Often Overlooked Factors in PIR Surfactant Development

Abstract

Polyisocyanurate (PIR) foams have been part of an evolving technology since their inception. The PIR foam producers have seen polyols change from polyethers to blends of polyethers, polyesters and compatiblizers to pure polyesters. The MDIs have changed viscosities. Indexes have varied. However, the most dramatic alterations have been to the blowing agent selection; from CFCs to CFC/HCFC blends, to HCFCs, to cyclopentane, to cyclo-/ isopentane, to iso-/n-pentane, to n-pentane. Each of these changes has placed different demands upon the surfactant mostly due to changes of compatibility and solubility of components. There have also been modifications to equipment and processes to adapt to the physical properties of the current set of ingredients. Blowing agents can be blended into polyol systems, or they can be introduced as a third chemical stream. This detail can place special requirements on formulations and chemicals, including surfactants. The unique techniques in the production of flexible metal-faced continuously laminated board-stock at high speeds must also consider various types of flow in order to insure proper cell formation and therefore the impact on foam properties. Surfactants impact especially on the flowability of the liquid reaction mixture as well as the volume flow of the expanding polymer. This article discusses various important factors in surfactant development for polyisocyanurate foams and clearly demonstrates, based on high-pressure machine evaluations, how optimized surfactants can improve foam processing and final foam properties.