Frequently Asked Questions
What is phenolic resin?
Phenolic resin or Phenol formaldehyde resins (PF) are synthetic polymers obtained by the reaction of phenol or substituted phenol with formaldehyde. Phenolic resins are mainly used in the production of circuit boards. They are better known however for the production of molded products including pool balls, laboratory countertops, and as coatings and adhesives. In the form of Bakelite, they are the earliest commercial synthetic resin.
Novolac resin compared Resol resin?
Novolacs are phenol-formaldehyde resins with a formaldehyde to phenol molar ratio of less than one. The polymerization is brought to completion using acid-catalysis such as oxalic acid, hydrochloric acid or sulfonate acids. The phenol units are mainly linked by methylene and/or ether groups. Novolac needs cross-linking by another chemicals such a Hexamine.
Base-catalysed phenol-formaldehyde resins are made with a formaldehyde to phenol ratio of greater than one (usually around 1.5). These resins are called resoles. Phenol, formaldehyde, water and catalyst are mixed in the desired amount, depending on the resin to be formed, and are then heated. The first part of the reaction, at around 70 °C, forms a thick reddish-brown tacky material, which is rich in hydroxymethyl and benzylic ether groups. Resol requires small heating to be cross-linked and becomes network.
What is Hexamine and How does HMTA work with phenolic resin?
Hexamethylenetetramine (HMTA) or methenamine is a heterocyclic organic compound with the formula (CH2)6N4. This white crystallinecompound is highly soluble in water and polar organic solvents. It has a cage-like structure similar to adamantane. It is useful in the synthesis of other chemical compounds, e.g. plastics, pharmaceuticals, rubber additives. It sublimes in vacuum at 280 °C. "hexamine" is a hardener added to crosslink novolac. At a temperature >90 °C, it forms methylene and dimethylene amino bridges.
What is suitable curing temperature for phenolic resin?
When the molar ratio of formaldehyde:phenol reaches one, in theory every phenol is linked together via methylene bridges, generating one single molecule, and the system is entirely crosslinked. This is why novolacs (F:P <1) do not harden without the addition of a crosslinking agent, and why resols with the formula F:P >1 will. (Ref: http://en.wikipedia.org)
Atmospheric curing temperature for both novolac with HMAT and resol would be 150°C and more to achieve completely cure of polymer and fully hardness. It is also related with curing time and heat transfer around heating oven or control volume.