Properties and flame retardant mechanism of sulfuretted DOPO derivative in epoxy resin
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摘要: 为了获得综合性能好的阻燃环氧树脂(EP)复合材料,将9,10-二氢-9-氧杂-10-磷杂菲-10-硫化物(DOPS)的衍生物应用于EP。首先,通过DOPS和马来酸酐(MAH)反应合成磷杂菲衍生物马来酸酐-9,10-二氢-9-氧杂-10-磷杂菲-10-硫化物(MAH-DOPS),采用FTIR、1H NMR、31P NMR等手段确定其结构;其次,分别将DOPS和MAH-DOPS添加到EP中,通过共混制备复合材料DOPS/EP和MAH-DOPS/EP;再次,对比了DOPS/EP和MAH-DOPS/EP的热稳定性、阻燃性能和力学性能;最后,探讨了MAH-DOPS对EP的燃烧性能和热降解行为的影响,深入分析其阻燃机制。通过对比发现:阻燃剂DOPS的初始分解温度(T5%,205.4℃)低于MAH-DOPS(235.2℃),在添加相同质量分数的阻燃剂时,复合材料DOPS/EP的热稳定性也低于MAH-DOPS/EP,与阻燃剂热稳定性一致;阻燃剂DOPS和MAH-DOPS均能改善EP的阻燃性能,MAH-DOPS/EP具有更优异的阻燃效果。当阻燃剂添加量为15wt%时,MAH-DOPS/EP和DOPS/EP的极限氧指数(LOI) 值分别为28.6%和29.1%,分别达到UL-94 V-0级和V-1级。力学测试结果表明,与EP相比,MAH-DOPS/EP的弯曲强度提高了45.8%,而DOPS/EP下降了62.5%,DOPS/EP体系的力学性能下降明显,几乎失去使用价值。锥形量热测试表明,复合材料MAH-DOPS/EP的平均热释放速率(av-HRR)和总热释放量(THR)显著降低。TG-IR结果表明,MAH-DOPS/EP热解产生的含磷自由基捕捉了H•、O•或HO•等自由基,起到了自由基淬灭作用;SEM-EDS结果表明,MAH-DOPS/EP能够形成更加完整致密的炭层,炭层中P含量较高。研究表明,MAH-DOPS通过抑制火焰和成炭分别在气相和凝聚相发挥阻燃作用,并以气相阻燃机制为主。
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关键词:
- 阻燃性能 /
- 环氧树脂 /
- 马来酸酐-9,10-二氢-9-氧杂-10-磷杂菲-10-硫化物(MAH-DOPS) /
- 热降解 /
- 成炭
Abstract: In order to obtain the flame retardant epoxy resin (EP) composites with good comprehensive properties, the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-sulfide (DOPS) derivative was applied to EP. First, maleic anhydride-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-sulfide (MAH-DOPS) was synthesized by the reaction of DOPS and maleic anhydride (MAH). The structure was determined by FTIR, 1H NMR and 31P NMR. Secondly, DOPS and MAH-DOPS were added to EP respectively, to prepare composites DOPS/EP and MAH-DOPS/EP by blending. Thirdly, the thermal stability, flame retardancy and mechanical properties of DOPS/EP and MAH-DOPS/EP were compared. Finally, the effects of MAH-DOPS on the combustion performance and thermal degradation behavior of EP were discussed, and its flame retardant mechanism was analyzed in depth. The results show that the initial decomposition temperature of flame retardant DOPS (205.4℃) is lower than that of MAH-DOPS (235.2℃), and the thermal stability of DOPS/EP is lower than that of MAH-DOPS/EP when the same mass fraction of flame retardants is added, which is consistent with the thermal stability of flame retardants. Both flame retardants DOPS and MAH-DOPS can improve the flame retardancy of EP, and MAH-DOPS/EP has better flame retardant effect. When the amount of flame retardant is 15wt%, limit oxygen index (LOI) values of MAH-DOPS/EP and DOPS/EP are 28.6% and 29.1%, reaching UL-94 V-0 and V-1 rating, respectively. The mechanical test results show that compared with EP, the bending strength of MAH-DOPS/EP increases by 45.8%, while DOPS/EP decreases by 62.5%. The mechanical properties of DOPS/EP system decrease obviously, and almost lose the use value. Cone calorimeter tests show that the average heat release rate (av-HRR) and total heat release (THR) of the composite MAH-DOPS/EP decrease significantly. The results of TG-IR show that the H•, O• or HO• free radicals are captured by the phosphorus-containing free radicals generated by the pyrolysis of MAH-DOPS/EP, and the free radicals are quenched. SEM-EDS results show that MAH-DOPS/EP can form a more complete and compact char layer, and the content of P in the char layer is higher. The study shows that MAH-DOPS plays a flame retardant role in gas phase and condensed phase through flame suppression and char formation respectively, and the gas phase flame retardant mechanism is the main one. -
