Preparation of Intumescent Fire Protective Coating for Fire Rated Timber Door

Home , Intumescent, Passive fire protection

coatings

Article Preparation of Intumescent Fire Protective Coating for Fire Rated Timber Door

Jessica Jong Kwang Yin 1, Ming Chian Yew 1,* , Ming Kun Yew 2 and Lip Huat Saw 1

1 Department of Mechanical and Material Engineering, Lee Kong Chian Faculty of Engineering and Science, University of Tunku Abdul Rahman, Cheras, Kajang 43000, Malaysia; [email protected] (J.J.K.Y.); [email protected] (L.H.S.) 2 Department of Civil Engineering, Lee Kong Chian Faculty of Engineering Science, University of Tunku Abdul Rahman, Cheras, Kajang 43000, Malaysia; [email protected] * Correspondence: [email protected] or [email protected]; Tel.: +6-039-086-0288

Received: 29 June 2019; Accepted: 24 October 2019; Published: 6 November 2019

Abstract: Intumescent flame-retardant coating (IFRC) provides a protective barrier to heat and mass transfer for the most efficient utilization of a wide variety of passive fire protection systems at the recent development. This article highlights the fire-resistance, physical, chemical, mechanical, and thermal properties of the IFRC using a Bunsen burner, furnace, Scanning Electron Microscope, freeze-thaw stability test, Instron Micro Tester, and thermogravimetric analysis (TGA) test. The five IFRC formulations were mixed with vermiculite and perlite for the fabrication of fire-resistant timber door prototypes in this research project. Additionally, the best fire-resistance performance of the fire-rated door prototype was selected and compared with a commercial prototype under the fire endurance test. An inventive fire-rated door prototype (P2), with a low density of 636.45 kg/m3, showed an outstanding fire-resistance rating performance, resulting in temperature reduction by up to 54.9 ◦C, as compared with that of the commercial prototype. Significantly, a novel fire-rated timber door prototype with the addition of formulating intumescent coating has proven to be efficient in preventing fires and maintaining its integrity by surviving a fire resistance period of 2 h.

Keywords: fire protection system; filler; fire rated timber door; flame retardant additives; intumescent coating

1. Introduction There are two kinds of fire protection systems in buildings, active and passive fire protection systems, which are an integral part of any modern-day building to protect lives and assets by enhancing the fire prevention and protection techniques [1]. The active fire protection system includes a fire or smoke alarm, sprinkler, and fire extinguishers. However, this system has required some actions to work efficiently in the event of a fire and this might fail due to lack of maintenance or other possible problems such as frozen pipes and inadequate water pressure. Whereas passive fire protection (PFP) system includes fire or smoke dampers, fire doors, and firewalls. This PFP system plays an essential role to provide fire safety protection by using flame-retardant materials. Therefore, with regards to this research, a new and innovative fire-resistant timber door is incorporated with the intumescent flame-retardant coating (IFRC) that acts as an effective PFP system and its potential application for lightweight fire-rated timber door. The intumescent coating reacts under the influence of fire and swells in a controlled manner to many times its original thickness, and thus produces an insulation carbonaceous char or foam that protects the substrate from the effects of the fire [2]. By such effectiveness, intumescent coating plays a critical role in protecting the building, and it may also gain

Coatings 2019, 9, 738; doi:10.3390/coatings9110738 www.mdpi.com/journal/coatings Coatings 2019, 9, 738 2 of 18 extra time for building occupants to escape safely during the outbreak of fire by trapping the fire and smoke as well as insulating the heat. IFRCs can either be coated as a thin film or act as a binder of PFPs to enhance the fire-resistance performance. Boards are rigid prefabricated materials that usually come along with hydraulic binders [3]. Common fire doors are made of magnesium oxide boards, gypsum boards and even heavy timber wood [4–6]. However, there is one common problem in all the existing commercial fire doors which is their high density [7]. According to Fire Industry Association, due to the sheer weight and force produced when the heavy fire doors are opened and closed (density > 1200 kg/m3)[8], it may cause human injury especially in places such as residential care or nursing homes. In this research study, intumescent coatings and lightweight flame-retardant materials such as vermiculite and perlite are used to construct the lightweight fire-resistant timber door prototypes (density is about 600 50 kg/m3) for 2-h fire rating. Intumescent paint is the recent trend in fire ± retarding products in construction building materials because of its many beneficial properties such as providing low-odor, lightweight, and is environmentally friendly. Exhaustive investigations have revealed that the intumescent flame retardant coating has achieved good flammability and physical and chemical performances though many linger widely on steel structure applications [9–12]. Up to today, the performance of fire-resistant boards has yet to be tested and investigated with the addition of intumescent fire protective coating for the development of a fire-resistant timber door. Furthermore, this research project has also highlighted huge potential for incorporating the intumescent coating composites, which consists of three main flame-retardant additives, namely ammonium polyphosphate (APP), an acid source; pentaerythritol (PER), a carbon source; and melamine (MEL), blowing agents, into the fire door. These are mixed in a weight ratio of 2:1:1 and are bonded together with flame retardant fillers and vinyl acetate (VA) copolymer as well as vermiculite and perlite which react together to form a protective thermal barrier at high temperature in fire doors [13]. It is important to note that flame-retardant additives are useful chemical compounds for fire retardant to provide varying degrees of flammability protection. A research study conducted by Xia and his co-workers has stated that adding too much APP into the intumescent formulation may reduce the mechanical properties of the intumescent coating. Hence, an appropriate ratio of APP/PER/MEL should be set prior to the development of intumescent coating [14]. One of the ingredients, titanium dioxide (TiO2), is important to formulate an intumescent coating in which it does not only provide the usual properties of colour and opacity, but it also likely takes place in the intumescence process which stabilizes the insulating foam at high temperatures when most of the carbon oxidizes and burn off [15]. Besides that, polymer binder is also one of the final key materials to produce a uniform cellular structure to provide good thermal insulation. In a research study conducted by Wang and Yang, the influence of the binder, vinyl acetate (VA), copolymer emulsion in the water-based coating is used to minimize the smoke and toxic fume emission without compromising the quality and effectiveness of the intumescent coating in fire protection [16]. In addition to that, vermiculite and perlite act as flame-retardant materials promoting a very low density, high porosity, good thermal insulation properties, chemical inertness, and good fire-retardant materials. This makes them attractive to be used widely as pore-forming additives for heat insulation applications [17]. Moreover, the uniqueness of the materials can insulate the heat from the fire by expanding with small particles under high temperatures. Besides that, a highly porous aggregate that can absorb moisture in varying degrees, the presence of moisture in the aggregate would turn into steam and evaporate from the materials during a fire test, and this will extend the fire duration [18]. As mentioned, the performance of the IFRC is based on the appropriate materials combination and the compatibility of the flame-retardant fillers with a polymer binder. Therefore, it is essential that the flame-retardant fillers provide good fire protective performance and fire retarding efficiency properties [19,20]. The grouping of aluminium hydroxide, Al(OH)3; calcium silicate, CaSiO3; magnesium hydroxide, Mg(OH)2; chicken eggshell (CES) powder (bio-filler derived from CES waste); and calcium carbonate, CaCO3 is used in this research project [20]. This project aims to formulate an Coatings 2019, 9, 738 3 of 18 appropriate combination of intumescent flame-retardant coating for the development of fire-resistant timber door prototype. The performances of fire protection, mechanical, chemical and physical properties of intumescent flame-retardant coatings are evaluated and investigated. This research work is intended to design, fabricate, and examine the fire-resistant timber door prototype by incorporating intumescent fire-protective coating in order to fulfil the 2-h fire rating.

