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Thermochimica Acta 526 (2011) 185– 191

Contents lists available at SciVerse ScienceDirect

Thermochimica Acta

jo ur n al homepage: www.elsev ier .com/ locate / tca

ffect of rare earth hypophosphite and melamine cyanurate on fire performancef glass-fiber reinforced poly(1,4-butylene terephthalate) composites

ei Yanga,b,c, Gang Tanga, Lei Songa, Yuan Hua,c,∗, Richard K.K. Yuenb,∗∗

State Key Laboratory of Fire Science, University of Science and Technology of China, and USTC-CityU Joint Advanced Research Centre, Suzhou, PR ChinaDepartment of Building and Construction, City University of Hong Kong and USTC-CityU Joint Advanced Research Centre, Suzhou, PR ChinaSuzhou Key Laboratory of Urban Public Safety, Suzhou Institute of University of Science and Technology of China, Suzhou, PR China

r t i c l e i n f o

rticle history:eceived 6 August 2011eceived in revised form6 September 2011ccepted 21 September 2011

a b s t r a c t

This work mainly deals with a novel flame retardant system for glass-fiber reinforced poly(1,4-butyleneterephthalate) (GRPBT) composites using trivalent rare earth hypophosphite (REHP) and melamine cya-nurate (MC) through melt blending method. Firstly, two types of REHP, lanthanum hypophosphite andcerium hypophosphite, were synthesized and characterized. Thermal gravimetric analysis (TGA) wasemployed to investigate the thermal decomposition behavior of REHP and flame retardant treated GRPBT

vailable online 1 October 2011

eywords:lass fibersolymer-matrix composites

composites. Thermal combustion properties were measured using microscale combustion calorime-ter. Fire performance was evaluated by limiting oxygen index, Underwriters Laboratories 94 and conecalorimeter. The results showed that the flammability of GRPBT is significantly reduced by the incorpo-ration of the flame retardant mixture. Mechanism analysis revealed that the addition of MC reduces the

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. Introduction

Glass-fiber reinforced poly(1,4-butylene terephthalate)GRPBT) composite is one of most important engineering materialshich has been widely used in electronic or electrical equipment,ilitary and civil infrastructure applications, because of its good

hermal, mechanical, electrical properties, low weight and lowost. However, the development and application of GRPBT arereatly limited by its flammability when subjected to elevatedemperature or combustion. Once ignited, GRPBT can producemounts of toxic gases, soot, and smoke, seriously harming theuman and environment. Fabrication and improvement of theame retarded GRPBT composites are thus the major concern forcademic institutions and industrial laboratories.

Up to now, the most commonly used flame-retardant sys-ems for glass-fiber reinforced polyester composites are mainlyomposed of halogenated additives. Nevertheless, the toxic andorrosive gases will be released in the increasing tempera-ure condition or combustion process of the halogen-containing

olymer composites. The main halogen-free flame retardantsre phosphorus-based, nitrogen-based and phosphorus–nitrogenompounds which have been successfully applied in polyesters

∗ Corresponding author. Tel.: +86 551 3601664; fax: +86 551 3601664.∗∗ Corresponding author. Tel.: +852 2788 7621.

E-mail addresses: yuanhu@ustc.edu.cn (Y. Hu), Richard.Yuen@cityu.edu.hkR.K.K. Yuen).

040-6031/$ – see front matter © 2011 Published by Elsevier B.V.oi:10.1016/j.tca.2011.09.022

P, but improves the flame inhibition in gas phase.© 2011 Published by Elsevier B.V.

