Simultaneously Improved Flame Retardance and Ceramifiable

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Applications of Polymer, Composite, and Coating Materials

Simultaneously Improved Flame Retardance and Ceramifiable Property of Polymer-Based Composites via the Formed Crystalline Phase at High Temperature Ying-Ming Li, Cong Deng, Xiaohui Shi, Bo-Ren Xu, Hong Chen, and Yu-Zhong Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b21664 • Publication Date (Web): 24 Jan 2019 Downloaded from http://pubs.acs.org on January 27, 2019

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ACS Applied Materials & Interfaces

Simultaneously Improved Flame Retardance and Ceramifiable Property of Polymer-Based Composites via the Formed Crystalline Phase at High Temperature Ying-Ming Li, Cong Deng, Xiao-Hui Shi, Bo-Ren Xu, Hong Chen, Yu-Zhong Wang College of Light Industry, Textile and Food Engineering, The Collaborative Innovation Center for Eco-Friendly and Fire-Safety Polymeric Materials, National Engineering Laboratory of Eco-Friendly Polymeric Materials (Sichuan), State Key Laboratory of Polymer Materials Engineering, Analytical and Testing Center, Sichuan University, Chengdu 610064, China Abstract: Ceramifiable polyolefin materials have an excellent application prospect in hightemperature-resistant wires and cables because of their excellent fire-safety performance via a ceramization process under fire conditions. During the ceramization process, the control of crystalline phase plays a vital role in determining final fire resistance and ceramifiable property. In this work, the ammonium polyphosphate/zinc borate (APP/ZB) was developed to achieve the highly efficient flame retardance and ceramization of ethylene-vinyl acetate/mica powder/organo-modified montmorillonite (EVA/MP/OMMT) composite. In combustion test, the EVA/MP/OMMT/APP/ZB system displayed obvious flame-retardance feature, showing much lower total heat

Corresponding author: Tel. & Fax: +86-28-85410259. E-mail address: [email protected] (C. Deng); [email protected] (Y.-Z. Wang).

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release and total smoke production than neat EVA. After treating at high temperatures, rigid ceramic products were formed for the EVA/MP/OMMT/APP/ZB. The ceramic that was formed at 900 °C had a flexural strength of 10.3 MPa for the EVA/MP/OMMT/APP/ZB containing 23 wt% of APP/ZB (9.9/13.1), increased by 2475.0%, 635.7%, and 586.7% compared to the corresponding values of EVA/MP/OMMT, EVA/MP/OMMT/ZB, and EVA/MP/OMMT/APP. For the latter two systems, the content of ZB or APP was 23 wt%. The APP/ZB showed a remarkable fluxing effect on the ceramization of MP-based EVA composite. The fluxing mechanism of APP/ZB was revealed by different measurements. Both APP and ZB led to the formation of a glass melt containing α-Zn3(PO4)2 and orthophosphate with increasing the temperature. Successively, the melt crystalline structure cohered the OMMT and MP together, accompanied by the gradual disappearance of mica phase and the generation of eutectic phenomenon. Finally, a ceramic with high flexural strength was formed, leading to the improved flame retardance and ceramifiable property of EVA-based composites. Keywords: ethylene-vinyl acetate; ammonium polyphosphate; zinc borate; ceramic; flame retardance; fluxing agent

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TOC

1. Introduction Currently, ceramifiable polymer composites have been extensively investigated in cables and insulated wires, transportation, construction and nuclear industries because of their high-temperature resistant property.1-4 According to the past research, it is confirmed that the ceramifiable composites may form glass ceramics with a crystalline region and a glass phase under high temperature. In a fire accident, the formed glass ceramics may block the propagation of flame and resist the strong water spray in fighting a fire due to their high-temperature resistance and excellent mechanical property.3,

5

Moreover, it could also act as an insulating layer in protecting inner

materials. For instance, a formed ceramic of cable may protect a copper wire from being melted, then make the cable in a regular work state during the fire and avoiding a serious disaster such as a nuclear accident in nuclear power station. Generally, low melting-point glass powders are indispensable in preparing the ceramifiable composites, which may ensure the high flexural strength of a formed 3



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ceramic.6-7 For the glass powders, they may melt in the temperature range of 300~700 °C and form an eutectic mixture with other inorganic fillers and residues such as silica.8-10 According to the fluxing mechanism of these glass fillers, a low melting temperature for most of ceramifiable glass fillers is attributed to the lead oxide. It is well known that the lead oxide is deleterious and may cause heavy metal poisoning and other detriments. Therefore, it is of great importance to develop other efficient and environment-friendly fluxing agents to prepare ceramifiable composites. Phosphates are extensively used as binders in refractory materials, metal protective coatings, and flame retardant systems due to their thermal and chemical stability.11-13 In phosphates, ammonium polyphosphate is an excellent non-halogen flame retardant and widely used in flame-retarding polymer materials. During a thermally decomposing process, it releases small molecules such as NH3 and H2O, and some cross-linking structures

including

polyphosphoric

acid,

etc.14-18

Actually,

the

produced

polyphosphoric acid, inorganic pyrophosphate, and other phosphates may act as sintering aids and adhere other inorganic fillers together, then lead to the formation of a porous and hard ceramic under high temperature.19 Gong et al.20 studied the selfsupporting property of ceramifiable composites via forming Mg3(PO4)2, Mg(PO3)2, and a-Mg2P2O7 crystalline phases on the basis of APP and magnesium hydroxide at high temperature. Although the decomposition of ammonium polyphosphate may contribute to the ceramization of ceramifiable composites, it could not lead to the formation of an impact 4


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and strong ceramic at high temperatures when it is used as a fluxing agent alone. To improve the mechanical properties of a formed ceramic, the addition of synergistic sintering aids is an efficient method, including CaO, P2O5, ZnO, SiO2, and B2O3.21-25 ZB is a typical synergistic flame retardant in fire-safety materials, it releases H2O and absorb the heat during burning.26-27 Moreover, it may form a glass ceramic layer at high temperature and deter the heat transmission.28-29 However, a flaw of ZB is that the resulting ceramic is not continuous and its mechanical properties are poor, so it is not an ideal fluxing agent when it is used alone.30-31 In current work, a novel fluxing agent APP/ZB was developed on the basis of their characteristics of thermal decomposition and used to achieve the highly efficient flame retardance and ceramization of MP-based EVA composite. The reason why the EVA was chosen is as follows. In current cables and wires field, EVA is widely used as the sheath for special cables and wires. In this work, the flame-retarding and ceramifiable polymer composites has a potential in cables and wires because of their excellent firesafety performance via a ceramization process under fire conditions. Therefore, EVA was chosen as the polymer matrix. Furthermore, the ceramics and decomposing behaviors of MP-based EVA composite containing APP/ZB were studied through different measurements. More importantly, the possible fluxing mechanism of a joint APP/ZB at high temperature was discussed in detail. 2. Experimental section 2.1. Materials 5



