Influence of zinc borate on the flame retardancy and thermal stability of intumescent flame retardant polypropylene composites

Influence of zinc borate on the flame retardancy and thermal stability of intumescent flame retardant polypropylene composites

Accepted Manuscript Title: Influence of zinc borate on the flame retardancy and thermal stability of intumescent flame retardant polypropylene composi...

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Accepted Manuscript Title: Influence of zinc borate on the flame retardancy and thermal stability of intumescent flame retardant polypropylene composites Author: Caimin Feng Yi Zhang Dong Liang Siwei Liu Zhenguo Chi Jiarui Xu PII: DOI: Reference:

S0165-2370(15)30095-4 http://dx.doi.org/doi:10.1016/j.jaap.2015.07.019 JAAP 3540

To appear in:

J. Anal. Appl. Pyrolysis

Received date: Revised date: Accepted date:

1-4-2015 28-7-2015 28-7-2015

Please cite this article as: Caimin Feng, Yi Zhang, Dong Liang, Siwei Liu, Zhenguo Chi, Jiarui Xu, Influence of zinc borate on the flame retardancy and thermal stability of intumescent flame retardant polypropylene composites, Journal of Analytical and Applied Pyrolysis http://dx.doi.org/10.1016/j.jaap.2015.07.019 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Influence of zinc borate on the flame retardancy and thermal stability of intumescent flame retardant polypropylene composites Caimin Feng1, 2, Yi Zhang1∗, Dong Liang3, Siwei Liu1, Zhenguo Chi1, Jiarui Xu1 (1. Key Laboratory for Polymeric Composite and Functional Materials of the Ministry of Education, DSAPM Lab, Materials Science Institute, School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou 510275, China; 2. Department of Applied Chemical Engineering, Shunde Polytechnic, Foshan 528333, China; 3. Guangdong Provincial Key Laboratory of Fire Science and Technology, School of Engineering, Sun Yat-sen University, Guangzhou 510275, China) Abstract

The influence of zinc borate (ZB) on the flame retardancy and thermal stability of intumescent flame retardant polypropylene composites (PP/IFR) containing ammonium polyphosphate (APP) and charring-foaming agent (CNCA-DA) were characterized by limiting oxygen index (LOI), UL-94 measurement, cone calorimeter test (CCT), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and thermogravimetry analysis (TGA). The results revealed that a small amount of ZB could effectively improve the LOI value, UL rating of the PP/IFR systems, and reduce the combustion performance of PP/IFR systems from CCT test, including heat release rate (HRR), total heat release (THR), smoke production rate (SPR) and total smoke production (TSP). The catalytic effectivity (CAT-EFF) results showed that when 1% ZB was added to PP/IFR, it had the highest CAT-EFF, and could enhance the LOI value from 27.1 to 30.7. The morphological structures observed by digital photos and SEM indicated that ZB could promote to remain more P and O, and B could participate the connecting reaction to form the more continuous and more compact intumescent char layer on the char surface to hinder heat diffusion and oxygen transmission effectively. The TGA data revealed that ZB could change the degradation behavior of the IFR and PP/IFR, improve the thermal stability of the PP/IFR systems at high temperature and increase the char residue. Keywords: intumescent flame retardancy, polypropylene, thermal stability, synergistic effect, zinc borate 1. Introduction

Polypropylene (PP) occupies large part in the polymer consumption duo to its excellent mechanical properties, low cost and easy processing and good chemical



Corresponding author. Tel.: 0862084112222; fax: 0862084114008. E-mail address: [email protected] (Y. Zhang)

resistance, such as automotive parts, architectural materials, furniture, electric shell and packages. However, its further applications have been limited severely by its flammability and burning with dripping. Therefore, it is imperative to enhance the flame retardancy of PP. In recent years, Intumescent flame retardants (IFR) have aroused a great attention and been considered as most promising candidates to substitute halogen-containing flame retardants due to its environmental-friendly properties, halogen-free, and anti-dripping compared with halogenated flame retardants and metal hydroxides [1-7]. The traditional IFR is composed by acid source, charring source and gas source. The most widely reported IFR systems are comprised by ammonium polyphosphate (APP) and pentaerythritol (PER) systems, and the optimal mass fraction of APP/PER is 3 [8-10]. However, the shortcomings of traditional IFR systems have restricted its application, such as poor flame retardant efficiency relatively to bromine-containing flame retardants, poor compatibility with matrix, lower thermal stability, and water-soluble, and these disadvantages are bad for the long-time flame retardancy. To solve these problems, researchers have made great efforts to develop oligomeric or polymeric IFRs with relatively higher molecular weight and synergistic agent have been sued to enhance the flame retardancy of IFR [11-14]. The previous studies showed that some silicon-containing compounds, boron-containing compound, transitional metal oxides, 4A zeotile, metal compounds could serve as synergistic agents to increase the strength and stability of char layer to enhance the flame retardant performance of the composites [15-23].

