The sorption and diffusion of water in bismaleimide resin

The Sorption and Diffusion of Water in Bismaleimide Resin INTRODUCI'IONIn the search for improved matrix resins for high performance composites increasing attention has been paid to polyimides and related materials.'-3The importance of the interaction of water with the matrix resin of a composite and its effect on physical and mechanical properties was recognized at an early stage in the development of epoxy composit.t~.4-~As part of an ongoing study of water sorption and transport in composite resin materials6-* results for a commercially available bismaleimide resin are reported on briefly and a comparison made with the Kapton polyimide (E.I.Dupont de Nemom Inc) and the resin MY720 (Ciba-Geigy Ltd). EXPERIMENTALCompimid6 M751 was kindly supplied by D r H. D. Stenzenberger (Technochemie GmbH-Verfahrensteclmik).A mould, which gave castings of 3 X 3 cm was made from two surfacetreated glass plates which were separated by a tailored "Teflon", glass-weave shin.The resin powder was dried and compressed into a pellet using a KBr die which could be evacuated.The pellet was placed on the lower plate held at 175°C by being positioned in the open press.The heated top plate, also at -175°C was carefully positioned over the molten globule and pressure (100-200 psi) applied.The mould was protected from the press by an interlayer conaisting of silicone rubber between Teflon, glass-weave sheeta.The cure was effected at 180°C for 4 h, 220°C for 2 h, and 6nally at 250°C for 17 h.Thin films of Kapton were supplied by E. I. Dupont de Nemours Inc., and typical valum of film thickness C, density p, and glass transition temperature TB are given in