Modified PF Resins for Composite Structures with Improved Mechanical Properties

Novel composites resins for civil engineering structures were synthesised. Resol phenolic resins were modified by the copolymerization of phenol with cardanol (obtained from CNSL). The modified PF resins were synthesized at different proportions of phenol to cardanol and also of the total phenol to formaldehyde. The synthesis was carried out under alkaline conditions and with a maximum content of 40 wt.% of cardanol. The effect of the partial substitution of phenol by cardanol on the thermal and mechanical properties of the CPF resins was investigated. An increase in the content of cardanol resulted in a proportional increase in the flexibility and in the fracture toughness together with a decrease in the flexural modulus of the cured CPF resins. The higher toughening effect of replacing phenol with cardanol was obtained with the total P:F molar ratio of 1.0:1.25. Also a direct proportionality between the amount of cardanol content and the decrease in crosslink density of the resins was observed. Simultaneous TGA-FTIR studies of the resins were carried out and the emitted gases were identified. The results confirmed that the thermal stability and the temperature of degradation of the cured CPF resins decreased as the amount of cardanol content increased. Gas emissions during the pyrolysis of the CPF resins also increased.