the application of ce-doped titania nanotubes in the intumescent flame-retardant ps/mapp/per systems

The application of Ce-doped titania nanotubesin the intumescent flame-retardant PS/MAPP/PER systemsYu Wu, Yongchun Kan, Lei Song and Yuan Hu*

In this work, we reported the synthesis, characterization of Ce-doped titania nanotubes (Ce-TNTs), and application inflame retardancy of an intumescent flame-retardant polystyrene (PS/IFR) system. The flame retardancy of polystyrene(PS) composite that was composed of pentaerythritol, microencapsulated ammonium polyphosphate, and PS wasenhanced significantly by adding a small amount (0.1wt%) of (Ce-TNTs). The thermal properties of the flame-retardantPSwere investigated by thermogravimetric analysis, limiting oxygen index (LOI), vertical burning test (UL-94), scanningelectronicmicroscopy, dynamic mechanical thermal analysis, and the real-time Fourier transform infrared spectrometry(FTIR). The maximal decomposition rate temperature of PS/IFR containing Ce-TNTs in air is much higher than that ofother PS composite without Ce-TNTs. The LOI value of PS/IFR that contained 0.1wt% of Ce-TNTs was increased from27.0 to 28.5, and the UL-94 rating was also enhanced to V-0 from no rating when the total loading of additive wasthe same. The real-time FTIR showed that the degradation process was changed after the addition of TNTs. All resultsindicated that Ce-TNTs had a significant synergistic effect on the flame retardancy of PS/IFR. Copyright © 2012 JohnWiley & Sons, Ltd.

Keywords: titania nanotubes; Ce ionized; polystyrene; intumescent flame retardant

INTRODUCTION

The fire protection of polymeric materials by intumescent flameretardants (IFR) is a typical condensed-phase flame retardantmechanism. The IFR system is commonly composed of a precursorof a carbonization catalyst, a carbonization agent, and a blowingagent. By the sequence of esterification, carbonization, expansion,and solidification, the intumescent char generated from IFR willcover the underlying material to protect it from the heat and slowthemass transfer.[1,2] Over the past decade, metallic oxides[3–6] andinorganic nanofillers[7–10] have been added to the IFR to improveits flame-retardant efficiency and thermal stability. As expected,the synergistic or catalytic effect induced by the addition willmodify the chemical and/or physical behavior of the char andimpart superior flame retardancy to polymeric materials, com-pared with those containing IFR alone.Titanium dioxide (TiO2) is an inexpensive, nontoxic, and

photostable material, which has a good photocatalytic andoptical properties for many applications. Titanium oxide existsin three most common crystalline phases: anatase, rutile, andbrookite.[11] Anatase, the phase with the widest scope of applica-tions, can be obtained through conventional routes usingchloride or sulfate as precursors. However, anatase phases haveshown limited specific surface area limiting their applicationswhere adsorption phenomena are involved such as catalysis.Recently, nanotubes of titania have been synthesized, whichrepresent an alternative to increase the specific subsurfacearea.[12,13] Nanotubes exhibit a large internal and externalsurface, along with a surface in the vertex and in the interlayerregions that compose the nanotube walls.[14,15]

Titanium dioxide has been attracting a numerous attentionbecause of many profitable potential applications in the fields

of photoelectric devices and photocatalysis.[16–20] However,there is still a problem that the photocatalytic efficiency of TiO2

needs to be improved because TiO2 is photoactive only undernear ultraviolet-light irradiation.[21] Recently, it has beenreported that metal oxides and noble metals doped TiO2 canenhance photocatalytic activity of pure TiO2. To the best of ourknowledge, there are little investigations on Ce-doped titaniananotubes (Ce-TNTs) or titania nanotubes (TNTs) application inpolymer. On the other hand, rare earth-based compounds playa catalytic role in some reactions, such as esterification anddehydrogenation [22,23]; because the carbonization process ofintumescent flame-retardant polymeric materials includes ester-ification and dehydrogenation, Ce-based compounds may be apromising synergist for IFR to promote the formation of carbona-ceous materials. Moreover, ceria has attracted much attentionbecause of its technological applications as an active catalyst.[24]

In this paper, titania nanotubes with Ce ions incorporated inthe nanotube wall (Ce-TNTs) is synthesized by the hydrothermalmethod and used as a nanofiller to prepare flame-retardant poly-styrene (PS) nanocomposites. The morphology of the Ce-TNTsis characterized by transmission electron microscopy (TEM) andX-ray photoelectron spectroscopy (XPS). The thermal stabilityand burning behavior of the intumescent flame-retardantpolystyrene composites are investigated by thermogravimetric

