Expandable graphite and dimethyl methylphosphonate synergistic flame retardant polymethyl methacrylate
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摘要: 聚甲基丙烯酸甲酯（PMMA）是一种用途广泛的高分子材料，为了改变其易燃烧的缺点，本文采用原位聚合法制备了一系列含甲基膦酸二甲酯（DMMP）和可膨胀石墨（EG）的聚甲基丙烯酸甲酯复合材料。通过极限氧指数、锥形量热仪和垂直燃烧测试研究了其阻燃性能,结果表明在添加10%复配阻燃剂，且DMMP与EG的比例为1∶1时， 复合材料5%DMMP-EG/PMMA的阻燃效果最好。样品通过UL-94 V-0评级，与未加阻燃剂的PMMA相比，其极限氧指数(LOI)从18%增加到27.4%。热释放速率峰值（pHRR）显著降低87%，总热释放量率（THR）降低33%。动态力学性能测试表明，5%DMMP-EG/PMMA的玻璃化转变温度和储能模量远远高于10%DMMP/PMMA，复配可膨胀石墨可以改善因磷酸酯加入导致的材料变软现象。最后， 通过TG-IR、不同温度下的红外光谱分析和残炭的拉曼光谱分析了复合材料的阻燃机制，良好的阻燃效果是由于DMMP与EG在气相与凝聚相两相中的协同阻燃作用。Abstract: Polymethyl methacrylate (PMMA) is a widely used polymer material. In order to change its flammability, a series of PMMA composites containing dimethyl methylphosphonate (DMMP) and expandable graphite (EG) were prepared by in-situ polymerization. The flame retardant properties of PMMA composites were studied by limiting oxygen index test (LOI), cone calorimeter test (CC) and vertical burning test (UL-94). The results showed that the flame retardant effect of 5%DMMP-EG/PMMA was the best when 10 % compound flame retardant was added and the ratio of DMMP to EG was 1∶1. The sample passed UL-94 V-0 rating, and its LOI value increased from 18 % to 27.4 % compared with PMMA. The peak heat release rate (pHRR) was significantly reduced by 87 %, and the total heat release rate (THR) was reduced by 33%. The dynamic mechanical properties test showed that the glass transition temperature and storage modulus of 5%DMMP-EG/PMMA were much higher than those of 10%DMMP/PMMA, and the composite expandable graphite could improve the softening of the material caused by the addition of phosphate ester. Finally, the flame retardant mechanism of the composites was analyzed by TG-IR, infrared spectroscopy at different temperatures and Raman spectroscopy of carbon residue. The good flame retardant effect was due to the synergistic flame retardant effect of DMMP and EG in the gas phase and condensed phase.
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图 1 PMMA复合材料的极限氧指数测试（LOI）
Figure 1. limiting oxygen index (LOI) of PMMA composite materials
图 2 PMMA复合材料:(a) HRR；(b) THR; (c) SPR; (d) TSP; (e) COP; (f) CO2P
Figure 2. Cone calorimetric analysis of PMMA samples:(a)HRR, (b)THR, (c)SPR, (d) TSP, (e)COP, (f)CO2P
图 3 PMMA复合材料在垂直燃烧测试中的视频截图
Figure 3. Video screenshots of PMMA composites during the vertical combustion test
图 5 PMMA复合材料的拉伸强度和断裂伸长率
Figure 5. The tensile strength、elongation at break of PMMA composites
图 7 PMMA复合材料：(a)储能模量曲线；(b)损耗模量曲线；(d)玻璃化转变温度曲线
Figure 7. PMMA composite material: (a)curve of storage with temperature; (b)curve of loss modulus with temperature; (c)curve of tan with temperature
图 8 PMMA复合材料的：(a)TGA曲线和（b）DTG曲线
Figure 8. (a) TGA curves of PMMA composites: (b) DTG curves of PMMA composite
图 10 锥形量热测试后的残炭数码照片:(a)PMMA；(b) 10%DMMP/PMMA；(c) 5%DMMP-EG/PMMA；(d) 10%EG/PMMA
Figure 10. Digital pictures of residues after the cone calorimeter test:(a)PMMA; (b) 10%DMMP/PMMA; (c) 5%DMMP-EG/PMMA; (d) 10%EG/PMMA
图 11 锥形量热测试后的残炭SEM图片:(a) 5%DMMP-EG/PMMA；(b) 10%EG/PMMA
Figure 11. SEM micrographs of char residue after calorimeter:(a) 5%DMMP-EG/PMMA; (b) 10%EG/PMMA
图 12 锥形量热测试后焦渣的拉曼曲线：（a）5%DMMP-EG/PMMA；（b）10%EG/PMMA
Figure 12. Raman curves of char residue after cone calorimeter test: (a) 5%DMMP-EG/PMMA; (b)10%EG/PMMA
图 13 PMMA复合材料的变温红外测试:(a)纯PMMA；(b) 5%DMMP-EG/PMMA
Figure 13. Infrared curves at different temperatures of PMMA composite: (a) PMMA; (b) 5%DMMP-EG/PMMA
图 14 (a) 纯PMMA的3 D光谱图；(b) 5%DMMP-EG/PMMA的3 D光谱图；(c)最大分解速率下的热解产物光谱曲线；(d)PMMA4在820 cm−1和1020 cm−1处的吸收曲线
Figure 14. 3 D images of thermal degradation products of PMMA (a) and 5%DMMP-EG/PMMA (b); (c) FTIR spectrum of gaseous pyrolysis products for PMMA and PMMA4 at the maximum evolution rate; (d) changes in absorbance of PMMA4 at 820 cm−1 and 1020 cm−1.
