The notched and unnotched Izod impact properties of a series of phenolic‐glass composites following thermal exposure at 180°C, 300°C, and 800°C have been investigated. Four phenolic resins; a resol, a novolac, a resol/novolac blend, and a furan‐novolac/resol copolymer were used to prepare the composites. The notched and unnotched impact properties of all S‐glass composites improved following thermal exposure at 180°C for times up to 28 days. The best results at 180°C were obtained for the copolymer‐based composite. However, thermal exposure at 300°C for times greater than 1 day led to significant reduction in the performance of this composite. The best retention of impact properties folowing exposure at 300°C and 800°C was found for the composite made with the resol/novolac blend. The results indicate that the impact properties of phenolic composites made with modified resins, that is, a blended resol/novolac or a furan‐novolac/resol copolymer resin, improve significantly. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 349–361, 1998

ABSTRACT:The notched and unnotched Izod impact properties of a series of phenolicglass composites following thermal exposure at 180ЊC, 300ЊC, and 800ЊC have been investigated. Four phenolic resins; a resol, a novolac, a resol/novolac blend, and a furan-novolac/resol copolymer were used to prepare the composites. The notched and unnotched impact properties of all S-glass composites improved following thermal exposure at 180ЊC for times up to 28 days. The best results at 180ЊC were obtained for the copolymer-based composite. However, thermal exposure at 300ЊC for times greater than 1 day led to significant reduction in the performance of this composite. The best retention of impact properties folowing exposure at 300ЊC and 800ЊC was found for the composite made with the resol/novolac blend. The results indicate that the impact properties of phenolic composites made with modified resins, that is, a blended resol/ novolac or a furan-novolac/resol copolymer resin, improve significantly.

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Changes in the dynamic response of glass‐reinforced phenolic composites following thermal exposure at 180oC for periods of time up to 28 days were monitored using dynamic mechanical analysis. Four phenolic resins were investigated: a resol/novolac blend, a phenolic–furan novolac/resol graft copolymer, a novolac, and a resol. Reactive blending and copolymerization of phenolic resins are currently being investigated to determine if these techniques will produce phenolic resins (and composites) that have improved impact properties and retain the excellent high‐temperature properties of resol and novolac phenolic resins. The results indicate that thermal aging at 180oC for 1 day led to a more complete cure of all four phenolic resins as indicated by an increase in the temperature of the maximum of plots of both loss modulus (E″) and tan δ versus temperature. The storage modulus (E′) of the composites at 40oC varied little following thermal aging at 180oC for 1 day but decreased with increasing exposure time for samples aged 2, 7, and 28 days. Thermal aging led to an increase in E′ at higher temperatures and the magnitude of E′ at a given temperature decreased with increasing exposure time. The magnitude of E″ and tan δ decreased with aging time for all resins, although E″ and tan δ were larger for the blend and copolymer composites than for the novolac and resol composites. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 385–395, 2001

Chemistry of Phenolics Novolacs Resols