* Correspondence to: Yuan Hu, State Key Laboratory of Fire Science, University ofScience and Technology of China, 96 Jinzhai Road, Hefei, Anhui 230026, P.R. ChinaE-mail: [email protected]

Y. Wu, Y. Kan, L. Song, Y. HuState Key Laboratory of Fire Science, University of Science and Technology ofChina, 96 Jinzhai Road, Hefei, Anhui, 230026, P.R. China

Research Article

Received: 14 November 2011, Revised: 18 January 2012, Accepted: 30 January 2012, Published online in Wiley Online Library

(wileyonlinelibrary.com) DOI: 10.1002/pat.3036

Polym. Adv. Technol. (2012) Copyright © 2012 John Wiley & Sons, Ltd.

analysis (TGA), the real-time Fourier transform infrared spec-trometry (FTIR), limiting oxygen index (LOI), and vertical burningtest (UL-94).

EXPERIMENTAL

Materials

Polystyrene was purchased from Shantou Ocean First PolystyreneResin Co., Ltd. Microencapsulated ammonium polyphosphate(MAPP), whichwasmicroencapsulated bymelamine–formaldehyderesin (melamine formaldehyde: APP is 1:10 by weight) and pentaer-ythritol (PER) were kindly provided by KeYan Co. TiO2, anatase,sodium hydroxide (NaOH), hydrochloric acid 36%~38% (HCl), andCerium nitrate hexahydrate (Ce(NO3)3 6H2O) were purchased fromShanghai Chemicals No. 1 Plant.

Synthesis of titania nanotubes and Ce-doped titaniananotubes

We stirred 2 g of TiO2 powder and 1 g of Ce(NO3)3 6H2O with35ml of 10M NaOH aqueous solution for 2 hr in a Teflon vessel.The mixture was placed in an autoclave and heated for 36 hr at acontrolled temperature of 130 �C. The brown, powdery TiO2

produced was washed with HCl (to pH= 7.5) in a glass filter forover 24 hr, then washed with water until the pH is 7. Finally,the particles were dried in an oven at 80 �C. The neat TiO2 nano-tubes were synthesized under the same experimental condition.

Preparation of flame-retardant polystyrene composites

The MAPP/PER (IFR, 3/2 by weight) PS/IFR composites were meltcompounded using a Brabender mixer at 180 �C for 15min at ascrew speed of 40 revolution per minute. To obtain the samples,

these additives were firstly melting blended with PS for 5min;IFR was then added and mixed for another 10min. All formula-tions contain a total loading of 25%; when nanofiller are usedtogether with the IFR, the IFR is reduced to maintain this totalloading. All formulations are given in Table 1.

Characterization

Transmission electron microscopy images are obtained on aJeol JEM-100SX transmission electron microscope with anacceleration voltage of 100 kV.The morphologic structures are observed by scanning elec-

tron microscopy (SEM) Hitachi X650.X-ray photoelectron spectroscopymeasurements are carried out

under ultra high vacuum (<10�6 Pa) at a pass energy of 20.0 eV ona Perkin–Elmer PHI 5000C ESCA system equippedwith a dual X-raysource by using Al–K anode. All binding energies are calibrated byusing contaminant carbon (C1s= 284.6 eV) as a reference.Vertical burning tests are conducted on a vertical burning test

instrument (CZF-2-type) (Jiangning, China) with sheet dimen-sions of 130� 13� 3mm3 according to ASTM D3801.The LOI values are surveyed on an HC-2 C oxygen index meter

(Jiangning, China) with sheet dimensions of 130*6.5*3mm3

according to ASTM D2863-97.The thermogravimetric analysis is carried out on the TGA

Q5000 IR thermogravimetric analyzer (TGA instruments) by usinga heating rate of 20 �Cmin�1 in air or nitrogen atmosphere (flowrate of 100mlmin�1).The real-time FTIR spectra are recorded with a Nicolet

MAGNA-IR 750 spectrometer using the KBr disk method in therange of room temperature (RT)–500 �C with a heating rateof 2 �Cmin�1. The relative intensities of related peaks weredetermined by the software of the spectrometer.Dynamic mechanical thermal analysis (DMA) are performed on

Rheome Tric DMA (Apparats, USA) using a heating rate of 5 �Cmin�1 from 25 to 200 �C.

