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01.Phenolic Resins And Their Degradation Behaviour (pp. 69-118)
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Phenolic Resins And Their Degradation Behaviour (pp. 69-118) $25.00
Authors:  Manfredi, L. B. and Vázquez, A. (University of Mar, Mar de Plata, Argentina)
The first part of this review article deals with the synthesis, characterisation and kinetic of polymerisation of the phenolic resins. Phenolic resins are polycondensation products of phenol and formaldehyde and are classified as novolaks and resols, depending on the type of catalyst and the molar ratio of reactants. Novolaks are catalysed by acids with a formaldehyde to phenol molar ratio (F/Ph) in the 0.5-0.8 range. Instead, resols are basecatalysed and F/Ph ranges from 1 to 3. The influence of the synthesis conditions such as: type and concentration of catalyst, pH, temperature and formaldehyde to phenol molar ratio have been thoroughly studied by many research groups using all kind of techniques. Then, the relationship between the synthesis conditions and the structure and mechanical properties of the cured resin was analysed. Physical and end-use properties are largely affected by the method of polymerisation. Novolak resins have low cross-linking and process like thermoplastics. Resols are highly crosslinked, versatile and stabile resins. The wide range of applications of phenolic resins includes coatings, adhesives, thermal insulators and matrix of composites. This is due to its low cost, dimensional stability, excellent chemical, moisture and heat resistant, and good fire-smoke-toxicity characteristics. Processing of phenolic-based materials requires a careful application of processing conditions that need an accurate knowledge of the polymerisation kinetics of the resin as a function of the temperature. So, kinetic models have been developed and applied to describe the chemical reactions of the phenolic resins. Further this article gives a survey about thermal degradation and fire resistant of the resins. The thermal degradation of phenolic resins have been widely reported, mainly focused on the chemistry of the principal volatile products and on the pyrolisis behaviour. Different mechanisms for the degradation process and for different ranges of temperature were proposed. The thermal degradation occurs by scission of polymer chains forming methane, phenol and phenolic compounds, and oxidative degradation leads to carbon monoxide, carbon dioxide, benzaldehyde, benzene and toluene. Phenolic resins have a great tendency to char thus reducing the formation of volatiles. Thermal stability of resol resins with different F/Ph molar ratio and the relationship between the chemical structure and their thermal and fire resistance was studied. Distinct kinetic models for degradation reactions proposed in the literature were applied to evaluate the activation energies for the degradation process of the phenolic resins. Nowadays, due to the toxicity of phenol and formaldehyde, there is an interest in replace them by products obtained from renewable resources. The properties and the resistance to thermal degradation of these natural resins were compared with the traditional phenolic resins. 

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Phenolic Resins And Their Degradation Behaviour (pp. 69-118)