The effect of 150μm expandable graphite on char expansion of intumescent fire retardant coating

The effect of 150μm expandable graphite on char expansion of intumescent fireretardant coatingSami Ullah, Faiz Ahmad, A. M. Shariff, and M. A. Bustam Citation: AIP Conference Proceedings 1621, 355 (2014); doi: 10.1063/1.4898492 View online: http://dx.doi.org/10.1063/1.4898492 View Table of Contents: http://scitation.aip.org/content/aip/proceeding/aipcp/1621?ver=pdfcov Published by the AIP Publishing Articles you may be interested in A study of cotton coated with intumescents flame retardant: Kinetics and effect of blends of used vegetable oilmethyl ester J. Renewable Sustainable Energy 5, 053121 (2013); 10.1063/1.4822259 Round an expanding world: A simple model to illustrate the kinematical effects of the cosmological expansion Am. J. Phys. 75, 331 (2007); 10.1119/1.2423041 Expanding upon the linear expansion experiment Phys. Teach. 27, 375 (1989); 10.1119/1.2342802 Thermal Expansion of Polycrystalline Graphite J. Appl. Phys. 41, 5092 (1970); 10.1063/1.1658613 Expansion of Annealed Pyrolytic Graphite J. Appl. Phys. 35, 1992 (1964); 10.1063/1.1713794

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The Effect of 150μm Expandable Graphite on Char Expansion of Intumescent Fire Retardant Coating

Sami Ullah1, a), Faiz Ahmad2, b), A.M. Shariff1, c) and M.A.Bustam1, d)

1Research Center for Carbon Dioxide Capture, Department of Chemical Engineering, Universiti Techologi PETRONAS, Bandar Sri Iskandar, Tronoh 31750 Perak, MALAYSIA

2Department of Mechanical Engineering Universiti Techologi PETRONAS, Bandar Sri Iskandar, Tronoh 31750 Perak, MALAYSIA

a) Corresponding author: [email protected]

b) [email protected] c) [email protected]

d) [email protected]

Abstract. Intumescent is defined as the swelling of certain substances to insulate the underlying substrate when they are heated. In this research work the effect of 150μm expandable graphite (EG) was studied on char expansion, char morphology and char composition of intumescent coating formulations (ICFs). To study the expansion and thermal properties of the coating, nine different formulations were prepared. The coatings were tested at 500 oC for one hour and physically were found very stable and well bound with the steel substrate. The morphology was studied by Scanning Electron Microscopy (SEM). The char composition was analysed by X-ray Diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) techniques. EG above than 10.8wt% expands the char abruptly with uniform network structure and affect the outer surface of the char.

INTRODUCTION

The need for fireproofing coatings became important in the nineteenth century due to the commercialization of cellulose nitrate plastic. These materials are highly flammable and present a major fire risk. In the early 1980’s a mixture of pentaerythritol and melamine was used as intumescent flame retardant systems, together with additives such as phosphates [1]. Both Aluminium Tri Hydrate (ATH) and halogenated compounds are still dominant. Antimony is now widely used with halogen compounds.

In the early 1990’s, market trends suggested that the market was beginning to move away from halogenated flame retardants 1 due to their toxic nature. These compounds work very well in most cases but release poisonous and corrosive gases when decomposing in fire and these retardants are not readily disposable after use. In Europe especially, the environmentalists are putting more pressure on companies to produce more environmentally friendly products to protect the environment and humans[2]. The flame retardant world market for 1990 was estimated approximately 500,000 metric tons [3]. Expandable graphite is a new generation fire retardant additive. It is formed by treating crystalline graphite with intercalates such as nitric or sulphuric acid [4]. Expandable graphite coatings can expand the carboneous char to a greater degree than the traditional intumescent coatings, and thus provide better insulation to the underlying substrate [5]. The objective of this research work is to study the effect of expandable graphite (150μm) on char expansion, morphology and composition of intumescent fire retardant coating.

