Phenolics and Carbon Matrices
Phenolic chemical structure- Fig 2-10
- Formed by reaction between phenol and formaldehyde
- Condensation reaction releases water as a byproduct.
- Initially low molecular weight, soluble and fusible, A-Stage resin
- Condensation reaction involves more and more phenol molecules that causes the resin to pass through a rubbery, thermoplastic state that is only partially soluble phase called B stage.
- Resin is cured and cross-linked thermoset resin, C- Stage.
- Other terms describing phenolic formation
- Resole: If phenol/formaldehyde reaction is carried out in excess formaldehyde and base catalyst is called resole at low molecular weight stage.
- Requires just heat to convert to C-stage (1 step)
- Novolac: If phenol/formaldehyde reaction is carried out in excess phenol with an acid catalyst is called novolac.
- Requires addition of a hardener (hexamethylenen tetramine) to achieve C- Stage in 2 steps. It provides acid to both reactants which speeds up reaction.
- Reinforcements are mixed with novolacs for composites. Bstaging is when any other resin is cured to an intermediate stage and cured by heating
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