The most researches about synergistic effect focused on the traditional IFR systems containing ammonium polyphosphate (APP)/ pentaerythritol (PER) or other char forming agent containing hydroxyl group [15-23]. However, the presentation of hydroxyl group in the IFR would deteriorate compatibility between the flame retardants and the matrix and increase the moisture sensitivity of the composites. Therefore, it is urgent to develop hydroxyl-free flame retardants and investigate the synergistic effect of between some synergistic agents and the hydroxyl-free flame retardants. ZB is used as a flame retardant and smoke suppressant, and the combination of zinc borate with some intumescent flame retardant systems could enhance the char formation and improve the char quality, resulting in the improvement of flame retardancy [24-27]. But there are few references about synergistic effect between ZB and IFR systems without hydroxyl group. In our previously work, a novel oligomeric triazine derivative charring agent (CNCA-DA) containing benzene and triazine ring (Scheme 1), was designed and synthesized in our lab, which was of higher thermal stability, without hydroxyl group and insoluble in water. In our previous work, CNCA-DA has been combined together with APP to form a novel IFR system, which has been proved to have good flame retardancy for PP [28]. Moreover, lanthanum oxide (La2O3) and 4A zeotile showed obvious synergistic effects on the flame retardancy of the PP/IFR systems [29-30]. In this work, ZB was selected to investigate the synergistic effect and mechanism with PP/IFR composite. Its effects on the flame retardancy and thermal degradation of

PP/IFR systems have been evaluated by limiting oxygen index (LOI), vertical burning test (UL-94), cone calorimeter test (CCT), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and thermogravimetry analysis (TGA).

2. Experimental

2.1. Materials Polypropylene (PP) resin (T30S, melt flow rate: 2-5 g/10min) used in this work was produced by Maoming Petroleum Chemical Company. Zinc borate (ZB: 2ZnO·3B2O3·3.5H2O) was offered by Sinopharm Chemical Reagent Co, Ltd, China. Ammonium polyphosphate (APP) was offered by Shenzhen Anzheng Chemicals Company, China. Antioxidant 1010 was produced by Ciba Specialty Chemicals, Switzerland. The charring-foaming agent (CNCA-DA) was synthesized in our laboratory. 2.2. Preparation of flame retardant PP composites The intumescent flame retardant polypropylene composites were fabricated by melt compounding of PP, APP and CNCA-DA or a small amount of ZB at 180 °C in a two-roll mill with a rotor speed of 60 rpm, and a mixing time of 8 min for each sample. Then the composites were pressed on a curing machine for 4 min to produce various thick sheets, which were used to produce various dimension sheets in all tests. For comparison, the pure PP sample was also prepared with the same procedures.

2.3. Flame retardancy tests The flame retardancy of all samples was characterized by limited oxygen index (LOI) and UL-94 methods. LOI data of all samples were carried out in a DRK304B oxygen index instrument (jinan Deruike Instrument Factory) at room temperature with the sample dimension of 130×10×4 mm according to the ISO4589-1984 standard. Vertical burning rates of all samples were measured on a CZF-2 instrument (Jiangning Analysis Instrument Factory), with sample dimensions of 125×12.5×3.2 mm according to the American National Standard UL-94. 2.4 Cone calorimeter test (CCT) The cone data were evaluated by a cone calorimeter performed in an Fire Testing Technology (UK) device in thickness and an incident flux of 35 kW·m-2 according to ISO 5660-1. All samples (100×100×4 mm3) were laid on a horizontal sample holder. The experimental error for all the mentioned parameters is ±10%. 2.5 Thermogravimetry analysis (TGA) tests Thermogravimetric

analysis

(TGA)

was

performed

on

a

TA Q500

thermogravimetric analyzer at a heating rate of 10 °C /min with a scan range from room temperature to 800 °C. In each case, 4-5 mg of the sample was examined under a N2 or air with a flowing rate of 40 mL/min. All thermal degradation data were obtained from the TG and DTG curves. 2.6 Scanning electron microscopy (SEM) Scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS)

were performed by using a FEI Quanta 400 SEM with accelerating voltage was 15 kV. The surface of the char residues which were obtained after cone calorimeter tests was sputter-coated with gold layer before examination.