表 1 阻燃环氧树脂的配方
Table 1. Formulation of flame retardant epoxy resin
Sample Composition/g EP MTHPA BDMA MAH-DOPS DOPS 5wt%MAH-DOPS/EP 100 85 1 9.79 — 5wt%DOPS/EP 100 85 1 — 9.79 10wt%MAH-DOPS/EP 100 85 1 20.67 — 10wt%DOPS/EP 100 85 1 — 20.67 15wt%MAH-DOPS/EP 100 85 1 32.82 — 15wt%DOPS/EP 100 85 1 — 32.82 Notes: EP—Epoxy resin; MTHPA—Methyl tetrahydrophthalic anhydride; BDMA—N,N-dimethylbenzylamine; MAH-DOPS—Maleic anhydride-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-sulfide; DOPS—9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-sulfide. 表 2 两种阻燃剂在氮气下的TG和DTG数据
Table 2. TG and DTG data of two flame retardants in N2
Sample T5%/℃ T10%/℃ T50%/℃ TP1/℃ TP2/℃ Rmax1 Rmax2 Char residue
at 600℃/%DOPS 205.4 216.9 341.6 225.5 381.5 0.31 0.83 3.57 MAH-DOPS 235.2 248.7 435.4 245.1 469.7 0.34 0.86 15.81 Notes: T5%, T10%, T50%—Temperature corresponding to weight loss 5%, 10% and 50% of material; TP—Temperature corresponding to maximum thermal degradation rate; Rmax—Maximum thermal degradation rate. 表 3 EP及其复合材料在氮气下的TG、DTG数据
Table 3. TG and DTG data of EP and EP composites in N2
Sample T5%/℃ T10%/℃ T50%/℃ TP1/℃ TP2/℃ Rmax1 Rmax2 Char residue at 600℃/% EP 345.1 369.7 410.1 407.6 — 1.61 — 7.22 5wt%MAH-DOPS/EP 271.2 326.5 400.8 402.6 — 1.50 — 8.90 10wt%MAH-DOPS/EP 292.8 342.8 393.2 395.1 — 1.53 — 11.42 10wt%DOPS/EP 230.2 276.5 409.8 308.1 449.7 0.37 0.79 3.52 15wt%MAH-DOPS/EP 319.2 357.1 402.8 392.5 — 1.49 — 11.93 表 4 EP及其复合材料的LOI和垂直燃烧测试(UL-94)数据
Table 4. LOI and vertical combustion test (UL-94) data of EP an EP composites
Sample LOI/% UL-94 t1/t2 Dripping Rating EP 19.5 — NO N.R. 5wt%DOPS/EP 26.2 >50/>50 NO N.R. 5wt%MAH-DOPS/EP 24.9 19.21/15.08 NO V-2 10wt%DOPS/EP 30.7 5.81/43.53 NO V-2 10wt%MAH-DOPS/EP 27.1 15.37/13.42 NO V-1 15wt%DOPS/EP 29.1 12.27/1.91 NO V-1 15wt%MAH-DOPS/EP 28.6 5.01/4.45 NO V-0 Notes: LOI—Limiting oxygen index; t1/t2—First and second combustion time in UL-94 test; N.R.—No rating. 表 5 EP和MAH-DOPS/EP的锥形量热测试(CONE)数据
Table 5. Cone calorimeter (CONE) data of EP and MAH-DOPS/EP
Sample TTI/s av-HRR/
(kW·m−2)PHRR/
(kW·m−2)THR/
(MJ·m−2)av-EHC/
(MJ·kg−1)TSR/
(m2·m−2)av-COY/
(kg·kg−1)EP 66 218.88 918.01 155.57 31.41 2251.69 0.21 5wt%MAH-DOPS/EP 55 129.55 697.83 96.98 28.31 2859.35 0.27 10wt%MAH-DOPS/EP 58 132.37 644.54 81.43 27.82 2873.67 0.33 15wt%MAH-DOPS/EP 52 137.43 603.67 71.37 28.75 3098.42 0.37 Notes: TTI—Time to ignition; av-HRR—Average heat release rate; PHRR—Peak heat release rate; THR—Total heat release; av-EHC—Average effective heat of combustion; TSR—Total smoke release; av-COY—Average carbon monoxide yield. 表 6 MAH-DOPS/EP残炭的EDS数据
Table 6. EDS data of char residues of MAH-DOPS/EP
Sample Char residue Composites C/wt% O/wt% P/wt% S/wt% P/wt% S/wt% 5wt%MAH-DOPS/EP 67.70 24.17 7.06 1.07 0.47 0.48 10wt%MAH-DOPS/EP 64.45 29.57 5.32 0.28 0.94 0.97 15wt%MAH-DOPS/EP 66.01 29.18 4.01 0.81 1.41 1.46 表 7 EP和MAH-DOPS/EP的力学性能
Table 7. Mechanical properties of EP and MAH-DOPS/EP
Sample Bending strength/MPa Bending modulus/MPa Tensile strength/MPa Notched izod impact strengh/(kJ·m−2) EP 96.47 2326.68 75.19 3.11 5wt%MAH-DOPS/EP 125.33 3224.83 52.39 2.94 10wt%MAH-DOPS/EP 140.66 4099.70 47.56 2.89 15wt%MAH-DOPS/EP 116.46 3258.97 30.63 2.67 -
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