[1–4]. However, it is difficult to achieve a high flame retarded clas-sification for polyesters with a low loading of these compounds.Recently, one kind of metal phosphinate has been used in polyesters[5–9]. Braun and Schartel [5] prepared a V-0 GRPBT compositeusing a flame retardant mixture (aluminium diethylphosphi-nate and melamine cyanurate) at a loading of 20 wt%. Veryrecently, inorganic compound aluminium hypophosphite has beenapplied as a flame retardant in glass fiber reinforced polyesters[10–12]. Costanzi and Leonardi [10] found that low fraction ofaluminium hypophosphite can provide high fire retardancy proper-ties in GRPBT composites. Nevertheless, the thermal stability andmechanical properties of glass fiber reinforced polyesters is dra-matically reduced by the addition of aluminium hypophosphite.

Inspired by the reported flame retardant effects provided by alu-minium hypophosphite, another metal hypophosphite was usedto improve the fire retardancy performance of GRPBT compos-ites. In this study, two kinds of trivalent rare earth hypophosphite,lanthanum hypophosphite and cerium hypophosphite, will be pre-pared. As a nitrogen-based flame retardant, melamine cyanuratewill be incorporated to establish a novel flame retardant system tofurther improve the fire retardancy. The aim of this work is to exam-ine the use of rare earth hypophosphite and melamine cyanurate ashalogen-free flame retardants for GRPBT composites. Synthesizedrare earth hypophosphite will be characterized. The thermal stabil-

ity and fire retardancy properties for GRPBT composites containingthe flame retardants will be studied by thermo-gravimetric anal-ysis, microscale combustion calorimeter, limiting oxygen index,Underwriters Laboratories 94 and cone calorimeter. Moreover, the

1 imica Acta 526 (2011) 185– 191

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ossible mechanism behind the fire retardant behavior will beescribed and discussed.

. Experimental

.1. Materials

Trivalent lanthanum chloride hydrate and cerium chlorideeptahydrate (Sinopharm Chemical Reagent Co., Ltd.) were ofnalytical grade. Sodium hypophosphite (analytical reagent) wasupplied by Tianjin Guangfu Fine Chemical Research Institute,hina. Poly(1,4-butylene terephthalate) (PBT) (4500) was a prod-ct of BASF Chemical Company, Germany. Silane coated short glassber (ECS-301CL, fiber diameter of 10 �m and initial fiber lengthf 3 mm) was supplied by Chongqing Polycomp International Co.,td., China. Melamine cyanurate (MC) was a commercial prod-ct from Shandong Shouguang Weidong Chemical Engineering Co.,td., China. Furthermore, the deionized water (ultrapure water) wassed in this work.

.2. Synthesis of rare earth hypophosphite

In a typical experiment [13], 2.00 g sodium hypophosphite wasissolved in pH 1.4 (KCl–HCl) buffer solution (20 ml). The solventsed for the buffer solution was deionized water. 2.4 g hydrated

anthanide chloride in the buffer solution (20 ml) was added. Theeaction mixture was heated to 40 ◦C under reflux in a nitrogentmosphere for 3 h. The resulting solids, were collected by suc-ion filtration, washed with deionized water, and dried at the oven.rivalent lanthanum hypophosphite (LHP) and cerium hypophos-hite (CHP) were synthesized via the typical method in this work.he products were analyzed by Fourier transform infrared spectrapectroscopy (Nicolet 6700 FT-IR spectrophotometer) and scanninglectron microscope (Hitachi S-4800).

.3. Preparation of flame retarded glass fiber reinforced PBTomposites

PBT, LHP, CHP, MC and glass fiber were dried at 80 ◦C overnightefore use. PBT was blended with additives using a twin-roll millXK-160, made in Jiangsu, China) at 235 ◦C for 10 min. The rollerpeed was 100 rpm for the preparation of all the samples. Theyere then molded by using a hot press at 235 ◦C under 5–10 MPa

or 10 min in order to obtain 3.2 or 1.6 mm thick plaques. The for-ulations of these composites were shown in Table 1.

.4. Pyrolysis analysis

Thermogravimetric analysis (TGA) was carried out using a5000 IR thermogravimetric analyzer (TA Instruments Waters,hina) at a linear heating rate of 20 ◦C/min under nitrogen atmo-phere. The weight of all the samples were kept within 5–10 mg.omposites in an open Pt pan were tested under an airflow rate of

× 10−5 m3 min−1 at temperature ranging from room temperatureo 700 ◦C.

