Utilization of MHSH as Synergistic Agent in Flame retarded PBS Composites

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1 nd International Conference on Material Engineering and Application (ICMEA 2015) ISBN: Utilization of MHSH as Synergistic Agent in Flame retarded PBS Composites Xiaopeng Yue, Pengjie Liu & Xu Cao College of Light Industry and Energy, Shaanxi Province Key Lab of Papermaking Technology and Specialty Paper, Shaanxi University of Science & Technology, Xi an , Shaanxi Province, China ABSTRACT: Basic magnesium hydroxide sulfate whisker (MHSH) was used as flame retarded synergistic agent of intumescent flame retardant (IFR) system, and to prepare flame retarded PBS composites. Furthermore, the mechanics performance, the limiting oxygen index (LOI) analysis and the flame retardant properties of the composites were investigated. Experimental data show that with the incorporation of MHSH, the LOI values and the UL 94 levels of composites improved in comparison with those of the composites without MHSH addition, indicating the synergistic effect of MHSH in composites. Furthermore, when the IFR and MHSH loading were 23% and 2 wt%, respectively, the UL 94 level achieved V0 rate. Simultaneously, as indicated by mechanical properties, illustrating that MHSH played a reinforcement effect in composites. 1 INTRODUCTION As a kind of novel biodegradable polymer, poly (butylene succinate) (PBS) has attracted more and more attention owing to its good performances. However, PBS is flammable and melt dripped seriously during combustion, which would ignites something else and then results in a fire hazard. Thus, to prepare flame-retarded PBS composites can expand the application field of PBS. Wang et al studied the influence of melamine phosphate (MP) and grapheme on the mechanical, thermal properties and flammability of the flame-retarded PBS. The results showed that with the addition of 18 wt% MP and 2 wt% grapheme, the LOI value of 34.0% and UL-94 V0 rate of composites could be achieved. Xin et al added hydroxyl ethyl phosphonate (PBPPS) into PBS, and to prepare flame-retarded PBS composites. The results showed that when the addition of PBPPS was 2.8 wt%, the LOI value of PBS/PBPPS composite reached 60%. Zeng et al studied the influence of ammonium polyphosphate (APP), red phosphorus (RP) and expanded graphite (EG) on the flame retardant properties of the PBS/wood fiber composites. When the ratio of APP, RP and EG was 1:1:4, the PBS/wood fiber composites with LOI value of 36.0% and UL-94 V0 rate could be obtained. However, the addition of flame retardant seriously 348

2 deteriorated the mechanical properties of the composites. Chen et al investigated the synergistic effect of fumed silica in flame-retarded PBS. It was revealed that the flame-retarded PBS exhibited both excellent flame retardance and antidripping properties when the three components of IFR (Ammonium polyphosphate, melamine, and fumed silica) coexisted at an appropriate proportion. The lowest total loading of flame retardant could be reduced to 17 wt % with the synergism of fumed silica, for the goal of UL-94 V0 rate. Basic magnesium hydroxide sulfate whisker (MHSH) is a new kind of halogen-free flame retardant. Normally, MHSH was used to reinforce metals, ceramics, rubber, plastic and other composites due to its high intensity, light quality, good mechanical properties and fibrous morphology. However, there have been no immediate reports focused on PBS/IFR/MHSH composites system. In this investigation, MHSH was used as flame-retarded synergistic agent of IFR system, and to prepare PBS based composites. The mechanical performance, the LOI value and the flame retardant properties of the composites were studied. Furthermore, the morphological characteristics of combusted char of composites were observed by scanning electron microscope (SEM). 2 EXPERIMENTAL 2.1 Materials PBS with trade name ECONORM1201, was purchased from Fuwin New Material Co., Ltd, Shandong Province, China. MHSH was purchased from Jiangxi Fengzhu new material technology Co., Ltd, Jiangxi Province, China. Sodium stearate was purchased from Yong sheng fine chemical Co., Ltd, Tianjin, China. HT-208 ammonium polyphosphate (the solubility in water was lower than 0.3 g / 100 ml, polymerization degree was 1000 under 25 was purchased from Jinan taixing chemical Co., Ltd, Shandong Province, China. Melamine (MA) ( 99%) was purchased from Kemiou chemical reagent Co., Ltd, Tianjin, China. 2.2 Composite manufacture PBS, MHSH, APP and MA were dried in an air blast oven at 80 overnight before compounding. The formulations are presented in Table 1. For example, the preparation of specimen Y2 is illustrated as follows: 75 wt% of PBS, 23 wt% of APP+MA (5:1) and 2 wt% of MHSH were melt-blended in an open mill for 15 min; the setting temperature was 100, and the roller speed was 30 rpm. The blended sample was 349

