Phenol-formaldehyde Novolak resin. In this article, I will explain and share all information related to phenol-formaldehyde Novolak preparation.
Phenol-formaldehyde Novolak preparation
Novalaks are formed by reacting phenol and formaldehyde in a molar ratio of 1:0.8 under acidic conditions.
There are slow reactions between reactants to form Ortho and para hydroxy methyl phenols. These then rapidly condense to form Bi’s hydroxyphenyl methane.
3 possible isomers of these compounds are the main product.
This molecule will slowly react with furtherer formaldehyde to form methylol derivatives which in turn rapidly reacts with further phenol to produce higher polynuclear products with 5-6 benzene ring per a molecule.
Novolak resin structures reaction
Novolak resin themselves contains no reactive methylol groups that do not form the crosslinking structure on heating.
Phenol:-100 parts by weight.
Formalin:-70 parts by weight.
Oxalic acid:-1.5 parts by weight.
Phenol-formaldehyde Novolak Resin manufacture tower image
The reaction mixture is heated and allowed to Reflux under atmospheric pressure at about a hundred degrees celsius at this stage all day is open and we’ll be is closed. Because the reaction is purely exothermic initially it may be necessary to use cooling water in the jacket at this stage.
In the condensation reaction, it will take several hours for example 2 to 4 hours since under the acidic condition the formation of phenol alcohols is rather slow. When the resin reaches the request degree of condensation as indicated by refractive index measurement the walls are changed over and the water present is distilled off.
In the case of phenol-formaldehyde Novolak presents, The distillation normally carried out without the application of a vacuum. As this reaction proceeds the water is driven off and the rise in temperature of the resin which may rich as high as 160 degrees Celsius at the end of the reaction.
At this temperature, the fluid is less viscous and More easily stirred. The endpoint may be checked by noting the extent of the flow of a heated pellet down of a given slope or by melting point measurements. Other control tests include alcohol solubility free phenol content and gelatin time with 10% Hexa.
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