Carbon Fiber Reinforced Rigid Polyurethane Foams
Experimental Investigation of Combustion Behavior of Carbon Fiber-Reinforced Rigid Polyurethane Foams Using Cone Calorimetry
Abstract
The production of lightweight components in the automotive industry is an important matter. For this reason, various studies are being conducted on alternative materials for use in interior and exterior assemblies. Carbon fiber is one of these alternative materials. Carbon fiber is used together with other materials in the production of various automotive parts. In this context, it has been determined that some automotive parts are produced using carbon fiber-reinforced rigid polyurethane foam to provide weight reduction and thermal insulation without interrupting passenger comfort and safety requirements. However, while carbon fiber is not a combustible material, it must be considered that rigid polyurethane foam is a readily ignitable and flammable material. In this study, the combustion properties of carbon fiber-reinforced rigid polyurethane foam were investigated using a cone calorimeter test apparatus. In the cone calorimeter experiments, low and medium intensity fire conditions were provided at heat flux rates of 15 kW/m2 and 35 kW/m2, respectively. When the foam materials were exposed to heat flux rates of 15 kW/m2 and 35 kW/m2, the heat release rate, total heat released, smoke, CO, CO2 and NO variations were obtained. It was determined that carbon fiber causes a significant increase in the combustion resistance of polyurethane foam material, particularly in low-intensity fires.Introduction
In the automotive industry, different criteria such as fuel consumption, safety, comfort and exhaust emissions exist in commercial competition among manufacturers. Therefore, structural lightness is an important matter for vehicles. For this reason, different studies are being conducted on alternative composite materials for interior and exterior assemblies of vehicles [1, 2, 3]. Carbon fiber is an important material that can be used in the production of composite materials for the automotive industry. Carbon fiber is used together with other materials to produce various automotive parts [4, 5, 6]. In this context, it has been determined that some automotive parts are produced using carbon fiber-reinforced rigid polyurethane foam to provide weight reduction and thermal insulation without interrupting passenger comfort and safety requirements [7, 8, 9]. However, although carbon fiber is not a combustible material, it should be considered that rigid polyurethane foam is combustible and can ignite easily. For this reason, research on the combustion properties of carbon fiber-reinforced composites needs to be conducted. Different tests exist to examine the combustion properties of polymer materials. Among these, the cone calorimeter test is one of the most commonly used methods to examine the combustion behavior of materials. [10, 11]. The cone calorimeter test enables the determination of important parameters such as heat release rate, total heat released, ignition time, peak heat release rate, smoke, CO, CO2 and NO emissions. In this study, the combustion properties of rigid polyurethane foam (PUR) and carbon fiber fabric-reinforced rigid polyurethane foam (PUR/CFF) were investigated with cone calorimeter tests. The combustion properties of the materials, such as heat release rate, total heat released, ignition time, smoke, CO, CO2 and NO emissions, were determined and compared with each other.Materials and Method Materials
The isocyanate (PMDI 92140) and polyol (Elastopor H2011/4) raw materials for rigid polyurethane foam (PUR) were purchased from TEKPOL (Turkey). Carbon fiber fabric (CFF) was obtained from Spinteks (Turkey).Sample Preparation
Polyurethane foam was produced by a batch process. The polyol and isocyanate components were mixed with a mechanical mixer at 3000 rpm for 12 seconds, and then the mixture was poured into an aluminum mold placed under a preheated press at 40 ± 2°C for 30 minutes. After the foams were removed from the mold, they were kept under laboratory conditions for 24 hours to complete the curing process. The foam materials were conditioned for 48 hours in a special conditioning chamber at 23 ± 1°C temperature and 50 ± 3% relative humidity before cone calorimeter tests. A similar process was applied to produce carbon fiber fabric-coated rigid polyurethane foam (PUR/CFF), but the carbon fiber fabric was placed on the bottom of the mold and on the underside of the mold cover.Cone Calorimeter Combustion Test
