novolakové

Novolak is a type of phenol-formaldehyde resin. It is synthesized by the condensation reaction of phenol with formaldehyde in the presence of an acid catalyst. The reaction typically proceeds under conditions where the molar ratio of formaldehyde to phenol is less than one, which results in a linear or branched thermoplastic polymer. The synthesis is characterized by the formation of methylene bridges connecting the phenolic rings, primarily at the ortho and para positions.

Novolaks are precursors to thermosetting resins. They are typically supplied as solid powders or flakes. To achieve cross-linking and form a rigid, insoluble, and infusible network, novolaks require the addition of a curing agent. The most common curing agent for novolaks is hexamethylenetetramine (HMTA). Upon heating, HMTA decomposes, providing both methylene and amino groups that react with the phenolic hydroxyls and remaining reactive sites on the novolak chains, forming a highly cross-linked structure.

These cured resins exhibit excellent thermal stability, good electrical insulating properties, and chemical resistance. Consequently, novolak-based thermosets find widespread applications in areas such as laminates for printed circuit boards, molding compounds for electrical components and automotive parts, adhesives, coatings, and as binders in abrasive materials and friction products. The specific properties of the final thermoset can be tailored by adjusting the molecular weight of the novolak and the curing conditions.