RESULTS AND DISCUSSION

Morphology of Ce-doped titania nanotubes

Transmission electron microscope measurements are performedto confirm the morphology. Figure 1 shows TEM images of thepristine titania nanotubes and the nanotubes submitted to Ce4+ ion-exchange reactions, respectively. Pristine titania nanotubeshave a tubular morphology, and they are multiwalled with anaverage outer diameter of 10 nm and a length of several tensof nanometers. In Fig. 1b, it could be observed that, after theCe ion doped, the tubular morphology and average diametersare preserved. There are no cerium oxide particles evident.

Table 1. Relative percentage (%) of different oxygen specieswith respect to total O 1s in pure TNTs and Ce-TNTnanocompositesa

Samples O 1s (1) O 1s (2) O 1s (3)

TNTs 54.1 39.5 6.5Ce-TNTs 59.2 30.8 10.1

TNTs, titania nanotubes; Ce-TNTs, Ce-doped titania nanotubes.aThe relative percentage of each oxygen species with respectto total O 1s refers to the peak area of each surface oxygenspecies divided by total peak areas of all kinds of surfaceoxygen species.

Figure 1. The transmission electron microscopy images of (a) titania nanotubes and (b) Ce-doped titania nanotubes

Y. WU ET AL.

wileyonlinelibrary.com/journal/pat Copyright © 2012 John Wiley & Sons, Ltd. Polym. Adv. Technol. (2012)

As shown in Fig. 2, doped Ce4+ within TNTs matrix is confirmedby XPS results. Peaks of Ti, O, Ce, and Na are observed in theCe-TNTs sample. The Ti ion and doped concentration of Ce metalanalyzed by XPS is 16.25% and 2.02%, respectively. The XPS

spectra of O 1s of pure TNTs and Ce-TNTs are fitted with thenonlinear least-squares fit program using Gauss–Lorentzian peakshapes, and three O 1s peaks are found after deconvolution(Table 1). The results imply that three oxygen species existed at

Figure 2. X-ray photoelectron spectroscopy spectra of (a) Ce-doped titania nanotubes (Ce-TNTs), (b) Ti 2p of Ce-TNTs and pure titania nanotubes(TNTs), (c) O 1s of TNTs, (d) O 1s of Ce-TNTs. This figure is available in colour online at wileyonlinelibrary.com/journal/pat

Table 2. Compositions, LOI, and UL-94 results of intumescent flame-retardant PS composites

Samples PS IFR TNTs LOI UL-94, 3.2mmbar

Rating t1/t2a (s) Dripping

PS0 100 0 0 18.0 No BC YesPS1 75 25 0 27.0 No BC YesPS2 75 24.9 0.1 28.0 V-1 0/15 NoPS3 75 24.8 0.2 28.0 V-1 0.1/22.5 NoPS4 75 24.5 0.5 28.0 V-2 0.1/27.3 YesPS5 75 24 1 28.0 No BC YesPS6 75 24 1(Ce-TNTs) 27.0 No BC YesPS7 75 24.5 0.5(Ce-TNTs) 27.0 V-1 0.3/18.7 NoPS8 75 24.8 0.2(Ce-TNTs) 28.0 V-0 0/8.4 NoPS9 75 24.9 0.1(Ce-TNTs) 28.5 V-0 0/3.1 NoPS10 75 24.9 0.1(CeO2+TNTs) 28.0 V-1 0.8/13.9 NoPS11 80 19.9 0.1(Ce-TNTs) 26.0 No BC YesPS12 74 25 1 (Ce-TNTs) 28.5 V-0 0.3/5.3 NoPS13 73 25 2 (Ce-TNTs) 27.0 V-0 0.2/4.8 NoPS14 70 30 0 30.5 V-0 0/2.4 No

BC, burns to clamp; IFR, intumescent flame retardant; LOI, limiting oxygen index; PS, polystyrene; TNTs, titania nanotubes; Ce-TNTs,Ce-doped titania nanotubes.at1 and t2, average combustion times after the first and second applications of the flame.