.5. Thermal combustion properties

Thermal combustion properties of plastics were measured using microscale combustion calorimeter (MCC, Govmark) according toSTM D 7309-07. 5 (±0.1) mg of each sample was heated at 1 ◦C s−1

rom 90 to 600 ◦C and held there for 30 s. During pyrolysis, theolatilized decomposition products are transferred in the streamf nitrogen to a high-temperature combustion furnace where purexygen is added and the decomposition products are completely

Fig. 1. FTIR spectra of LHP (a) and CHP (b).

combusted. The amount of oxygen consumed is measured with anoxygen analyzer and used to calculate a heat release rate (HRR).

2.6. Combustion testing

One group of combustion experiments were determined by lim-iting oxygen index (LOI) and Underwriters Laboratories (UL) 94testing according to ASTM D2863 and the standard [14] respec-tively. An HC-2 oxygen index meter (Jiangning Analysis InstrumentCompany, China) was used in the LOI testing. The specimens usedfor the test were of dimensions 100 mm × 6.5 mm × 3.2 mm. UL94 testing was carried out on a CFZ-2-type instrument (JiangningAnalysis Instrument Company, China). The specimens used were ofdimensions 130 mm × 13 mm × 3.2(or 1.6) mm.

The other combustion experiments were performed in acone calorimeter (Fire Testing Technology) according to ASTME 1354/ISO 5660. Each specimen (100 mm × 100mm × 3.2 mm)was wrapped in an aluminium foil and exposed horizontally to35 kW/m2 external heat flux. Some residues collected in the conetesting were further analyzed by means of the scanning elec-tron microscope (SEM). The SEM micrographs were obtained witha scanning electron microscope AMRAY1000B at an acceleratingvoltage of 20 kV. The specimens were sputter-coated with a con-ductive layer.

3. Results and discussion

3.1. Characterization of rare earth hypophosphite

Infrared spectra of lanthanum hypophosphite (LHP) and CHPare shown in Fig. 1. The bands in the region of 2300–2450 cm−1

observed in the two compounds are attributed to PH2 stretchingmodes [15]. The bands between 1100 cm−1 and 1250 cm−1 corre-spond to the bending modes of PH2 [16]. The medium intensitypeak at 809 cm−1 is assigned to the rocking mode of PH2. The weakpeak at 1079 cm−1 is attributed to P–O modes. The absence of char-acteristic bands of water molecules in the infrared spectra indicatesthat the two compounds are anhydrous.

The SEM micrographs of the two compounds are shown inFig. 2. Both the two micrographs illustrate the rod-like crystals,while having nonuniform sizes. The small rod-like crystals of LHP

have sizes of about 1.0–6.0 �m in length and 0.3–0.7 �m in width,while the large ones have sizes of about 8.0–24.0 �m in length and0.6–4.2 �m in width. The fragments of CHP are smaller than thoseof LHP, having irregular morphology. The large rod-like crystals of

W. Yang et al. / Thermochimica Acta 526 (2011) 185– 191 187

Table 1Formulations and TGA, DTG data under nitrogen atmosphere for each sample (20 ◦C/min, 5–15 mg; errors ±0.5 wt%, ±1 ◦C).

Sample Composition (wt%) T−3% (◦C) Tmax (◦C) Residue (wt%) at 700 ◦C

PBT Glass fiber LHP CHP MC

GRPBT 70 30 0 0 0 369 403 31.6GRPBT/MC 50 30 0 0 20 346 384 33.3GRPBT/LHP 50 30 20 0 0 361 417 48.1GRPBT/CHP 50 30 0 20 0 366 413 50.1GRPBT/LHP + MC 50 30 10 0 10 356 415 41.2GRPBT/CHP + MC 50 30 0 10 10 356 413 40.0

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HP have sizes of about 4.0–20.0 �m in length and 0.9–4.8 �m inidth.

