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Progress in Organic Coatings 97 (2016) 1–9

Contents lists available at ScienceDirect

Progress in Organic Coatings

j o ur na l ho me pa ge: www.elsev ier .com/ locate /porgcoat

he novel epoxy/PEPA phosphate flame retardants: Synthesis,haracterization and application in transparent intumescent fireesistant coatings

anchao Shi a, Guojian Wang a,b,∗

School of Materials Science and Engineering, Tongji University, 4800 Cao’an Road, Shanghai 201804, ChinaKey Laboratory of Advanced Civil Engineering Materials, Ministry of Education, 4800 Cao’an Road, Shanghai 201804, China

r t i c l e i n f o

rticle history:eceived 12 October 2015eceived in revised form 18 February 2016ccepted 29 February 2016

eywords:poxyEPAlame retardanthosphateransparentntumescent fire resistant coating

a b s t r a c t

A series of novel epoxy/PEPA phosphate (EPP) flame retardants were synthesized by 1-oxo-4-hydroxymethyl-2,6,7-trioxa-l-phosphabicyclo[2.2.2]octane (PEPA), polyphosphoric acid (PPA), andepoxies of bisphenol A epoxy resin E51 (EP) and 1,4-butanediol diglycidyl ether (BDE) with differentproportions. The structure of EPP was characterized by 1H nuclear magnetic resonance (1H NMR) andFourier transform infrared spectroscopy (FTIR). Then EPPs as flame retardants were blended with aminoresin to prepare the transparent intumescent fire resistant coatings. The fire protection test showed thatthe best fire protection was obtained when the ratio of EP/BDE was 1/2. The char layers of coatings wereinvestigated by intumescence ratio and scanning electron microscopy (SEM). The intumescence ratioresult illustrated that the intumescence ratio of char layers decreased with the increase of EP/BDE ratio.The SEM images demonstrated that incorporation of EP could significantly improve the foam structure ofchar layers when the ratio of EP/BDE was no more than 1/2. Next, the thermal decomposition behaviors

of the coatings were studied by thermogravimetric analysis (TGA) under nitrogen and air. The resultsdemonstrated that incorporation of EP could enhance the thermal stability and residual weight of fireresistant coating as well as the thermo-oxidation resistance of the char layers. Finally, the real-time FTIRproved that the decomposition process of fire resistant coatings included three stages bellow 550 ◦C,which was consistent with the result in TGA.

© 2016 Elsevier B.V. All rights reserved.

. Introduction

In recent years, intumescent fire resistant coatings are widelypplied in various materials to meet the increasing requirementsf more stringent fire safety regulation and the decreasing demandsor reduction of the fire hazard in many fields, such as steel, plastics,extiles, wood, etc. [1–4]. In order to improve the fire protectionroperty, different kinds of fire retardant additives (acid source,arbon source, blowing agent and other additives) are directlylended into the fire resistant coatings, which result in the opacityf coatings [5–7]. However, some special facilities, such as ancientuildings, heritage conservations, high-class furniture, need to

ain the original appearance to meet the decoration or some

pecial reasons. Therefore, transparent intumescent fire resistantoatings are nowadays increasingly attracting attention [8–10].

∗ Corresponding author at: Key Laboratory of Advanced Civil Engineering Mate-ials, Ministry of Education, 4800 Cao’an Road, Shanghai 201804, China.

E-mail address: wanggj@tongji.edu.cn (G. Wang).

ttp://dx.doi.org/10.1016/j.porgcoat.2016.02.023300-9440/© 2016 Elsevier B.V. All rights reserved.

Phosphorus-containing compounds instead of conventionalhalogenated compounds are considered as the promising flameretardants due to their less toxic gases and smokes during com-bustion [11,12]. PEPA and its derivatives possess the caged bicyclicstructure, presenting high flame retardant efficiency [13–15]. How-ever, there are some drawbacks of PEPA in the fire resistantcoatings, such as leaching, migration and the poor matrix com-patibility. Therefore, PEPA-containing polymeric flame retardant isproposed to overcome these problems in transparent fire resistantcoatings.