EVA (Elvax 260, 28% of vinyl acetate) was produced by DuPont Company (USA). Commercial APP (form II) was supplied by Taifeng Fire Retardants Co., Ltd (China). Commercial ZB was purchased from Taixing Fire Retardants Co., Ltd (China). Commercial MP was purchased from Huashuo Mineral Products Processing Factory (China), which consists of Fe2O3+TiO2+MaF2 (4.5%), K2O (11.8%), Al2O3 (38.5%), SiO2 (45.2%), and minor oxides. The OMMT (I.44P) was purchased from Nano Co. Ltd. (USA). 2.2. Sample preparation Table 1 shows the formulation of ceramifiable EVA composites. Here, the weight percentage of EVA, MP, and OMMT was maintained at 55/17/5, which was discussed in our previous work.32 First, all the raw materials were dried at 60 °C for 10 h in a vacuum oven. Then, the EVA composites with different weight ratios of additives were blended by a twin-screw extruder (Kebeilong Keya Nanjing Machinery Co., Ltd, China), and then pressed into different samples by a plate vulcanizer (Qingdao Yadong Rubber Machinery Co. Ltd. China) at 170 °C for different tests. The formed ceramics were prepared by a muffle furnace (KSL-1200X, Hefei Kejing Material Technology Co. Ltd., China) at the treating temperature of 800, 900 or 1000 °C for half an hour using the composites samples with the dimension of 90.0 mm  5.0 mm  3.2 mm. The preparation of the residue of APP/ZB for thermal expansion coefficient test is as follows. The APP and ZB powders were first mixed uniformly, then the mixture was pressed into a cylindrical rubber tube with 8.0 cm length and 0.5 cm diameter. Afterwards, both 6


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ends of the rubber tube were blocked up by glass rods. Finally, the rubber tube which was filled with APP/ZB was treated at 800 oC for 30 min. The resulting product was a cylinder with 5.2 cm length and 0.5 cm diameter. Table 1. Formulation of the composites. Composition*

EV

APP

ZB

MP

OMMT Ceramic#

A

/phr

/phr

/phr

/phr

0

17

/phr EVA/MP/OMMT

55

0

5

ceramic(0, 800), ceramic(0, 900) ceramic(0, 1000)

EVA/MP/OMMT/

55

0

23

17

5

ZB

ceramic(ZB, 1000)

EVA/MP/OMMT/

55

23

0

17

5

APP EVA/MP/OMMT/

EVA/MP/OMMT/

55

11.5

11.5

17

5

ceramic(1:1, 800), ceramic(1:1, 900) ceramic(1:1, 1000)

55

9.9

13.1

17

5

APP/ZB3:4 EVA/MP/OMMT/

ceramic(APP, 800), ceramic(APP, 900) ceramic(APP, 1000)

APP/ZB1:1

ceramic(3:4, 800), ceramic(3:4, 900) ceramic(3:4, 1000)

55

7.7

15.3

17

5

APP/ZB1:2 *The

ceramic(ZB, 800), ceramic(ZB, 900)

ceramic(1:2, 800), ceramic(1:2, 900) Ceramic(1:2, 1000)

ratios at the lower right corner represent the ratio of APP/ZB.

7



#The

first part in the brackets represents the category of fluxing agent or the ratios of

APP/ZB and the “0” illustrates there is no fluxing agent in the composite; the second part in the brackets represents the ceramization temperature. 2.3. Measurements Tensile test was performed on a CMT2000 machine (China) according to the procedures in GB/T 1040.3-2006 under a speed of 20 mm/min. All specimens are the dumbbell with the dimension of 50 mm  4 mm  1 mm. The flexural strengths of ceramics were measured according to the procedure in GB 6569-2006 via the 3-point bend method on a testing machine (CMT2000, SANS Inc., China), and the loading rate was 0.5 mm/min. The surface morphologies of all samples were observed using a JSM 5900LV scanning electron microscopy (SEM) which was produced by JEOL (Japan) under an accelerating voltage of 5 kV. The digital photos for ceramics were taken by a D3200 digital camera (Nikon, Japan). Thermal expansion coefficient test was performed by a DIL402C thermal dilatometer (NETZSCH, Germany) with a heating rate of 10 °C/min in nitrogen atmosphere and the temperature range was from 25 to 700 °C. Fourier transform infrared spectroscopy (FTIR) spectra were measured in the wave number range of 4000~400 cm-1 using KBr disks through a 170SX FTIR spectrometer (Nicolet, USA). Limited oxygen index (LOI) values were measured by an HC-2C oxygen index instrument (Jiangning, China) according to ASTM D2863-97. The dimension of sheets is 130 mm × 6.5 mm × 3.2 mm. The flammability of samples was measured by a cone calorimeter device (Fire Testing Technology, UK), and samples 8


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with the dimension of 100 mm × 100 mm × 3 mm were exposed to a radiant cone under a heat flux of 50 kW/m2. The dilatometric experiment and thermal gravimetric analysis (TGA) test were respectively performed on a Model DIL 402 horizontal dual-rod dilatometer and a 209F1 thermogravimetric analyzer under a heating rate of 10 °C/min, and both instruments were produced by NETZSCH (Germany). In TGA test, the nitrogen flowing rate was 50 ml/min and the temperature range was from 40 to 700 °C. The pyrolysis-gas chromatography/mass spectrometer (Py-GC/MS) test was performed in a pyrolyzer (CDS5200). The pyrolysis chamber was under helium atmosphere, the samples (500 μg) were heated from ambient temperature to 530 °C at a rate of 1000 °C/min and kept for 10 s. The pyrolyzer was coupled with DANI MASTER GCTOF-MS systems, and the carrier gas was helium. The MS indicator was operated in the electron impact mode at electron energy of 70 eV, and the temperature of the ion source was kept at 180 °C. The detection of mass spectra was carried out using a NIST library. X-ray diffraction (XRD) test was performed under 0.06o/s from 5o to 90o on a DX-1000 CSC power diffractometer (Dandong Fangyuan Instrument Co., Ltd, China), and the radiation was from the Cu Ka. Solid-state 31P nuclear magnetic resonance (NMR) analysis was performed on an AVANCEⅢ400 MHz spectrometer (Bruker Corp., Germany) under a spinning speed of 12000 Hz. Additionally, the relative chemical shift spectra of 31P were referred to that of 85% phosphoric acid which was set at 0 ppm. Xray photoelectron spectroscopy (XPS) test was conducted on a XSAM80 instrument (Kratos Corp., UK) with the Al-Ka excitation radiation (hν-1486.6 eV). 9



