Characterisation of Phenolic Resin

Here n is the number phenolic units in the chain. The methylene bridges are characterised by C-NMR spectroscopic analysis. The characteristics peaks for o, o, o, p and p, p methylene carbons are 30,35 and 40 ppm. The free phenol is characterised from peaks at 115 ppm and 120 ppm. The free phenol content of a resin sample is determined by dissolving the sample in acetone and gas chromatographic analysis of the solution using m-cresol as an internal standard. The -OH and -CO functional groups are characterised by Fourier transform infra red spectroscopy (FT-IR) from their characteristic peaks at 3350-3500 cm and 1730 cm , respectively [7]. 

When resole solution is subjected to a thermal cure with or without an acid catalyst, the molecular weight increases leading to an intermediate gel state (B-stage), which 

Markovic and co-workers [13] investigated the effects of the phenol to formaldehyde ratio used for the preparation of novolac and the nature of methylene linkages on the curing behaviour of the novolac/HMTA system using rheological studies. Cure kinetics were described by a third-order phenomenological equation, which took into account the self-acceleration effect that arises from the chemical reaction and phase separation. The reaction rate was found to increase with an increase in phenol to formaldehyde ratio. For the same phenol to formaldehyde ratio, the reaction rate increased with an increase in o, o methylene linkages (Table 2.2). 

Phenol to formaldehyde ratio Molecular weight (g/mole) Content of o-o isomer (%) Reaction rate (per min) Gel point (min) 

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