2. Experimental Program

2.1. Materials and Sample Preparation The first part of this project is to synthesize the water-based intumescent paint using a high-speed disperse mixer for 30 min at room temperature until it is completely homogenous. The formulations of intumescent coatings are tabulated in Table1. APP, PER, and MEL were used as flame-retardant additives. The aluminium hydroxide, magnesium hydroxide, calcium silicate, chicken eggshell (CES) powder, calcium carbonate, and titanium dioxide were used as flame-retardant fillers, and vinyl acetate (VA) copolymer emulsion acts as a water-based polymer binder in this study. The fire resistance and physical properties of the intumescent coatings were characterized and assessed through a series of tests such as Bunsen burner test, furnace test, scanning electron microscope (SEM) analysis test, adhesion strength test, freeze-thaw cycle test, and thermogravimetric analysis (TGA) test.

Table 1. Speciﬁcations of experimental materials.

Ingredients (wt.%) Samples Flame-Retardant Flame Retardant Additives Filler Flame-Retardant Fillers (Pigment) Vinyl Acetate (VA) APP PER MEL TiO Al(OH) Mg(OH) CaSiO CES CaCO Copolymer 2 3 2 3 3 Emulsion J1 20 10 10 50 4.0 3.0 – 3.0 – – J2 20 10 10 50 4.0 3.0 – – 3.0 – J3 20 10 10 50 4.0 – 3.0 3.0 – – J4 20 10 10 50 4.0 – 3.0 – 3.0 – J5 20 10 10 50 4.0 – 3.0 – – 3.0

The second part of this project is to design and fabricate the fire-resistant timber door prototype with a dimension of 300 mm (length) 300 mm (width) 40 mm (thickness). The fire protective × × performance of the fire timber door prototype is determined through a small-scale fire test. Table2 shows the details of the experimental prototypes.

Table 2. Details of experimental prototypes.

Fire Door Prototype Dimensions: 300 mm (L) P1 P2 P3 P4 P5 300 mm (W) 40 mm (H)× × Weight (g) 2565 2578 2589 2605 2610 Density (kg/m3) 633.44 636.45 639.23 643.22 644.52

Moreover, the fire endurance test and the temperature rise test are conducted to compare and determine the best fire timber door prototype as compared to the commercial prototype in terms of heat transmission and integrity failure or a significant leakage. The flow chart of the experimental work details and the engineering drawing of the fire-resistant timber door prototype as well as thermocouple locations (T1 and T2) are shown in Figure1. Coatings 2019, 9, 738 4 of 18 Coatings 2019, 9, x FOR PEER REVIEW 4 of 20

Part 1: Sample characterization of IFRC

• Bunsen burner test Part 2: Prototype testing • Furnace test Sample • Scanning Electron Microscopy preparation  Small scale fire test (SEM) test • Fire endurance test • Adhesion strength test • Temperature rise test • Freeze-thaw cycle test • Thermogravimetric analysis (TGA) test

FigureFigure 1. 1.Flow Flow chartchart ofof thethe experimentalexperimental work and the the dimensions dimensions of of the the prototype. prototype.

2.2.2.2. Testing Testing for for Coated Coated Samples Samples 2.2.1. Bunsen Burner Test 2.2.1. Bunsen Burner Test The coating samples were coated on a 100 mm 100 mm 3 mm steel plate with a thickness of The coating samples were coated on a 100 mm ×× 100 mm × ×3 mm steel plate with a thickness of 2 2 0.2 mm. The thermocouple plate is attached at the backside of the steel plate coated with ±± 0.2 mm. The thermocouple plate is attached at the backside of the steel plate coated with intumescentintumescent flame-retardantflame-retardant coatingcoating andand thenthen connected to to a a digital digital handheld handheld thermometer thermometer for for temperaturetemperature measurement. measurement. FigureFigure2 2 shows shows thethe experimentalexperimental setup of the Bunsen burner burner test test for for the the coatedcoated samples. samples. The The sample sample waswas exposedexposed toto a Bunsen burner flame flame spray spray gun gun blow blow torch torch for for 1 1h hat at a a temperaturetemperature flame flame of of about about 10001000 ◦°C.C. TheThe BunsenBunsen burner gas consumption consumption is is about about 160 160 g/h g/h and and the the distancedistance between between the the sample sample and and BunsenBunsen burnerburner nozzlenozzle is about 7 cm.

CoatingsCoatings 20192019,, 99,, 738x FOR PEER REVIEW 55 ofof 1820

FigureFigure 2.2. Schematic of the experimental setupsetup forfor coatedcoated samples.samples.

2.2.2.2.2.2. Furnace Test For the furnace test, all steel plates (dimensions: 50 mm 50 mm 1 mm) were coated with For the furnace test, all steel plates (dimensions: 50 mm ×× 50 mm ×× 1 mm) were coated with IFRCs with a thickness of 2 0.2 mm. The coated samples were then placed into the furnace IFRCs with a thickness of 2 ±± 0.2 mm. The coated samples were then placed into the furnace (Barnstead(Barnstead ThermolyneThermolyne 62700, 62700, Barnstead Barnstead Thermolyne, Thermolyne, Dubuque, Dubuque, IA, IA, USA) USA) with with high high temperatures temperatures of 500of 500 and and 600 600◦C, °C, respectively respectively (heating (heating rate rate is 20 is ◦20C/ min).°C/min). After After that, that, the the thickness thickness of the of the char char layer layer for eachfor each sample sample was was measured. measured. Up to Up date, to date, there there is no standardis no standard test to test study to thestudy strength the strength of a char of sample. a char Insample. this experimental In this experimental work, a small-scale work, a small-scale compressive compressive strength of strength char test of was char designed test was and designed conducted and byconducted stacking by up stacking the 50 g coin-shapeup the 50 g metals coin-shape one by metals one, whichone by acts one, as which a static acts load as on a static the char load layer on forthe measuringchar layer for and measuring evaluating and the evaluating char strength the ofchar the strength sample. of the sample. 2.2.3. Scanning Electron Microscopy (SEM) Analysis 2.2.3. Scanning Electron Microscopy (SEM) Analysis For SEM examination/analysis, all samples are initially coated with gold in order to eliminate For SEM examination/analysis, all samples are initially coated with gold in order to eliminate the possible charging eﬀects. A low beam energy with 1 kV is conducted to decrease the possibility the possible charging effects. A low beam energy with 1 kV is conducted to decrease the possibility of any thermal damage to the samples. The main objectives of the SEM analysis are to conduct a of any thermal damage to the samples. The main objectives of the SEM analysis are to conduct a detailed examination using Hitachi EDAX S3400–N Scanning Electron Microscopy (SEM) machine detailed examination using Hitachi EDAX S3400–N Scanning Electron Microscopy (SEM) machine manufactured by Hitachi High Technologies America, Inc. in America and analysis on the IFRC manufactured by Hitachi High Technologies America, Inc. in America and analysis on the IFRC coating samples’ morphology and thus to determine and identify the interfacial bonding of each type coating samples’ morphology and thus to determine and identify the interfacial bonding of each of coating sample on the steel substrate. type of coating sample on the steel substrate. 2.2.4. Adhesion Strength Test 2.2.4. Adhesion Strength Test Figure3 shows the experimental setup for the measurement of adhesion strength of the coating samples.Figure The 3 samplesshows the were experimental coated with setup a thickness for the me of 2asurement0.2 mm of IFRC adhesion on one st siderength of the of the cylindrical coating ± steelsamples. rod. The After samples that, the were coated coated cylindrical with a thickness steel rod of was 2 ± then 0.2 mm attached IFRC toon a one bare side cylindrical of the cylindrical steel rod usingsteel rod. an epoxy After gluethat, withthe coated a thickness cylindrical of 2 steel0.2 mm. rod Twowas cylindricalthen attached steel to rods a bare were cylindrical then tested steel using rod ± theusing Instron an epoxy Micro glue Tester–Universal with a thickness Testing of 2 ± machine0.2 mm. Two manufactured cylindrical by steel Instron rods in were Norwood, then tested MA, using USA withthe Instron a constant Micro rate Tester–Universal of 1 mm/min continually Testing drawn machine apart manufactured in tensile mode by untilInstron the coatingin Norwood, samples MA, on theUSA cylindrical with a constant steel rods rate tore of apart.1 mm/min The adhesion continuall strengthy drawn of apart the coating in tensile sample mode in MPauntil is the calculated coating basedsamples on on the the following cylindrical Equation steel rods (1) [ 21tore]: apart. The adhesion strength of the coating sample in MPa is calculated based on the following Equation (1) [21]:F fb= (1) A (1) = ( ) = ( ) = 2 where,where, fb adhesion adhesion strength strength MPa;; F maximum load at rupturemaximum load at ruptureNN; ; A adhered area adhered areammmm. .