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3. Results and discussion 3.1 Mechanical properties of ceramifiable EVA composites and its ceramics 3.1.1 Mechanical properties of ceramifiable EVA composites First, it must be noted that both MP and OMMT play an important role in forming a ceramic. The optimal amounts and functions of MP and OMMT in the ceramifiable composites were discussed in a previous report.32 In this work, the weight ratio of EVA/MP/OMMT was maintained at 55/17/5. The mechanical properties of ceramifiable EVA composites were measured through tensile test, and the result is shown in Table 2. For pure EVA, the tensile strength is 11.6 MPa; the elongation at break is 562.8%; the elastic modulus is 3.2 MPa. When OMMT and ceramifible filler MP were added in EVA, both tensile strength and elastic modulus declined slightly, while the elongation at break was enhanced greatly. When APP or ZB was added in the EVA/MP/OMMT. The three performances mentioned above were deteriorated to some extent. However, the APP/ZB with a certain weight ratio was incorporated into the EVA/MP/OMMT. The mechanical properties of EVA/MP/OMMT/APP/ZB system were maintained at a higher level than that of EVA/MP/OMMT/APP,

but

no

obvious

EVA/MP/OMMT/ZB.

Moreover,

the

advantage

compared

elongations

at

to

that

break

of for

EVA/MP/OMMT/APP/ZB system are lower than that of EVA/MP/OMMT/ZB. Interestedly, the elastic moduli of EVA/MP/OMMT/APP/ZB are significantly higher than that of EVA/MP/OMMT/APP or EVA/MP/OMMT/ZB. When the APP/ZB was 10


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from 1/1 to 1/2, the mechanical properties of EVA/MP/OMMT/APP/ZB system have no obvious change. Table 2. Mechanical properties of ceramifiable EVA composites. Composition

Tensile strength

Elongation at

Elastic modulus

(MPa)

break (%)

(MPa)

Neat EVA

11.6±1.4

562.8±33.8

3.2±0.3

EVA/MP/OMMT

8.7±0.4

948.6±49.0

0.8±0.1

EVA/MP/OMMT/ZB

6.5±0.9

910.6±55.9

35.3±1.6

EVA/MP/OMMT/APP

4.8±0.2

649.4±53.6

0.6±0.1

EVA/MP/OMMT/APP/ZB1:1

6.4±0.4

681.8±37.3

52.7±4.3


7.5±1.3

759.1±58.9

56.9±0.8


6.9±0.9

678.4±66.1

59.4±6.6

3.1.2 Mechanical properties of the ceramics of ceramifiable EVA composites Table 3 shows the flexural strengths and modulus of different ceramics. For EVA/MP/OMMT, flexural strengths of its ceramics formed at 800, 900, and 1000 oC are less than 1 MPa, and the maximum flexural modulus is about 18.6 MPa. For the ceramifiable EVA composites with individual APP or ZB as fluxing agent, their ceramics formed at the three temperatures are higher than the corresponding values of the ceramics of EVA/MP/OMMT. Generally, the flexural strength higher than 10 MPa is a prerequisite in the practical application of a ceramic during a fire for cables and wires.32-33 So the ceramics for EVA/MP/OMMT/ZB and EVA/MP/OMMT/APP 11



systems are not ideal. After incorporation of different ratios of APP/ZB into the EVA/MP/OMMT, the ceramics with different flexural strengths were formed at 800 oC.

For the EVA/MP/OMMT/APP/ZB3:4 system, the flexural strength and modulus of

ceramic(3:4, 800) are about 5.7 and 374.7 MPa, both higher than that of the ceramic(1:1, 800) or ceramic(1:2,

800).

After further increasing the temperature to 900 oC, the flexural

strengths of the ceramic(3:4,

900)

and ceramic(1:2,

900)

achieved to 10.3 and 15.6 MPa,

higher than 10.0 MPa. Meanwhile, their flexural moduli were 723.2 and 1295.5 MPa, respectively. For EVA/MP/OMMT/APP/ZB1:1, the flexural strength and modulus of the ceramic(1:1,

900)

are about 4.7 and 340.0 MPa. Apparently, the flexural strength and

modulus of the formed ceramic increased with raising the content of ZB in APP/ZB under the ceramization temperature of 900 oC, which might be ascribed to the decomposition products such as B2O3 and ZnO.28-29 When the temperature was increased to 1000 oC, all the ceramics of ceramifaible EVA composites with three ratios of APP/ZB achieved the flexural strength higher than 10 MPa. Remarkably, the effect of the ratio of APP/ZB on the flexural strength of the formed ceramic became more intensive under the ceramization temperature of 1000 oC for ceramifiable EVA composites. Moreover, the flexural modulus of ceramic(3:4, 1000) attained 1436.1 MPa. According to the mechanical test result, it is known that the ratio of the APP/ZB has a remarkable effect on the ceramization of EVA/MP/OMMT/APP/ZB composites. Moreover, the APP/ZB (3:4 or 1:2) led to the formation of a ceramic with a flexural strength higher than 10.0 MPa under 900 oC for EVA/MP/OMMT composite. Therefore, 12


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the APP/ZB should be an efficient fluxing agent for the ceramizaiton of EVA/MP/OMMT composite. Table 3. Flexural strengths of the ceramics formed at different temperatures. Composition

Flexural strength (MPa)/ Flexural modulus (MPa)

EVA/MP/OMMT

EVA/MP/OMMT/ZB

EVA/MP/OMMT/APP




800 oC

900 oC

1000 oC

0.1±0.0/

0.4±0.1/

0.5±0.1/

0.4±0.1

6.0±1.3

18.6±2.7

1.5±0.1/

1.4±0.3/

3.7±0.5/

65.7±6.2

113.3±7.0

262.5±42.9

1.3±0.4/

1.5±0.3/

1.2±0.1/

50.3±8.6

84.7±6.3

76.3±5.2

1.5±0.4/

4.7±1.2/

12.4±3.3/

60.0±9.4

340.0±62.5

1023.0±91.7

5.7±1.1/

10.3±1.0/

21.2±4.2/

374.7±24.0

723.2±112.7

1341.6±76.2

3.8±0.7/

15.6±4.9/

25.1±6.3/

167.9±21.1

1295.5±113.5

1436.1±227.3

3.2 Morphologies and microstructures of the formed ceramics Analysis on the morphologies of the formed ceramics may directly illustrate the effect of APP/ZB on the ceramization of EVA/MP/OMMT. First, the ceramics formed 13



