Basic chemistry of phenol formaldehyde resin: Part 2

Chemistry of Novolak resin:

The word Novolak is derived from two words Novo + lack. Latin word "Novo" refers to novel or new and Swedish word "lack" refers to lacquer. The name Novolak was termed since it had replaced the natural lacquers like shellac and copal resin.

Novolak resins are formed by reaction of excess moles of phenol to moles of formaldehyde in the presence of acid catalysts. Generally, the mole ratio (formaldehyde: phenol) of Novolak resins range from 0.5 to 1.0 depends on the demand from the application. Novolaks are stable at room temperature and therefore shelf life of the resin is longer and generally it's six months. But, it can last long if its stored in controlled conditions.

In chemistry point of view, in the first step, addition of formaldehyde forms a methylol group in either ortho-para positions of phenol. Under normal conditions, o-p isomer has more possibility compared to p-p' and o-o' bridges. As a next step, methylol group further reacts with phenol and form methylene bridges which makes it a stable structure. Water comes out of the reaction and the residual phenol present in the system is distilled out as per the required properties. If required adjustment on pH, adjustment of viscosity and addition of additives are done as per the application or customer requirements. Since Novolak resins have stable methylene bridges and do not have methylol groups, it requires an additional curing agent (hexamine) to cure the resin.

  General raw materials used for the manufacturing of Novolak resin



 Novolak resin production:



Applications of Novolak resin




Refer the Basic chemistry of Phenol Formaldehyde Resins : Part 3 for further information.

For more queries and consultancy services on Phenolic Resins, please write to hemapolymercs@gmail.com

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