Synthesis of phenolic-type matrices

Phenolic resins are highly versatile, which has led to a broad range of applications in the aircraft, aerospace, automotive, electrical and electronic industries (Pilato et ah, 2008) as well as in the interiors of mass-transit cars and architectural and marine components (Lewark, 2007). Phenolic resins with diverse structures and properties can be obtained from different phenols, aldehydes and catalysts. In addition, resins with different properties can be prepared from a given set of parental or substituted phenol/aldehyde/catalysts by diversifying parameters sueh as the phenol/formaldehyde ratio and the reaction temperature and duration. 

The novolae phenolic resins can be obtained in a moderately acidic medium (pH 4—6) in the presence of divalent metal acetate catalysts (Ca, Mg, Zn, Cd, Pb, Cu, Co and Ni) or in a strongly acidic medium (pH 1 ). Novolae resins obtained in a moderately acidie medium have many ortho-ortho linkages and are known as high-ori/io novolaes . The accessibility of free para positions leads to a high curing rate in this resin (Knop and Pilato, 1985 Pilato, 2010a). 

Novolae obtained in a strongly aeidie medium is synthesized by reacting formaldehyde with a molar excess of phenol (1 mol of phenol to 0.75-0.85 mol of formaldehyde) (Fig. 2.2(a)). The most frequently used catalysts are 

7 Phenolic resins and composites Timeline of some key events. 

2 Schematic formation of (a) novolac thermoset and (b) resole thermoset (Pilato, 2010a). 

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