Epoxy, with outstanding mechanical strength, chemical resis-tance and adhesion, has been widely in the fire resistant coatings[16–19]. However, due to the high flammability, plenty of flameretardant additives are added in epoxy, which greatly restrict itsapplication in transparent fire resistant coatings. By far, incorpo-ration of phosphorus-containing compounds into the backbones

of epoxy is considered as efficient method to improve its flameretardant efficiency [20,21].

2 Y. Shi, G. Wang / Progress in Organic Coatings 97 (2016) 1–9

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In this work, a series of novel epoxy/PEPA phosphate (EPP) flameetardants were synthesized by PEPA, PPA, and epoxies of EP andDE with different proportions as shown in Fig. 1. Their structuresere characterized by FTIR and 1H NMR. The influences of EP/BDE

atio on the fire protection and thermal degradation of fire resistantoatings were investigated by fire protection test, intumescenceatio, SEM, TGA and real-time FTIR.

. Experimental

.1. Materials

1-oxo-4-hydroxymethyl-2,6,7-trioxa-l-hosphabicyclo[2.2.2]octane (PEPA) was supplied by Jiangsuictory Chemical Co., Ltd., Jiangsu, China. Polyphosphoric acid

PPA), bisphenol A epoxy resin E51 (EP), 1,4-butanediol diglycidylther (BDE), p-toluenesulfonic acid, acetonitrile and 1,4-dioxaneere bought from Sinopharm Chemical Reagent Co., Ltd. Melamine

ormaldehyde resin (MF, MELCROSS-25, 78–82% in isobutanol)as kindly provided by P&ID Co., Shanghai, China.

.2. Synthesis

.2.1. Synthesis of PEPA dihydrogen phosphate (PDHP)A three-neck flask was charged with PPA (33.8 g, 0.1 mol), dried

,4-dioxane (100 mL) and acetonitrile (400 mL), and heated to 50 ◦C.he solid PEPA (54 g, 0.3 mol) was added gradually at 50 ◦C and theixture was stirred under refluxing for 6 h. Then the reaction was

ooled to room temperature. The suspension was filtered and theolid was washed with acetonitrile to give the white solid (60.8 g,8% yield).

.2.2. Synthesis of epoxy/PEPA phosphate (EPP) flame retardantThe mixture of PDHP, EP and BDE in ethanol/acetonitrile was

tirred under refluxing for 96 h. After cooled to room tempera-ure, the mixture was concentrated under reduced pressure to

e of PDHP and EPP.

remove the solvent. The epoxy/PEPA phosphate flame retardantwas obtained as a light yellow viscous liquid. Five kinds of EPPswith different ratios of EP/BDE were synthesized (marked as EPP1,EPP2, EPP3, EPP4 and EPP5) and the data were present in Table 1.

2.3. Preparation of transparent intumescent fire resistantcoatings

20 g of EPP, 20 g melamine formaldehyde resin and 0.40 g ofp-toluenesulfonic acid were dissolved in water/ethanol (9/1, v/v)and mixed well. The prepared coating was coated on plywoodboards (15 cm × 15 cm × 0.45 cm) and cured at 50 ◦C. The processwas repeated until the thickness of film got to 0.4 mm ± 0.02 mm.Fiver kinds of transparent fire resistant coatings were prepared byfive kinds of EPPs (EPP1, EPP2, EPP3, EPP4 and EPP5) and the cor-responding transparent fire resistant coatings were marked as F1,F2, F3, F4 and F5, respectively.

2.4. Measurements and characterization

2.4.1. 1H NMR spectra analysis1H spectra were measured on a Mercury Plus NMR (400 MHz,

Varian Co., USA). 1H spectra of PDHP was recorded using D2O as asolvent while 1H spectra of EPP4 was recorded using DMSO-d6 asa solvent.