Coatings 2019, 9, 738 6 of 18 Coatings 2019, 9, x FOR PEER REVIEW 6 of 20

FigureFigure 3. SchematicSchematic of of the the experimental experimental setup setup for for adhesion adhesion strength. strength. 2.2.5. Freeze-Thaw Cycle Test 2.2.5. Freeze-Thaw Cycle Test The freeze–thaw resistance test was used to determine the ability of the coating sample to The freeze–thaw resistance test was used to determine the ability of the coating sample to withstand the highly destructive forces of cyclic freezing and thawing. The coating samples were withstand the highly destructive forces of cyclic freezing and thawing. The coating samples were coated onto different sets of 50 mm 50 mm 1 mm steel plates with a thickness of 2 0.2 mm. The coated onto different sets of 50 mm ×× 50 mm × 1 mm steel plates with a thickness of 2 ±± 0.2 mm. The coating samples were placed in an air flow at 25 C for 8 h and then placed in the freezer at 20 C for coating samples were placed in an air flow at 25 ◦°C for 8 h and then placed in the freezer at −20 °C◦ for another 8 h. Lastly, the coating samples were heated in a drying oven at 50 C for another 8 h. This another 8 h. Lastly, the coating samples were heated in a drying oven at 50 ◦°C for another 8 h. This process is noted as a freeze–thaw cycle period [22]. process is noted as a freeze–thaw cycle period [22]. 2.2.6. Thermogravimetric Analysis (TGA) Test 2.2.6. Thermogravimetric Analysis (TGA) Test Thermogravimetric analysis (TGA) was carried out using Perkin Elmer STA8000 model manufacturedThermogravimetric by Perkin analysis Elmer Inc., (TGA) Waltham, was carried MA, USA. out Testusing samples Perkin withElmer about STA8000 5–8 mg model thick manufactured by Perkin Elmer Inc., Waltham, MA, USA. Test samples with about 5–8 mg thick thin thin films were placed in a crucible and heated from 30 to 1000 ◦C at a heating rate of 20 ◦C/min under filmsnitrogen were gas. placed in a crucible and heated from 30 to 1000 °C at a heating rate of 20 °C/min under nitrogen gas. 2.2.7. Testing for Fire Resistant Timber Door Prototype 2.2.7. Testing for Fire Resistant Timber Door Prototype Small Scale Fire Test • Small Scale Fire Test The small-scale fire test was conducted on prototype 1–5; the intumescent binders for each prototype,The small-scale which is based fire test on thewas formulation conducted J1–J5 on pr thatototype is provided 1–5; the in Tableintumescent1, is shown binders in Section for each 2.1. prototype,After that, thewhich fire is protection based on performancethe formulation of theJ1–J5 prototypes that is provided was tested in Table using 1, the is Bunsenshown in burner Section at 2.1.about After 1000 that,◦C forthe 2 fire h. The protection temperature performance profile of of the the backside prototypes of the was fire-resistant tested using timber the Bunsen door prototype burner atwasCoatings about measured 2019 1000, 9, x °CFOR and for PEER recorded 2 h.REVIEW The using temperature a digital handheldprofile of thermometer.the backside of Figure the fire-resistant4 shows a small-scale timber 7door of fire 20 prototypetest experimental was measured setup for and the fire-resistantrecorded using timber a di doorgital prototype.handheld thermometer. Figure 4 shows a small-scale fire test experimental setup for the fire-resistant timber door prototype.

Figure 4. SchematicSchematic of of the the experimental experimental setup for fire-resistant ﬁre-resistant timber door prototype.

Coatings 2019, 9, 738 7 of 18 Coatings 2019, 9, x FOR PEER REVIEW 8 of 20

• FireFire Endurance Endurance and and Temperature Temperature Rise Rise Tests Tests for for the the Timber Timber Door Door Prototype Prototype • The fire fire endurance endurance test test was was carried carried out out using using the the Bunsen Bunsen burner burner to determine to determine and and compare compare the fire-resistancethe fire-resistance rating rating and and integrity integrity of ofthe the best best prototype prototype and and commercial commercial prototype. prototype. For For the the fire fire endurance test, the tested prototype can be qualified qualified as a standard fire-rated fire-rated timber door if it can maintain its integrity when exposed to 2 h firefire (at about 1000 ◦°C)C) without an integrity failure or displaying a significantsignificant leakage [[23].23]. Whereas, Whereas, the the temperature rise rise is also recorded over a 30-min interval until until 120-min, 120-min, this this is is to to examine examine the the heat heat rise rise on the on thebackside backside of the of fire-resistant the fire-resistant timber timber door prototype.door prototype. The thermocouples The thermocouples are fixed are fixed at two at two poin pointsts of ofthe the fire-resistant fire-resistant timber timber door door prototype (centre (T1) and edge (T2)) to measure the transmission of heat from one point to another point of the prototype. ThisThis isis toto ensure ensure that that the the prototype prototype has ha takens taken adequate adequate fire fire protection protection byreducing by reducing the heat the heattransmission transmission rate andrate flame and flame propagation propagation so that so it canthat prolongit can prolong the evacuation the evacuation time for thetime building for the buildingoccupants occupants if there is if a there fire. is a fire.

3. Experimental Results and Discussion on Findings

3.1. Bunsen Bunsen Burner Test The purposepurpose ofof thisthis specified specified test test is is to to characterize characterize the the physical physical and and chemical chemical reactions reactions of the of char the charformation formation of the of IFRC. the TheIFRC. temperature The temperature profiles ofprofile the steels of plates the steel coated plates with coated five IFRC with formulations five IFRC (J1–J5)formulations and the (J1–J5) bare steel and plate the werebare comparedsteel plate after were 60 mincompared of fire testing.after 60 In min this experimentalof fire testing. work, In this the experimentaltemperature of work, 400 ◦ Cthe was temperature chosen as the of critical400 °C temperaturewas chosen as for the the critical coated temperature sample with IFRCfor the [24 coated]. The samplefire protection with IFRC results [24]. of theThe coated fire protection steel plates results were thenof the plotted coated as steel a function plates ofwere time then and presentedplotted as ina functionFigure5. of time and presented in Figure 5.

450 Critical temperature (400 ℃) 400

350 J5

) J3 300 ℃ J4 250 J1 200 J2

150 Temperature (

100

0 0 102030405060 Time (min) Critical temperature Coating J1 Coating J2 Coating J3 Coating J4 Coating J5

Figure 5. Evolution of temperature on the coated steel plates.

The thickness of the char layer and equilibrium temperature of the intumescent coatings with the influences influences of different different types of flame-retardantflame-retardant fillersfillers are shown in Table3 3.. TheThe firstfirst 1010 minmin havehave showed that there is a similar pattern of temperatur temperatureses for the coated samples, which is is below below 300 300 °C.◦C. After that, the temperatures startedstarted to fluctuatefluctuate at 20 min due to the physical and chemical reactions of the coating formulations during the high-temperature test. The temperature continues to rise for 30 min, it is observed that the coating J5 starts to rapidly increase until reaching 360 °C at 42 min. This may possibly be due to the fact this coated sample has started to lose its adherence strength or

Coatings 2019, 9, 738 8 of 18

30 min, it is observed that the coating J5 starts to rapidly increase until reaching 360 ◦C at 42 min. This may possibly be due to the fact this coated sample has started to lose its adherence strength or interfacial bonding from the steel plate during the ﬁre test. Whereas coating J1 drops rapidly after reaching 205 ◦C at 43 min, this might due to the reduction of gas pressure from the Bunsen burner ﬂame spray gun blow torch.

