Epoxy is one of the most common materials used in the construction chemicals industry. You might hear it commonly when we talk about resinous flooring, or in protective coating systems, etc.
But did you know that not all epoxies are created the same? Let’s take a look at some of the different kinds of epoxies:
- Bisphenol-based epoxy:
Most of the epoxy products used today are bisphenol-based epoxies. In fact, 75-90% of epoxy resins used globally are bisphenol-A epoxies. - Aliphatic epoxy:
while epoxies are famous for its poor UV-resistance, aliphatic epoxies perform much better when exposed to sunlight or UV-rays compared to all the other families of epoxies. - Glycidylamine epoxy:
Usually used in aerospace applications due to its excellent mechanical properties & thermal resistance. - Novolac epoxy:
Highly cross-linked polymer formed, making it highly thermal & chemical resistant.
In this article, we will be touching further into the topic of novolac epoxies.
Novolac Epoxy
Novolacs are produced by reacting phenols with formaldehyde (methanal). These are highly functional resins, which carries around 2 to 6 epoxy groups per molecule, and results in a highly cross-linked polymer upon curing.
Bisphenol F, which is also synthesized using phenols & formaldehyde, can be thought of the simplest form of novolac. However, bisphenol F epoxy resins do not the same functionality and properties as that of a true novolac.
| Type of Epoxy Resin | Bisphenol A | Bisphenol F | Novolac |
| Molecular Weight | ~370 | ~370 | ~504 |
| Functionality | 1.9 | 2.1 | 2.6 – 3.5 |
| Viscosity (at 25oC) | 11000 – 15000 cps | 2500 – 5000 cps | 20000 – 50000 cps |
| Reactants | Phenol + Acetone | Phenol + Formaldehyde | Phenol + Formaldehyde |
As seen from the table above, novolac epoxy resins have a much higher functionality and viscosity as compared to that of the bisphenol-based epoxy resins. With its higher functionality & formation of a denser cross-linked polymer, it results in a material of superior chemical resistance. In fact, it is the only epoxy that is able to withstand up to 98% sulphuric acid!
Choosing the Right Epoxy for Your Usage
While novolac epoxy resins are exceptional in their properties, the material cost is much higher compared to the bisphenol-based resins. Hence, they are usually only used in crucial & critical conditions, where the substrate must be protected from highly acidic or corrosive chemicals.
Some application areas of novolac epoxies are such as:
- Wastewater treatment tanks
- Corrosion protection lining for storage tanks
- Bund lining for manufacturing facilities with exposure to corrosive chemicals
- Desalination plants
- Food processing plants
- Pump and paper mills
- Fertilizer & insecticide plants
- Petroleum refineries
For a high performance novolac epoxy-based coating, Dritech Chemical recommends Dri-Gard EP 1800. The fully cured Dri-Gard EP 1800 coating is resistant to various chemicals, including:
| Acetic acid 25% | Ethylene glycol | Methyl isobutyl ketone |
| Ammonium hydroxide * | Hydrogen peroxide, H2O2, 20%sol | Mineral spirit |
| Benzene | Fatty acids | Nicotinic acid * |
| Benzoyl chloride | Formaldehyde 37% | Nitric acid 30% |
| Benzyl alcohol | Gasoline | Phenol 50% in IPA |
| Bleach (Sodium hypochlorite) | Hexamine 25% | Phosphoric acid 85% |
| Boric acid * | Hexane | Potassium hydroxide * |
| Brake fluid | Hydraoine 35% | Propylene glycol |
| Brine 10% | Hydrochloric acid 35% | Sea water |
| Car oil | Hydrofluoric acid 25% | SKydrol |
| Carbon tetrachloride | Jet fuel | Sodium hydroxide * |
| Castor oil | Isopropanol | Sulphuric acid * |
| Deionised water | Ethylene glycol monoethyl esther | Tartaric acid 50% |
| Diesel fuel | Kerosene | Toluene |
| Diethanolamine 88% | Lactic acid 20% | Vegetable oils |
| Xylene |
(* Any concentration in water)
by Elyse Kymberly Teoh (21 Jan 2021)
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