CFC-Free Polyether Polyurethane Systems for Footwear Applications

Abstract

The removal of CFCs from polyurethane systems for footwear applications is an environmental necessity. However this has proven technically difficult for polyether based systems. Although polyether systems have a much superior hydrolytic stability to polyesters the physical properties are inherently lower. In the past this problem was resolved by using CFCs as blowing agents. Such materials blow very efficiently in the interior of the moulded material but much less efficiently in the regions adjacent to the cool mould wall. Hence high density boundaries - or integral skins - are thus formed. The high density layer has improved physical properties which match the needs of modern footwear applications. Potentially therefore there are at least two methods to eliminate CFCs from polyether based systems. Firstly, to improve the inherent physical properties of the polyether systems - so eliminating the need for the high skin density. Secondly to identify alternative blowing agents which, similarly to CFCs, produce the high density boundary layers in a cool mould. ICI Polyurethanes has been active in both these areas of research. Several CFC free polyether systems have been developed which are now commercially available. Such systems are characterized by their improved physical properties over CFC blown systems at the same density. The usual advantages of polyether systems (liquidity, hydrolytic stability, etc.) are left unchanged, whilst the strength properties such as tensile and, tear are improved.