3 Results and discussions 3.1 Flame retardancy of PP/IFR/ZB composites and catalytic effects of ZB LOI and UL-94 rating are common flammability measure methods. Figure 1 presents the LOI values and UL rating of PP/IFR composites with 20% IFR and different ZB loading. The LOI value of PP, PP/1%ZB, and PP/IFR is 17.0% [28], 17.5% and 27.1%, respectively. The LOI value of PP/IFR composite is 27.1%, and reaches the UL-94 V-O rating. It can be found that the LOI values firstly increases rapidly with increasing the amount of ZB in the PP/IFR composites, but these values decreases slightly with more than 2% ZB loading. When the ZB loading is 2%, the LOI value of the PP/IFR composite reaches the maximum of 32.2%, and passes the UL-94 V-0 rating. When the concentration of ZB is 4%, the LOI value reduces slightly to 31.9%, and still reaches V-0 rating with higher LOI value than that of PP/IFR composite. The LOI and UL-94 rating results reveal that a proper amount of ZB could improve the flame retardant performance of PP/IFR, and clearly exhibit synergistic effect between ZB and IFR, higher loading of ZB would deteriorate the balance between foaming and charring function of PP/IFR composites [31]. The catalytic efficiency (CAT-EFF) are calculated according to formulation (1)

[32-33], and Table 1 shows the CAT-EFF results of ZB for PP/IFR composites. The results illustrate that as the increasing amount of ZB, the CAT-EFF value decreases. When the ZB loading is 1%, CAT-EFF value reaches the maximum 11.33. Although the composite with 2% ZB addition has higher LOI value than that of PP/IFR/1%ZB composite, PP/IFR/1%ZB composite has the highest CAT-EFF value, which indicates that 1% ZB addition is more effective for PP/IFR composites with 20% IFR. Thus, in order to understand the synergistic effect of ZB on flame retardant performance of PP/IFR composites, the PP/IFR/1%ZB composite has been chosen to pursue further investigation. 3.2 Combustion performance of PP/IFR/ZB composites Cone calorimeter is often used to evaluate the flammability properties of composites, and the results are helpful to predict the combustion behavior of materials in real fires. The parameters include the heat release rate (HRR), the total heat release (THR), smoke produce rate (SPR), total smoke produce (TSP) and mass loss rate (MLR) [26-30]. Figure 2-4 show the curves and the data of combustion behavior for PP, PP/IFR and PP/IFR/1%ZB samples obtained from the cone calorimeter test at a heat flux of 35 kW•m-2. The HRR and THR curves of PP, PP/IFR and PP/IFR/1% ZB are presented in Figure 2 (a) and (b). It can be found that neat PP burned rapidly after ignition, and it reaches a sharp peak (PHRR) and THR of 817 kW•m-2 and 157 MJ•m-2•Kg, whereas, the PHRR and THR values of PP/IFR are 154 kW•m-2 and 59 MJ•m-2•Kg respectively,

which were reduced by 81.1% and 62.4%. It clearly showed that PP/IFR and PP/IFR/1%ZB presented lower HRR and THR values, and with the addition of 1% ZB, the PHRR and THR values of PP/IFR/1%ZB reduced to 151 kW•m-2 and 45 MJ•m-2•Kg respectively. Also, the HRR curve of PP/IFR system showed three peaks, but only two identifiable peaks emerged in PP/IFR/1%ZB. Also, the second peak of PP/IFR/1%ZB appeared a little later than that of PP/IFR composite, and the time at the second peak shifted from 200 to 220 s. Furthermore, the combustion time of the PP/IFR and PP/IFR/1%ZB composites was prolonged in comparison with that of pure PP, which increased from 450 s to about 650 s. The results may be contributed to that by introduction of ZB into PP/IFR composite, ZB could improve the flame retardant performance and reduce the flammability of PP/IFR composites. Figure 3 (a) and (b) show the SPR and TSP curves of the three samples, which are similar to the HRR and THR curves. As can be seen, the curves and the values of the PP/IFR and PP/IFR/1%ZB were much lower than that of PP, and decreased from 0.070 to 0.020 and 0.01 m2•s-1 at first peak, and the time at the second peak of PP/IFR/1%ZB was a little later than that of PP/IFR. At the same time, the TSP value of PP/IFR/1%ZB is 2.9 m2, which is far lower than those of PP and PP/IFR. The reason is that there is a synergistic effect between ZB and IFR, and ZB can promote to form a stable char layer, which serves as a thermal insulator and restricts smoke production. The residual mass curves (Figure 4) of PP, PP/IFR and PP/IFR/1%ZB during combustion presents that pure PP lost its mass faster than PP/IFR and PP/IFR/1%ZB

composites, and nothing was left, while there were 34.9% and 37.9% residue for PP/IFR and PP/IFR/1%ZB respectively at combustion time of 450s. The results revealed that much more residual char was formed when ZB was added, which decreased the evolution of combustible gas during the combustion process. 3.3 Morphologies of final char residues The surface morphology of the char could be a key factor to influence the flame retardant performance of polymeric materials. Figure 5 (a) and (b) give the digital photos for residual char of PP/IFR and PP/IFR/ZB composites after cone calorimeter tests. Both of them had formed intumescent and compact char layers, and relative loose structure including some small holes appeared on the outer char surface of PP/IFR composite (pointed out by the arrow B). Surprisingly, more continuous and compact char layer without visible hole on the outer surface had been formed when 1%ZB was incorporated into PP/IFR system, as shown in Figure 5 (b) and pointed out by arrow C, which may serve as an excellent thermal barrier, holding back the heat and oxygen, and thus improving the flame retardant properties and reducing the combustion parameters of PP/IFR/1%ZB composite. In order to clarify the relationship between the flame retardant performance and the microstructure of intumescing chars, the intumescing char residue (inner and outer) of PP/IFR and PP/IFR/1%ZB after cone calorimeter tests were examined by SEM with modification of 500 and 5000 times. As can be seen from Figure 6, both samples (with or without ZB) produced a continuous, compact and intumescent outer surface,

