Resins and reinforced plastic laminates for continuous use at 650°f—II

Abstract

AbstractThis paper is the third in a series describing work done under Air Force sponsorship to develop high temperature polyimide laminates for radomes and other parts for supersonic aircraft.Twelve resin compositions are described and evaluated. Most were prepared from benzophenonetetracarboxylic dianhydride and one or more aromatic diamines. Modifying linkages such as amide, ether, benzimidazole, and oxadiazole were present in some cases.A variety of precure and pressing conditions were studied, best results being obtained with a fully cured prepreg pressed at about 700°F and 200–1000 psi. Most of the laminates were made with E glass cloth, but some work was done also with S glass, Refrasil, and carbon cloth.Initial flexural strengths on E glass of 35–60,000 psi at room temperature, and 20–40,000 psi at 600°F were observed for the better resins. On S glass, slightly higher strengths were observed together with values of about 10,000 psi at 700–1000°F. Aging data on E glass laminates show retention of at least 10,000 psi flexural strength at temperature for about 250 hrs. at 650°F, 1000 hrs. at 600°F, 5000 hrs. at 527°F, and 30,000 hrs. at 482°F.Dielectric constant and dissipation factor at 10 Gc were found to be nearly constant at 3.5–4.4 and 0.005–0.01, respectively, for temperatures up to 662°F and for aging up to 1000 hrs. at 600°F. At frequencies of 60 c and 1 Kc, an increase of dissipation factor with temperature was found and was used as a measure of Tg.