The application of Ce-TNTs in the IFR/PS systems

Polym. Adv. Technol. (2012) Copyright © 2012 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/pat

the surface of pure TNTs and Ce-TNTs composites, whichare assigned to lattice oxygen (O 1s[1]), surface hydroxyl oxygen(O 1s[2]), and adsorbed oxygen (O 1s[3]), respectively, on the basisof the corresponding binding energy. The relative percentages ofdifferent oxygen species with respect to total O 1s in pure TNTsand Ce-TNTs are calculated and summarized in Table 1. From thesedata, we can see that more adsorbed oxygen species existed at thesurface of Ce-TNTs compared with pure TNTs. The results indicatethatmore adsorbed oxygen species are generated at the surface ofCe-TNTs owing to the presence of Ce in the TNTs matrix. For theTNTs, the bending energies of Ti 2p3/2 and Ti 2p1/2 are atapproximately 458.8 and 464.6 eV, respectively, which are assignedto the presence of typical Ti4+.[25] With the doping by Ce, thebinding energies of Ti 2p3/2 and Ti 2p1/2 shift to lower values afterformation of Ce-TNTs compared with pristine TNTs; this is due tothe electronic interaction between Ce and Ti in nanotubes. Theseresults mean that Ce is doped in the TNTs successfully.

Burning behavior

Limiting oxygen index and UL-94 tests

To investigate the flame retardancy of PS/IFR samples, we testedthe LOI values and vertical burning ratings (UL-94) of the samples.The effect of the content of TNTs on the flame retardancy of PS/IFRsamples is listed in Table 2. The LOI value of the PS/IFR withoutTNTs is quite high and reaches 27 with a total loading of 25wt%IFR composed of MAPP and PER. The LOI values initially increasewith the amount of TNTs until a maximum in LOI is reached, butwith the further increase in TNTs content, the LOI value starts todecrease. The highest LOI value obtained is 28.5 when 0.1wt% ofCe-TNTs is added. No rating in the UL-94 standard is observedwhen PS/IFR contains no TNTs. However, if even a small amount(0.1wt%) of Ce-TNTs is added in the PS/IFR, it could preventdripping, which is observed when the PS matrix contains onlythe same amount of the flame retardant, and the UL-94 rating isimproved to V-0. But, there is no rating when the amount ofCe-TNTs added is 1wt%. Keep the IFR at 25wt% and increase theloading of Ce-TNTs; the LOI and UL-94 rating are improved too(Table 2). A mixture of 0.1 wt% that is composed with TNTs andCeO2, according to the ratio of Ti and Ce from XPS, is addedin the PS/IFR, and the UL-94 rating is improved to V-1. The flame-retardant properties of PS/IFR system can be improved by Ce ions.However, when the loading of IFR added to 30wt%, the UL-94rating is improved to V-0 too. The addition of TNTs and Ce-TNTscould improve the LOI value and UL-94 rating of PS; some impor-tant conclusions could be drawn: there exists a synergistic effectbetween TNTs and the IFR system at a low content of TNTs, thesynergistic effect of Ce-TNTs is better than the simple mixture ofTNTs and CeO2, the performance start to become worse whenmore than 0.5wt% of Ce-TNTs or TNTs are presented, there couldbe the lack of enough IFR, and there is an optimal TNTs contentin this system for the best flame retardancy of PS.

The morphology of residues

To further investigate the synergistic effect of TNTs in PS/IFR duringcombustion, the morphologies of the char for the samples afterLOI test are observed via SEM. The char form in Fig. 3a, whichcomes from the sample without TNTs, does not have obviousbubbles but have obvious cracks. Theremay be the primary reasonfor poor flame retardancy for PS1. In Fig. 3b, which shows thesurfaces of the residual char from PS2 (containing 0.1wt% of TNTs),

the morphology of the residual char changes a lot. The morphol-ogy of residual char form PS2 shows a better expansion effect thanform PS1. Interestingly, there are many obvious holes in the resi-dues of PS2, which is the primary reason for poor flame retardancyfor PS2. Figure 3c shows the surfaces of the residual char from PS9.The surfaces of the char are more compact than PS2 and havebetter expansion effect than PS1, which play an important role inkeeping the oxygen and the heat away from the polymer matrix.There are almost no flaws on the surface and compact enoughto prevent the penetration of gases and heat. On the basis of theseresults, it is easy to understand the results of UL-94 rating.