which could hinder to heat transmission and gas diffusion. A relatively less perfect structure including some small holes on the outer surface can be observed (Figure 6 (A1) and (A2)), which is contributed to insufficient char formation during combustion. In contrary, the char layer for PP/IFR/1%ZB composite is more smooth and homogenous without visible holes and cavities as shown in Figure 6 (C1) and (C2). It is surprising that some particles were observed on the image Figure 6 (C2), and the chemical composition was determined by EDS, as shown in Figure 7 and Table 2. The results showed that the particle was comprised by B, C, O and P element, which indicated that ZB was divided into ZnO and B2O3, and B took part in the chemical reaction during combustion to form more crosslinking network. Relative to PP/IFR system, the inner surface of PP/IFR/1%ZB was also more compact with more homogeneous bubbles scattering on their surfaces (shown in Figure 6 B1, B2, D1 and D2). The results suggested that ZB could decomposed to ZnO and B2O3, and B2O3 participated to form crosslink network in the char, resulting in a more compact char layer with better mechanical performance, and consequently the improved char layer can enhance the flame retardant properties and increase higher thermal stability of composites [19-20]. Thus, the enhanced char layer hinder heat transmission and heat diffusion into the flame zone for PP/IFR/1%ZB. 3.4 Chemical composition of final char residue In order to understand the synergistic mechanism of ZB, the chemical composition of the final residual char after cone calorimeter test of PP/IFR and PP/IFR/1%ZB composites was investigated by EDS, and the spectra and results were

presented in Figure 8 and Table 3. It is found that the outer and inner char surface of PP/IFR has similar atomic content and relative content of P, O and C. When 1% ZB was introduced into PP/IFR, the P and C contents on the outer char surface were higher than those in PP/IFR, but the relative content of P and O on the inner char surface of PP/IFR/1%ZB, was similar to that of PP/IFR. This inferred that the high temperature was an important factor to carry out the catalytic reaction, and ZB could promote to remain more P and O in the outer char layer and increase the crosslinking network during the combustion processes. EDS was employed to characterize the P and O content of residual char of PP/IFR and PP/IFR/1%ZB after soaked in water for 7 days to detect whether the P and O were connected to the polyaromatic ring directly or not. Figure 9 gives the EDS spectra and the results are listed in Table 4. The char still contained P and O elements, but the contents were much lower than those before soaked in water, indicating that most of P and O were in polyphosphate or other complex containing P and O [32-33]. Compared with PP/IFR, the char of PP/IFR/1%ZB after soaked in water contains more P (2.28 %) and O (12.19 %), inferring that ZB could promote more P and O entering onto the polyaromatic ring to form more interconnected network and enhance the strength of the char layer [29-31, 35]. 3.5 Thermal degradation behavior of IFR/ZB and PP/IFR/ZB The thermal stability of IFR and IFR/ZB are analyzed by TGA under nitrogen, and the mass fraction of IFR to ZB is 20:1. Figure 10 (a) and (b) show the TGA and

DTG curves for IFR and IFR/ZB, and the results are listed in Table 5. It was found that IFR’s initial decomposing temperature was 280 °C based on the 5% mass loss (T5%), and DTG curves of IFR could be divided into three steps. The peak of step one was at 295 °C, which assigned to the release of water and ammonia, and the second one was contributed to the decomposition and char-forming of IFR, which happened at 364 °C. The third one occurred at 518°C, and could be assigned to the decomposition of char residue [29-30]. It can be seen from Figure 10 and Table 5 that ZB did improve the initial degradation temperature of IFR systems from 280 and 314 to 287 and 320 °C based upon the 5% and 10% mass loss (T5% and T10%), The DTG curve of IFR/ZB system showed that its thermal degradation behavior was classified in two steps, whose peaks are at 302 and 364 °C, which were similar to those of IFR. The third peak of IFR/ZB was not apparent, and the char residue of IFR/ZB was 52.8, 50.1 and 45.8 % at 600, 700 and 800°C, respectively, which were much higher than those of IFR and the calculation results of IFR/ZB. These results indicated that ZB did improve the char-forming ability of IFR. Curve of IFR/ZB (calculation) is the result calculated from curves of IFR and ZB based on their percentage in IFR/ZB system according to formula (2). Comparing to the curves of IFR/ZB and IFR/ZB (calculation), the thermal degradation behavior of IFR/ZB presented great difference in the range of high temperature, with similar behavior before 450 oC. The third peak on IFR/ZB system disappeared, which revealed that by incorporation of ZB into IFR, the thermal degradation behavior of