Table 3. Thickness of char layer and the equilibrium temperature of coated samples.

Coating Samples Thickness of Char Layer ( 0.1 mm) Equilibrium Temperature of Coating ( C) ± ◦ Original Steel Plate – >Critical Temperature (400 ◦C) J1 5.8 238 J2 6.0 217 J3 2.8 306 J4 3.8 279 J5 4.3 325

It is also observed that the temperature of all the coatings starts to fluctuate again until reaching 50 min. After 50 min of the test, the temperature reaches an equilibrium value and almost remains unchanged until the last stage of the test. The equilibrium temperature of coating J2 that is 217 ◦C is considered to be significantly lower than the other coatings and thus it has showed to have the best result for fire protective performance. The char combined the positive effects of the flame retardant additives, intumescent paint and fillers (3 wt.% of Al(OH)3 and CES), promoting a good fire-protective barrier and producing the thickest and most excellent char layer (i.e. about 6.0 mm) to block the fire while safeguarding the formation of a uniform foam structure, which is in good agreement with other researchers, as highlighted by Wang and Yang, 2010. With regards to the other observation, coating J5 has the highest equilibrium temperature of 325 ◦C, almost reaching the critical temperature (400 ◦C) after 40 min of fire exposure. The equilibrium temperature of coating J5 might be due to its char layer showing porosity and lightness, resulting in the loss of adherence of the char to the steel plate or by a loss of cohesion of the char layer; similar observations have been made by other researchers too [24].

3.2. Furnace Test The purpose of the furnace test is to investigate and critically assess the fire protection performance of the coated samples by measuring the thickness of the char layer at temperatures of 500 and 600 ◦C. The thicknesses of the char layer have been measured and recorded in Figure6. Based on the results, all of the char layers have expanded from 500 to 600 ◦C except coating J3. From the result obtained, it can be observed that the char layer of coatings J3, J4 and J5 with the addition of magnesium hydroxide has a slightly less thick char layer as compared to coatings J1 and J2. These phenomena are due to the flame-retardant filler (i.e., magnesium hydroxide) that has a negative contribution toward a fire-protective performance. It has a poor char expansion and resulted in failing to provide the required thick insulating barriers to protect the underlying steel plate from the heat. The thickness of coating J3 increased at 500 ◦C, this is because of the gaseous water phase during the decomposition of Mg(OH)2 filler envelop the flame, and thereby excluding the oxygen and diluting flammable gases [25]. Whereas the thickness of the char layer of coating J3 decreased at 600 ◦C, this is due to the fire that propagated through the fire-protective barrier which thus led to a decrease of thickness of the char layer. Coatings 2019, 9, 738 9 of 18 Coatings 2019, 9, x FOR PEER REVIEW 10 of 20

J2 6 J1

5 J2 J1 J5 4 J4 J3 J4 J5 3 J3

1 Thickness of char layer (mm) layer Thickness of char

0 500 600 Temperature (℃)

Figure 6. Thickness of char layer of the coated samples at 500 and 600 ◦°C.C.

The coating J2 has the thickest char layer of 4.6 mm and 6.0 mm at temperatures of 500 ◦°CC and 600 °C,◦C, respectively. respectively. This This indicates indicates that that it ithas has the the highest highest expansion expansion value value of a of char a char layer layer due dueto the to additionthe addition of Al(OH) of Al(OH)3 and3 andCES CESthat thathave have significantly significantly exhibite exhibitedd the expansion the expansion of the of char the charlayer. layer. The formationThe formation of a ofcohesive a cohesive structure structure during during burning burning can can potentially potentially be be initiated initiated by by decarbonation. decarbonation. Decarbonation ofof CESCES can can release release carbon carbon dioxide dioxide which which can trapcan thetrap degraded the degraded product product into the into residue the residueand induce and induce swelling swelling [11]. The[11]. thicknessThe thickness of the of charthe char layer layer of coatingof coating J1 J1 was was 4.3 4.3 mm mm at at 500500 ◦°CC and 5.4 mmmm at at 600 600◦C. °C. The The expansion expansion value value of the thicknessof the th ofickness the char of layerthe ofchar coating layer J1 of is approximatelycoating J1 is 1.1approximately mm. The char 1.1 layermm. The of coating char layer sample of coating J1 is considered sample J1 to is be considered thicker than to thebe thicker coating than samples the coatingJ3, J4 and samples J5, which J3, J4 is and again J5, due which to theis again addition due ofto Al(OH)the addition3, providing of Al(OH) the3, strong providing reversibility the strong of reversibilitydehydration reactionof dehydration with water reaction released with inside water the released particle recombininginside the particle to the reactive recombining surface to of the reactivefreshly formed surface alumina,of the freshly resulting formed in a alumina, good flammability resulting in resistance a good flammability filler and expansion resistance of filler the charand expansionlayer [25]. Theof the expansion char layer values [25]. Th ofe the expansion thickness values of the of char the layers thickness of coatings of the char J4 and layers J5 were of coatings 0.4 mm J4and and 1.2 J5 mm, were respectively. 0.4 mm andAlthough 1.2 mm, respectively. the addition Alth of CESough in the coating addition J4 and of CES the addition in coating of J4 CaCO and 3thein additioncoating J5 of showed CaCO3 in significantly coating J5 showed good flame-retardant significantly good fillers, flame-retardant the combination fillers, of CESthe combination and/or CaCO of3 withCES and/or Mg(OH) CaCO2 filler3 with may Mg(OH) have led2 tofiller poorer may fire-resistance have led to poorer performance. fire-resistance Hence, performance. it can be deduced Hence, that it canMg(OH) be deduced2 filler can that restrict Mg(OH) the formation2 filler can of restrict the char the layer formation by declining of the the char fire-protection layer by declining performance. the fire-protectionIn addition, performance. the strength of the char layer has also been determined for each coating sample after reachingIn addition, the maximum the strength heating of temperaturethe char layer of has 600 also◦C throughbeen determined the furnace for test. each The coating weight sample load afterof 50 reaching g coin-shape the maximum metal is stacked heating up temperature on-top of the of char600 °C layer through one by the one furnace until the test. char The layer weight has loadcompletely of 50 g cracked. coin-shape In summary, metal is stacked only coatings up on-top J1, J2 of and the J5 char have layer undergone one by this one test until as thethe charchar layerslayer hasof coatings completely J3 and cracked. J4 already In summary, cracked after only heating coatings up J1 to, J2 600 and◦C J5 in have the furnace. undergone The this strength test as of the the char layerslayer of of coating coatings J2 J3 can and withstand J4 already the cracked maximum after loadheating up toup 650 to 600 g, as °C compared in the furnace. to coatings The strength J1 (400 of g) theand char J5 (600 layer g). of This coating experimental J2 can withstand test has the proven maximu thatm coating load up J2 to can 650 achieve g, as co thempared best fire to coatings protection J1 (400performance g) and J5 and (600 the g). strongest This experimental char layer against test has the proven fire. that coating J2 can achieve the best fire protection performance and the strongest char layer against the fire. 3.3. Surface Morphology of Char Layer of Coated Samples 3.3. SurfaceMicroscopic Morphology analyses of Char are executedLayer of Coated with theSamples scanning electron microscope (SEM) to examine and analyzeMicroscopic the surface analyses morphology are executed of the intumescent with the sc coating.anning Theelectron SEM micrographicmicroscope (SEM) images to of examine all char andlayers analyze of coated the samplessurface aftermorphology the Bunsen of the burner intume testscent are shown coating. in Figure The SEM7. The micrographic orange color images indicates of all char layers of coated samples after the Bunsen burner test are shown in Figure 7. The orange color indicates the holes and voids in the char layer of the coated samples. The images of coatings J1, J3, J4

