Many Phenolic Adhesive

Many kind of phenolic adhesive can be founded on the market like, phenol formaldehyde and phenolic epoxy adhesive.

Phenol Formaldehyde resin commonly called a phenolic glue or more simply a "P.F." glue, means a condensation product of formaldehyde and a monohydrate phenol including phenol itself, cresol and xylenols.Although the phenolic tannins of vegetable origin consist of both monohydridic and polyhidric molecular structure, it is more appropriate to discuss them in this section than under resorcinol formaldehyde "R.F." adhesive. The later and also resorcinol/phenol adhesive are discussed in the next section.Resol and NovolaksCondensation products of phenol and formaldehyde can be either potentially thermosetting and known as "Resols," or thermoplastic and known as "Novolaks."

The hot setting phenolic glues have their important place in making plywood. They are usually made with a molar ratio of about 1.5 - 2.25 formaldehyde to 1 of phenol. If prepared under weakly alkaline conditions, as formation of the resin proceeds, separation into two layers takes place an aqueous layer above. Under more strongly alkaline conditions, above pH of about 10 but depending on molecular ratio and degree of condensation, a homogeneous solution is formed, this makes the resin appear water soluble, whereas it is in fact soluble in the aqueous alkali.

The adhesion to metal of unmondified phenolic resins can increased by adding an epoxy resin, in particular a bisphenol a resin, and furthermore, since this addition reduces brittleness, band strength is increased. It, however, hot strength is nor to be seriously reduced, the amount of bisphenolic, it follows therefore that the cross linking of the epoxy resin (assuming no other curing agent is added) is provided for by the large excess of phenolic resin.