Dynamic mechanical thermal properties

Dynamical mechanical tests over a wide range of temperatureare performed to see the physical and chemical structuralchanges of the polymers and the composites. The glass transi-tions or secondary transitions that yield information about themorphology of polymers are determined. Storage modulus canreflect the elastic properties of materials, and the loss factor is

Figure 3. Scanning electron micrographs of the outer surface of theintumescent char obtained from the samples after limiting oxygen indextest. (a) PS1, (b) PS2, and (c) PS9

Y. WU ET AL.


related with the energy loss. Energy loss is caused by thepolymer chain segments friction movement. Glass transitiontemperature (Tg) corresponds to the loss peak temperature.The results of dynamic tests are presented in Fig. 4 in thetemperature range from RT to 140 �C. It can be seen from Fig. 4that with the addition of TNTs or Ce-TNTs, the storage modulusof composites are increased; that means the elasticity of thematerial has been enhanced. However, the Tg of composites isreduced by pure TNTs addition, which may be caused by thepoor compatibility between TNTs and polymer matrix. Becauseof Ce ions doped in the TNTs improving the interfaceperformance, making a strong interaction with the polymermatrix, and impeding the movement of polymer chains, the Tgof PS9 is higher.

Thermal decomposition behaviors

Thermogravimetric analysis is one of the commonly utilizedtechniques for rapid evaluation of the thermal stability ofmaterials, and it also indicates the decomposition of polymersat various temperatures. To understand the effects of TNTs andCe-TNTs in PS/IFR, the thermal degradation behaviors arecompared from TGA test for the various samples. TGA tests ofPS1, PS2, and PS9 are carried out in N2 at a heating rate of 20 �Cmin�1. TGA and differential thermogravimetric (DTG) curves arepresented in Fig. 5. The similar TGA behaviors are observedunder these experimental conditions for the PS/IFR samples. Itcan be observed that basically, there is no difference for thesamples, with or without TNTs. That means the TNTs andCe-TNTs have no effect under the condition of nitrogen.

Figure 4. Behavior of (a) storage modulus and (b) loss modulus withtemperature of the samples

Figure 5. The (a) thermogravimetric analysis and (b) differentialthermogravimetric curves of intumescent flame-retardant polystyrenesamples in N2 atmosphere

Figure 6. The (a) thermogravimetric analysis (TGA) and (b) differentialthermogravimetric (DTG) curves of intumescent flame-retardant polysty-rene samples in air atmosphere



Thermogravimetric analysis tests of PS1, PS2, and PS9 arecarried out in air at a heating rate of 20 �Cmin�1. TGA and DTGcurves are presented in Fig. 6. The similar TGA behavior isobserved under these experimental conditions. The addition ofCe-TNTs increases the max decomposition rate temperatures ofthe PS/IFR samples; the maximal decomposition rate tempe-rature, Tmax, is defined as the temperature at which the maxmass loss occurs. The Tmaxs of PS1, PS2, and PS9 are 360, 363,and 382 �C, respectively.

Chemical structural changes during thermal degradation

The real-time Fourier transform infrared spectra are employed toexplore the details of the thermal oxidative behavior of PS/IFRcomposites. Figure 7 shows the real-time FTIR spectra of PS1. Ascan be seen, peaks at about 2900, 1600, 1300–1400, 1250, 1070,900, 750, and 700 cm�1 are the characteristic absorptions of PS/IFR. The absorbance for P=O vibration at 1250 cm�1 decreases attemperatures above 330 �C. On the other hand, two new peaks at1265 and 1285 cm�1 appear. The peak at 1265 cm�1 can beassigned to C–O stretching vibration for P–O–R structure, where Rrepresents an aromatic group.[26,27] The peak at 1285 cm�1 can beassigned to P=O vibration, which may be in the structures, suchas trimethyl phosphate or P–O–R structure.[28,29] The existence ofa P–O–R structure is very possible because this peak may be

assigned to the same chemical structure with the peak at1265 cm�1 as both appear simultaneously but decrease withtemperature raised to 500 �C. This implies that the phosphategroup deviates from the MAPP and re-links to the aromaticstructure at the temperature of above 330 �C.The peaks at 1090, 1027, and 900 cm�1 decrease at 330 �C but

