What Does Epoxy Phenol Novolac (EPN) Mean?
An epoxy phenol novolac (EPN) is an epoxy resin where the epoxide functional group is attached to the phenolic oxygen of a phenolic novolac. As such, each phenol oxygen of the novolac resin is attached with a –CH2-(C2H3O) group, where -(C2H3O) is a three-membered epoxide ring. A single EPN polymer contains many epoxide groups, making the molecule multifunctional. When cured to make an epoxy coating or adhesive, the multi-functionality allows for a high degree of cross-linking, leading to high resistances.
In industrial settings, EPN resins are used for the epoxy coating of tanks, pipes, floors, automotive parts, electronic parts, etc. High chemical, solvent and temperature resistance of EPNs are especially useful for high-performance applications and corrosion resistance.
Corrosionpedia Explains Epoxy Phenol Novolac (EPN)
Epoxy phenol novolac resins are produced by the reaction of a phenol novolac with epichlorohydrin in the presence of sodium hydroxide (NaOH). The hydroxide ions (OH-) remove the proton (H+) from the phenol hydroxyl (R-OH) group to create a nucleophilic phenyl hydroxide (R-O-). The latter hydroxide substitutes the chloride in epichlorohydrin (Cl-CH2-(C2H3O)), which links the phenolic unit with the epoxide (R-O-CH2-(C2CH3O)). Both the novolac resin and epoxide group may be modified with other functional groups to alter the properties of the EPN. Along those lines, the family of EPN resins range in their relevant properties:
- Viscosity at 52°C (126°F): 600-50,000 cP
- Epoxide equivalent weight (EEW): 160 – 270 g/eq
- Functionality: 2.2-3.8
- Color: 1-3 (Gardner color scale)
The choice of EPN resin may be determined by the particular advantages of a selected formula. Some resins are easier to apply and dry faster. Others have extra high resistance properties. Others retain their properties along a large temperature range. The best EPN product depends on the application’s needs and environment.