IFR changed. The possible reason for this is the interaction between APP and metallic Zn. Zn may replace ammonia in APP to occur crosslinking reaction between polyphosphoric acid chains and metal atoms resulting in the reduction of the volatility of polyphosphoric acid. Therefore, more polyphosphoric acid will be available to esterify with charring agent to improve the char-forming ability of the systems [34-35]. Polymeric materials are usually used in air, thus, it is more practical to evaluate the thermal properties of materials in air. The TGA (a) and DTG (b) curves of PP and PP composites were presented in Figure 11, and the results were listed in Table 6. PP started to degrade at 250 °C (T5%), and decomposed completely at above 350 °C with only 0.2% left at 600 °C. As to PP/1%ZB composite, it had a little higher initial decomposition temperature than that of PP, and the Tp move from 282 to 289 °C. These results showed that ZB could lower the degradation rate of PP, and increase the decomposition temperature of the PP/1%ZB composite. For PP/IFR composite, its initial decomposition temperature (T5%) and Tp increased from 250 and 282 to 260 and 349 °C respectively, and the char residue increased from 0.5 to 10.7% at 600 °C. When ZB was introduced into PP/IFR composite, the Tp of PP/IFR/1%ZB decreased remarkably from 349 to 299 °C. The char residue increased from 10.7, 4.7, 3.2% to 13.1, 7.3, 4.6% at 600, 700 and 800 °C, respectively after 1% ZB addition, high temperature.

indicating more char residue was formed under

4 Conclusions The incorporation of ZB into PP/IFR systems based on APP and CNCA-DA exhibited an evident synergistic effect in the flame retardant properties and combustion performance of the composites, and ZB served as an effective flame retardant synergist. A small amount of ZB could enhance the flame retardancy of PP/IFR with the increase of LOI value and reduction of flammability and smoke of the composites according to the LOI, UL-94 and CCT tests and the optimum amount was 1%. The morphological structure of the inner and outer char residue revealed that the addition of ZB into PP/IFR system was helpful to form a compact and homogeneous intumescent char layer on the outer and inner surface of the material during burning, which proved to be of the most critical reason for the flame retardant performance. The studies of EDS revealed that ZB could promote more P and O to connect onto to the polyaromatic ring directly, and B could participate the connecting reaction, thus ZB enhanced the strength of char and improved the flame retardancy of the IFR/PP system during combustion.

Acknowledgments The financial supports by the National 973 Program of China (2014CB643605 and 2011CB606100), the National Natural Science Foundation of China (51373204, 51173214),

National

Natural

Science

Foundation

of

Guangdong

China

(2014A030310316), Foundation for Distinguished Young Teachers in Higher

Education of Guangdong China (YQ2014001), and the Doctoral Fund of the Ministry of Education of China (20120171130001) are gratefully acknowledged.

Reference [1] Lu S, Hamerton I. Recent developments in the chemistry of halogen-free flame retardant polymers. Prog Polym Sci 2002; 27(8): 1661-1712. [2] Bourbigot S, Duquesne S. Fire retardant polymers: recent development and opportunities. J Mater Chem 2007; 17(22): 2283-2300. [3] Chen L, Wang YZ. A review on flame retardant technology in China. Part : development of flame retardants. Polym Adv Technol 2010; 21(1): 1-26. [4] de Wit Cynthia A. An overview of brominated flame retardants in the environment. Chemosphere 2002; 46(5): 583-624. [5] Sain M, Park S.H, Suhara F, Law S. Flame retardant and mechanical properties of natural fibre–PP composites containing magnesium hydroxide. Polym Degrad Stab 2004; 83(2):363-367. [6] Liang JZ, Zhang YJ. A study of the flame-retardant properties of polypropylene/Al(OH)3/Mg(OH)2 composites. Polym In. 2010; 59(4): 539-542. [7] Marosfoi BB, Garas S, Bodzay B, Zubonyai F, Marosi G. Flame retardancy study on magnesium hydroxide associated with clays of different morphology in polypropylene matrix. Polym Adv Technol 2008; 19(6): 693-700. [8] Camino G, Martinasso G, Costa L. Thermal degradation of pentaerythritol diphosphate, model compound for fire retardant intumescent systems: Part I Overall thermal degradation. Polym Degrad Stab 1990; 27(3):285-296. [9] Camino G, Costa L, Trossarelli L. Study of the mechanism of intumescence in fire retardant polymers: Part I Thermal degradation of ammonium polyphosphate/pentaerythritol mixtures. Polym Degrad Stab 1984; 6(4): 243-252. [10] Camino G, Costa L, Trossarelli L. Study of the mechanism of intumescence in fire retardant polymers: Part V Mechanism of formation of gaseous products in the thermal degradation of ammonium polyphosphate. Polym Degrad Stab 1985; 12(3): 203-211. [11] Hu XP, Li WY, Wang YZ. Synthesis and Characterization of a Novel Nitrogen-Containing Flame Retardant. J App Polym Sci 2004; 94(4): 1556-1561. [12] Li B, Xu MJ. Effect of a novel charring-foaming agent on flame retardancy and thermal degradation of intumescent flame retardant polypropylene. Polym Degrad Stab 2006; 91(6): 1380-1386. [13] Lai XJ, Zeng XR, Li HQ, et al. Synergistic Effect Between a Triazine-Based Macromolecule and Melamine Pyrophosphate in Flame Retardant Polypropylene. Polym composite, 2012, 33(1): 35-43. [14] Song PA, Fang ZP, Tong LF, et al. Synthesis of a Novel Oligomeric Intumescent

