New developments in chemical modification of fire-safe rigid polyurethane foams Wojciech Zatorski a, * , Zbigniew K. Brzozowski a , Andrzej Kolbrecki b a Central Institute for Labour Protection – National Research Institute, Department of Chemical and Aerosol Hazards Laboratory of Chemical Technology, 16 Czerniakowska Street, 00-701 Warsaw, Poland b Building Research Institute, Fire Testing Laboratory, 21 Ksawero ´w Street, 02-656 Warsaw, Poland article info Article history: Received 15 July 2007 Received in revised form 8 May 2008 Accepted 12 May 2008 Available online 3 August 2008 Keywords: Layered silicate nanoclay Polyurethane–polyisocyanurate foam Flame retardant Reactive bromine Reactive phosphorous Zinc stannate abstract This work reports the preparation of polyurethane–polyisocyanurate (PUR–PIR) foams containing different amounts of flame retardants (FRs) and a layered silicate nanoclay. An environmentally friendly blowing agent, a mixture of 1,1,1,3,3-pentafluorobutane and 1,1,1,2,3,3,3-heptafluoropropane (HFC 365/ 227), with small amount of water was used. The flame retarded PUR–PIR foams showed better fire resistance in comparison to classical PUR and unmodified PUR–PIR foams without deterioration of their functional properties. It was observed that when nanoclay was used in conjunction with flame retardants containing reactive bromine and phosphorus compounds, and zinc stannate, the flammability was significantly reduced. Expandable graphite was also used in some samples. As control samples for reference purposes three foam systems without any flame retardant were frothed: PUR, PUR–PIR and foams PUR–PIR modified by carbodiimide groups. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction The main aim of this research was to form polyurethane foams with good fire retardant properties. So far, the application of rigid polyurethane (PU) foams is limited by their high flammability. Any solution of this problem will increase their application in industry, where strict standards with respect to flammability are imposed. Polyurethane foam is the most efficient insulating material. Any attempt to reduce heat conduction by further reduction of density will cause a rise in radiation transfer. Thermal conductivity of polyurethane foam is from about 0.018 up to 0.028 W/(mK). The thermal conductivity factor of polyurethane foam is two times lower than that of polystyrene which is an alternative material for insulation purposes. On the other hand the physical and mechan- ical properties of polyurethane foam are superior to those of polystyrene. Among the isocyanate-based foams, both flexible and rigid polyurethane foams are flammable. Due to serious fire hazards of polyurethane foams, strict fire regulations have been imposed by regulatory bodies for their use in furniture for public trans- portation. In addition, the use of rigid urethane foams as building insulation materials is also under strict fire regulations. For these reasons, studies to find effective flame retardants have been carried out by many researchers in industry and universities over a long period of time, but so far there is a limited success. Recent public concerns about the problem of ozone layer depletion led to the establishment of the United Nations Envi- ronmental Program Protocol, also referred to as the Montreal Protocol. This protocol originally required a complete phase out of chlorofluorocarbon (CFC) and ‘‘soft’’ hydrochlorofluorocarbons (HCFCs) as blowing agents by 2004, hence the interest in finding alternative solutions grew. Blowing agents not harmful for the ozone layer are based on hydrofluorocarbons (HFCs), carbon dioxide or pentane isomers. Foams blown with derivatives of pentane, hydrofluorocarbons and water are environmentally friendly. They show ozone depletion potential (ODP) equal to zero, low global warming potential, low or no toxicity, low thermal conductivity (k) and good physical properties of the resulting foams [1]. A great disadvantage of using pentane and its derivatives is linked to their high combustibility, which results in increase of the flammability of polyurethane foams [2,3]. Polyurethane foams can be rendered fireproof by introducing reactive flame retardants based on halogen and phosphorus pol- yols [4–7] or chemical modification of polyurethane by intro- ducing isocyanurate rings or carbodiimides [8–10]. The carbodiimide linkage is a thermally stable linkage suitable for modifying isocyanurate foams having low friability and high flame * Corresponding author. Tel.: þ48 022 6234693; fax: þ48 022 6233693. E-mail addresses: wozat@ciop.pl, zbigbi@ch.pw.edu.pl (W. Zatorski), a.kolbrecki@itb.pl (A. Kolbrecki). Contents lists available at ScienceDirect Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab 0141-3910/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymdegradstab.2008.05.032 Polymer Degradation and Stability 93 (2008) 2071–2076