.2. Thermal decomposition behavior

TGA and DTG curves of LHP, CHP and MC are shown in Fig. 3.o significant loss below 300 ◦C is observed in these compounds.he decomposition of LHP begins from 334 ◦C (T−3%). The low massoss between 100 ◦C and 321 ◦C can be attributed to the release ofhe adsorbed water. Mass loss in the region of 321–700 ◦C is causedy the formation and release of phosphine [13]. CHP decomposesrom 323 ◦C (T−3%). The temperature at mass loss rate of CHP isower than that of LHP. Phosphine is also the main product. Thehermal decomposition of MC begins from 308 ◦C (T−3%) with the

aximal mass loss rate at 378 ◦C. Only a few residues (1.2 wt%) areemained at 700 ◦C. It is indicated that many gas phase productsre released in the decomposition of MC.

ig. 3. TGA analysis for MC, LHP and CHP: (top) mass loss curves and (bottom) massoss rate curves.

P (a) and CHP (b).

The TGA and DTG curves of the GRPBT composites are shownin Fig. 4, and the results are summarized in Table 1. The thermaldecomposition of GRPBT under nitrogen atmosphere is character-ized by a single decomposition step with maximum mass loss rateat 403 ◦C (Table 1). The residue at 700 ◦C is of about 31.6 wt% andhence mainly composed of glass fibers. According to the tempera-tures at 3 wt% mass loss (T−3%), the initial thermal stability of GRPBTcomposites are all reduced by the loading of MC, LHP and CHP.The resulting residues for GRPBT/LHP and GRPBT/CHP mainly con-tain inorganic chars. The presence of MC in GRPBT/LHP + MC andGRPBT/CHP + MC results in the further reduction of thermal sta-bility compared with GRPBT/LHP and GRPBT/CHP. However, thetemperatures at mass loss rate for GRPBT composites are signif-icantly increased by the introduction of LHP or CHP. Meanwhile,the maximum mass loss rate of GRPBT/LHP and GRPBT/CHP arereduced. The results show that the thermal decomposition ofGRPBT is retarded by the additives. The incorporation of MC intoGRPBT/LHP and GRPBT/CHP increases the maximum mass loss rate.The results show that the presence of the flame retardant mixturepromotes the decomposition of GRPBT composites.

3.3. Thermal combustion properties

MCC is a thermal combustion analysis instrument that directlymeasures the heat of combustion of the gases evolved during con-trolled heating of milligram-sized samples [17]. In this work, allcomposites were screened by MCC testing. The heat release ratecurves and heat release data are shown in Fig. 5 and summarizedin Table 2 respectively. GRPBT is a flammable polymer matrix com-posite, having high peak of heat release rate (PHRR), heat releasecapacity (HRC) and total heat release (THR) (Table 2). When addingMC to GRPBT, these values are slightly reduced because of the gasdilution effect caused by the decomposition of MC. The PHRR valueis significantly reduced by the addition of LHP, which decreases

from 330 W/g for GRPBT to 157 W/g for GRPBT/LHP with a reduc-tion of 52%. The weak peak at around 335 ◦C is attributed to thecombustion of phosphine in the decomposition of LHP. The PHRRvalue of GRPBT/LHP + MC is higher than that of GRPBT/LHP, and

188 W. Yang et al. / Thermochimica Acta 526 (2011) 185– 191

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ig. 4. TGA analysis for GRPBT composites: (top) mass loss curves and (bottom)ass loss rate curves.

ower than that of GRPBT/MC. The result shows that there is not aynergistic effect in the flame retardant mixture. The heat releaseate curves and MCC results for GRPBT/CHP and GRPBT/CHP + MCre similar with those for GRPBT composites containing LHP.

