Antioxidant Systems for Stabilization of Flexible Polyurethane Slabstock Foams

Abstract

The flexible slabstock polyurethane foam industry has been undergoing regulatory changes in recent years. The mandated reduction in halogenated blowing agents (CFCs) has profound implications for the development of adequate heat stabilization systems for the slabstock foam. Increased bun temperatures and concomitant scorching can result when CFCs are not present to assist in heat removal from the bun. Newer forced cooling processes (blown air or carbon dioxide) still incur high bun temperatures, and the possibility exists for loss of volatile stabilizer additives which could result in bun scorching and discoloration. The historical, and still prevalent stabilization approach utilizes BHT as a primary phenolic antioxidant, with an alkylated diphenylamine as co-stabilizer in some cases. However, the volatilization and loss of BHT from slabstocks during manufacture is known, resulting in inadequate bun stabilization, staining, etc. Consequently, antioxidant strategies utilizing lower volatility additives still are sought that inhibit the free radical, autocatalytic mechanisms of degradation. This paper will review and contrast traditional stabilization strategies for polyols and flexible foam polyurethanes. Emphasis on lower volatility antioxidant replacements for BHT will be discussed. Data to be presented include thermal analysis (DSC, OIT) testing of polyols and flexible foams. Since color evaluations in scorched foams have been related to the effectiveness of the stabilization system used, these data will be discussed for polyurethane foams that were prepared in the laboratory and subjected to microwave oven scorch testing.