3 hot-pressed at 120 under 10 MPa for 5 min into sheet with the thickness of about 4.0 mm and 1.5 mm. Table 1. The composition and naming of the composites. Formulation name name PBS (wt%) APP+MA(5:1)(wt%) MHSH (wt%) PBS Y Y Y Y Y Note: The specimen Y1 consists of IFR (APP, MA) and PBS. 2.3 Characterization The tensile strength of composites was tested according to GB/T on a JDL tension tester (TianFa Experiment Machinery Co., Ltd, Jiangsu Province, China). The bending strength of composites was tested according to GB/T on a JDL tension tester (TianFa Experiment Machinery Co., Ltd, Jiangsu Province, China). Limiting oxygen index (LOI) tests were measured according to GB/T on a XYC-75 oxygen index meter apparatus. The specimens used for the test were of dimensions 100 mm 6.5 mm 3 mm. UL-94 vertical burning tests were measured according GB/T2048 on a Tech-GBT vertical burning apparatus. The plastic specimens of dimensions mm, suspended vertically above a cotton patch (Taisi testing instrument technology Co., Ltd, Jiangsu Province, China). The combusted specimens were coated with gold. The morphological characteristics of the char were characterized with scanning electron microcopy (SEM) on a JEOL JSM-6390 apparatus. The acceleration voltage was 20.0 kv. 350

4 3 RESULTS AND DISCUSSION 3.1 Mechanical properties Figure 1 illustrates the tensile strength and bending strength of PBS/MHSH/IFR composites. As indicated from Figure 1, the tensile strength of all composites decrease in comparison with pure PBS. However, the tensile and bending strengths of the composites increase with the increasing MHSH loading in comparison with that of specimen Y1. When the loading of MHSH is 2 wt%, the tensile strength of Y2 increases by 33.4% in comparison with that of specimen Y1. When the MHSH loading exceeds 2 wt%, the tensile strength of the composites decrease with the increasing MHSH loading. When the loading of MHSH is 2 wt%, the bending strength of Y2 decreases by 7.6% in comparison with that of specimen Y1. According to the mechanical properties of composites, MHSH plays a reinforcement effect in composites. Possible reason is that the microstructure of MHSH is fibrous structure. 3.2 Combustion Characteristics: LOI and UL-94 From the LOI and UL-94 analysis data of pure PBS and flame-retarded PBS composites listed in Table 2, it can be seen that the LOI value of the composites increases with the increasing MHSH loading, With the maximum value being achieved when the loading of MHSH is 2 wt%, increased by 6.1% in comparison with that of specimen Y1. The LOI value of the composite, then, declines when the loading of MHSH exceeds 2 wt%, and a UL-94 V0 rate is achieved. The results show that the LOI value and the UL-94 levels of composites improve in comparison with those of the composites without MHSH addition, indicating the synergistic effect of MHSH in composites. Possible reason is that the compact magnesium oxides are produced in heating decomposition of MHSH. Magnesium oxide slows down the heat and mass transfer rate between air and composites. 3.3 Morphological Characterization of the Char Residue SEM images of Figure 2 showed the microstructures of outer and inner char of Y1 and Y2 after being combusted in oxygen index testing apparatus. As shown in Figure 2 (a, b), it can be observed that there are some cracks and holes on the outer char surface of Y1, and its inner char is fragmental. On the contrary, as shown from Figure 2 (c, d), both the outer and inner char of Y2 are more compact than those of Y1. It can be inferred that as a kind of synergistic agent, MHSH provides a flame shield during combustion, slowing down the heat and mass transfer rate between air and composites. 351

5 30 40 Bending strength (MPa) Tensile strength (MPa) PBS Y1 Y2 Y3 Y Y5 PBS Composite samples Y1 Y2 Y3 Y4 Y5 Composite samples Figure 1. The tensile and bending strengths of PBS/MHSH/IFR composite. a b c d Figure 2. SEM micrographs of the char after combustion, a) Y1 300, b) Y K, c) Y2 300, d) Y K. 352

6 Table 2. LOI and UL-94 results of pure PBS and flame-retardant PBS composites. Formulation Ignite the LOI(vol%) UL-94 rate Dripping name absorbent cotton PBS 24.0 NR Yes Yes Y V-0 No No Y V-0 No No Y V-0 No No Y V-0 No No Y V-1 Yes No 4 CONCLUSIONS With the incorporation of MHSH, the LOI values and the UL-94 levels of composites improved in comparison with those of the composites without MHSH addition, indicating the synergistic effect of MHSH in composites. Simultaneously, MHSH also played a reinforcement effect in composites. When the IFR and MHSH loading were 23% and 2 wt%, respectively, the UL-94 level achieved V0 rate. The mechanical properties of MHSH modified composites exhibited obviously improvement in comparison with those of composites without MHSH addition. Analysis of SEM indicated that MHSH provided a flame shield during combustion, slowing down the heat and mass transfer rate between air and composites, playing a role of synergistic agent in composites. ACKNOWLEDGEMENT This work was supported by Open Fund of Key Laboratory of Pulp and Paper Science & Technology of Ministry of Education of China (Contract Grant Numbers: ) and Academic Leader Team Program of Shaanxi University of Science and Technology (Contract Grant Numbers: 2013XSD25) for financial support. Corresponding author: Xiaopeng Yue, College of Light Industry and Energy, Shaanxi University of Science and Technology, Xi an , China. yuexiaopeng@sust.edu.cn. REFERENCES T, Bin. J., P., Qu. L., M., Liu. Y., H., Feng. S., X., Hu. & X.C. Yin, Non-isothermal crystallization kinetics and dynamic mechanical thermal properties of poly(butylene succinate) composites reinforced with cotton stalk bast fibers, Thermochimica Acta 525 (2011)

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