A cone calorimeter apparatus shown in Figure 1 was used to investigate the combustion behavior of PUR and PUR/CFF materials. The cone calorimeter apparatus was manufactured according to ASTM E-1354 [12] and ISO 5660 [13] standards. The test samples were cut to dimensions of 100 x 100 x 50 mm and, after being wrapped with 0.04 mm thick aluminum foil, were placed in the sample holder of the calorimeter. The samples were exposed horizontally to heat flux rates of 15 kW/m2 and 35 kW/m2 representing low and medium intensity combustion scenarios. Temperatures, mass loss, smoke, CO, CO2 and NO production were simultaneously recorded at 1 second time intervals with special software. To compare the combustion resistance of different materials, important parameters such as ignition time (TTI), heat release rate (HRR), total heat released (THR) and peak heat release rate (PHRR) were determined.Figure 1. Cone calorimeter apparatus and combustion image of the sample
Results and Discussion
PUR and PUR/CFF foams were tested at two different heat flux rates of 15 kW/m2 and 35 kW/m2. The HRR values of PUR and PUR/CFF foams are shown in Figure 2. At a heat flux rate of 15 kW/m2, it is clearly seen that CFF reinforcement delayed ignition time (TTI) by approximately 10 seconds and significantly reduced HRR values. The PHRR values of PUR and PUR/CFF are approximately 95 kW/m2 and 50 kW/m2, respectively. However, at a heat flux rate of 35 kW/m2, it was determined that CFF reinforcement did not significantly affect the ignition and combustion behavior of the foam, and the PHRR values of PUR and PUR/CFF were found to be 146 kW/m2 and 112 kW/m2, respectively.Figure 2. HRR variations of PUR and PUR/CFF materials at (a) 15 kW/m2 and (b) 35 kW/m2 heat flux rates
Figure 3 shows the THR values of PUR and PUR/CFF at two different heat flux rates. While the THR value of PUR material at a heat flux rate of 15 kW/m2 was approximately 11.2 MJ/m2, CFF reinforcement reduced the THR value by approximately 87% to 1.5 kW/m2. However, when the heat flux was increased to 35 kW/m2, the THR values of PUR and PUR/CFF during a 400 second combustion period were approximately 15.1 MJ/m2 and 11.9 MJ/m2, respectively. In this case, the reduction in THR was determined to be only approximately 21%. Figures 4 and 5 show images of PUR and PUR/CFF materials after cone calorimeter tests at heat flux rates of 15 and 35 kW/m2, respectively.Figure 3. THR variations of PUR and PUR/CFF materials at (a) 15 kW/m2 and (b) 35 kW/m2 heat flux rates
Figure 4. Image of PUR foam after cone calorimeter test at (a) 15 kW/m2 and (b) 35 kW/m2 heat flux rates
Figure 5. Image of PUR/CFF foam after cone calorimeter test at (a) 15 kW/m2 and (b) 35 kW/m2 heat flux rates
Smoke and CO production during combustion of rigid polyurethane foams is also an important matter. Because these emissions are the main cause of poisoning during fires. Figures 6 and 7 show the smoke and CO production of PUR and PUR/CFF foam samples during combustion. It is clearly visible that CFF reinforcement reduces the smoke and CO production of the material. However, CFF is more effective at a heat flux rate of 15 kW/m2. In the application of 35 kW/m2 heat flux, CO production continues in both PUR and PUR/CFF materials after 200 seconds. Although no flame is visible at the 400 second mark, the presence of significant CO emission can be explained by the continuation of flameless combustion in rigid polyurethane foam materials.Figure 6. Smoke production of PUR and PUR/CFF materials at (a) 15 kW/m2 and (b) 35 kW/m2 heat flux rates
Figure 7. CO production of PUR and PUR/CFF materials at (a) 15 kW/m2 and (b) 35 kW/m2 heat flux rates
CO2 production of the foams during combustion is shown in Figure 8. As expected, CO2 variations closely resemble HRR variations. Because CO2 production is related to the amount of material being burned. Additionally, Figure 9 shows NO production of the foams during combustion. NO is another cause of poisoning during fires. It is seen that CFF significantly reduces NO formation, particularly in the low heat flux application.Figure 8. CO2 production of PUR and PUR/CFF materials at (a) 15 kW/m2 and (b) 35 kW/m2 heat flux rates
