Phenolic foams: A review of mechanical properties, fire resistance and new trends in phenol substitution

Phenolic foams (PF) have a combination of properties that make them attractive for a number of engineering applications such as insulation, lightening, energy absorption and fire protection. Phenolic foams exhibit excellent fire-retardant behaviour but have insufficient mechanical properties (e.g. fatigue, flexural properties and friability) for different applications in comparison to other foam materials. Hence, numerous studies have tried to improve these mechanical properties without deteriorating its excellent fire-retardant behaviour. Different approaches have been investigated, such as the addition of fibres and particles or the chemical modification of the PF base resin. This work will first briefly present generalities from resin synthesis to foam production. The main part will review the existing papers dealing with the improvement of the compressive and flexural strength as well as the friability. Moreover, evolution of the cell size with these mechanical properties will be presented, although there is no well-defined link between them. Then, the influence of these modifications on the fire-retardant behaviour of PF will be discussed. Finally, the last part will present work to substitute phenol from petroleum sources to environmental friendly sources.