2.4.2. Fourier transform infrared spectroscopy (FTIR) analysisFTIR was carried out by EQUINOX55 FTIR spectrometer (Bruker

Co., Germany) using KBr pellet. The transmission mode was usedand the wavenumber range was set from 4000 to 570 cm−1.

Real-time FTIR was employed to study the chemical structure

changes of fire resistant coating on EQUINOX55 FTIR spectrometer(Bruker Co., Germany) equipped with a temperature controllableheating device. The temperature was raised with a linear heatingrate of 20 ◦C/min from 40 ◦C to 600 ◦C under air.

Y. Shi, G. Wang / Progress in Organic Coatings 97 (2016) 1–9 3

Table 1The proportions of PDHP, EP and BDE in EPPs.

Samples Composition (mol%) EP/BDE

PDHP EP BDE

EPP1 50 0 50 0/1EPP2 50 10 40 1/4EPP3 50 16.7 33.3 1/2EPP4 50 25 25 1/1EPP5 50 50 0 1/0

Fig. 2. The previous method to synthesize PDHP with POCl3 as the starting material.

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Fig. 3. The reaction mech

.4.3. Gel permeation chromatography analysisGPC analysis was taken out on a HP 1100 Gel Permeation Chro-

atographer (Agilent, USA) with N,N-dimethylformamide as theolvent. The flow rate was 0.5 mL/min and temperature was 25 ◦C.

.4.4. Thermogravimetric analysis (TGA)The thermal degradation process of fire resistant coatings F1–F5

as studied by TGA analyzer (PerkinElmer Co., USA). The measure-ents were performed from 50 ◦C to 800 ◦C at a heating rate of

0 ◦C/min under nitrogen and air.

.4.5. Fire protection testThe fire retardant property of fire retardant coatings was studied

y fire protection test. During the test, the coated side of ply-ood board was exposed to the flame. Meanwhile, the temperature

n the other side of plywood board was recorded by the digitalhermometer (Center305, Center Co., Taiwan). Moreover, the intu-

escence ratio of the char layers was calculated according to Eq.1):

= (d2-d0)/(d1-d0) (1)

here d0 is the thickness of the plywood board, d1 is the thicknessf the sample board coated by transparent fire resistant coating, and

between PPA and PEPA.

d2 is the thickness of the sample when the backside temperaturebegan to come into relative stable stage.

2.4.6. SEM observationScanning electron microscopy (SEM, S-2360 N, Hitachi Co.,

Japan) was used to observe the morphology of intumescent charlayers of fire resistant coatings.

3. Results and discussion

3.1. Synthesis of PEPA dihydrogen phosphate (PDHP) andepoxy/PEPA phosphate (EPP) flame retardants

Four kinds of EPPs with different ratios of EP/BDE were syn-thesized through a two-step reaction as shown in Fig. 1. Theintermediate PDHP was prepared by PEPA and PPA, which wasa novel method that had never been reported. Compared withthe previous method with POCl3 as the starting material in Fig. 2[22,23], the novel method using PPA instead of POCl3 included some

advantages. Firstly, PPA was a milder phosphorylation reagent withlower toxicity than POCl3. Secondly, the operation was simpler foronly one-step reaction and safer for no toxic HCl produced. Thirdly,PEPA only reacted with P O P but not with P OH, so the products

4 Y. Shi, G. Wang / Progress in Orga

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Fig. 4. FTIR spectra of PEPA, PDHP and EPP4.

ere only PDHP and phosphoric acid without multi-substitutedroduct. The reaction mechanism was descripted in Fig. 3. In therevious method, it was a two-step reaction and the purity of prod-ct was almost determined by the first step reaction. It was reportedhat the byproduct diPEPA-substituted product was reached up to1% when the ratio of PEPA/POCl3 was 1/1. Moreover, the PEPA-ubstituted product was difficult to be isolated at the two steps.n order to suppress the formation of byproduct, a large excess ofOCl3 was often used, which increased the risk of operation andhe cost of production. Finally, the yield was satisfactory, up to8% without complex purification. Next, the macromolecular phos-hate esters (EPPs) containing hydroxyl groups were prepared byhe step polymerization of PDHP and equimolar epoxies with differ-nt EP/BDE ratios. In addition, the formed hydroxyl groups couldmprove EPPs’ water solubility and compatibility with melamineormaldehyde resin.

