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International Journal of Enhanced Research Publications, ISSN: XXXX-XXXXVol. 2 Issue 4, April-2013, pp: (1-4), Available online at: www.erpublications.com

Thermal Performance of Glass Fiber Reinforced Intumescent Fire Retardant Coating for Structural

ApplicationFaiz Ahmad1*,Sami Ullah1, Hammad Aziz1 and Nor Sharifah Omar1

1 Mechanical Engineering, Universiti Teknologi PETRONAS, Malaysia* [email protected]

Abstract: The results of influences of glass fiber addition into the basic intumescent coating formulation towards the enhancement of its thermal insulation properties are presented. The intumescent coatings were formulated from expandable graphite ammonium polyphosphate, melamine, boric acid, bisphenol A epoxy resin BE-188, ACR Hardener H-2310 polyamide amine and fiberglass (FG) of length 3.0 mm. Eight different intumescent formulations were developed and the samples were tested for their fire performance by burning them at 450, 650 and 850 ºC in the furnace for two hours. The effects of each fire test at different temperatures; low and high temperature were evaluated. Scanning Electron Microscope, X-Ray Diffraction technique and Thermo gravimetric Analysis were conducted on the samples to study the morphology, the chemical components of char and the residual weight of the coatings. The formulation, FG08 containing 7.0 wt% glass fiber provided better results with the enhanced thermal insulation properties of the coatings.

Keywords: Component, intumescent coating, expandable graphite, fiberglass

Introduction

The use of fire-retardant coatings is one of the easiest, oldest and most efficient ways to protect steel substrates against fire [1-2]. It is important to protect materials against fire in the construction and petrochemical industries to ensure safe evacuation of people from the building before the steel structures start to deteriorate when exposed to temperature above 450°C [3].The application of intumescent coating does not change the basic properties of the material (e.g. mechanical properties), can be easily processed and applied on several materials including metallic, polymers, textiles and wood [1-2,4].

Intumescent is defined as the swelling of certain substances when they are heated [5-6]. Intumescent coatings form an expanded multicellular layer upon heating; namely char, which acts as thermal barrier that effectively protects the substrate against rapid increase of temperature and thereby maintaining the structural integrity of the building. The physical structure of the charring layer plays a very important role in the performance of flame retardant. Formation of homogeneous high volume of residual char of suitable thickness ensures longer fire-endurance time and better performance of the flame retardant coating [7]. In recent years, price efficiencies and improvements in technology have created a situation for intumescent coatings to dominate the structural fire protection market [8-9].

Several studies have demonstrated the use of filler and binder as reinforcing agent that helped to increase the efficiency of the intumescent coatings in terms of providing longer protection to the structural steel [9-11]. Smaller number of studies focused on the effect of using fiberglass to increase the thermal insulation properties of the intumescent coatings. Fiberglass has been used as reinforcement of the char strength [7, 12]. It helps to maintain the char integrity and provides a higher mechanical resistance of the charring element [12]. In terms of fire safety, fiberglass insulation is naturally noncombustible as it is produced from sand and recycled glass [7-8].

The objective of this study was to investigate the thermal insulation properties of intumescent coating with varying amount of fiber glass added into the basic intumescent formulations. The optimum intumescent formulation with fibreglass, which provides the best thermal insulation properties against fire, was determined [7]. The study on the thermal insulation property of the intumescent coating will allow determination of exact temperature at which the charring of the mixture begins.

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EXPERIMENTAL MATERIALS AND METHOD

A. MaterialsAmmonium polyphosphate (Exolit AP422) containing 20 percent phosphorus used as the acid source was provided by Clariant (Malaysia) Sdn Bhd. Bisphenol A epoxy resin BE-188 (BPA) used as a binder with ACR Hardener H-2310 polyamide amine also known as tetraethylene tetramine (TETA) were bought from Mc-Growth Chemical Sdn Bhd. Malaysia. Structural steel A36M was supplied by TSA Steel Industries (Ipoh) Sdn. Bhd. Malaysia. Melamine used as a blowing agent and boric acid as an additive were purchased from Sigma-Aldrich (M) Sdn Bhd. Malaysia. Bhd. Graphite and short fiberglass (FG) of length 3.0 mm were purchased from Premier East West Malaysia Sdn. Bhd.