3rd International Conference on Fundamental and Applied Sciences (ICFAS 2014)AIP Conf. Proc. 1621, 355-362 (2014); doi: 10.1063/1.4898492

© 2014 AIP Publishing LLC 978-0-7354-1258-3/$30.00

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MATERIALS AND METHODS

Flake graphite (150μm), melamine (Mel) and boric acid (BA) were purchased from Sigma-Aldrich (M) Sdn Bhd. Malaysia. Ammonium poly phosphate (APP) was provided by Clariant (Malaysia) Sdn Bhd. Acetic acid, sulphuric acid, KMnO4, binder is bisphenol A epoxy resin BE-188 (BPA) and ACR Hardener H-2310 polyamide amine were bought from Mc-Growth chemical Sdn Bhd. Malaysia. Structural steel A36M was supplied by TSA industries (Ipoh) Sdn. Bhd. Malaysia.

Preparation of Expandable Graphite

Expandable graphite (EG) was prepared as reported in literature [6, 7]. 50g of natural flake graphite, 100g of glacial acetic acid, 25g of 98% sulphuric acid and 3.5g of potassium permanganate were placed into a dry three-necked flask equipped with a thermometer, a stirrer and a condenser. After this mixture in the flask was stirred and reacted for 2 hours at the temperature of 25oC, the EG was prepared. It was then washed in water to neutrality, dehydrated and dried at a temperature of 50-60oC.

Coating Preparation

The weight percentage of expandable graphite was increased from 5.8 to 10.8 with all the intumescent ingredients were mixed with their respective weight percentage. The shear mixer was used for the mixing of coating at 40rpm for 30min. The structural steel plate area 100cm2 was used as a substrate. The coating was applied using brush on the steel substrate and thickness of coating was maintained at 1.5mm and it was measured by digital vernier caliper. The coated substrate was cured in the oven at 60oC for 24 hour. Nine intumescent coating formulations (ICFs) were prepared to study the effects of EG on char expansion, char morphology, char composition and residual weight of the coating formulations. The formulations were further characterized by SEM, XRD and FTIR.

Characterization of ICFs

Furnace Test

To analyse the physical properties of char such as char expansion and char structure after fire test. The intumescent coatings were burned in a Carbolite Furnace. For the first 15 minutes, the furnace temperature was set at around 50°C, then the temperature was raised up to 500°C and this temperature was kept for 60 minutes to ensure the sample has burnt completely [8]. Ensuring complete burning, the samples were cooled in the furnace for approximately 60 minutes to avoid cracking of char.

Scanning Electron Microscopy

Charring layers of intumescent coating and their morphological structures were observed and analyzed by SEM Carl Zeiss Leo1430VP.

X-ray Diffraction

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

FTIR Analysis

The functional groups of residual char composition were analyzed by Shimadzu FTIR in the ranges 4000–400cm-1.

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RESULT AND DISCUSSION

ICFs with EG particle size 150μm

Nine formulations were prepared with 150μm particle size of EG. The physical appearance and observation of the 150μm EG coatings before and after fire test are described below in Table 1 and 2, respectively.

TABLE 1. Intumescent formulations of 150μm EG before furnace test. Formulation IF-1 Formulation IF-2 Formulation IF-3

Physical

appearance

Observations Less viscous

Easy to stir with mixer Easy to apply with brush Touch dry after 8 day

Less viscous Easy to stir with mixer Easy to apply with brush Touch dry after 8 days

Less viscous Easy to stir with mixer Easy to apply with brush Touch dry after 8 days

Formulation IF4 Formulation IF-5 Formulation IF6

Physical

appearance

Observations Less viscous

Severe coagulation of solid particles after a while

Touch dry after 7 days

Less viscous Severe coagulation of solid particles after a while

Touch dry after 6 days

High viscous Severe coagulation of solid particles after a while

Touch dry after 6 days Formulation IF-7 Formulation IF-8 Formulation IF-9

Physical

appearance

Observations Black colour High viscous Severe coagulation of solid particles after a while