.2. Characterizations of PDHP and EPP

The structures of PDHP and EPP were characterized by FTIR andhe spectra of PEPA, intermediate PDHP and EPP4 were shown inig. 4. The characteristic peaks of PEPA were observed at 3426 cm−1

O H), 1293 cm−1 (P O), 1016 cm−1 (P O C), and 854, 842 cm−1

caged phosphate) [24]. In the FTIR spectra of PDHP, it could be seenhat the absorption at 3426 cm−1 corresponding to O-H stretch-ng vibration disappeared, while the typical absorption peaks of

O H at 2844, 2308, 1236 and 958 cm−1 appeared [25]. It indi-ated that PDHP was synthesized successfully by the esterificationf OH- in PEPA and P O P in PPA. In the FTIR spectrum of EPP4, aroad absorption around 3407 cm−1 attributed to O H stretchingibration appeared again, while the absorption at 915 cm−1 corre-ponding to epoxy groups and the peaks at 2844, 2308, 1236 and58 cm−1 corresponding to P O H were almost disappeared. Theesults demonstrated that EPP had been prepared by the reactionetween epoxy groups and P O H, which led to the formation ofydroxyl groups at the same time.

To further confirm the structures of PDHP and EPP, 1H NMReasurements were employed to characterize the products and

he 1H NMR spectra were displayed in Fig. 5. Evidence for syn-hesis of PDHP was confirmed by the chemical shift of exo-cyclicrotons (labeled b) of caged bicycled phosphate, which moved to

.72–3.73 ppm in the spectrum of PDHP from 3.50 ppm in the spec-rum of PEPA. In the spectrum of EPP4, the signals at 4.58–4.64 ppmas corresponded to the characteristic intra-cyclic protons (labeled

) of the caged bicycled phosphate. The multiplet between 6.80 and

nic Coatings 97 (2016) 1–9

7.10 ppm was assigned to the aromatic protons (labeled c and d) forbenzene rings. The signal at 1.57 ppm was ascribed to the protons(labeled e) on methyl groups of bisphenol A. The peak at 1.52 ppmwas assigned to the protons (labeled g) on the middle of two methy-lene groups of BDE. In addition, the protons of exo-cyclic methylene(labeled b), glycerol ether (labeled h) and methylene on 1- and 4-positions of 1,4-butanediol ether (labeled f) overlapped in the rangeof 3.07–4.12 ppm.

Gel-permeation chromatography revealed number-averagemolecular weight (Mn) of EPP1, EPP2, EPP3, EPP4 and EPP5 were3390, 3301, 3475, 3277 and 3089 g/mol, respectively. It indicatedthat target products of macromolecular phosphate ester EPP wereprepared successfully and had similar number-average molecularweight.

From the above analysis, it could be confirmed that the targetproduct EPP had been synthesized successfully as shown in Fig. 1.

3.3. Fire protection of coatings and intumescence ratio

Fire protection is an important performance criterion to eval-uate the fireproof properties of fire resistant coatings. The fireprotection tests of F1–F5 were carried out to compare their fire-proof properties and the curves of backside temperature versustime were displayed in Fig. 6.

Fig. 6 showed that the backside temperature of the coatingsincreased rapidly in first few minutes and then came into a slowgrowth stage until the backside temperature reached to 220 ◦C. Thefire protection times of F1-F5 and uncoated plywood board were926 s, 980 s, 1176 s, 404 s, 124 s and 94 s, respectively. It indicatedthat the fire protection properties of coatings was firstly increasedand then decreased with increase of EP/BDE ratio. Moreover, it wasnoted that the fire protection time of F3 was up to 1176 s, which wasa promising transparent fire resistant coating for industry applica-tion.