Figure 9. NO production of PUR and PUR/CFF materials at (a) 15 kW/m2 and (b) 35 kW/m2 heat flux rates
Concluding Remarks
In this study, fire behaviors of neat and carbon fiber fabric reinforced rigid polyurethane foam materials were investigated with a cone calorimeter running at different heat fluxes, namely 15 and 35 kW/m2, which simulate the small, and the medium sized fire conditions, respectively. The heat release rate, the total heat released, smoke, CO, CO2 and NO variations of the foams with time were determined and compared each other. It was determined that although the carbon fiber fabric can significantly enhance the fire resistance of rigid polyurethane foam in small sized fire conditions, the beneficial effects of CFF decrease in the medium sized fire conditions.Acknowledgements
The authors would like to thank Pamukkale University Scientific Research Council (BAP) and TUBITAK (The Scientific and Technological Research Council of Turkey for supporting this study. Fatih Demiryuğuran Pamukkale University Research Assistant Prof. Dr. Nazım Usta Pamukkale University Department of Mechanical EngineeringReferences [1] Q. Dai, J.C. Kelly, A. Elgowainy. Life Cycle Analysis of 1995-2014 U.S. Lighth-Duty Vehicle Fleet: The Environmental Implications of Vehicle Material Composition Changes, SAE International Journal of Materials and Manufacturing, 10, 3, 378-384, 2017. [2] M. Juraeva, K.J. Ryu, S.H. Noh, D.J. Song. Lightweight material for the speed reducer housing of a car chassis, Journal of Mechanical Science and Technology, 3, 7, 3219-3224, 2017. [3] K. Albrecht, T. Osswald, S. Wartzack, J. Müssig. Natural Fibre-Reinforced, Injection Moulded Polymers For Light Weight constructions - Simulation Of Sustainable Materials For The Automotive Industry, 20th International Conference on Engineering Design (ICED), Milan, ITALY, JUL 27-31, 2015. [4] M. T. Mastura, S. M. Sapuan, M. R. Mansor, A. A. Nuraini. Conceptual design of a natural fibre-reinforced composite automotive anti-roll bar using a hybrid approach, International Journal of Advanced Manufacturing Technology, 91, 5-8, 2031-2048, 2017. [5] V. Rajesh, P.M.V. Rao, N.Sateesh. Investigation of Carbon Composites Subjected to Different Environmental Conditions, 5th International Conference on Materials Processing and Characterization (ICMPC), Gokaraju Rangaraju Inst Engn & Technol, Hyderabad, INDIA, MAR 12-13, 2016. [6] D.C. Silveira, N. Gomes, M.C. Rezende, E.C. Botelho. Electromagnetic Properties of Multifunctional Composites Based on Glass Fiber Prepreg and Ni/Carbon Fiber Veil, Journal of Aerospace Technology And Management, 9, 2, 222-231, 2017. [7] V. Yakushin, U. Stirna, L. Bel'kova, L. Deme, I. Sevastyanova. Properties of Rigid Polyurethane Foams Filled With Milled Carbon Fibers, Mechanics of Composite Materials, 46, 6, 679-688, 2011. [8] B. Dahlke, H. Larbig, H. D. Scherzer, R. Poltrock. Natural Fiber Reinforced Foams Based on Renewable Resources for Automotive Interior Applications, Journal of Cellular Plastics, 34, 4, 361-379, 1998. [9] M.C. Silva, J. A. Takahashi, D. Chaussy, M. N. Belgacem, G. G. Sil, Composites of rigid polyurethane foam and cellulose fiber residue, Journal of Applied Polymer Science, 117, 6, 3665–3672, 2010. [10] M. Checchin, C. Cecchini, B. Cellarosi, F.O. Sam. Use of cone calorimeter for evaluating fire performances of polyurethane foams. Polymer Degradation and Stability, 64, 3, 573-576, 1999 [11] N. Usta. Investigation of fire behavior of rigid polyurethane foams containing fly ash and intumescent flame retardant by using a cone calorimeter, Journal of Applied Polymer Science, 124, 4, 3372-3382, 2012. [12] ASTM E1354-14, Standard Test Method for Heat and Visible Smoke Release Rates for Materials and Products Using an Oxygen Consumption Calorimeter, ASTM International, West Conshohocken, PA, U. S. A., 2004. [13] ISO 5660-1: Reaction to fire tests heat release, smoke production and mass loss rate, part 1: heat release rate (cone calorimeter method), 2002.
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