch mixed.
- Thin it with solvent.
Not this one. Thinning changes the resin and is not an approved fix.
On a real job, the SRM decides.
Limits — when NOT to use this
- One resin’s numbers. 8552 is a 350 °F prepreg system; a room-temperature wet layup epoxy is a different resin.
- No ratio here. Mix ratios come from the resin data sheet and are by weight.
Where to buy
Distributors coming soon.
Sources
- Hexcel HexPly 8552 Product Data Sheet (US units, 2020) — neat resin properties, prepreg physical properties, cure procedure, storage life.
- FAA-H-8083-31B, AMT Handbook — Airframe, Volume 1 (2023), Chapter 7 — epoxy resin (pp. 7-6 to 7-7); pot life (glossary).
- AC 43.13-1B, Change 1, Chapter 3, Fiberglass and Plastics — paragraph 3-2 (pp. 3-1 to 3-2).