3.4. Intumescence ratio analysis of char layers

In order to illustrate the influence of EP/BDE on the fire protec-tion of coatings, the intumescence ratios of F1–F5 were comparedin Fig. 7.

Fig. 7 showed that the intumescence ratios of F1–F5 were 80.6,72.8, 47.2, 19.8 and 5.4, respectively. The intumescence ratios ofcoatings decreased gradually with the increase of EP/BDE ratio. Theresult might be explained by the difference of rate of char formationof the aromatic groups and the aliphatic groups. During the fire pro-tection test, it could be seen that coating of F5 decomposed quicklyunder flame and then the black solidified char covered on the sur-face of the plywood. The quickly formed char layer was assigned todecomposition of aromatic groups from EP. However, in the processof the degradation of F1, it could be found that the coating formedthe molten char first, and then gradually expanded to form the intu-mescent char layer. This phenomenon can be attributed to the slowrate of char formation of aliphatic groups from BDE. Therefore, withthe increase of EP/BDE, the ratio of molten char decreased corre-spondingly, which led to the decrease of the intumescence ratio ofcoating. F4 and F5 with high ratios of EP/BDE had the poor fire pro-tection properties due to their low intumescence ratios while F1–F3with low ratios of EP/BDE exhibited good fire protection propertiesbecause of their high intumescence ratios.

3.5. Morphology of intumescent char layers

The insulation efficiency of the intumescent char layer stronglydepends on the foam structure [26]. The inner foam structures ofF1–F4 char layers were investigated by SEM and the images were

Y. Shi, G. Wang / Progress in Organic Coatings 97 (2016) 1–9 5

ra of P

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Fig. 5. 1H NMR spect

ompared in Fig. 8. The char layer of F5 was not shown in the figureor its low intumescence ratio and weak foam structure.

Fig. 8a showed that the foam structure of F1 was uneven and hadome large pores with the diameters more than 500 �m. The flame

EPA, PDHP and EPP4.

and heat could easily transfer to the substrate, which resulted in thedecrease of fire protection. With the increase of EP/BDE, the pores offire resistant coatings F2 and F3 became smaller and more uniform,which could block the heat transfer more effectively. Although the

6 Y. Shi, G. Wang / Progress in Organic Coatings 97 (2016) 1–9

ihfibbdpp

3

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Fig. 6. Fire protection curves of fire resistant coatings.

ntumescence ratio of F1 was higher than those of F2 and F3, theigher insulation efficiency of F2 and F3 led to the improvement ofre protection. When the ratio of EP/BDE was 1/1, the pores of F4ecame uneven with big holes and cracks, which might be causedy high content of non-intumescent solid char produced from theecomposition of EP. Meanwhile, the low intumescence ratio andoor foam structure of F4 resulted in the sharply decrease of firerotection.

.6. Thermal degradation analysis

In order to demonstrate the influence of the EP/BDE ratio, TGAas used to test the thermal degradation behaviors of fire resistant

oatings. TGA and derived TGA (DTG) curves of F1–F5 under nitro-

en were shown in Fig. 9 and the data were summarized in Table 2.he thermogravimetric analyses under air were only carried outn F1, F2 and F3 due to their good fire protection. The results werehown in Fig. 10, and the relevant data were listed in Table 3.

Fig. 8. The SEM images of the char lay

Fig. 7. The intumescence ratios of fire resistant coatings.