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at different temperatures for EVA composites were analyzed through their digital photos. Fig. 1 shows that the ceramics which were formed at 800, 900 and 1000 °C are fragile

and

loose

for

EVA/MP/OMMT,

EVA/MP/OMMT/ZB,

and

EVA/MP/OMMT/APP systems, and obvious bubble-like swelling exists at their surfaces. In addition, the ceramic(ZB, 900) and ceramic(ZB, 1000) have apparent deformation for EVA/MP/OMMT/ZB system. When the APP/ZB was incorporated into the EVA/MP/OMMT, morphologies of the formed ceramics of EVA/MP/OMMT/APP/ZB have no significant difference compared to the morphologies of ceramic(0,

800),

ceramic(ZB, 800), and ceramics(APP, 800). However, a big difference can be found when the ceramization

temperature

EVA/MP/OMMT/APP/ZB

was have

900

and

a

1000

rectangle

°C.

The

shape

ceramics of

of

original

EVA/MP/OMMT/APP/ZB samples. Especially, the ceramic(1:1, 1000) and ceramic(3:4, 1000) have a clear rectangle shape. Moreover, no bubble exists at their surfaces, which contributes to their good mechanical properties. For the change of bubbles in the ceramic with increasing the ceramization temperature, the reason may be explained as follows. During the ceramization process of EVA/MP/OMMT/APP/ZB composite, the volatilization of gas was affected by the ceramic melt. With increasing the ceramization temperature, the viscosity of ceramic melt decreased, which contributed to the volatilization of gas and then resulted in the decrease of the average size of bubbles.20 Therefore, the final ceramic became more compact. Here, the ceramic(1:2, 1000) has a clear deformation, which should be due to the immigration of OMMT during the 14


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ceramization process.34 The morphologies of samples illustrate that the joint action of APP/ZB affected the ceramizaiton of EVA/MP/OMMT.

Fig. 1 Digital photos of the formed ceramics of ceramifiable EVA composites. The change information for the sizes of ceramics along three typical directions in the three dimensional space are also provided in Table 4. Here, the sizes of ceramics along different directions were confirmed according to the mode shown in Fig. 1. For each sample, five sections were measured to obtain b and c values, and the average value from the five sections was the final size. For instance, the b1 value was obtained through measuring the distance between two parallel planes at section 1, and then b2, b3, b4, and 15



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b5 were obtained through measuring the corresponding distance between two parallel planes, and finally the b value was obtained, which is equal to (b1 + b2 + b3 + b4 + b5)/5. Even though the ceramic was deformed, the b value was also obtained according to the same mode, as shown in the ceramic(ZB,

900)

in Fig. 1. For the c value, it was also

obtained through the above-mentioned mode. In addition, the size of a was obtained according to a simple mode shown in the ceramic(0,

800)

and ceramic(ZB,

900)

Fig. 1.

According to Table 4, three sizes of the ceramics formed at 800 and 900 oC for EVA/MP/OMMT/APP/ZB have a little change at three directions compared to the corresponding

sizes

for

EVA/MP/OMMT,

EVA/MP/OMMT/ZB,

or

EVA/MP/OMMT/APP. With increasing the ceramization temperature, the joint action of APP/ZB affected the three sizes of the formed ceramic more intensively. At 1000 oC, three sizes of ceramic(3:4, 1000) was 57.3 mm  3.9 mm  3.2 mm along three directions, apparently lower than 75.3 mm  4.5 mm  4.0 mm of ceramic(0,

1000).

For

EVA/MP/OMMT/APP/ZB system, three sizes of the ceramic formed at 900 or 1000 oC remarkably reduced with increasing the ratio of ZB. The ceramic(1:2, 1000) was 50.4 mm  3.4 mm  2.4 mm, much lower than 61.7 mm  4.2 mm  3.6 mm of ceramic(1:1, 1000). According to the analysis presented above, it is known that both ceramization temperature and the ratio of APP/ZB have an influence on the compactness of the ceramic formed at high temperature. Table 4. Sizes of the ceramics formed at different temperatures along X, Y, and Z (a  b  c) /mm  mm  mm

Composition 16


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800 oC

900 oC

1000 oC

EVA/MP/OMMT

84.4  5.6 4.3

76.2  4.7 4.5

75.3  4.5  4.0

EVA/MP/OMMT/ZB

78.1  5.5  5.0

66.8  5.2  4.2

60.3  3.5  3.0

EVA/MP/OMMT/APP

77.7  5.3  5.5

76.3  5.2  4.7

70.3  5.1  4.5

EVA/MP/OMMT/APP/ZB1:1 83.2  5.3  4.1

76.6  4.6  3.8

61.7  4.2  3.6

EVA/MP/OMMT/APP/ZB3:4 80.7  5.3  3.7

67.7  4.6  3.1

57.3  3.9  3.2

EVA/MP/OMMT/APP/ZB1:2 79.0  5.1  3.6

60.3  3.6  3.1

50.4  3.4  2.4

According to the mechanical test result, it is known that the formed ceramic(3:4, 900) has a flexural strength higher than 10.0 MPa, corresponding to a lower ceramization temperature than that of the ceramic(3:4,

1000)

or ceramic(1:2,

1000),

and meeting the

application requirement in a fire accident. Therefore, the formed ceramic(3:4, 900) was chosen to analyze in microstructural analysis. For the purpose of comparison, the ceramic(0, 900), ceramic(ZB, 900), and ceramic(APP, 900) were also investigated. Fig. 2a shows that the ceramic(0,

900)

looks very loose, and they is no apparent adhesion between

different blocks, which must be an important reason for its low flexural strength. For the ceramic(ZB, 900) and ceramic(APP, 900), there are a large number of holes, which is in accordance with the digital photos shown in Fig. 1 in which the bubble-like swelling is very clear. Actually, a large amount of holes may deteriorate the mechanical properties of ceramics. For the ceramic(3:4,

900),

there is no obvious stripe gap and only small

amount of small holes exist in the formed ceramic. In addition, no obvious mica plane can be observed, which should be caused by the strong cohesion between mica phase 17



and glassy phase. Evidently, the APP/ZB led to the formation of a glassy and sticky material under 900 °C, leading to a tight adhesion of mica and OMMT. Finally, the integrated ceramic with small amount of small holes was formed due to the fluxing action of APP/ZB.