The HRC and THR are also important measures of the fire haz-rd of a material. From HRC and THR values for all composites,t can be seen that the presence of LHP or CHP promotes theeduction of these values. In comparison with GRPBT, the HRC andHR values of GRPBT/LHP are respectively reduced by 53% and2%, which for GRPBT/LHP are also remarkably decreased. How-ver, these values are increased when MC is incorporated intoRPBT/LHP or GRPBT/CHP composites. Meanwhile, the char yield

esults are similar with those from TGA. In combination with theGA results, it has been known that the maximum mass loss rate

or GRPBT/LHP + MC or GRPBT/CHP + MC is higher than that forRPBT/LHP or GRPBT/CHP. The release of decomposition products

esults in the increasing fire hazards. The temperatures at peak

able 2CC results for each sample. (HRC: heat release capacity, ±5 J/g K; PHRR: peak of

eat release rate, ±5 W/g; THR: total heat release, ±0.1 kJ/g; TPHRR: temperature atHRR, ±2 ◦C; CY: char yield, ±0.5%.)

Sample HRC (J/g K) PHRR (W/g) THR (kJ/g) TPHRR (◦C) CY (%)

GRPBT 333 330 12.9 419 31.2GRPBT/MC 224 227 8.2 415 32.6GRPBT/LHP 158 157 7.5 408 49.0GRPBT/CHP 179 174 7.6 410 50.5GRPBT/LHP + MC 196 191 7.7 409 40.7GRPBT/CHP + MC 197 196 8.0 412 40.3

Fig. 5. HRR curves for GRPBT composites from MCC testing.

heat release rate (TPHRR) for GRPBT composites containing addi-tives are all lower than that for GRPBT. This is attributed to thedecomposition of flame retardant additives.

3.4. Fire performance

Underwriters Laboratories 94 and LOI tests were performed todetermine the flame class of each composite. In order to studythe fire performance in detail, the specimens with two differentthicknesses (3.2 and 1.6 mm) were performed in UL 94 testing. Theresults are summarized in Table 3. GRPBT is a flammable polymericcomposite with a LOI of 22%. In UL 94 test, GRPBT could not self-extinguish after the removal of flame in the first application. Theaddition of MC does not evidently improve the flame class of GRPBT.When adding LHP or CHP, the LOI for GRPBT/LHP or GRPBT/CHPis significantly increased, and the specimen (3.2 mm) can obtaina V-0 classification in UL 94 testing. However, GRPBT/LHP andGRPBT/CHP both fail in UL 94 testing with 1.6 mm bar. With theincorporation of the flame retardant mixture, the LOI values arefurther improved. The average flame times during UL 94 test-ing (3.2 mm) are reduced. Moreover, the specimen (1.6 mm) forGRPBT/LHP passes the UL 94 testing with a V-1 classification, andthat for GRPBT/CHP obtains a V-0 classification. This means that the

addition of MC to GRPBT/LHP or GRPBT/CHP enhances the flameinhibition effect. Additionally, the flame retardancy for GRPBT/CHPis more improved than that for GRPBT/LHP in LOI and UL 94 testing.

W. Yang et al. / Thermochimica Acta 526 (2011) 185– 191 189

Table 3Results of UL 94 and LOI testing for each sample.

Sample LOI UL 94, 3.2 mm bar UL 94, 1.6 mm bar

t1/t2a (s) Dripping Rating t1/t2 (s) Dripping Rating

GRPBT 22 ± 0.5 BCb Yes NRc BC Yes NRGRPBT/MC 24 ± 0.5 BC Yes NR BC Yes NRGRPBT/LHP 28 ± 0.5 1.2/7.8 No V-0 BC Yes NRGRPBT/CHP 28.5 ± 0.5 1.2/6.9 No V-0 BC Yes NRGRPBT/LHP + MC 29.5 ± 0.5 1.2/4.1 No V-0 7.7/14.8 No V-1GRPBT/CHP + MC 30 ± 0.5 1.4/3.7 No V-0 1.1/6.1 No V-0