Flame Retardant and its Applieation in Polypropylene. Polym Eng Sci, 2009, 49(7): 1326-1331. [15] Marosi G, Marton A, Anna P, Bertalan G, Marosfoi B, Szep A. Ceramic precursor in flame retardant systems. Polym Degrad Stab 2002; 77: 259-265. [16] Estevao LRM, Le BrasM, Delobel R, Nascimento RSV. Spent refinery catalyst as a synergistic agent in intumescent formulations: influence of the catalyst’s particle size and constituents. Polym Degrad Stab 2005; 88 : 444-455. [17] Wu Q, Qu BJ. Synergistic effects of silicotungstic acid on intumescent flame retardant polypropylene. Polym Degrad Stab 2001;74(2): 255-261. [18] Demir H, Arkıs x E, Ulku S. Synergistic effect of natural zeolites on flame retardant additives. Polym Degrad Stab 2005; 89(3): 478-483. [19] Li YT, Li B, Dai JF, Jia H, Gao SL. Synergistic effects of lanthanum oxide on a novel intumescent flame retardant polypropylene system. Polym Degrad Stab 2008; 93(1): 9-16. [20] Dogan M, Yilmaz A, Bayramli E. Synergistic effect of boron containing substances on flame retardancy and thermal stability of intumescent polypropylene composites. Polym Degrad Stab 2010; 95(12): 2584-2588. [21] Ren Q, Wan CY, Zhang Y, Li J. An investigation into synergistic effects of rare earth oxides on intumescent flame retardancy of polypropylene/ poly(octylene-co-ethylene) blends. Polym Adv Technol 2009; 22(10): 1414-1421. [22] Fina A, Abbenhuis HCL, Tabuani D, Camino G. Metal functionalized POSS as fire retardants in polypropylene. Polym Degrad Stab 2006; 91(10): 2275-2281. [23] Song PA, Fang ZP, Tong LF, Jin YM, Lu FZ. Effects of metal chelates on a novel oligomeric intumescent flame retardant system for polypropylene. J Anal Appl Pyrolysis 2008, 82(2): 286-291. [24] Tugba Orhan T, Isitman NA, Hacaloglu J, Kaynak C. Thermal degradation mechanisms of aluminium phosphinate, melamine polyphosphate and zinc borate in poly(methyl methacrylate). Polym Degrad Stab 2011; 96(10): 1780-1787. [25] Shen KK, Kochesfahani S, Jouffret F. Zinc borates as multifunctional polymer additives. Polym Adv Technol 2008; 19(6): 469-474. [26] Braun U, Schartel B, Fichera MA, Jager C. Flame retardancy mechanisms of aluminium phosphinate in combination with melamine polyphosphate and zinc borate in glass-fibre reinforced polyamide 6, 6. Polym Degrad Stab 2007; 92(8): 1528-1545. [27] Wu ZP, Hu YC, Shu WY. Effect of Ultrafine Zinc Borate on the Smoke Suppression and Toxicity Reduction of a Low-Density Polyethylene/Intumescent Flame-Retardant System. J App Polym Sci 2010, 117(1): 443-449. [28] Feng CM, Zhang Y, Liu SW, Chi ZG, Xu JR. Synthesis of novel triazine charring agent and its effect in intumescent flame retardant polypropylene. J App Polym Sci 2012, 123(6): 3208-3216. [29] Feng CM, Zhang Y, Liu SW, Chi ZG, Xu JR. Synergistic effect of La2O3 on the flame retardant properties and the degradation mechanism of a novel PP/IFR system. Polym Degrad Stab 2012; 97(5): 707-714. [30] Feng CM, Li ZW, Liang MY*, Huang JG*, Liu HB*. Preparation and

characterization of a novel oligomeric charring agent and its application in halogen-free flame retardant polypropylene. J Anal Appl Pyrolysis, 2015, (111): 238-246. [31] Dogan M, Yilmaz A, Bayramli E. Synergistic effect of boron containing substances on flame retardancy and thermal stability of intumescent polypropylene composites. Polym Degrad Stab 2010; 95(12): 2584-2588. [32] Lewin M, Endon M. Catalysis of intumescent flame retardancy of polypropylene by metallic compounds. Polym Adv Technol 2003; 14(1): 3-11. [33] Lewin.M. Synergism and Catalysis in Flame Retardancy of Polymers. Polym Adv Technol 2001; 12(3-4): 215-222. [34] Chen XC, Ding YP, Tang T. Synergistic effect of nickel formate on the thermal and flame-retardant properties of polypropylene. Polym Int 2005; 54(6): 904-908.