Fig. 2 SEM micrographs of the ceramic(0, 900) (a1, a2, a3), ceramic(ZB, 900) (b1, b2, b3), ceramic(APP, 900) (c1, c2, c3), and ceramic(3:4, 900) (d1, d2, d3). 3.3 Combustion performance of ceramifiable EVA composites The LOI results of neat EVA and EVA composites are shown in Table 5. Both neat EVA and EVA/MP/OMMT are easily flammable, and their LOI values are 19.0% and 20.5%, respectively. When ZB was incorporated into EVA/MP/OMMT, its LOI raised 18


Page 18 of 44

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to 21.4%, indicating that the ZB had an influence on the flammability of EVA/MP/OMMT; when APP was added in EVA/MP/OMMT, its LOI value remarkably increased to 25.7%, showing an obvious increase. For the EVA/MP/OMMT composites with different ratios of APP/ZB, their LOI values are higher than that of neat EVA or EVA/MP/OMMT, which are 23.6%, 24.0% and 24.3% for

the

corresponding

and

EVA/MP/OMMT/APP/ZB1:2,

EVA/MP/OMMT/APP/ZB3:4,

EVA/MP/OMMT/APP/ZB1:1. Obviously, the APP/ZB promoted the flame retardancy of EVA/MP/OMMT composites although the LOI value of EVA/MP/OMMT/APP/ZB slightly decreased with reducing the APP. Table 5. The LOI results of neat EVA and EVA composites Composition

LOI (%)

Neat EVA

19.0

EVA/MP/OMMT

20.5

EVA/MP/OMMT/ZB

21.4

EVA/MP/OMMT/APP

25.7


23.6


24.0


24.3

The digital photos shown in Fig. 3 illustrated the burning process of EVA/MP/OMMT and EVA/MP/OMMT/APP-ZB3:4 under the LOI of 24.0%. For the EVA/MP/OMMT system, its burning was quite intensive, and the flame reached to the 19



mark at 5 cm at about 120 s. When APP/ZB was incorporated into the EVA/MP/OMMT, the flame retardancy was remarkably enhanced. It can be seen that the flame gradually developed during 15~60 s, then the burning became weaker and even extinguished at 120 s. According to the burning test result shown in Fig.3, it is concluded that that the APP/ZB greatly promoted the flame retardancy of EVA/MP/OMMT.

Fig. 3 Digital photos of EVA/MP/OMMT (a) and EVA/MP/OMMT/APP-ZB3:4 (b) composites under the LOI of 24.0%. Cone calorimeter test is an effective method to analyze the combustion behavior of flame-retarding polymeric materials. Here, four typical samples are chosen to assess the combustible behaviors of ceramifiable EVA composites, including neat EVA, EVA/MP/OMMT/ZB, EVA/MP/OMMT/APP and EVA/MP/OMMT/APP/ZB3:4. The 20


Page 20 of 44

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cone calorimeter result is shown in Fig. 4 and Table 6. Compare to neat EVA, the times to ignition for the other three systems were slightly prolonged, illustrating the fire safety of the three systems is higher than that of neat EVA. Cone calorimeter result confirmed that neat EVA was flammable. After the ignition, a very sharp peak of heat release rate (PHRR) of 1355.6 kW/m2 appeared at about 150 s, and its total smoke production (TSP) and total heat release (THR) were 13.2 m2 and 116.5 MJ/m2, respectively. For EVA/MP/OMMT/ZB, the PHRR and THR were 231.7 kW/m2 and 84.8 MJ/m2 respectively. For EVA/MP/OMMT/APP system, the PHRR and THR were 250.9 kW/m2 and 84.1 MJ/m2, respectively. Obviously, both PHRR and THR values of EVA/MP/OMMT/ZB

and

EVA/MP/OMMT/APP

decreased

significantly

in

comparison with the corresponding values of neat EVA. However, the TSP values of EVA/MP/OMMT/ZB and EVA/MP/OMMT/APP were 16.5 and 22.6 m2, higher than that of neat EVA, which should be due to the dehydration of ZB and gas release of APP. When APP/ZB3:4 was incorporated into EVA/MP/OMMT, its PHRR reduced to 179.6 kW/m2, decreased by 86.7% compared with that of neat EVA, and it is also much lower than that of EVA/MP/OMMT/ZB or EVA/MP/OMMT/APP. Due to the longer combustion time during cone calorimeter test, the THR of EVA/MP/OMMT/APP/ZB3:4 did not show significant decrease compared to that of EVA/MP/OMMT/ZB or EVA/MP/OMMT/APP. However, the TSP of the former is lower than the corresponding values of the latter two systems. Obviously, the APP/ZB3:4 exhibited higher efficiency in reducing the smoke release of EVA/MP/OMMT than APP or ZB. 21



Page 22 of 44

Fig. 4 Cone calorimetric cures of EVA and ceramifiable EVA composites, HRR (a), THR (b), and SPR (c). Table 6. Cone calorimetric data of neat EVA and ceramifiable EVA composites. Neat

EVA/MP/

EVA/MP/

EVA/MP/OMMT

EVA

OMMT/ZB

OMMT/APP /APP/ZB3:4

TTI (s)

31

42

39

39

THR (MJ/m2)

116.5

84.8

84.1

86.9

PHRR (kW/m2)

1355.6

231.7

250.9

179.6

TSR (m2/m2)

1490.2

1867.8

2561.2

1694.4

TSP (m2)

13.2

16.5

22.6

15.0

Residue (%)

2.2

45.9

36.7

40.5

Composition

Digital photos of the residues of neat EVA and ceramifiable EVA composites are shown in Fig. 5. There is no left residue for neat EVA after the combustion test. However, the typical char layer was formed after incorporation of the MP/OMMT/ZB, MP/OMMT/APP, and MP/OMMT/APP/ZB. Moreover, the residual char layers have obvious differences for the three systems. For the residue of EVA/MP/OMMT/ZB composite, obvious gaps and many cracks exist in the char layer, illustrating the poor 22


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continuity. For EVA/MP/OMMT/APP, the residue looks continuous. However, it is loose and porous. Although there are some cracks for the residue of EVA/MP/OMMT/APP/ZB3:4, the residue is much more rigid and continuous than that of EVA/MP/OMMT/ZB composite, which contributes to protecting the underlying materials from burning. According to the past report,28 the formed ceramic-like rigid residue improved the flame retardance of polymer composites when the ZB existed in the composites. Obviously, the ZB played a typical condensed role during the burning of EVA/MP/OMMT/APP/ZB3:4. In addition, the digital photos shown in Fig. 5 illustrate

that

the

APP

facilitated

the

continuity

of

the

residue

of

EVA/MP/OMMT/APP/ZB3:4. In the past reports,35-36 it was confirmed that the APP decomposed to phosphoric acid, polyphosphoric acid, and metaphosphoric acid, leading to the formation of continuous char layer. For the EVA/MP/OMMT/APP/ZB3:4, the enhanced continuity of the residue must be related to the APP. On the basis of the analysis presented above, a synergistic action between APP and ZB enhanced the flame retardance of EVA/MP/OMMT/APP/ZB3:4.