The thermal stability of fire resistant coatings was evaluatedby the temperature of initial 5% weight loss (T5%). Table 1 andTable 2 showed that the T5% and final residual weights of thecoatings all decreased with the increase of EP/BDE either undernitrogen or under air. It indicated that EP had better thermal sta-bility and char-forming ability than BDE. Meanwhile, it was notedthat the residual weights of coatings increased with the increaseof EP/BDE ratio at high temperature under air. Specially, therewas an obviously improvement when the ratio of EP/BDE was1/2. It demonstrated that the addition of EP could improve thethermo-oxidation resistance of coatings and further enhance thefire protection performance. In addition, the residual weights ofcoatings decreased sharply above 550 ◦C and had lower residualweights than those under nitrogen, which was attributed to thethermo-oxidation at high temperature.

From Fig. 9 and Fig. 10, the degradation process of all the

coatings either under nitrogen or under air could be divided intothree stages bellow 550 ◦C. The first stage was in the temperaturerange of 50–200 ◦C corresponding to the cross-linking of amino

ers: (a) F1; (b) F2; (c) F3; (d) F4.

Y. Shi, G. Wang / Progress in Organic Coatings 97 (2016) 1–9 7

Table 2Thermogravimetric data of fire resistant coatings F1–F5 under nitrogen.

Samples T5% (◦C) Weight loss (wt%) Residue at 800 ◦C

50–200 ◦C 200–370 ◦C 370–550 ◦C

F1 170 7.4 31.4 21.5 35.4F2 170 7.5 31.1 21.5 36.2F3 178 6.6 30.4 21.8 37.3F4 180 6.7 28.3 23.1 37.7F5 185 6.1 26.3 24.8 38.2

Table 3Thermogravimetric data of fire resistant coatings F1–F3 under air.

Samples T5% (◦C) Weight loss (wt%) Residue at 800 ◦C

50–200 ◦C 200–370 ◦C 370–550 ◦C

F1 168 6.0 29.5 17.9 15.6F2 175 6.0 29.1 18.2 16.8F3 183 5.6 23.2 19.0 21.0

F

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ig. 9. TGA (a) and DTG (b) curves of fire resistant coatings F1–F5 under nitrogen.

esin to release some small molecules, which led to little weightoss (<7.5 wt%). The second stage was in the temperature range of00–370 ◦C corresponding to a strong DTG peak, which ascribed

o the decomposition of EPP and amino resin. EPP was decom-osed the phosphoric acid derivatives and alkene, which formedhe molten char. Amino resin was decomposed to nonflammableases, which could make the molten char expansion to form

Fig. 10. TGA (a) and DTG (b) curves of fire resistant coatings F1–F3 under air.

intumescent char layer. The third degradation stage in the tem-perature of 370–550 ◦C was assigned to the thermal pyrolysis ofuncarbonized segment, unstable structure or the oxidation of the

residue. From Table 1 and Table 2, it was observed that 42.1–52.9%weight loss came from the second and third stage, which illus-trated that the main decomposition was in the temperature range

8 Y. Shi, G. Wang / Progress in Organic Coatings 97 (2016) 1–9

F3

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Table 4Assignment of FTIR absorption bands of F3.

Peaks position (cm−1) Assignment Ref.

3401 N-H stretching vibrations [27]2933 Asymmetric and symmetric CH2 stretch [27]1662 C N stretching vibration [27]1657, 1492 Aromatic ring [27]1612 Cyameluric ring [28,29]1309 (1289) P O [25]1080 P O P stretching vibration [30]1024 P O C stretching vibration [31]

ig. 11. Real-time FTIR spectra of F3 at different temperatures: (a) 40–320 ◦C; (b)20–600 ◦C.

f 200–550 ◦C except the thermo-oxidative decomposition above50 ◦C under air. Additionally, the weight losses of F1–F3 under airere lower than those under nitrogen at 200–550 ◦C. It indicated

hat oxygen in air took part in the decomposition of fire resistantoating and kept in the char layer at 200–550 ◦C. This thermal oxida-ive reaction delayed the degradation rate of fire resistant coatings.