Coatings 2019, 9, 738 10 of 18 theCoatings holes 2019 and, 9, x voids FOR PEER in the REVIEW char layer of the coated samples. The images of coatings J1, J3, J4 and11 of J520 illustrated larger holes and voids. These holes are formed because of trapped gas by its blowing agent and J5 illustrated larger holes and voids. These holes are formed because of trapped gas by its when the coating is exposed to fire [26]. The tiny holes and void structures can be the consequence blowing agent when the coating is exposed to fire [26]. The tiny holes and void structures can be the of fire and heat propagation. The fire and heat propagated to the crack lines on the foam structure consequence of fire and heat propagation. The fire and heat propagated to the crack lines on the can also lead to a poor fire-protective performance of the coating [14]. On the other hand, the char foam structure can also lead to a poor fire-protective performance of the coating [14]. On the other layer of coating J2 has displayed a more uniform and denser foam structure which can strongly adhere hand, the char layer of coating J2 has displayed a more uniform and denser foam structure which to the steel substrate after the fire test. This rigid formation can contribute to the enrichment of the can strongly adhere to the steel substrate after the fire test. This rigid formation can contribute to the fire-protective performance on the coated steel substrate and subsequently lead to better characteristic enrichment of the fire-protective performance on the coated steel substrate and subsequently lead to properties of the coating. Therefore, a fire protective performance which indicates the competency better characteristic properties of the coating. Therefore, a fire protective performance which of the char layer in fire resistance is highly dependent on its physical structure of the coating [27]. indicates the competency of the char layer in fire resistance is highly dependent on its physical Hence, when selecting the specified formulation of flame-retardant fillers, it is worth noting that the structure of the coating [27]. Hence, when selecting the specified formulation of flame-retardant coating needs to be able to enhance the intumescent coating performance in terms of fire protection fillers, it is worth noting that the coating needs to be able to enhance the intumescent coating and thermal properties. performance in terms of fire protection and thermal properties.

Figure 7. Cont.

Coatings 2019, 9, 738 11 of 18 Coatings 2019, 9, x FOR PEER REVIEW 12 of 20

Figure 7. SurfaceSurface morphology morphology of of the the various various char char layer samples.

3.4. Adhesion Adhesion Strength Strength of of Coated Coated Samples Samples This test is carried out to determine the adhesionadhesion strength of the coatedcoated samples.samples. The average adhesion strengthstrength amongstamongst all all coating coating samples samples is tabulatedis tabulated and presentedand presented in Figure in Figure8. All the 8. coatingAll the coatingsamples samples show good show adhesion good adhesion strength strength values. Thevalues. coatings The coatings J1–J5 have J1–J5 showed have highershowed adhesion higher adhesionstrength values strength ranging values from ranging 1.05 to from 1.45 MPa.1.05 to The 1.45 increased MPa. The adhesion increased strength adhesion can be strength interpreted can due be interpretedto the influence due to of the influence carbonyl groupof the carbonyl between VAgroup copolymer between and VA thecopolymer surface oxideand the or surface hydroxide oxide of orsteel hydroxide substrate of that steel has substrate created a strongerthat has carbon–hydrogencreated a stronger (CH) carbon–hydrogen bond in the mixture (CH) ofbond the coating.in the mixtureThe intermolecular of the coating. bonding The intermolecular between the flame-retardant bonding between fillers’ the molecules flame-retardant has further fillers’ improved molecules the hasinteraction further betweenimproved the the coating interaction and the between steel substrate the coating as well and as the between steel themselvessubstrate as [ 28well]. This as between is not to themselvesdisregard the [28]. carbon–hydrogen This is not to bonding, disregard which the in carbon–hydrogen fact has a significant bonding, role inthe which adhesive in fact properties has a significantof the coating. role Thein the carbon–hydrogen adhesive properties bonding of th ise formed coating. between The carbon–hydrogen a strongly electronegative bonding is atom formed that betweenis usually a oxygenstrongly and electronegative a hydrogen atom. atom Thethat hydrogenis usually bondsoxygen are and formed a hydrogen between atom. a monomer The hydrogen of the bondsVA copolymer are formed molecule between and a monomer the steel substrate. of the VA copolymer molecule and the steel substrate. Judging from the results obtained, it is revealed that the coating J5 with the addition of Mg(OH)2 and CaCO3 have shown the highest adhesion strength that is 1.45 MPa. The increase in adhesion strength of coating J5 is due to the strong bonding strength between the steel substrate surface and the VA copolymer binder with the addition of Mg(OH)2 and CaCO3 fillers, which distribute stresses effectively. Mechanical stress can encourage the development of voids in the matrix caused by the loss of adhesion between the coating and the filler [29], whereas the coatings J2 and J4 with the addition of Al(OH)3 + CES and Mg(OH)2 + CES show higher adhesion strength of 1.25 MPa and 1.26 MPa, respectively, as compared to other coatings. The addition of CES filler has indeed shown improvement in adhesion strength due to the improved reinforcement properties between the CES filler and VA copolymer binder [30]. However, the adhesion strength of coating J4 with the addition of Mg(OH)2 and CES is higher than the adhesion strength of the coating J2 with the addition of Al(OH)3 and CES due to the Al(OH)3 filler leading to the reduction of adhesion strength. This is due to the aluminium hydroxide which reduces the adhesion strength in the particular case under the influence of moisture where the

Coatings 2019, 9, 738 12 of 18 oxide layer transforms into a hydroxide with a morphological change. The adhesion strengths of the coatings J1 and J3 with the addition of calcium silicate have showed lower adhesion strength of 1.05 and 0.95 MPa, respectively. This indicates that the coating formulation incorporated with calcium silicate would decrease the adhesion strength. Therefore, choosing an appropriate flame-retardant filler strongly influences the interfacial bonding strength between the intumescent coating and the steel substrate [31]. Coatings 2019, 9, x FOR PEER REVIEW 13 of 20

50 J5 45 J4 40 J2

35 J1 J3 30

Adhesion Strength (MPa) Adhesion Strength 10

0 Coating Samples

Figure 8. Adhesion strength of the coating samples.

3.5. Freeze-ThawJudging from Cycle the Test results obtained, it is revealed that the coating J5 with the addition of Mg(OH)This2 testand is CaCO conducted3 have to shown evaluate the the highest effect adhesion of room temperature, strength that freezing is 1.45 temperatureMPa. The increase and high in temperature,adhesion strength symbolizing of coating diff erentJ5 is due weather to the conditions strong bonding such as winter,strength spring, between autumn, the steel and substrate summer onsurface the coating and the surface. VA copolymer Figure9 shows binder the resultswith the of alladdition coated samplesof Mg(OH) before2 and and CaCO after 213 fillers, freeze–thaw which cycledistribute tests. stresses The coated effectively. samples Mechanical are visually stress inspected can encourage for cracks, blisters,the development coagulated ofparticles, voids in andthe changesmatrix caused of color. by Inthe this loss research of adhesion study, between all the coatedthe coating samples and remainthe filler unchanged [29], whereas and the free coatings from any J2 visibleand J4 crackswith the and addition coagulated of Al(OH) particles3 + after CES freeze–thaw and Mg(OH) cycles.2 + CES All show coating higher samples adhesion have proven strength to beof e1.25fficient MPa in and withstanding 1.26 MPa, therespectively, highly destructive as compared forces to of other cyclic coatings. freezing The and addition thawing. of CES filler has indeed shown improvement in adhesion strength due to the improved reinforcement properties between the CES filler and VA copolymer binder [30]. However, the adhesion strength of coating J4 with the addition of Mg(OH)2 and CES is higher than the adhesion strength of the coating J2 with the addition of Al(OH)3 and CES due to the Al(OH)3 filler leading to the reduction of adhesion strength. This is due to the aluminium hydroxide which reduces the adhesion strength in the particular case under the influence of moisture where the oxide layer transforms into a hydroxide with a morphological change. The adhesion strengths of the coatings J1 and J3 with the addition of calcium silicate have showed lower adhesion strength of 1.05 and 0.95 MPa, respectively. This indicates that the coating formulation incorporated with calcium silicate would decrease the adhesion strength. Therefore, choosing an appropriate flame-retardant filler strongly influences the interfacial bonding strength between the intumescent coating and the steel substrate [31].