Fig. 5 SEM micrographs of the residues obtained from CC test: (a) EVA,(b) EVA/MP/OMMT/ZB, (c) EVA/MP/OMMT/APP and (d)

23



EVA/MP/OMMT/APP/ZB3:4. To know about the main breakthrough of this work, we compared the performance of typical polymer-based composites in previous related research with that in our work, and the result is shown in the following Table 7. The common characteristic of these typical systems and the prepared EVA/MP/OMMT/APP/ZB in this work is that they are ceramifiable systems without traditional fluxing agent. According to Table 7, for the SiR/K2O/MgO/Al2O3/SiO2,6 SiR/mica/peroxide and SiR/mica A/mica B/peroxide composites,4 they have poor ceramifiable performance, showing low flexural strengths for their ceramics formed at different high temperatures. Almost all of these ceramics formed in the temperature range from 600 to 1000 °C have flexural strengths lower than 1.0 MPa. For the SiR/DCBP/APP/MH,20 it has a better ceramifiable performance than the three system mentioned above. However, the flexural strengths of ceramics formed at 800 and 1000 °C for SiR/DCBP/APP/MH are lower than the corresponding values in our work. In addition, the SiR/K2O/MgO/Al2O3/SiO2, SiR/mica/peroxide, and SiR/mica A/mica B/peroxide composites mentioned above did not show typical flameretarding characteristic. In Mansouri and co-workers’s work,3 the prepared siliconebased ceramifiable composite showed an obvious decrease in the peak of heat release rate. However, the flexural strength of the formed ceramic for the silicone-based ceramifiable composite was only 3.2 MPa at 1050 °C. In our work, EVA/MP/OMMT/APP/ZB showed an obvious flame-retarding feature and its ceramic formed at high temperature was over 10.0 MPa, much higher than 3.2 MPa. Therefore, 24


Page 24 of 44

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the main breakthrough of this work is that the joint action of a well-designed novel composition “APP/ZB” achieved simultaneously excellent flame retardancy and ceramifiable performance of polymer-based composites. Table 7. Flexural strengths of the ceramics formed at high temperatures. Composition

Flexural strength of the ceramic (MPa) 600 °C

700 °C

800 °C

900 °C

≥1000 °C

SiR/ K2O/MgO/Al2O3/SiO2

0.3

-

0.8

-

-

SiR/mica/peroxide

-

-

0.34

-

0.64

SiR /mica A/mica B/peroxide

0.12

0.42

-

0.93

SiR/DCBP/APP/MH

-

3.0

4.0

-

6.5

SiR/Mica/DCP

-

-

-

-

3.2

This work

-

-

5.7±1.1

10.3±1.0

21.2±4.2

“-” means there is no the corresponding result in the work. 3.4 The thermally decomposing behaviors of neat EVA and its composites First, the TGA was performed to illustrate the effect of APP/ZB on the thermally decomposing behavior of EVA/MP/OMMT, and the result is shown in Fig. 6a and Table 8. Fig. 6a shows that there were two thermal decomposing steps for neat EVA. The first and second decomposition steps respectively occurred at 300~400 °C and 400~500 °C. The first decomposition is attributed to the scission of carbon–carbon bond along the backbone and the loss of gaseous acetic acid. The second decomposition step is due to the volatilization of the formed carbonaceous residue and the scission of 25



Page 26 of 44

unsaturated chains.37 For pure EVA, the initial decomposing temperature (the decomposing temperature at 5.0 wt% weight loss, T5%) occurred at 337 °C, the first and second maximum weight losses occurred at 326 °C (TMax1) and 470 °C (TMax2), respectively. When increasing the temperature to 700 °C, there was only 0.5 wt% residue. Fig. 6a shows that EVA composites experienced a similar thermally decomposing process to neat EVA. For EVA/MP/OMMT system, the T5% declined slightly compared to that of neat EVA, but both TMax1 and TMax2 increased, which should be attributed to the incorporation of MP/OMMT.37-39 When the ZB or APP was incorporated into EVA/MP/OMMT alone, both ceramifiable composites showed a similar thermal decomposition process. Both T5% values of EVA/MP/OMMT/ZB and EVA/MP/OMMT/APP are slightly higher than that of EVA/MP/OMMT, and their TMax1, TMax2, and residues at 700 °C are also a little higher than the corresponding values of EVA/MP/OMMT. When the joint APP/ZB was incorporated into the EVA/MP/OMMT, the T5% of EVA/MP/OMMT/APP/ZB further decreased. However, their TMax1 and TMax2 have a little promotion compared to the corresponding values of EVA/MP/OMMT/ZB or EVA/MP/OMMT/APP. In addition, the residue of EVA/MP/OMMT/APP/ZB

is

also

higher

than

that

of

EVA/MP/OMMT,

EVA/MP/OMMT/APP, or EVA/MP/OMMT/ZB. Obviously, a joint APP/ZB affected the decomposing behavior of EVA/MP/OMMT.

26


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Fig. 6 TGA (a) and DTG (b) curves of neat EVA and EVA composites under N2.