图 15 EG/DMMP阻燃体系的阻燃机制
Figure 15. Flame retardant mechanism of EG/DMMP flame retardant system
表 1 PMMA中阻燃剂的配方
Table 1. The formulation of all PMMA samples
Sample PMMA 10%DMMP/PMMA 2%DMMP-EG/PMMA 5%DMMP-EG/PMMA 8%DMMP-EG/PMMA 10%EG/PMMA MMA/wt% 100 90 90 90 90 90 DMMP/wt% 0 10 8 5 2 0 EG/wt% 0 0 2 5 8 10 Notes: PMMA- Polymethyl methacrylate; DMMP- Dimethyl methylphosphonate; EG- Expandable graphite 
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表 2 PMMA复合材料的阻燃性能具体数据
Table 2. Results of the Cone Calorimeter Test
PMMA 10%DMMP/PMMA 5%DMMP-EG/PMMA 10%EG/PMMA pHRR/(kW·m−2) 1039 1144 136 1561 THR/(MJ·m−2) 110 86 75 82 pSPR/(m2·s−1) 0.036 0.075 0.010 0.002 TSP/m2 2.66 5.91 1.45 0.22 pCOPR/(g·s−1) 0.0043 0.0554 0.0002 0.0002 TTI/s 20 24 28 20 Av-EHC/(MJ·kg−1) 31.8 23.4 26.6 27.8 FPI/(m2·s·kW−1) 0.019 0.021 0.206 0.128 FGI/(kW·m−2·s−1) 9.62 11.32 0.49 0.77 Notes: pHRR-Peak value of heat release rate; THR-Total heat release; pSPR- Peak value of Smoke release rate; TSP- Total Smoke release rate; TTI-Time to ignition; Av-EHC-Average effective heat of combustion; FPI-Fire performance Index; FGI-Fire growth Index
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表 3 PMMA复合材料的UL-94测试等级
Table 3. UL-94 test grade of PMMA composites
Sample Dripping Rating PMMA No NR 10% DMMP/PMMA No NR 5%DMMP-EG/PMMA No V-0 10% EG/PMMA No NR
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表 4 PMMA复合材料力学测试的具体数据
Table 4. Results of PMMA composite material mechanics test
Impact Strength/
(kJ·m−2)TensileStrength/
MPaElongationat break/% Hardness/
HDTg(DMA)/
℃PMMA 14.43 51.24 2.71 90 136.3 10%DMMP/PMMA 15.93 43.04 8.42 80 78.6 2%DMMP-EG/PMMA 13.75 38.26 2.91 84 5%DMMP-EG/PMMA 12.52 30.17 0.63 87 136.0 8%DMMP-EG/PMMA 10.55 24.07 0.27 87 10%EG/PMMA 9.78 14.48 0.18 88 136.0 Notes: Tg-Glass transition temperature
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表 5 PMMA复合材料的热重数据
Table 5. TGA data of the PMMA composites
T5%/℃ Tmax/℃ Char Residue/% PMMA 272 373 0.5% 10%DMMP/PMMA 219 391 0.7% 5%DMMP-EG/PMMA 248 382 6.3% 10%EG/PMMA 161 379 9.1% Notes: T5%-5% mass loss temperature ; Tmax-Maximum mass loss temperature.
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