3.5. Freeze-Thaw Cycle Test This test is conducted to evaluate the effect of room temperature, freezing temperature and high temperature, symbolizing different weather conditions such as winter, spring, autumn, and summer on the coating surface. Figure 9 shows the results of all coated samples before and after 21 freeze– thaw cycle tests. The coated samples are visually inspected for cracks, blisters, coagulated particles, and changes of color. In this research study, all the coated samples remain unchanged and free from any visible cracks and coagulated particles after freeze–thaw cycles. All coating samples have proven to be efficient in withstanding the highly destructive forces of cyclic freezing and thawing.

Coatings 2019, 9, 738 13 of 18 Coatings 2019, 9, x FOR PEER REVIEW 14 of 20

Before Freeze–Thaw After 21 Freeze–Thaw Before Freeze–Thaw After 21 Freeze–Thaw Testing Cycles Testing Cycles

Coating Sample J1 Coating Sample J4

Coating Sample J2 Coating Sample J5

Coating Sample J3

FigureFigure 9. 9.Before Before and and after after the the freeze–thaw freeze–thaw cyclescycles testtest ofof the coated samples.

3.6.3.6. Thermogravimetric Thermogravimetric Analysis Analysis (TGA) (TGA) Test Test ThisThis test test is is to to determine determine the the thermal thermal degradationdegradation byby calculatingcalculating the residual weight weight of of the the intumescentintumescent coatings. coatings. FromFrom thethe resultsresults obtainedobtained in Figure 10 under nitrogen gas, gas, the the thermal thermal decompositiondecomposition is is mainly mainly observed observed atat aa temperaturetemperature betweenbetween 200–450200–450 ◦°C.C. However, the the thermal thermal decompositiondecomposition can can also also occur occur at at di differentfferent stages. stages. InIn thisthis study,study, thethe generalgeneral thermogram profiles profiles are are quitequite similar similar but but the the curves curves are are found found to to be be slightly slightly shiftedshifted towardstowards higher temperature ranges ranges with with gradualgradual increments increments in in heating heating rates. rates. From From 30 30 to to 100 100◦ °C,C, aroundaround 2%2% ofof the initial weight is lost. lost. This This is is possiblypossibly due due to to the the release release of of moisture. moisture. Between Between 100–200100–200 ◦°C,C, J1J1 and J2 showed slight weight weight loss loss of of approximatelyapproximately 1%–2%, 1%–2%, where where J3, J3, J4 J4 and and J5 J5 showered showered around around 5%5% ofof thethe initialinitial weight losses. Between Between 200–300200–300◦C, °C, a weighta weight loss loss of of 10% 10% of of the the initial initial weight weight is is observed. observed. BetweenBetween 300–450 °C,◦C, a a measured measured weightweight loss loss of approximatelyof approximately 45% 45% is calculated.is calculated. However, However, between between 450–1000 450–1000◦C, °C, the weightthe weight loss loss is only is 10%only of the10% initial of weightthe initial observed. weight This canobserved. be attributed This tocan the be fact thatattributed the degradation to the /factdecomposition that the reactiondegradation/decomposition has reached a relatively reaction stable has stage reached in the a mixture. relatively stable stage in the mixture. In summary, the residual weights of J1, J2, J3, J4, and J5 at 950 °C are 34.28%, 34.55%, 32.77%, In summary, the residual weights of J1, J2, J3, J4, and J5 at 950 ◦C are 34.28%, 34.55%, 32.77%, 33.82%, and33.82%, 31.34% and respectively. 31.34% respectively. The TG curves The TG have curves clearly have demonstrated clearly demonstrated that the residue that the weight residue of weight coating sampleof coating J2 has sample the highest J2 has residualthe highest weight residual which weight indicates which that indicates the addition that the of addition aluminum of aluminum hydroxide andhydroxide CES fillers and content CES infillers intumescent content binderin intumescen could enhancet binder anti-oxidation could enhance of theanti-oxidation coatings [32 of]. the coatings [32].

Coatings 2019, 9, 738 14 of 18 Coatings 2019, 9, x FOR PEER REVIEW 15 of 20

Figure 10. TGA curves of each coating sample.

3.7. Testing for Fire-Resistant TimberTimber DoorDoor PrototypesPrototypes

3.7.1. Small Scale Fire Test This test is to characterize the firefire protectiveprotective performance of the fire-resistantfire-resistant timber door prototypes (P1–P5). The The re resultssults of of each each coating coating sample sample plotted plotted as as a function a function of oftime time are are presented presented in inFigure Figure 11. 11 The. The results results show show that that the the temperature temperature of of each each fire-resistant fire-resistant ti timbermber door prototype has increased gradually.gradually. From From the the results results obtained, obtained, all the temperaturesall the temperatures of prototypes of increaseprototypes significantly increase insignificantly the first 15 in min, the first revealing 15 min, a revealing similar pattern. a simila Thisr pattern. phenomenon This phenomenon is because is of because the good of the thermal good insulationthermal insulation of vermiculite of vermiculite and perlite. and Theseperlite. porous These materials porous materials can dissipate can dissipate the heat whenthe heat exposed when toexposed fire. After to fire. 15 After min, P415 hasmin, started P4 has to started increase to increase rapidly andrapidly gradually and gradually until 20 until min. 20 This min. may This be may due tobe thedue physical to the physical and chemical and reactionschemical ofreactions the intumescent of the intumescent coating during coating the fire during test. Afterthe fire 20 min,test. allAfter the 20 prototypes min, all the have prototypes showed ahave similar showed pattern a simi oflar temperature pattern of profilestemperature until profiles reaching until 120 reaching min. On top of that, P2 has the lowest temperature of 140.7 C at the center of the prototype as compared to Coatings120 min. 2019 On, 9, topx FOR of PEER that, REVIEW P2 has the lowest temperat◦ure of 140.7 °C at the center of the prototype16 of as20 othercompared types to of other prototypes. types of It prototypes. has also been It has indicated also be thaten indicated this prototype, that this P2, prototype, has resulted P2, in has the resulted best fire protectivein the best performancefire protective in performance retarding the in fire. retarding the fire.

Figure 11. EvolutionEvolution of temperature of fire-resistant ﬁre-resistant timber door prototypes.

3.7.2. Fire Endurance and Temperature RiseRise TestsTests As a building safetysafety requirement,requirement, the the safety safety and and the the reliability reliability of of the the fire fire door door is is the the key key aspect aspect to determiningto determining the the eff ectivenesseffectiveness during during the the outbreak outbreak of the of fire.the fire. In this In researchthis research project, project, there there are only are commercialonly commercial prototypes, prototypes, and the and lowest the lowest equilibrium equilibri temperatureum temperature of P2 have of P2 been have selected been toselected undergo to undergo the fire endurance [33] and temperature rise tests [34] to compare the fire-resistance rating and heat transmission rate by visual observation/inspection. The fire endurance test is to characterize the ability of the fire-resistant timber door prototypes to survive at a specified fire condition for a certain time without an integrity failure or a significant leakage. In this project, the magnesium oxide board acts as the commercial fire-resistant door prototype, which is used to compare with prototype P2. The results of fire endurance and temperature rise of prototypes after the 2 h fire is shown in Figure 12. As a result, both prototypes achieved the 2-h fire-resistance rating without an integrity failure or a significant leakage.

Coatings 2019, 9, 738 15 of 18 the fire endurance [33] and temperature rise tests [34] to compare the fire-resistance rating and heat transmission rate by visual observation/inspection. The fire endurance test is to characterize the ability of the fire-resistant timber door prototypes to survive at a specified fire condition for a certain time without an integrity failure or a significant leakage. In this project, the magnesium oxide board acts as the commercial fire-resistant door prototype, which is used to compare with prototype P2. The results of fire endurance and temperature rise of prototypes after the 2 h fire is shown in Figure 12. Coatings 2019, 9, x FOR PEER REVIEW 17 of 20 As a result, both prototypes achieved the 2-h fire-resistance rating without an integrity failure or a significant leakage.

