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Epoxy Resin
Woody

Created by

Woody

22. September 2026NO
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Epoxy Resin

Pierre Castan, a Swiss chemist at the dental firm De Trey Frères, was looking for a resin for dentures. He reacted a phenol carrying two hydroxy groups with epichlorohydrin, then hardened the product with an acid anhydride, and got a hard, clear, unusually adherent solid. Ciba licensed it and sold it as Araldite; in the US Sylvan Greenlee developed epoxies independently. **US 2,324,483**, "Process of preparing synthetic resins", Castan, granted 20. July 1943, claims condensing "a polybasic carboxylic acid anhydride" with the product of "a phenol having at least two phenolic hydroxy groups and of an epichlorhydrine". It does not single out bisphenol A, the phenol most epoxies use today. **Epichlorohydrin is a carcinogen; you start from a two-part kit.** You glue pine lap joints at the right ratio and four wrong ones, then test hardness and break the joints.
Beginner
2 hours plus 24 h cure

Instructions

1

Cut the joint pieces

Saw ten pine strips 100 x 25 mm. Sand one face of each end with 120 grit and dust off. Label five pairs 1:1, 1.25:1, 1:1.25, 1.5:1 and 1:1.5.

Materials for this step:

Pine BoardPine Board1 piece
SandpaperSandpaper1 sheet
Masking TapeMasking Tape1 roll

Tools needed:

Hand SawHand Saw
Steel RulerSteel Ruler
PencilPencil
2

Measure by syringe

Gloves on. For each ratio draw resin and hardener in separate syringes (1:1 = 2 ml + 2 ml; 1.25:1 = 2.5 + 2; and so on) into its own cup. This assumes a 1:1-by-volume kit - scale to your label.

Materials for this step:

Two-Part EpoxyTwo-Part Epoxy25 ml

Tools needed:

Nitrile GlovesNitrile Gloves
Syringe SetSyringe Set
Graduated Mixing CupsGraduated Mixing Cups
Clear Safety GlassesClear Safety Glasses
3

Mix thoroughly

Stir each cup 2 minutes, scraping the walls and bottom. Unmixed streaks behave like a wrong ratio.

Tools needed:

Stirring RodStirring Rod
4

Glue and pour

Spread each mix on the sanded ends of its pair, overlap them 25 mm and spring-clamp over wax paper. Pour the rest as a coin-sized puddle on wax paper beside it.

Materials for this step:

Wax PaperWax Paper1 sheet

Tools needed:

Spring ClampSpring Clamp
5

Cure 24 hours

Leave everything at room temperature, 20 °C or warmer, for 24 hours. Cold slows the cure.
6

Pencil hardness

Sharpen pencils 6B to 6H and flatten the tips on 400 grit. Push each at 45° across a puddle, from hard down, until one no longer scratches. Record that grade.

Tools needed:

Graphite Pencil SetGraphite Pencil Set
Magnifying LoupeMagnifying Loupe
7

Break the joints

Clamp one strip of a joint in the vise and tap the free end sideways with the mallet until it breaks. Estimate how much of the bond face is torn wood.

Tools needed:

Bench ViseBench Vise
Rubber MalletRubber Mallet
Clear Safety GlassesClear Safety Glasses
8

Ratio, leftovers, results

Loading Jupyter Notebook...
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History & Context

**What the patent specifies:** a resin from a two-hydroxy phenol and epichlorohydrin, hardened by a polybasic acid anhydride. **Modern build (derived):** a two-part kit, most with an amine hardener that cures at room temperature. Epoxy became the glue that holds metal, the matrix of fibreglass and carbon-fibre parts, and the boat-builder's resin. Its limits: it yellows in sunlight, softens with heat, and uncured resin and hardener sensitise skin - which is why the gloves stay on every time.

Materials

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Tools Required

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