[35] Samyn F, Bourbigot S, Duquesne S, Delobel R. Effect of zinc borate on the

thermal degradation of ammonium polyphosphate. Thermochim Acta 2007; 456(2), 134-144.

Figure captions

Figure 1 Effect of ZB on the flame retardant properties of PP/IFR composites Figure 2 The HRR (a) and THR (b) curves of PP, PP/IFR and PP/IFR/1%ZB Figure 3 The residual Mass curves of PP, PP/IFR and PP/IFR/1%ZB Figure 4 The SPR (a) and TSP (b) curves of PP, PP/IFR and PP/IFR/1%ZB Figure 5 Digital photos of chars of PP/IFR (a) and PP/IFR/1% ZB (b) A and B are outer and inner surface of char residue of PP/IFR, and C and D are outer and inner surface of char residue of PP/IFR/1%4A Figure 6 SEM photographs of char residue of PP/IFR (A1: outer×500, A2: outer×5000, B1: inner×500, B2: inner×5000) and PP/IFR/1%4A (C1:

outer×500, C2: outer×5000, D1: inner×500, D2: inner×5000) Figure 7 EDS of particles of outer char layer for PP/IFR/ZB Figure 8 EDS spectra of outer and inner char surface; (a) outer surface of PP/IFR;(b) inner surface of PP/IFR;(c) outer surface of PP/IFR/1% ZB;(d) inner surface of PP/IFR/1% ZB Figure 9 EDS spectra after soaked in water; (a) PP/IFR;(b) PP/IFR/1% ZB Figure 10 TGA (a) and DTG (b) curves of IFR systems with and without ZB under N2 Figure 11 TGA (a) and DTG (b) curves of PP/IFR composites with and without ZB under air

N N

NHCH2CH 2NH N

n

NH

Scheme 1 Structure of

CNCA-DA

Table 1 Catalytic effects of ZB on PP/IFR

ZB%

LOI/%

△LOI/%

Zn/wt% a

CAT-EFF b

0 1 2 3 4

27.1 30.5 32.2 32.0 31.9

--3.4 5.1 4.9 4.8

--0.30 0.60 0.90 1.20

--11.33 8.50 5.44 4.00

a: Mn/wt% means La concentration in PP/IFR/ZB

b: CAT-EFF=△LOI/wt(Mn)%

(1)

Table 2 EDS result of particles of outer char layer for PP/IFR/ZB Element BK CK OK PK Totals

Weight% 13.93 27.76 42.11 16.19 100

Atomic% 19.08 34.21 38.97 7.74 100

Table 3 EDS anslysis results of chars PP/IFR PP/IFR/1%ZB Outer surface inner surface Outer surface inner surface a b At% Rc At% rc At% rc At% rc 49.15 -49.22 -39.59 -49.33 -CK 40.01 0.81 40.24 0.82 45.35 1.15 38.26 0.78 OK 10.84 0.22 10.54 0.21 15.06 0.38 12.41 0.25 PK a:At% means the molar content of elements。 b:rc means relative molar content of other elements to carbon; Elements

Table 4 EDS anslysis results of chars after soaked in water PP/IFR

Elements

a

b

PP/IFR/1%ZB At% rc 85.53 -12.19 0.14 2.28 0.027

At% rc 93.29 -CK 6.21 0.067 OK 0.50 0.0054 PK a:At% means the molar content of elements。 b:rc means relative molar content of other elements to carbon;

Table 5 TGA data of IFR with and without ZB under nitrogen

d

T1%/°C

IFR a 228

IFR/ZB b 207

IFR/ZB Calculation c 200

d

T5%/°C T10%/°C d T50%/°C e Tp/°C f W600°C /% f W700°C /% f W800°C /%

280 314 534 364 43.6 38.4 31.6

d

285 320 704 364 52.8 50.1 45.8

275 311 545 360 45.1 40.1 33.7

a: IFR is composed by APP and CNCA-DA, and the mass ratio of APP:CNCA-DA is 2:1 b: The mass ratio of APP:CNCA-DA is 2:1; and The mass ratio of IFR:ZB is 20:1; c:Wcalculation=WIFR×95.33%+WZB×4.67%

(2);

d: T1%, T5%, T10%

and T50% are the temperature at which 1%, 5%, 10% and 50% weight loss occurs, respectively. e: Tp is the temperature at which the maximum of weight loss rate take place. f: W600°C /%, W700°C /% and W800°C /% are the residue of materials at 600, 700 and 800 °C.