Touch dry after 4 days

Black colour High viscous Severe coagulation of solid particles after a while

Touch dry after 4 days

Black colour High viscous Severe coagulation of solid particles after a while Touch dry after 4 days

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TABLE 2. Intumescent formulations of 150μm EG after furnace test. Formulation IF-1 Formulation IF-2 Formulation IF-3

Physical

appearance

Observations Ave coating thickness: 1.50 mm

Ave char thickness: 4.80 mm Expansion: 3.20 times Soft char No void Small bubbles on surface

Ave coating thickness: 1.2mm Ave char thickness: 5.4 mm Expansion: 4.50 times Hard char Large void in middle Small bubbles on surface

Ave coating thickness: 1.50mm Ave char thickness: 10.20 mm Expansion: 6.80 times Hard char Small void in middle

Formulation IF-4 Formulation IF-5 Formulation IF-6

Physical

appearance

Observations Ave coating thickness: 2.10 mm

Ave char thickness: 23.70 mm Expansion: 11.30 times Hard char

Ave coating thickness: 2.25 mm Ave char thickness: 10.10 mm Expansion: 4.50 times Hard char

Ave coating thickness: 1.80 mm Ave char thickness: 12.40 mm Expansion: 6.90 times Soft and weak char

Formulation IF-7 Formulation IF-8 Formulation IF-9

Physical

appearance

Observations Ave coating thickness: 1.70 mm

Ave char thickness: 15.00 mm Expansion: 8.80 times Weak char

Ave coating thickness: 2.10 mm Ave char thickness: 9.25 mm Expansion: 4.40 times Cracked and weak char

Ave coating thickness: 1.90 mm Ave char thickness: 4.40 mm Expansion: 2.30 times Cracked and weak char

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Char expansion of 150μm EG ICFs

Figure 1 represents the char expansion of formulation IF-150μm after fire test. The char expansion by each formulation is 3.20 times (IF-1), 4.50 (IF-2), 6.80 (IF-3), 11.30 (IF-4), 4.50 (IF-5), 6.90 (IF-6), 8.82 (IF-7), 4.40 times (IF-8), 2.30 times (IF-9) showed in Fig. 1. The maximum char expansion was obtained 9.38 time of IF-4 with 8.8wt of EG. Formulation IF-5, IF-6, IF-7, IF-8 and IF-9 decreased the char expansion by increased the wt. % of EG as illustrated in Fig. 1. It is clear from the physical appearance of char described in Tabled 2 that the char expansion is decreased due to cracks on the surface of the char. These cracks are due to the rapid expansion of EG with excess wt. % of certain limit. EG expand 100 or more times from original graphite [6].

5.8% 6.8% 7.8% 8.8% 9.8% 10.8%11.8%12.8%13.8%0

2

4

6

8

10

2.30

4.40

8.82

6.90

4.50

11.30

6.80

4.50

Cha

r Exp

ansi

on x

times

Weight% of 150 m EG coating

3.20

FIGURE 1. Char expansion of 150μm EG formulations.

Char morphology of 150μm EG ICFs

Three char samples IF-2, IF-4 and IF-6 were chosen based on the physical appearance and char expansion of intumescent coating after fire test. Figure 2(a) represents the outer char surface of IF-2 which showed thick surface of the char with cracks. These cracks and holes with a diameter of 10–60μm in the char structure are presented in Fig. 2(a). Air can lower the heat transfer in these holes; the speed of heat transfer increased if the diameter of these holes is larger than 40μm [9]. The inside char microstructure, bubbles were observed due to emission of nonflammable gases as shown in Fig. 2(b). These bubbles expanded the char due the emission of N2, NH3 and CO2 [10-12]. It explains the dehydration of APP, boric Acid and frothing of melamine proceeds in the range of rather appropriate temperature. The intumescent charring layers with bubbles act as the effect of the flame retardant, heat insulation and protecting inner matrix substrate. Figure 3(a) showed the upper surface of the char IF-4, it is smooth and no hole or bubbles observed on the surface of the char which showed the complete insulation on substrate and protected from fire. The inside micro images of IF-4 in Fig. 3 (b, c and d) showed the formation of bubbles and cracks respectively. The morphology of IF-6 presented in the Fig. 4 (a, b), it has similar outer surface structure compared to IF-2 in Fig. 1, while holes and cracks are noted in Fig. 4.