B. Preparation of intumescent formulationsExpandable graphite (EG) used as the carbon source was prepared by grinding and sieving the graphite powder into smaller particle size of 300μm. A mixture of concentrated sulfuric acid (98%) acetic acid (37.5%), (150g), graphite powder (75g) and potassium permanganate (5.25 g) were stirred at room temperature for 1 hour. The treated graphite was filtered, washed with distilled water until pH level was close to 6-7 and dried at 100-110°C in the oven for approximately 4 hours.

Fig. 1 shows the flowchart of preparation of the coating. APP, MEL and boric acid were weighed and grinded into smaller particles to prevent the formation of bubbles in the coating. bisphenol A epoxy resin BE-188 (BPA) and ACR hardener was weighed and mixed together in the Ultra Turrax mixer to achieve a homogenous mixture. This was followed by addition of expandable graphite and fiberglass into the mixture and stirred well until uniform dispersion was achieved. The coatings were then applied on 3.5 mm thickness steel plates of dimensions 15 x 50 mm 2 and were left for curing at room temperature for 2 weeks. Eight formulations of the intumescent coating developed in this study are shown in Table 1.

Figure 1: Experimental flow chart

Table 1: Wt% of intumescent coating ingredients

No EG APP MEL BA Epoxy Hardener FGFG01 5.50 11.10 5.50 11.50 44.60 22.20 0FG02 5.50 11.10 5.50 11.50 42.76 21.38 1FG03 5.50 11.10 5.50 11.50 42.10 21.00 2FG04 5.50 11.10 5.50 11.50 41.42 20.71 3FG05 5.50 11.10 5.50 11.50 40.76 20.38 4FG06 5.50 11.10 5.50 11.50 40.10 20.00 5FG07 5.50 11.10 5.50 11.50 39.40 19.71 6FG08 5.50 11.10 5.50 11.50 39.10 19.00 7

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Analysis and Characterization

A. Fire TestThe intumescent coating samples were burnt at three different temperatures; 450ºC, 650ºC and 850ºC for two hours in the furnace. The char expansion of each sample was measured by using digital Vernier caliper before and after fire test. The char morphology and compounds of char of each sample was determined using SEM and XRD.

B. Thermal Insulation TestA Bunsen burner was used to fire the intumescent samples according to the UL 94 standard. In every test, the coated steel was wired with a digital thermocouple to record temperature of the steel substrate. The temperature versus time measurements was recorded using an electric data logger. The temperature of the steel plate was measured for 60 minutes at an interval of 1 minute.

C. Scanning Electron Microscope

The charring layer and the morphological structures of the inside and outside of char were observed and analyzed using Oxford Instrument SEM. UK

D. X-Ray Diffraction (XRD)The composition of the residual char of intumescent coating was analysed by XRD and measurements were performed on a Diffractometer Bruker AXS D8 Advance, Germany using Cu Kα radiation and a nickel filter (k = 0.150595 nm) in the range (10 < 2θ < 90).

E. Thermogravimetric AnalysisThe residual weight of intumescent coatings was analysed using TGA. The thermogravimetric analysis of samples (approximately 10mg) was carried out at 10°C/min under N2 over the whole range of temperature (50°C–800°C) using Perkin-Elmer TGA Q50.

Results and Discussions

A. Char Expansion Fire test at 450 ºC and 650ºC

The intumescent coating sample, FG07 showed the highest expansion followed by samples FG06 and FG08. After the fire test, the coatings swelled and expanded into charring elements that protected the substrate steel from severe fire. The char had a very rough surface with large cracks. The microstructure of samples FG07 and FG08 were examined using SEM. Fig 2 shows the burnt samples of coating FG07 and FG08 at 650oC. Fig. 3 shows the graph of expansion ratio shown by each sample burnt at 450 ºC and 650 ºC.

