The Use of Secondary Aromatic Diamines in Rigid Isocyanurate-Based Foams

Abstract

Commercial isocyanurate foams are generally modified with urethane groups. Other groups, such as amide, imide, carbodiimide, or oxazolidone linkages, have been used to modify such foams in order to improve physical properties (brittleness, friability). In the present work, urea modification was studied through the addition of a secondary aromatic diamine. The urea modification was studied in urethane-polyisocyanurate foams as well as foams in which the aromatic secondary diamine was the only source of active hydrogen. Exceptions were those foams in which water was used as the blowing agent. High isocyanate indices were employed so that the latter foams contained only urea and isocyanurate linkages. These foams were modified in the above manner in an effort to create a highly fire-resistant foam since the thermal stability and the rigidity of urea groups are known to be higher than that of urethane groups.

The introduction of the aromatic secondary diamine into rigid foams has been shown to result in significantly improved compressive strength values, especially perpendicular to foam rise. This has led to the improvement of the isotropy of the foams. This improvement was verified by optical microscopy studies of the cell structure. These studies indicate that the incorporation of the additive resulted in much smaller cells with less elongation in the rise direction. As a result of the finer cells, slightly lower k-factors were obtained. This observation was true for freshly made foam samples as well as for samples aged at —20°C and 70°C. The dimensional stabilities of the aged samples were also consistent with these observations in that the addition of the aromatic diamine resulted in improved stabilities.