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FIGURE 2. (a) The IF-2 outer surface of the char with rough and cracks, (b) inside the charring layers contained bubbles.

FIGURE 3. (a) IF-4 with smooth surface area on the upper surface, (b) with small bubbles on inside char (c) Inside bubbles with

thick char of IF-4, (d) Cracks in side char.

FIGURE 4. (a) Rough outer surface of IF-6 (b) holes and cracks in side of the char.

(a) (b)

(b) (a)

(d) (c)

(b) (a)

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Composition of 150μm EG ICFs char

The residue char of sample IF4 is analyzed by X-ray diffraction using EVA software. Figure 5 illustrated the XRD analysis of IF4 char which shows three peaks represents the presence of borophosphate, carbon (graphite) and boron oxide peaks , first and second peaks represent the boron phosphate and carbon (graphite) at 2θ=25, 26.5o, d value 3.61 and 3.37 respectively. The formation of H3BO3 that has been shown due to the dehydration to aid the formation of B2O3, glass-like material which increase the viscosity and avert the gaseous decomposition products evading feed the flame [7, 13].

Functional groups of 150μm EG ICFs Char

The residues char have been analyzed using spectroscopic tools to know the mechanism of interaction between, EG APP, melamine, boric acid, epoxy and hardener. FTIR spectra are shown in Fig. 6 of coating IF4. The FTIR spectrum of IF4 char residue which contains 8.8wt% of EG is shown in Fig. 6. This spectrum shows B-O-P bending motions at 631cm−1 and O-P-O in borophosphate which appeared at around 1189-933cm-1 represents the region of tetrahedral BO4 [14]. A strong band at 1446cm-1 represents the CH2 or CH3 vibration due to melamine and poly amide hardener, and the peak at 1588cm-1is assigned to amino group NH2 in melamine and APP [15]. The peak at 1629cm-1 shows the C=C stretching vibration, while the peaks at 2342 and indicate a stretching vibrations due to the presence of C=N ascribed to polyamide hardener. The O-H bond stretching that appeared at 3193cm-1 is due to epoxy resin. The results recommend that there are two major phase of the thermal degradation of coating formulations, the degradation at 200-400oC fit in the first stage and at 400-500oC stay with the second stage. These results have the same opinion with the analysis of X-ray diffraction.

Lin

(Cou

nts)

0

10

20

30

40

50

60

70

80

90

100

2-Theta - Scale2 10 20 30 40 50 60 70 8

d=3.

6419

3d=

3.38

124

d=2.

2617

1

4000 3500 3000 2500 2000 1500 1000 500

0.00

0.05

0.10

0.15

0.20

0.25

631

933

109611

89

1446

1629

2342

3193

3797

T%

Cm-1 FIGURE 5. XRD of IF-4 FIGURE 6. FTIR of IF-4

CONCLUSION

EG with 150μm particle size showed highest in char expansion 11.30 times from the original thickness of the coating with 8.8 wt. %. SEM image showed char morphology of burnt coating contained cavities, cracks, in the char structure, while in some structures it was also shown the smooth surface without any crack and thick char flakes which are strong barrier between fire and substrate. The 150μm EG char samples showed the better char structure with better char expansion which help to the thermal stability of the coatings. XRD results showed the presence of, boron oxide, boron phosphate in the residual char helped to decrease the fire effects on the basic substrate. The XRD results are further inveterate by the presence of the respective functional groups in the residual char using FTIR analysis.

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