Environmental effects on thermoplastic and elastomer toughened cyanate ester composite systems

The effects of temperature and moisture on thermal and mechanical propertie s of high-temperature cyanate ester composite materials were investigated. A resin transfer molding process was used to impregnate glass fiber fabrics with matrices that underwent thermoplastic or elastomeric toughness modifi cations. The elastomer-modified material obtained the highest mode I fractu re toughness values primarily because the toughener did not phase separate. Extended exposure to 200 degrees C, however, deteriorated initial toughnes s improvements regardless of the modifier utilized. Although the thermal st ability was increased by using thermoplastic modifiers in comparison to the elastomer-modified material, the degradation was mainly governed by the cy anate ester network. Gaseous degradation products caused delaminations and therefore reduced strength when the materials were exposed to 200 degrees C : for 1000 h, Also, upon immersion in water at 95 degrees C, the matrices a bsorbed up to 3.3 wt % more than previous values reported in the literature . Fiber/matrix interfacial phenomena were responsible for this behavior bec ause fiber/matrix adhesion also was reduced drastically as shown by the str ong reduction in flexural strength. (C) 2000 John Wiley & Sons, Inc.