(a)

(b)

Figure 12. TemperatureTemperature rise rise ratings ratings at at the the center center (T1) (T1) ( (aa)) and and the the edge edge (T2) (T2) ( (bb)) of of the the P2 and commercial prototypes.

Based onon thethe results results obtained, obtained, P2 P2 has has shown shown the bestthe relativelybest relatively low-temperature low-temperature rise rating rise duringrating duringa 120 min a fire,120 whichmin fire, can which be considered can be toconsidered have possessed to have a good possessed quality ofa lowgood heat quality transmission of low atheat T1 transmissionand T2, as compared at T1 and to aT2, commercial as compared prototype. to a commercial By analyzing prototype. the temperature By analyzing rises at the di fftemperatureerent points rises(T1 and at T2),different P2 has points also indicated (T1 and theT2), best P2 firehas retardancyalso indicated properties the best by promotingfire retardancy a lower properties equilibrium by promotingtemperature a than lower the commercialequilibrium prototype. temperature Moreover, than thethe maximumcommercial temperatures prototype. of Moreover, the commercial the maximumprototype aretemperatures merely 195.6 of (T1) the and commercial 40.0 ◦C (T2), protot respectively.ype are merely For P2, the195.6 maximum (T1) and temperatures 40.0 °C (T2), at respectively.T1 and T2 are For merely P2, the 140.7 maximum and 32.0 temperatures◦C, respectively. at T1This and hasT2 are clearly merely indicated 140.7 and that 32.0 P2 has°C, respectively. a higher fire Thisresistance has clearly than the indicated commercial that prototype.P2 has a higher This phenomenon fire resistance can than be due the to commercial the density prototype. differences, This i.e., 3 phenomenonthe density of can P2 be (density due to the= 636.45 density kg differences,/m ) is lower i.e., as the compared density of to P2 the (density current = 636.45 existing kg/m commercial3) is lower 3 asprototype compared (density to the curren= 873.71t existing kg/m ).commercial prototype (density = 873.71 kg/m3). Besides that, an appropriate combination of intumescent flame-retardant coating with vermiculite and perlite can also lead to a lower heat transmission and reveal less surface cracks, resulting in the reduction of temperature up to 54.9 °C as compared to the commercial prototype after the 2 h fire test, as seen in Figure 13. Furthermore, the higher temperatures of the commercial prototype measured at T1 and T2 are also higher than those measured for the P2 prototype as evident in Figure 13b with numerous cracks on the surface of the prototype providing higher rates of heat transfer to the backside of the prototype.

Coatings 2019, 9, 738 16 of 18

Besides that, an appropriate combination of intumescent ﬂame-retardant coating with vermiculite and perlite can also lead to a lower heat transmission and reveal less surface cracks, resulting in the reduction of temperature up to 54.9 ◦C as compared to the commercial prototype after the 2 h ﬁre test, as seen in Figure 13. Furthermore, the higher temperatures of the commercial prototype measured at T1 and T2 are also higher than those measured for the P2 prototype as evident in Figure 13b with numerous cracks on the surface of the prototype providing higher rates of heat transfer to the backside Coatingsof the prototype.2019, 9, x FOR PEER REVIEW 18 of 20

a b

FigureFigure 13. 13. FireFire door door prototypes prototypes ( (aa)) P2 P2 and and ( (bb)) commercial commercial after after th thee 2-h 2-h fire ﬁre test. test.

4.4. Conclusions Conclusions FromFrom the series of experimentalexperimental tests,tests, thethe following following conclusions conclusions can can be be deduced. deduced. The The selection selection of ofsuitable suitable combinations combinations of flame-retardant of flame-retardant materials ma canterials directly can affdirectlyect the fire-protectiveaffect the fire-protective performance performanceand the mechanical and the propertiesmechanical of properties the intumescent of the intumescent flame-retardant flame-retardant coating as coating well as as the well fire as door the fireprototype. door prototype. Amongst Amongst all the coating all the samples coating usedsample/manufactureds used/manufactured in this research in this project, research the project, coating the J2 coatingwith the J2 addition with the of 3addition wt.% of aluminumof 3 wt.% of hydroxide aluminum and hydroxide 3 wt.% of renewableand 3 wt.% CES of bio renewable filler is concluded CES bio fillerto have is concluded the best fire-protective to have the best performance, fire-protect thermal,ive performance, mechanical, thermal, physical, mechanical, and chemical physical, properties. and chemicalOn top of properties. that, the P2 On prototype top of that, with the the P2 addition prototype of J2with intumescent the addition coating of J2 reveals intumescent to a better coating fire revealsprotective to a result better (temperature fire protective reduction result (temperature by up to 54.9 reduction◦C), as comparedby up to 54.9 to the°C), existing as compared commercial to the existingfire-resistant commercial timber doorfire-resistant prototype. timber door prototype. ToTo summarize the conclusions based on the expe experimentalrimental results, an innovative intumescent flame-retardantflame-retardant paint paint incorporated incorporated into into the the lightwei lightweightght fire-resistant fire-resistant timber timber door door prototype prototype (P2) (P2) has has indeedindeed demonstrateddemonstrated toto be be more more effi efficientcient in reducing in reducing the heat the transmissionheat transmission by maintaining by maintaining its integrity its integritywithout showingwithout showing a significant a significan leakaget against leakage the against 2-h fire the test. 2-h fire test.

AuthorAuthor Contributions:Contributions: Conceptualization,Conceptualization, J.J.K.Y J.J.K.Y and and M.C.Y.; M.C.Y.; Methodology, Methodology, J.J.K.Y.; J.J.K.Y.; Software, Software, J.J.K.Y.; Validation, J.J.K.Y.; M.C.Y., M.K.Y. and L.H.S.; Formal Analysis, J.J.K.Y. and M.C.Y.; Investigation, J.J.K.Y. and M.C.Y.; Resources, Validation,M.C.Y.; Data M.C.Y., Curation, M.K.Y. J.J.K.Y. and and L.H.S.; M.C.Y.; Formal Writing–Original Analysis, J.J.K.Y. Draft and Preparation, M.C.Y.; Investigation, J.J.K.Y.; Writing–Review J.J.K.Y. and & M.C.Y.; Editing, Resources,M.C.Y. and M.C.Y.; M.K.Y.; Data Visualization, Curation, M.K.Y.J.J.K.Y. andand L.H.S.; M.C.Y.; Supervision, Writing–Original M.C.Y.; Draft Project Preparation, Administration, J.J.K.Y.; M.C.Y. Writing– and ReviewM.K.Y.; Funding& Editing, Acquisition, M.C.Y. and M.C.Y. M.K.Y.; Visualization, M.K.Y. and L.H.S.; Supervision, M.C.Y.; Project Administration,Funding: This projectM.C.Y. wasand fundedM.K.Y.; byFunding University Acquisition, of Tunku M.C.Y. Abdul Rahman Research Scheme (UTARRF) with Funding:project number: This project IPSR/ RMCwas /fundedUTARRF by/2018-C2 University/Y03. of Tunku Abdul Rahman Research Scheme (UTARRF) with projectAcknowledgments: number: IPSR/RMC/UTARRF/2018-C2/Y03.The authors would like to thank University of Tunku Abdul Rahman (UTAR) for the UTARRF funding support. Acknowledgments: The authors would like to thank University of Tunku Abdul Rahman (UTAR) for the UTARRFConﬂicts funding of Interest: support.The authors declare no conﬂict of interest.

Conflicts of Interest: The authors declare no conflict of interest.