.7. Real-time FTIR analysis

In order to confirm the chemical structure changes of trans-arent intumescent fire resistant coating during the thermalecomposition under air, the residues of F3 at different temper-tures were investigated by FTIR. Fig. 11 showed the real-time FTIRpectra of F3 at different temperatures. The assignments of theajor bands observed were summarized in Table 4.

The FTIR spectra of the coating almost unchanged below 160 ◦C,hich illustrated that the coating had good thermal stability.

here was a distinct difference when the temperature increasedo 200 ◦C. The absorption at 3401 cm−1 assigned to N H vibra-ions almost disappeared at 200 ◦C, which could be explained by

he crosslinking of amino resin. Meanwhile, the aliphatic compo-ents (2933 cm−1), triazine ring (1662 cm−1), the aromatic ring1567 and 1492 cm−1), P O C bonds (1024 cm−1) and typical oficyclic structures (854 cm−1) decreased remarkably at 200 ◦C,

872 Vibration of PO2/PO3 [32]854 Typical of bicyclic structures [33]

suggesting that EPP and amino resin started to decompose. Whenthe temperature rose up to 320 ◦C, these peaks almost disappearedexpect the P O C bonds. The structure changes at 200–320 ◦Cdemonstrated that the decompositions of EPP and amino resin hap-pened at this stage, which was consistent with the TGA result.At this stage, aliphatic groups and phosphate in EPP decomposedand formed the molten char, which expanded to foam char layerby the nonflammable gases from the decomposition of blowingagent (amino resin). It was worth noting that a new broad peakat 1612 cm−1 appeared at 320 ◦C. It was supposed that formationof cyameluric rings resulted from the breakage and rearrange-ment of triazine rings and aliphatic groups. Furthermore, with theincrease in temperature, the structure changes of residue weremainly come from the phosphorus-containing compounds and therearrangement of the unstable structure. The P O C (1024 cm−1)absorption decreased gradually and disappeared at 560 ◦C; P O Pvibration (1080 cm−1) appeared at 200 ◦C, increased at 200–440 ◦Cand decreased gradually above 440 ◦C; The absorptions at 872 cm−1

ascribed to PO2/PO3 complexes appeared at 360 ◦C and decreasedgradually from 480 ◦C. These results implied that the decompo-sition of phosphorus-containing compounds composed of threestages: phosphate, poly(phosphoric acid) and PO2/PO3 complexes.Additionally, broad peak at 1612 cm−1 corresponding to cyameluricrings decreased gradually above 320 ◦C. It suggested that hetero-cyclic structure was unstable under high temperature.

4. Conclusion

In summary, five kinds of novel epoxy/PEPA phosphate (EPP)flame retardants with different ratios of EP/BDE were synthesizedby a two-step reaction. Their structures were confirmed by FTIRand 1H NMR. Meanwhile, a new method was developed to preparethe intermediate PDHP, which was simpler and safer than previousmethod using POCl3 as well as without the formation of byproductdiPEPA-substituted product.

The properties of fire resistant coatings were strongly influencedby the EP/BDE ratio. The results of fire protection test showed thatcoating obtained the best fire protection when the EP/BDE ratiowas 1/2. The intumescence ratio results demonstrated that theintumescence ratios of char layers decreased with the increase ofEP/BDE ratio. That’s because that the fast char formation of aromaticgroups and resulted in no molten char formed. SEM proved that thefoam structure of char layers was significantly improved when theratio of EP/BDE was no more than 1/2. TGA results showed thatincorporation of EP in EPP was beneficial to improve the thermalstability and char-forming ability of coatings as well as the thermo-oxidation resistance of the char layers at high temperature. Besides,the decomposition process of fire resistant coatings at 50–550 ◦C

was studied by TGA and real-time FTIR, and included three stages:(1) the cross-linking of amino resin; (2) decomposition of EPP andamino resin at 200–370 ◦C; (3) the thermal pyrolysis of unstablestructure or oxidation of the residue at 370–550 ◦C.

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