Figure 2: Char of FG07 and FG08 after fire test at 650 ºC

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FG07 FG08


Figure 3: Expansion ratio of coating burnt at 450ºC and 650ºC

The coating samples FG08 and FG07 showed maximum char expansion. The surface of the char was very rough surface with small cracks and effectively attached to the steel substrate.

Char Expansion at 850 ºC

The results from the fire test conducted at temperature 850°C were the formation of white powder (ashes) from the coating. The formations of the ashes were due to the high fire temperature in the furnace. Fig. 4 shows the burnt intumescent coating samples of FG07 and FG08. Glass fibres are not susceptible to oxidation, but begin soften around temperatures of 650 to 970°C and melt above 1225°C [12, 13].

Figure 4: Char of FG07 (left) and FG08 (right) after fire test at 850 ºC

B. Thermal Insulation of Coatings The thermal properties of the intumescent coating with and without fiberglass were compared and shown in Fig. 5. The coating without fiberglass was observed to reach the highest back steel temperature of 367ºC while the coating FG04, FG05 and FG06 were 346, 329 and 278oC after 60 minutes fire test, respectively. The coating FG07 and FG08 with 6.0 wt. % and 7.0 wt. % of glassfiber recorded the lowest temperature of substrate i.e 217oC and 189oC after 60 minutes exposure to fire. Initially the temperature of FG07 and FG08 increased rapidly within 10-18 minutes. It reached to 160oC after ten minutes to 185oC after another 8 minutes of fire test. After the formation of carboneous char on the substrate steel, the temperature was gradually increased. It was concluded that the use of glassfiber in the intumescent coating formulations helped to increase the thermal insulation properties of the coating, prolong the lifetime of steel structures and improved the strength of the char.

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Figure 5: Temperature versus Time of exposure to fire

C. Scanning electron microscopy (SEM) analysis

The SEM micrographs of outer and inner surface of chars of sample FG07 and FG08 burnt at 450 ºC and 650 ºC were obtained using magnifications of 50x and 100x (outer surface) and 500x (inner surface).

Char Morphology at 450 ºCSEM micrograph of char of FG07 showed bubbles, holes and cracks on the outer layer. However, the intumescent performance was good and substrate temperature was also low. The outer layer was smooth and confirmed a good intumescent performance. Bubbles were formed due to emission of N2, ammonia, CO2 gases and dehydration of water occurred [3, 14] during the burning process of the intumescent coating. The graphite flakes appeared in the inner surface and produced a heat barrier to protect the steel (substrate). Small holes observed were due to the heat dissipation that occurred and prevented transfer of heat from fire to the surface. Fig. 6 shows SEM micrograph of the outer surface of the char., which shows small bubbles.

Figure 6: SEM micrograph of FG07 coating (char) for inner surface: 100X

Fig. 7 shows the outer surface of the char of FG08 coating. The sample demonstrates a good intumescent behavior. The outer surface was smooth with bubbles, small cracks and folding structures. The formation of bubbles was due to the emission of N2 and ammonia gases during burning process. The FG08 char swells nicely since there are emissions of N 2, NH3 and CO2 gases and dehydration of water which occurred inside the charring layer [6]. Graphite flakes appeared in the inner surface which acts a heat barrier to protect the steel substrate.

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Figure 7: SEM micrograph-outer surface of char, FG08: 50X

Char Morphology at 650 ºCThe SEM micrograph of char for sample FG07 burnt at 650ºC showed formation of large holes and white powder on the outer surface with cracks in the inner surface of the charring layer. The presence of white powder (ashes) as in Fig. 8 on the surface was the result at 650 ºC of the coatings which turned small portions of the coating into ashes. The surface of the coating swells properly due to emission of gas from the holes. Large holes within the char were helpful to minimize the heat penetration from the source to the surface of substrate.