References

Coatings 2019, 9, 738 17 of 18

References

1. Mróz, K.; Hager, I.; Korniejenko, K. Material Solutions for Passive Fire Protection of Buildings and Structures and Their Performances Testing. Procedia Eng. 2016, 151, 284–291. [CrossRef] 2. Weil, E.D. Fire-protective and flame-retardant coatings—A state-of-the-art review. J. Fire Sci. 2011, 29, 259–296. [CrossRef] 3. Ariyanayagam, A.D.; Mahendran, M. Fire tests of non-load bearing light gauge steel frame walls lined with calcium silicate boards and gypsum plasterboards. Thin Walled Struct. 2017, 115, 86–99. [CrossRef] 4. Kolaitis, D.I.; Asimakopoulou, E.K.; Founti, M.A. Fire protection of light and massive timber elements using gypsum plasterboards and wood based panels: A large-scale compartment fire test. Constr. Build. Mater. 2014, 73, 163–170. [CrossRef] 5. Azieyanti, N.A.; Hakim, A.; Hasini, H. Mixture of natural fiber with gypsum to improve the fire resistance rating of a fire door: The effect of kapok fiber. J. Phys. Conf. Ser. 2017, 914.[CrossRef] 6. Fateh, T.; Guillaume, E.; Joseph, P. An experimental study of the thermal performance of a novel intumescent fire protection coating. Fire Saf. J. 2017, 92, 132–141. [CrossRef] 7. Mustapa, S.A.S.; Ramli Sulong, N.H. Performance of solvent-borne intumescent fire protective coating with Palm oil clinker as novel bio-filler on steel. IOP Conf. Ser. Mater. Sci. Eng. 2017, 210.[CrossRef] 8. Azmi, J.K.; Amin, R.Z.; Zaihan, J. Fire Performance of Timber Door Frames. J. Trop. For. Sci. 2013, 25, 429–436. 9. Otáhal, R.; Veselý, D.; Násadová, J.; Zíma, V.; Nˇemec,P.; Kalenda, P. Intumescent coatings based on an organic-inorganic hybrid resin and the effect of mineral fibres on fire-resistant properties of intumescent coatings. Pigment Resin Technol. 2011, 40, 247–253. [CrossRef] 10. Grigonis, M.; Maˇciulaitis,R.; Lipinskas, D. Fire resistance tests of various fire protective coatings. Medziagotyra 2011, 17, 93–98. [CrossRef] 11. Yew, M.C.; Ramli Sulong, N.H. Fire-resistive performance of intumescent flame-retardant coatings for steel. Mater. Des. 2012, 34, 719–724. [CrossRef] 12. Yew, M.C.; Kun Yew, M.; Saw, L.H.; Ng, T.C.; Durairaj, R.; Beh, J.H. Influences of nano bio-filler on the fire-resistive and mechanical properties of water-based intumescent coatings. Prog. Org. Coat. 2018, 124, 33–40. [CrossRef] 13. Chiu, S.H.; Wang, W.K. Dynamic flame retardancy of polypropylene filled with ammonium polyphosphate, pentaerythritol and melamine additives. Polymer 1998, 39, 1951–1955. [CrossRef] 14. Beh, J.H.; Yew, M.C.; Yew, M.K.; Saw, L.H. Fire protection performance and thermal behavior of thin film intumescent coatings. Coatings 2019, 9, 483. [CrossRef] 15. Li, H.; Hu, Z.; Zhang, S.; Gu, X.; Wang, H.; Jiang, P.; Zhao, Q. Effects of titanium dioxide on the flammability and char formation of water-based coatings containing intumescent flame retardants. Prog. Org. Coat. 2015, 78, 318–324. [CrossRef] 16. Md Nasir, K.; Ramli Sulong, N.H.; Johan, M.R.; Afifi, A.M. An investigation into waterborne intumescent coating with different fillers for steel application. Pigment Resin Technol. 2018, 47, 142–153. [CrossRef] 17. Yew, M.C.; Sulong, N.H.R.; Yew, M.K.; Amalina, M.A.; Johan, M.R. Eggshells: A novel bio-filler for intumescent flame-retardant coatings. Prog. Org. Coat. 2015, 81, 116–124. [CrossRef] 18. Guo, C.; Zhou, L.; Lv, J. Calcium Carbonate and modified ammonium polyphosphate on the flame-retardant and mechanical properties of wood flour-polypropylene composites. Polym. Polym. Compos. 2013, 21, 449–456. [CrossRef] 19. Bilotta, A.; De Silva, D.; Nigro, E. Tests on intumescent paints for fire protection of existing steel structures. Constr. Build. Mater. 2016, 121, 410–422. [CrossRef] 20. Yew, M.C.; Sulong, H.R.; Yew, M.K.; Amalina, M.A.; Johan, M.R. The formulation and study of the thermal stability and mechanical properties of an acrylic coating using chicken eggshell as a novel bio-filler. Prog. Org. Coat. 2013, 76, 1549–1555. [CrossRef] 21. Nishimura, A.; Hirose, I.; Tanaka, N. A New Method for Measuring Adhesion Strength of IC Molding Compounds. J. Electron. Packag. 1992, 114, 407–412. [CrossRef] 22. Yew, M.C.; Ramli Sulong, N.H.; Yew, M.K.; Amalina, M.A.; Johan, M.R. Fire propagation performance of intumescent fire protective coatings using eggshells as a novel biofiller. Sci. World J. 2014, 2014.[CrossRef] [PubMed] Coatings 2019, 9, 738 18 of 18

23. Xu, Q.; Chen, L.; Harries, K.A.; Zhang, F.; Liu, Q.; Feng, J. Combustion and charring properties of five common constructional wood species from cone calorimeter tests. Constr. Build. Mater. 2015, 96, 416–427. [CrossRef] 24. Yew, M.C.; Sulong, H.R.; Yew, M.K.; Amalina, M.A.; Johan, M.R. Influences of flame-retardant fillers on fire protection and mechanical properties of intumescent coatings. Prog. Org. Coat. 2015, 78, 59–66. [CrossRef] 25. Hornsby, P.R.; Watson, C.L. A study of the mechanism of flame retardance and smoke suppression in polymers filled with magnesium hydroxide. Polym. Degrad. Stab. 1990, 30, 73–87. [CrossRef] 26. Souza Santos, P.; Souza Santos, H.; Toledo, S.P. Standard transition aluminas. Electron microscopy studies. Mater. Res. 2000, 3, 104–114. [CrossRef] 27. Li, Z.; Qu, B. Flammability characterization and synergistic effects of expandable graphite with magnesium hydroxide in halogen-free flame-retardant EVA blends. Polym. Degrad. Stab. 2003, 81, 401–408. [CrossRef] 28. Packham, D.E. Work of adhesion: Contact angles and contact mechanics. Int. J. Adhes. Adhes. 1996, 16, 121–128. [CrossRef] 29. Fredj, N.; Cohendoz, S.; Feaugas, X.; Touzain, S. Effect of mechanical stress on kinetics of degradation of marine coatings. Prog. Org. Coat. 2008, 63, 316–322. [CrossRef] 30. Toro, P.; Quijada, R.; Yazdani-Pedram, M.; Arias, J.L. Eggshell, a new bio-filler for polypropylene composites. Mater. Lett. 2007, 61, 4347–4350. [CrossRef] 31. Netting, K. Thermosets for electric applications. In Thermosets Structure Properties, and Application, 2nd ed.; Elsevier Ltd.: Amsterdam, The Netherlands, 2018; pp. 439–452. [CrossRef] 32. Wang, G.; Yang, J. Influences of binder on fire protection and anticorrosion properties of intumescent fire resistive coating for steel structure. Surf. Coat. Technol. 2010, 204, 1186–1192. [CrossRef] 33. Xu, Q.; Wang, Y.; Chen, L.; Gao, R.; Li, X. Comparative experimental study of fire-resistance ratings of timber assemblies with different fire protection measures. Adv. Struct. Eng. 2016, 19, 500–512. [CrossRef] 34. Izydorczyk, D.; S˛edłak,B.; Papis, B.; Turkowski, P. Doors with Specific Fire Resistance Class. Procedia Eng. 2017, 172, 417–425. [CrossRef]

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).