Thermal degradation behavior of rigid polyurethane foams prepared with different fire retardant concentrations and blowing agents Zhong Tang a , M. Mercedes Maroto-Valer a, * , John M. Andre ´sen a , John W. Miller b , Mark L. Listemann b , Paula L. McDaniel b , David K. Morita b , Wayne R. Furlan b a The Energy Institute and Department of Energy and Geo-Environmental Engineering, Pennsylvania State University, 405 Academic Activities Building, University Park, PA 16802-2303, USA b Air Products and Chemicals Inc., 7201 Hamilton Boulevard, Allentown, PA 18195-1501, USA Received 3 May 2002; received in revised form 20 August 2002; accepted 22 August 2002 Abstract In order to understand the effect of flame retardant (FR) and blowing agents on the thermal stability of rigid polyurethane foams and their resultant chars, two series of polyurethane foams produced with different blowing agents (HCFC-141b and pentane) and various concentrations of a FR (0 – 50 wt%) were investigated using standard flammability test (ASTM, D-3014), solid-state 13 C NMR, TGA and Py – GC/MS. The unique combination of these analytical techniques has proved to be a valuable method for understanding the thermal degradation of rigid polyurethane foams. The standard flammability tests indicate an optimum FR concentration of about 15 wt% for foams using HCFC-141b as the blowing agent, while no optimum condition was determined with pentane. The percent mass retained (PMR) values or char yields have a linear relationship with combustion flame temperature in both series of blowing agents. The solid-state 13 C NMR studies clearly show that pentane is chemisorbed during the polymerization and is retained within the foam matrix. The chars have lower concentrations of methylene and oxygenated aliphatic carbons, but a subsequent increase in aromatics is observed. The FR investigated preserves the chemical structure of the polyurethane foam, and, therefore, results in a higher PMR or char yield. The TGA experimental data showed that the maximum combustion reactivities of the chars have a linear relationship with the FR concentration in the parent foams. Py – GC/MS results indicate that the aliphatic oxygenated functional groups are the first to evolve during the pyrolysis and combustion of the polymeric structure. Finally, this study has shown that the addition of FR to the foam formulation results in lower concentrations of small molecules being volatilized, and therefore, preserving the original chemical structure of the parent foam. However, the FR investigated does not seem to be as effective for the pentane series, and gives higher char aromaticities and PMR values than those reported for the HCFC-141b series. q 2002 Published by Elsevier Science Ltd. Keywords: Rigid polyurethane foams; Thermal degradation; Flame retardant 1. Introduction Polyurethanes are copolymers containing blocks of low- molecular-weight polyesters or polyethers covalently bonded by a urethane group (–NHCO–O–) [1]. The most important commercial polyurethane products are foams that are commonly classified as either flexible or rigid depending on their mechanical performance and cross-link densities. Rigid polyurethane foams are widely used in building insulation and domestic appliances, due to their superior mechanical properties and low density [2]. However, the polyurethane industry is facing environmental challenges due to the type of auxiliary blowing agents used during the polymerization process. Chlorofluorocarbons (CFCs) have traditionally been the predominant blowing agents for rigid polyurethane foams [2]. Unfortunately, CFCs are one of the major causes for the destruction of the ozone layer due to their high ozone depletion potential (ODP), and therefore, are being phased out as blowing agents in the polyurethane foam industry. The polyurethane industry is searching for alternative blowing agents with low to zero ODPs, and has identified hydrochlorofluorocarbons (HCFCs) such as HCFC-141b (1,1-dichloro-1-fluoroethane), hydrocarbons like pentane and hydrofluorocarbons (HFCs) such as HFC- 245fa (1,1,1,3,3-pentafluoropropane) and HFC-356mffm (1,1,1,4,4,4-hexafluorobutane) as possible substitutes 0032-3861/02/$ - see front matter q 2002 Published by Elsevier Science Ltd. PII: S0032-3861(02)00602-X Polymer 43 (2002) 6471–6479 www.elsevier.com/locate/polymer * Corresponding author. Tel.: þ 1-814-863-8265; fax: þ1-814-863-8892. E-mail address: mmm23@psu.edu (M.M. Maroto-Valer).