Figure 8: SEM micrograph of outer surface of char, FG07: 500X

Fig. 9 shows the SEM micrograph of chars of inner surface for sample GF08. The formation of holes, folding structure and white powder on the charring layer can be observed. The outer surface of the coating was smooth with small holes and the presence of white powder (ashes) due to high temperature of the fire test at 650 ºC. Inside the coating, the emission of N2, NH3 and CO2 gas and dehydration of water [14] occurred. Small holes were observed too which were helpful to prevent the heat from transferring to the surface.

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Figure 9: SEM micrograph-inner surface of char, FG08 : 500X

D. X-ray diffraction (XRD) analysis

XRD analysis was carried out to investigate the residual char composition of the intumescent coating after fire test at 450 ºC. After the residue char of the intumescent coating was oxidized at high temperature, the residue was amorphous carbon and inorganic materials [14]. The inorganic compounds were considered as forming the main protective layer at later stages of burning. The facial residue of samples FG07 and FG08 were analyzed using XRD technique.

Figs. 10-11 showed the XRD peaks of the facial residue char of sample FG07 and FG08 burnt at 450 ºC. Several XRD peaks of the residue char at 5.929, 3.61734, 3.38003, 3.18150, 2.95135 and 2.23516 were assigned according to JCPDS card.

F607

12-0212 (D) - Graphite - C - Y: 50.00 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 2.46400 - b 2.46400 - c 6.73600 - alpha 90.000 - beta 90.000 - gam06-0297 (Q) - Boron Oxide - B2O3 - Y: 50.00 % - d x by: 1. - WL: 1.5406 - Cubic - a 10.05500 - b 10.05500 - c 10.05500 - alpha 90.000 - beta 90.00074-1169 (C) - Boron Phosphate - BPO4 - Y: 50.00 % - d x by: 1. - WL: 1.5406 - Tetragonal - a 4.33200 - b 4.33200 - c 6.64000 - alpha 90.000 - beta 9Operations: Smooth 0.150 | Smooth 0.150 | Smooth 0.150 | Smooth 0.150 | Smooth 0.150 | Smooth 0.150 | Smooth 0.150 | Smooth 0.150 | BackgroF607 - File: F607.raw - Type: 2Th/Th locked - Start: 2.000 ° - End: 80.000 ° - Step: 0.100 ° - Step time: 1. s - Temp.: 25 °C (Room) - Time Started: 131

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Figure 10: XRD curve of the residue char of sample FG07 burnt at 450 ºC

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F608

74-1169 (C) - Boron Phosphate - BPO4 - Y: 50.00 % - d x by: 1. - WL: 1.5406 - Tetragonal - a 4.33200 - b 4.33200 - c 6.64000 - alpha 90.000 - beta 906-0297 (Q) - Boron Oxide - B2O3 - Y: 50.00 % - d x by: 1. - WL: 1.5406 - Cubic - a 10.05500 - b 10.05500 - c 10.05500 - alpha 90.000 - beta 90.00012-0212 (D) - Graphite - C - Y: 50.00 % - d x by: 1. - WL: 1.5406 - Hexagonal - a 2.46400 - b 2.46400 - c 6.73600 - alpha 90.000 - beta 90.000 - gamOperations: Smooth 0.150 | Smooth 0.150 | Smooth 0.150 | Smooth 0.150 | Smooth 0.150 | Smooth 0.150 | Smooth 0.150 | Background 1.000,1.000F608 - File: F608.raw - Type: 2Th/Th locked - Start: 2.000 ° - End: 80.000 ° - Step: 0.100 ° - Step time: 1. s - Temp.: 25 °C (Room) - Time Started: 131

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Figure 11: XRD curve of residue char of sample FG08 at burnt at 450 ºC

The peak at 5.929 was assigned to boron oxide. The peak at 3.65237 assigned to boron phosphate and at 3.3803 assigned to graphite. The major peak at 3.15807 assigned to sassolite and 2.16149 were assigned to boron phosphate oxide. The dehydration of boric acid yielded boron oxide while the reaction between APP and boron oxide yield some boron phosphate in the charring element. The formation of sassolite (mineral acid of boric acid H3BO3) that has been shown due to the dehydration to support the formation of B2O3, glass-like material which increase fire retardancy of char [4,14].