Table 8. TGA data of EVA and ceramifiable EVA composites under N2. Composition (phr)

T5%

TMax1

TMax2

Residues at

(oC)

(oC)

(oC)

700 oC (wt %)

EVA

337

326

470

0.5

EVA/MP/OMMT

328

341

472

25.5

EVA/MP/OMMT/ZB

334

342

480

37.7

EVA/MP/OMMT/APP

331

342

478

35.8


328

345

484

39.1


328

342

482

38.1


327

346

483

37.9

To

further

illuminate

the

thermal

decomposition

process

of

EVA/MP/OMMT/APP/ZB, the Py-GC/MS test was performed for neat EVA and EVA/MP/OMMT/APP/ZB3:4, and the results are shown in Fig. 7 and Table 9. First, it should be pointed out that the pyrolysis temperature was 530 oC (about 50 oC higher 27



than the maximum decomposing temperature of EVA/MP/OMMT/APP/ZB3:4 composite). For neat EVA, more than fourteen kinds of pyrolysis products were detected, mainly including acetic acid, long chain alkanes, and alkenes, corresponding to the peak 1, 3~13, and 15, which are ascribed to the scission of carbon–carbon bond along the backbone, the loss of gaseous acetic acid, the volatilization of the formed carbonaceous residue, and the scission of unsaturated unsaturated chains.40 Attributing to the detection limit of the instrument is higher 30 of m/z, some small molecules like NH3 and H2O decomposed from APP and ZB were not detected, which contributed to the enhancement of flame retardance.16,

41

For EVA/MP/OMMT/APP/ZB3:4 system,

peak 2 is ascribed to the ammonium acetate, which should be from the decomposition of EVA and APP. Fig. 7 shows that the peak 3~10 disappeared for EVA/MP/OMMT/APP/ZB3:4 composite, which should be caused by the carbonization process between polyphosphoric acid and polymer matrix, the scission of carbon– carbon bond along the backbone, and the loss of gaseous acetic acid for EVA. In addition, the long chain alkenes for the peak 11, 14, 16~17, and the pyrolysis products for the peak 18~20 were from the scission of unsaturated chains and the volatilization of the formed carbonaceous residue.

28


Page 28 of 44

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Fig. 7 Pyrograms of neat EVA and EVA/MP/OMMT/APP/ZB3:4. Table 9. Compounds identiﬁed from the pyrograms of neat EVA and EVA/MP/OMMT/APP/ZB3:4 Retention time Peak

m/z

Compounds

Assigned structure

(min) O

1

1.21

60

Acetic acid OH O

2

1.34

77

Ammonium acetate

3

2.36

112

Octane

4

3.70

126

1-nonene

5

4.98

140

1-decene

6

6.14

154

1-undecene

7

7.18

168

1-dodecene

8

8.14

182

1-tridecene 29


H O

H N

H H


9

8.95

146

1,11-dodecadiene

10

9.89

252

l-octadecene

11

10.66

136

5-tetradecene

12

10.81

194

1,13-tetradecadiene

13

11.50

222

1,15-hexadecadiene

14

12.05

358

Eicosane

15

12.11

266

1-nonadecene

16

12.91

198

Tetradecane

17

13.73

308

1-docosene

Page 30 of 44

Ndimethylaminomethyl18

14.19

N

189

P

tert-butylisopropylphosphine Carbonic acid, 219

15.65

106

diethylaminoethyl ethyl

o

o

N

o

ester Phthalic acid, 4O

20

16.76

362

O

methylpent-2-yloctyl

O O

ester 3.5 Thermal expansion coefficient of the formed ceramic To investigate the ceramization process, the thermal expansion coefficients of the 30


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residue of APP/ZB and the ceramic(3:4, 1000) were analyzed. Here, the ceramic(3:4, 1000) was chosen as a representative to analyze the effect of APP/ZB on the thermal expansion coefficient of ceramic. In addition, the residue of APP/ZB was formed at 800 oC.

Fig. 8a shows that the thermal expansion coefficient almost increased linearly with

raising the temperature to 600 oC and then reached a softening temperature of about 657.2 °C. With further increasing the temperature, the ceramic deformed and yielded. Finally, the thermal expansion coefficient began to decrease linearly. For the ceramic(3:4, 1000)

shown in Fig. 8b, its ceramic showed a softening temperature of 662.6 oC, near to

657.7 °C of the residue of APP/ZB. According to previous reports,38, 42 both MP and OMMT have a softening temperature higher than 700 °C. Therefore, the softening of ceramic(3:4, 1000) at 662.6 °C must be caused by the yielding of the residue of APP/ZB. This result directly illustrates that the joint APP/ZB affected the thermally decomposing behaviors of EVA/MP/OMMT, and its fluxing behavior might occur below 662.6 oC. In combination with the SEM result, the fluxing action of APP/ZB led to the formation of a glassy and sticky materials at high temperature, and then it adhered other inorganic fillers together to form a ceramic.

Fig. 8 The thermal expansion coefficients of the residue of APP/ZB (a) and the 31



ceramic(3:4, 1000) (b). 3.6 Flame-retardance and ceramization mechanisms of EVA/MP/OMMT/APP/ZB To further know the effect of APP/ZB on the flame retardance and ceramization of EVA/MP/OMMT, the FTIR, XRD, and Solid-state 31P NMR tests were performed for the residues of APP, ZB, APP/ZB, and formed ceramics of EVA/MP/OMMT and EVA/MP/OMMT/APP/ZB3:4 composites. Fig. 9a shows that the FTIR spectra of the residues of APP, ZB, and APP/ZB. For the residue of APP, the peak at 3418 cm-1 is assigned to the vibration of -OH in P-OH, the peak at 914 cm-1 is attributed to the vibration of P-O bond. For the residue of ZB, two peaks at 1371 and 714 cm-1 are ascribed to the stretching vibration of B-OH and BO respectively.43 When the APP/ZB experienced a thermal process at 1000 oC, the vibration of its residue at 1197, 1094 and 637 cm-1 belongs to the absorbance of PO43tetrahedron in phosphates.20 For EVA/MP/OMMT/APP/ZB3:4, the FTIR spectra of the ceramics which were formed at different temperatures are similar, as shown in Fig. 9b. The peak at 3446 cm-1 corresponds to the vibration of O-H bond; the peaks at 1015 and 799 cm-1 are ascribed to the vibration of Si-O-Si in fluoride mica.32, 44 The characteristic vibration peak at 1015 cm-1 for mica phase weakened gradually with increasing the ceramization temperature, illustrating that more and more bridging oxygen bonds broke in the mica crystal phase during the heating process. For the residue of EVA/MP/OMMT, it can be found that the peak corresponding to the bridging oxygen bonds has no obvious change with increasing the temperature, which is almost 32


Page 32 of 44

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composed of plane mica. In addition, it can be seen that the characteristic vibration peaks at 1099 and 631 cm-1 of PO43- exist in the FTIR spectra of these ceramics. Compared to the loose residue of EVA/MP/OMMT, the formed ceramics of EVA/MP/OMMT/APP/ZB3:4 not only consist of residual mica phase, but also contain the PO43- tetrahedron which is ascribed to phosphates. Obviously, the addition of APP/ZB in EVA/MP/OMMT played a key role in forming the mica-based ceramic. Moreover, a higher ceramization temperature led to the enhancement of the fluxing action of APP/ZB, which may be clearly illustrated by the mechanical test result of ceramics.

