Halogen-Free Flame Retardants in Polyurethane Foam Systems

Sustaining and enhancing the current export capacity of industry segments that produce raw materials and auxiliary chemicals used in polymer-based material manufacturing is highly important for our country. For this reason, developing more environmentally friendly and health-conscious products and manufacturing higher value-added polyurethane foam end products that can compete with other countries has become increasingly critical. Retarding the combustion of polyurethane foam products is the most important property that needs to be imparted to these materials. Legal requirements imposed on flame-retardant chemicals used in polyurethane foam products are forcing manufacturers to develop environment-friendly products that do not harm human health [1]. Flame retardant additives are used in polyurethane foams and other polymer-based materials to provide fire resistance in end products. Flame retardants are classified into two main categories: reactive and additive. Reactive flame retardants contain heteroatoms (N, P, Si) in their chemical composition and have structures that provide fire resistance in the polymer main chain. Additive flame retardants are mixed into formulations by physical means. Reactive flame retardants undergo chemical reactions with the polymer structure, while additive flame retardants are physically mixed into the polymer structure and do not undergo chemical reactions [2]. Commonly used flame retardants are boron, aluminum, phosphorus, antimony, chloride and bromide [3]. Nowadays, flame-retardant properties are imparted to polymers through halogen-containing additives. Although halogen-containing flame retardants provide suitable results for fire resistance, these additive materials have drawbacks: they gradually migrate from the surface causing a decrease in flame-retardant properties, release toxic gases when burned, and have negative effects on human health and the environment. For these reasons, the use of such products is declining and their use is restricted or banned in many countries due to legal requirements [4]. For these reasons, national and international companies continue their work on halogen-free flame retardants and are developing products that exhibit flame-resistant behavior. [caption id="attachment_104346" align="aligncenter"] Figure 1. Schematic representation of combustion mechanism[/caption]   Polyurethane foams are generally polymeric materials produced as a result of an exothermic reaction between polyols containing "OH" groups and diisocyanates containing "NCO" groups with appropriate catalysts and blowing agents. In the reaction between diisocyanate and hydroxyl groups, carbon dioxide gas (CO2) is formed, which causes the material to expand. To achieve greater expansion of the material, i.e., to obtain lower density material, various blowing agents such as pentane derivatives, methylal and water to some extent can be added to the foam formulation. [caption id="attachment_104347" align="aligncenter"] Figure 2. Schematic representation of rigid polyurethane foam formation[/caption]   In addition to these materials used to create polyurethane foam, special accelerators, special cell regulators, and flame-retardant additives can be added to the mixture to improve the combustion properties of the foam. In rigid polyurethane foams, phosphorus and bromine-containing polyols are used as flame-retardant additives, and Tris(1-chloro-2-propyl) phosphate (TCPP) and Triethyl phosphate (TEP) are used as additive agents. Polyisocyanurate (PIR) foams are also highly preferred as fire-resistant materials [5]. [caption id="attachment_104348" align="aligncenter"] Figure 3. Chemical structure representation of TCPP and TEP flame-retardant materials[/caption] [caption id="attachment_104349" align="aligncenter"] Figure 4. Combustion test appearances of PUR and PIR foams[/caption]   In the polyurethane foam sector, where we operate as the Kimpur family, nearly all domestic companies work on product formulations using imported raw materials through physical mixing methods. This situation creates serious economic problems for both the chemical sector and our national economic strategies. At the national technological level, polyurethane foam system manufacturers largely use halogen-containing additive agents in their systems to ensure fire resistance. Our company is increasing its R&D efforts daily to prepare innovative, economical and environmentally friendly products. Within this scope, our work continues on the synthesis and production of flame-retardant agents within our company. Currently, as the Kimpur family, we offer unique solutions for sandwich panel manufacturer companies with our KimRIGID PIR systems regarding fire resistance. KimRIGID PIR systems are products with compressive strength values in the range of 130-150 kPa, densities of 38-42 g/ml, thermal conductivity coefficient of 21 mW/mK, and fire resistance at minimum B s2 d0 level according to the European standard SBI (Single Burning Item).

References 1. Market study flame retardants, http://www.ceresana.com/en/market-studies/additives/flame-retardants, 26 May 2016. 2. Flame Retardants, Specialty Chemicals Update Program, https://ihsmarkit. com/products/chemical-flame-retardants-scup.html, September 2017. 3. D.K. Chattopadhyay, Dean C. Webster, Thermal stability and flame retardancy of polyurethanes, Progress in Polymer Science, Volume 34, Issue 10, October 2009, Pages 1068-1133

4. L.J. Qian, F.F. Feng, S. Tang, Bi-phase flame-retardant effect of hexa-phenoxy-cyclotriphosphazene on rigid polyurethane foams containing expandable graphite, Polymer, Volume 55 Issue 1, 2014, Pages 95–101. 5. M. Zhang, Z. Luo, J. Zhang, S. Chen, Y. Zhou, Effects of a novel phosphorus–nitrogen flame retardant on rosin-based rigid polyurethane foams, Polymer Degradation and Stability, Volume 120, 2015, Pages 427–434.

  Dr. Emre Baştürk Head of R&D Kimpur