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.5. Cone calorimeter testing

Cone calorimeter is one of the most effective bench-scale meth-ds to evaluate the fire performance of polymeric materials, whichan offer important parameters including time to ignition (TTI),HRR and THR. The cone calorimeter data obtained at a heat fluxf 35 kW/m2 for the GRPBT and its composites are summarized inable 4. The HRR curves are shown in Fig. 6. The PHRR value has no

undamental reduction when adding MC into GRPBT. But the TTIs increased, resulting from the fuel dilution effect of MC [5]. MCs endothermically decomposing into ammonia which is a vapor

Fig. 6. HRR curves for GRPBT composites from cone testing.

flame.

phase flame retardant keeping the polymer cool enough to preventsustained ignition.

The loading of LHP or CHP significantly reduces the PHRR, THRand average mass loss rate (AMLR). The PHRR value decreases from417 kW/m2 for GRPBT to 101 kW/m2 for GRPBT/CHP with a reduc-tion of 76%. The THR value for GRPBT/CHP is reduced by around 20%.The reduction for PHRR and THR may be attributed to the remark-able decrease of the mass loss rate. In comparison with GRPBT, theAMLR value for GRPBT/CHP is reduced by around 69%. The conecalorimeter data for GRPBT/LHP composites are similar with thosefor the composites containing CHP. One of the differences is thatthe ASEA value for GRPBT/CHP is lower than that for GRPBT/LHP.It is indicated that the incorporation of CHP can suppress the pro-duction of smoke.

The PHRR and THR values are increased for GRPBT containingflame retardant mixture, which are similar with the MCC results.The results show that there is no synergistic effect between rareearth hypophosphite and MC. The reason for the increased PHRRand THR values may be that the addition of MC could inducethe aminolysis reaction of the polyester to speed the pyrolysis ofpolyester matrix leading to the escape of decomposition products[18]. Although the fire hazards of GRPBT composites are increasedby the incorporation of the flame retardant mixture, the increas-ing TTI value resulted from the addition of MC shows a better fireretardancy property.

The fire behaviors can also be reflected through the combustionefficiency, represented by the carbon monoxide/carbon dioxideratio from the cone calorimeter data. In this work, R value meansthe average CO yield/average CO2 yield ratio. It can be observedthat the addition of MC decreases the R value, indicating that thecombustion of GRPBT/MC is more complete than that of GRPBT. Theincorporation of LHP and CHP to GRPBT significantly increase theR value, which decreases when using the flame retardant mixture.The results are consistent with PHRR and THR values. The evidencedemonstrates that the combustion of GRPBT is inhibited by theintroduction of rare earth hypophosphite or the flame retardantmixture.

3.6. Flame retardancy mechanism

From the combustion testing, it can be concluded that thefire hazards for GRPBT/LHP and GRPBT/CHP are lower than thatfor GRPBT/LHP + MC and GRPBT/CHP + MC. However, the GRPBTcomposites containing flame retardant mixture have better fireretardancy properties. In order to understand the flame retar-dancy mechanism of GRPBT composites, the residues of GRPBT/LHP,GRPBT/CHP, GRPBT/LHP + MC and GRPBT/CHP + MC after cone test-ing were analyzed by SEM (Fig. 7). As shown in Fig. 7(a) and (b), it is

clearly observed that the glass fibers are covered by the char layer.It has been known that the high flammability of glass-fiber rein-forced polymer composites (GRPs) is mainly caused by the wickeffect of glass fibers [19]. The alignment and contact of the filled

190 W. Yang et al. / Thermochimica Acta 526 (2011) 185– 191

Table 4Cone calorimeter data for each sample at 35 kW/m2. (TTI: time to ignition, ±2 s; PHRR: peak heat release rate, ±15 kW/m2; THR: total heat release, ±0.5 MJ/m2; AMLR:average mass loss rate, ±0.1 g/s/m2; ASEA: average specific extinction area, ±20 m2/kg; ACOY: average CO yield, ±0.005 kg/kg; ACO2Y: average CO2 yield, ±0.008 kg/kg;R = ACOY/ACO2Y; CY: char yield, ±0.5%.)