Fig. 9 FTIR spectra of the residues of APP, ZB, and APP/ZB (a); FTIR spectra of the ceramics of EVA/MP/OMMT and EVA/MP/OMMT/APP/ZB3:4 (b). The XRD measurement was also used to illustrate the effect of APP/ZB on the ceramization of EVA/MP/OMMT. Fig. 10a shows the XRD result of MP and the ceramics of EVA/MP/OMMT and EVA/MP/OMMT/APP/ZB3:4. Typical diffraction peaks of MP can be seen in its XRD pattern. The diffraction peaks of these formed ceramics have no obvious difference with changing the ceramization temperatures. The 33



typical diffraction peaks of ceramic(0, 800), ceramic(0, 900), ceramic(0, 1000) are similar to that of MP, illustrating that there is mainly the residual MP phase after a ceramization process for EVA/MP/OMMT. Comparing the ceramics of EVA/MP/OMMT and those of EVA/MP/OMMT/APP/ZB3:4, some typical diffraction peaks corresponding to the MP became very weak in the ceramics of EVA/MP/OMMT/APP/ZB3:4, and even disappeared with increasing the ceramization temperature to 1000 °C. Moreover, some new peaks (as marked by stars) appeared at the 2θ of 20.6o, 21.8o, 23.2o, and 43.1o except for some peaks of MP in the ceramics of EVA/MP/OMMT/APP/ZB3:4, ascribing to the α-Zn3(PO4)2 glass and orthophosphate which could act as agglomerant and cohere other inorganic fillers together to form ceramics.20, 45 Solid-state 31P NMR test was used to further illustrate the formation of α-Zn3(PO4)2 glass and orthophosphate in the ceramic of EVA/MP/OMMT/APP/ZB3:4. In Fig. 10b, the spinning sidebands are marked by stars (*), which are ascribed to the isotropic chemical shift of 31P. In Fig. 10b, the narrow two peaks at about -1.7 and -4.5 ppm are attributed to the α-Zn3(PO4)2 and orthophosphate, respectively.45 Obviously, the chemical reaction between APP and ZB occurred under high temperature. The reaction process may be explained as follows. First, the polyphsosphoric acid was produced during the pyrolysis of APP. Then, the formed acid solubilized the ZB. Successively, a chemical reaction occurred between the polyphsosphoric acid and ZB. Finally, both α-Zn3(PO4)2 and orthophosphate were formed.

34


Page 34 of 44

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Fig. 10 XRD result of the ceramics of EVA/MP/OMMT and EVA/MP/OMMT/APP/ZB3:4 (a); 31P NMR spectra of the ceramic(3:4, 1000) (b). The XPS result was also used to further illustrate the effect of APP/ZB on the ceramization of EVA/MP/OMMT/APP/ZB3:4. In Fig. 11a, the P2p peaks at 134.5 and 135.6 eV correspond to the PO4 and P2O5, illustrating that the APP participated in the ceramization process. Meanwhile, the Zn2p peaks at 1022.9, 1023.7, and 1046.5 eV exist for the ceramic(3:4,

1000),

indicating that the ZB was also involved in the

ceramization process. Moreover, the binding energies of P2P (134.5 eV) and Zn2p (1023.7 eV) are attributed to the α-Zn3(PO4)2 glass, further demonstrating both APP and ZB might melt and then lead to an eutectic mixture with MP and OMMT.46-47

Fig. 11 XPS P2p (a) and Zn2p (b) spectra of the ceramic(3:4, 1000). 35



According to the TGA, Py-GC/MS, FTIR, XRD, XPS, Solid-state

Page 36 of 44

31P

NMR, and

thermal expansion coefficient tests, the effects of the crystalline phase on the flame retardance and ceramization of EVA/MP/OMMT/APP/ZB are concluded as follows. As shown in Scheme 1, the APP/ZB first decomposed under high temperature and then a glassy and sticky melt was formed, in which a large amount of α-Zn3(PO4)2 glass and orthophosphate were generated during the thermally decomposing process. The formed melt cohered the MP, OMMT, and other residues together on the basis of its fluxing action, and a resulting eutectic reaction also occurred during this period, in which all the MP, OMMT, APP, ZB, and EVA were involved. Finally, a ceramic was formed after the complicated thermal reaction, leading to the improved flame retardance and ceramifiable property of EVA/MP/OMMT/APP/ZB in comparison with that of EVA/MP/OMMT.

Scheme 1 The ceramization process of EVA/MP/OMMT/APP/ZB. 4. Conclusions In this work, a joint APP/ZB as a novel sintering aid was developed to achieve the highly efficient flame retardance and ceramization of EVA/MP/OMMT composite. With increasing the ceramization temperature, the mechanical properties of the formed ceramics gradually increased for EVA/MP/OMMT/APP/ZB composites, the ceramic(3:4, 36


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900)

reached the flexural strength of 10.3 MPa, meeting the practical application in a fire

accident. Meanwhile, the fire safety of EVA/MP/OMMT was enhanced after incorporation of the APP/ZB. Furthermore, TGA, Py-GC/MS, thermal expansion coefficient, FTIR, SEM, XRD, Solid-state 31P NMR, and XPS tests confirmed that the joint APP/ZB achieved its highly efficient fluxing action during the thermal decomposition process. The analysis of flame-retardance and ceramization mechanisms revealed that both APP and ZB led to the glass melt containing α-Zn3(PO4)2 and orthophosphate under high temperature, which adhered the OMMT, residual mica, and other residues together. A following typical eutectic reaction led to the generation of a ceramic. The APP/ZB has a potential application value in flame-retarding and ceramifiable composites. Acknowledgements Thanks very much for the financial support of NSFC of China (Grant No. 51721091), and the Graduate Student’s Research and Innovation Fund of Sichuan University (2018YJSY085). References (1) Al-Hassany, Z.; Genovese, A.; Shanks, R. A. Fire-retardant and fire-barrier poly(vinyl acetate) composites for sealant application. Express. Polym. Lett. 2010, 4, 79-93. (2) Fan, F.-q.; Xia, Z.-b.; Li, Q.-y.; Li, Z. Effects of inorganic fillers on the shear viscosity and fire retardant performance of waterborne intumescent coatings. Prog. Org. 37



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