Table 6 TGA data of PP/IFR/ZB systems under Air b

T1%/°C T5%/°C b T10%/°C b T50%/°C c Tp/°C d W600°C /% d W700°C /% d W800°C /% b

PP 239 250 257 282 282 0.5 0.4 0.3

PP/1%ZB 249 257 262 287 289 1.2 1.1 1.1

PP/IFR a 246 260 273 345 349 10.7 4.7 3.2

PP/IFR/1%ZB 249 259 267 323 299 13.1 9.8 6.6

a: The mass ratio of APP:CNCA-DA is 2:1, and mass fraction of IFR is 20%. b: T1% and T5% and T10% and T50% are the temperature at which 1% and 5% and 10% and 50% weight loss occurs, respectively. c: Tp is the temperature at which the maximum of weight loss rate take place. d: W600°C /%, W700°C /% and W800°C /% are the residue of materials at 600, 700 and 800 °C.

0.5 Deriviate Weight/%·min

-1

100

Weight/%

(a) 80

60

40 200

IFR IFR/ZB IFR/ZB Calculation

400 600 o Temperature/ C

800

0.4 0.3

(b)

IFR IFR/ZB IFR/ZB Calculation

0.2 0.1 0.0 200

400 600 o Temperature/ C

800

Figure 10 TGA (a) and DTG (b) curves of IFR systems with and without ZB under nitrogen

2.5

100 PP PP/1% ZB PP/IFR PP/IFR/1% ZB

60

2.0 Weight/%

80

40

(a)

20 0 200

400

600

1.5

PP PP/1% ZB PP/IFR PP/IFR/1% ZB

1.0 0.5

800

0.0 200

400 600 o Temperature/ C

800

Figure 11 TGA (a) and DTG (b) curves of PP/IFR systems with and without ZB under air

2.5

100 PP PP/1% ZB PP/IFR PP/IFR/1% ZB

60

2.0 Weight/%

80

40

(a)

20 0 200

400

600

1.5

PP PP/1% ZB PP/IFR PP/IFR/1% ZB

1.0 0.5

800

0.0 200

400 600 o Temperature/ C

800

Figure 11 TGA (a) and DTG (b) curves of PP/IFR systems with and without ZB under air

0.075

12.5

0.045 0.030 0.020 0.010

0.015 0.000

0.010

0

0.010

(a) 150

300 450 Time/s

600

-1

PP PP/IFR PP/IFR/1% ZB

10.0 7.5

TSP/MJ· m · Kg

2

SPR/m ·s

-1

0.060

-2

0.070

12.3

PP PP/IFR PP/IFR/1% ZB

5.0 3.6 2.9

2.5

(b) 0.0 0

150

300 Time/s

450

600

Figure 3 The SPR(a) and TSP(b) curves of PP, PP/IFR and PP/IFR/1%ZB

900

160

450 300 150 1 111 0

1' 68 0 100

2 136 2' 151

200

3 154

300 400 Time/s

157

120

PP PP/IFR PP/IFR/1% ZB

-2

THR/MJ· m · Kg

-2

HRR/KW·m

PP PP/IFR PP/IFR/1% ZB

600

-1

817

750

80

59 45

40

(a) 500

600

(b) 0 0

150

300 450 Time/s

600

Figure 2 The HRR (a) and THR (b) curves of PP, PP/IFR and PP/IFR/1%ZB

Figure 5 Digital photos of chars of PP/IFR (a) and PP/IFR/1% ZB (b)

A C

B

(a)

(b)

0.075

12.5

0.045 0.030 0.020 0.010

0.015 0.000

0.010

0

0.010

(a) 150

300 450 Time/s

600

-1

PP PP/IFR PP/IFR/1% ZB

10.0 7.5

TSP/MJ· m · Kg

2

SPR/m ·s

-1

0.060

-2

0.070

12.3

PP PP/IFR PP/IFR/1% ZB

5.0 3.6 2.9

2.5

(b) 0.0 0

150

300 Time/s

450

600

Figure 3 The SPR(a) and TSP(b) curves of PP, PP/IFR and PP/IFR/1%ZB

Figure 7 EDS of particles of outer char layer for PP/IFR/ZB

100 PP PP/IFR PP/IFR/1% ZB

Mass/%

80 60

37.9

40

34.9

20 0

0

0

150

300 450 Time/s

600

Figure 4 The residual mass loss curves of PP, PP/IFR and PP/IFR/1%ZB

Figure 9 EDS spectra after soaked in water; (a) PP/IFR;(b) PP/IFR/1% ZB

Figure 5 Digital photos of chars of PP/IFR (a) and PP/IFR/1% ZB (b)

A C

B

(a)

(b)