Sample TTI (s) PHRR (kW/m2) THR (MJ/m2) AMLR (g/s/m2) ASEA (m2/kg) ACOY (kg/kg) ACO2Y (kg/kg) R CY (%)

GRPBT 49 417 53.6 6.24 520 0.052 1.64 0.032 31.5GRPBT/MC 64 367 46.6 4.51 350 0.029 1.47 0.020 32.5GRPBT/LHP 36 105 43.8 1.87 692 0.128 1.52 0.084 52.5GRPBT/CHP 38 101 42.8 1.94 349 0.122 1.42 0.086 53.2GRPBT/LHP + MC 56 138 49.6 2.83 477 0.054 1.22 0.044 36.5GRPBT/CHP + MC 61 173 47.5 2.99 457 0.073 1.44 0.051 37.9

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lass fibers can form a continuous mass path and thus speed theammable mass to the burning area. On one hand, the formation ofondensed char layer can reduce the mass loss rate of the polymeratrix resulting in the reduction of flammable mass concentration

n the burning area. On the other hand, the char layer can effec-ively reduce the heat conduction of glass fibers and cut off the

ass transfer path to decrease the wick effect of glass fibers.The residue morphology for GRPBT/LHP + MC exhibits a bubble-

ike char around glass fibers. But no obvious bubble-like chars observed in the morphology for GRPBT/CHP + MC. The reason

ay be that the char layer for GRPBT/LHP + MC is more stablehan that for GRPBT/CHP + MC. The advantage of the thermally

table char is that the combustible mass is probably retardedesulting in the reduction of fire hazards. Therefore, the PHRRalue for GRPBT/LHP + MC is lower than that for GRPBT/CHP + MC.he disadvantage is that the part of released volatiles from MC

P; (b) GRPBT/CHP; (c) GRPBT/LHP + MC; (d) GRPBT/CHP + MC.

may be trapped by the char layer of GRPBT/LHP + MC leadingto the reduction of fuel dilution effect of MC. The time to igni-tion for GRPBT/LHP + MC from cone testing is thus lower thanthat for GRPBT/CHP + MC. Additionally, the higher classification forGRPBT/CHP + MC from UL 94 testing (1.6 mm) is obtained, in com-parison with GRPBT/LHP + MC. From Fig. 7(c) and (d), it is alsoobserved that there are almost no residues covered on the surfaceof glass fibers. This means that there is no fundamental influenceon the wick effect of glass fibers. Consequently, the fire risk isincreased.

4. Conclusion

Halogen-free fire retarded glass-fiber reinforced poly(1,4-butylene terephthalate) (FR-GRPBT) composites were fabricatedusing a novel flame retardant system composed of rare earth

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ypophosphite (REHP) and MC. Two types of REHP, lanthanumypophosphite and cerium hypophosphite, were successfullyynthesized. TGA was employed to investigate the thermal decom-osition behavior of REHP and FR-GRPBT composites. The thermaltability of FR-GRPBT was slightly reduced by the addition of flameetardant mixture. Thermal combustion properties were measuredsing a microscale combustion calorimeter, indicating a remark-ble reduction in heat release rate. Fire performance was evaluatedy limiting oxygen index, Underwriters Laboratories 94 and conealorimeter. The results showed that the flammability of GRPBTs significantly reduced by the incorporation of the flame retar-ant mixture. Mechanism analysis revealed that the addition ofC reduces the condensed phase effect, but improves the flame

nhibition in gas phase.

cknowledgements

The work was financially supported by the joint fund of NSFCnd Guangdong Province (No. U1074001), the joint fund of NSFCnd CAAC (No. 61079015) and specialized research fund for theoctoral program of higher education (20103402110006).

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