Flammability Characteristics of CO2 Blown Rigid Polyurethane Spray Foam

Abstract

In view of the ozone depletion potential of HCFC-141b and other HCFCs, processing challenges with gaseous HFC-134a, and flammability potential with pentanes as blowing agents, significant efforts have been deployed in the development of environmentally friendly, all carbon dioxide blown rigid polyurethane spray foams. These foams are primarily used for the insulation of roofs, storage tanks, vessels, walls and piping. The Mannich base initiated Polyol A, developed by The Dow Chemical Company [1], with viscosity of ∼2000 cps at 77°F and OH# of ∼312 was manufactured using patented technology. This OH# is significantly lower than that of the dominating spray foam polyols (OH# 470). The low viscosity and higher equivalent weight of this polyol are designed to alleviate the processing difficulties of typical carbon dioxide blown spray applied systems. Some of the important requirements in spray systems are the flammability characteristics. Most carbon dioxide blown foams, however, suffer from high heat release, smoke and weight loss in small scale burn tests like the Ohio State University (OSU; ASTM E-906) test when compared to the corresponding results with HCFC-141b as the primary blowing agent. A series of formulations containing Polyol A, aromatic polyester polyols and commercially available fire retardants were evaluated at different isocyanate indices. Flammability properties were determined using a variety of small scale test methods including cone calorimeter and ASTM E-906. In an attempt to understand factors contributing to burn properties, several analytical techniques, such as FTIR (Fourier Transform Infrared Spectrometry), TGA (Thermo-Gravimetric Analysis) and DMS (Dynamic Mechanical Spectroscopy) were utilized. Analysis of the FTIR spectra leads to an estimate of conversion of isocyanate end groups and trimerization reactions where applicable. TGA reflects the chemical stability of the polymer network to thermal decomposition and DMS reflects the physical stability of the polymer network. A correlation of these data with the weight loss data after burning has been investigated. A combination of these techniques leads to a systematic approach for the development of spray polyurethane foams with improved flammability characteristics.