E. Thermogravimetric analysis (TGA)

The thermogravimetric analysis of samples carried out under controlled atmosphere and temperature conditions resulted in an overview of the degradation process of the coating. The residual weight was plotted against the temperature to examine the effectiveness of intumescent coating. This test was performed to achieve a high level of homogenous and large amount of char. This residue condensed the heat transfer to the substrate thus reducing the gases feeding combustion process. A slow degradation rate of coating resulted in a more homogenous char.

As illustrated in Fig. 12 the TG curves of sample FG01, FG07 and FG08 showed three steps of thermal degradation. In the range of 0-200oC, the residual weight was 96 -90%; this weight loss was attributed to two events, firstly H 2O being released from cured epoxy resin and, secondly the decomposition of boric acid into meta boric acid [13]. The residual weight was 90-75% in the range of 200-350oC due to decomposition of melamine and APP releasing N2, H2O and NH3

gas. In the range of 350-500oC, APP decomposed into polyphosphoric acid, and meta phosphoric acid, epoxy and hardener decomposed into CO2 and H2O [6]; resulting reduction in residual weight to 35-31%. At this stage, it might be possible that APP reacted with boric acid to form a thermally stable compound assumed as borophosphate [3].There should be high amount of residue left at temperature higher than 800ºC in order for the coatings to effectively protect the steel [15]. Some residues were observed after degradation over 800ºC. The FG01 contained the residual weight 19.73%. Sample FG08 with 7.0 grams of fiberglass left 26.58wt% and FG07 with 6.0 grams of fiberglass left 24.13wt% residues of char at 800ºC. It shows that FGO8 have 10 percent higher residual weight compared to FG07 and 34.71 percent higher than FG01. The residual weight was increased due to increase in the weight percentage of fiberglass. The former gave enough charring to allow a good char expansion in the fire test.

The TGA results were confirmed by DTGA curves of FG08 illustrated in Fig. 13 which indicated six steps of thermal degradation at 117, 138, 279, 341, 404 and 454oC. The first degradation at 117oC indicates degradation of cured epoxy, and conversion of boric acid into meta boric acid; while the second degradation at 138oC was the conversion of meta boric acid into boron oxide. Melamine decomposed at 279oC. The decomposition of BPA epoxy resin, EG and APP occurred at 341oC, 404oC and the degradation of polyamide hardener occurred at 454oC.

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Figure 12: TG curves of sample FG01, FG07 and FG08

Figure 13: DTGA curves of sample FG08

Conclusion

This study was focused into the preparation of the expandable graphite as char former and fiberglass as an insulating reinforcement in enhancing the thermal insulation property of the coating. This investigation led to the following conclusions; various amount of fiberglass ranging from 1.0-7.0 wt% were reinforced into the basic intumescent coating formulations. Formulation FG08, 7.0 wt% glass fiber recorded the best results in terms of the enhanced thermal insulation properties of the coatings. FG08 coating recorded the best expansion during fire test at 450ºC and 650ºC with 5-7 times more than the original thickness. The lowest back steel temperature was 200ºC during thermal test. Thermal insulation test illustrated good coating characteristics after analysis using SEM. These coatings also recorded the presence of graphite, boron oxide and boron phosphate after XRD testing and with good residue after degradation analysis using TGA. The residual weight increased due to increase in weight percentage of fiberglass in the intumescent coating. Thus, it was concluded that the addition of fiberglass into the basic intumescent formulations helps to enhance the thermal characteristic of the coating and assists to maintain the substrate materials for longer time.

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Acknowledgement

The authors acknowledge the assistance and the support received from the Mechanical Engineering Department of Universiti Teknologi PETRONAS, Malaysia.

References

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[12].Amir, N., Ahmad F. and Megat-Yusoff, P.S.M., “Study on the Fibre Reinforced Epoxy-Based Intumescent Coating Formulations and their Char Characteristics”, Journal of Applied Sciences, 2011, 11(10): pp1678-1687.

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