1090 and 900 cm�1 increase when raising the temperatureabove 330 �C, as shown in Fig. 7. The peak at 1150 and1027 cm�1 can be assigned to the stretching vibration of P–O–Cand PO2/PO3 in phosphate–carbon complexes.[30] The peaks at1090 and 900 cm�1 can be assigned to the symmetric andasymmetric stretching vibrations of P–O–P bond [31], respec-tively. From the alteration of FTIR peaks form RT to 500 �C, it isconcluded that the degradation process can be divided intotwo steps. Form RT to 330 �C, the degradation is mainlyattributed to the hydroxyl groups, some of alkyl chain, and fastdegradation of MAPP. When temperature increases to over330 �C, the PS matrix starts to break quickly. Although thephosphate groups degrade quickly at lower temperature, mostof them remain in the material as phosphorus compounds.These compounds are reacted with each other to from a P–O–P structure, which acts as a cross-linker to link different aromaticspecies, forming complex cross-linking structures.The similar real-time FTIR spectra of PS2 and PS9 are

presented in Figs 8 and 9. With the temperature increasing,

Figure 7. The real-time Fourier transform infrared spectrometry spectraof PS1 at different pyrolysis temperatures. This figure is available incolour online at wileyonlinelibrary.com/journal/pat



Figure 10. The curves of R1600/R2930 with time from PS1, PS2, and PS9.This figure is available in colour online at wileyonlinelibrary.com/journal/pat

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both 2930 (�CH2) and 1600 cm�1 (C6H5) peaks are reduced.However, the intensity decay rate of these two peaks isdifferent in the three samples. The 2930 cm�1 peak disap-pears, whereas peak intensity of 1600 cm�1 is relatively greatat 380 �C in PS2 and PS9. For more detailed comparison ofthe difference for the peak intensity decay rate in the threesamples, R1600/R2930 results are normalized (the absorptionintensity ratio at room temperature is 1) as shown in Fig. 10.The results are unchanged basically in PS1. However, theratio of PS2 increases as the temperature is rising, whichmeans the loss rate of vinyl is faster than the benzene ringin the matrix. The result of PS9 is similar with PS2, but theratio increases are greater, which means that Ce-TNTs havestronger cracking catalytic for vinyl group or strongeradsorption capacity for phenyl group.

Mechanism discussion

The combination of the results for the TGA, DMA, burningbehavior, and real-time FTIR could initially infer that becauseof the oxygen adsorption capacity of TiO2 as the componentof oxygen sensor that has been widely used, TNTs adsorboxygen on its surface and reduce the oxygen concentrationon the other parts of the system. On the basis of effectiveIFR (>24.5 wt%), the thermal stability of PS/IFR is increasedbecause of the lower oxygen concentration slowing thethermal oxidative degradation of the polymer. Because ofCe ions doping into titanium nanotubes leading to latticedefects increase and improving its adsorptive catalyticperformance, the thermal stability of PS9 is increased higherthan PS2. The formation of char is a major contributionfrom the IFR, and there are no differences in amount amongPS/IFR (PS1), PS/IFR/TNTs (PS2), and PS/IFR/Ce-TNTs (PS9).Therefore, a possible route of the synergistic effect ofCe-TNTs is shown in Scheme 1. Because of the adsorptioncapacity form Ce-TNTs for oxygen and pyrolysis products,an effective charring reaction center for PS/IFR systemand a bridging function to the char residue is formation.Therefore, the more effective it is for the char layer toprotect the polymer.

CONCLUSIONS

In this work, Ce-TNTs were synthesized by the hydrothermalmethod, and TEM and XPS confirmed that the Ce ion was dopedin TNTs wall successfully. The thermal stability and burningbehaviors of PS/IFR were improved by introducing Ce-TNTs. Itwas noted from the TGA data that the Tmax of PS/IFR sampleunder air atmosphere, with 0.1wt% of Ce-TNTs, was about20 �C higher than the pure PS/IFR and PS/IFR/TNTs. The LOI valueof the PS/IFR with 0.1wt% of Ce-TNTs could be increased to 28.5,and its residual char was more compact and stronger than thatof the PS/IFR and PS/IFR/TNTs. Meanwhile, the UL-94 rating ofPS/IFR system was improved from no rating to V-0. The resultsof the real-time FTIR indicated that the addition of Ce-TNTschanged the decomposition process to make the residual charmore compact. All results indicated that Ce-TNTs had asignificant synergistic effect on the flame retardancy of PS/IFR.

Acknowledgements

The work was financially supported by the joint fund of NSFC andGuangdong Province (No. U1074001), National Basic ResearchProgram of China (973 Program) (2012CB719701), and OpeningProject of State Key Laboratory of Environmental Adaptability forIndustrial Product.

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the application of ce-doped titania nanotubes in the intumescent flame-retardant ps/mapp/per systems

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