Blends of unsaturated polyester and phenolic resins for application as fire-resistant matrices in fibre-reinforced composites. Part 2: Effects of resin structure, compatibility and composition on fire performance

The effects of co-curing blends of an unsaturated polyester (UP) with inherently fire-retardant and char-forming phenolic resoles (PH) on the thermal stability and fire retardancy of the resulting resins have been investigated. To overcome the challenge of UP/PH incompatibility, arising from their different chemical structures and curing mechanisms (radical vs. condensation), different phenolic resoles have been used: ethanol-soluble, epoxy-functionalized, and allyl-functionalized. A traditional water-based resole has also been used to give a reference non-compatible system. In Part 1 of this series of publications it was shown that the compatibility of the two resins increases with functionalization; the allyl-functionalized resole showing the best compatibility with UP. Limiting oxygen index measurements and cone calorimetry have shown that fire performance of the functionalized PH resins and their blends with UP is worse than that from the unfunctionalized PH resin, but still significantly better than that of the UP. To understand this behaviour, thermal analyses coupled with infrared spectroscopy of volatile degradation products have been used on all resins and their blends, based on which, mechanisms of their decomposition and interactions are proposed, and the effects of these on flammability are discussed.