Synthesis and flame-retardant properties of the epoxy resin based on phenanthroline and magnolol
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摘要: 商用环氧树脂主要由不可再生的石油基原料制得，且存在易燃、离火不自熄的问题，限制了它在电子电气和轨道交通等领域的广泛应用。因此，以生物质化合物厚朴酚、9,10-二氢-9-氧杂-10-磷杂菲-10-氧化物 (DOPO)和环氧氯丙烷为原料，合成了一种磷杂菲-厚朴酚基环氧低聚物(ED-0.5)，并以4,4'-二氨基二苯基甲烷(DDM)为环氧固化剂，制备高阻燃效率的环氧固化树脂(ED-0.5/DDM)。通过FTIR、NMR表征了其化学结构，利用DSC和TGA研究了环氧固化树脂的固化动力学和热稳定性，采用极限氧指数、垂直燃烧、锥形量热仪探究了环氧固化树脂的阻燃性能，通过TG-FTIR 和SEM分别对固化物热解气相组成和燃烧后残炭形貌结构进行了分析，探究其阻燃机制。结果表明，ED-0.5/DDM树脂热稳定性和热机械性能均优于传统双酚A环氧树脂，固化反应活化能略高。ED-0.5/DDM环氧固化树脂极限氧指数(LOI)可达到52.5%，UL-94测试达到V-0等级，热释放速率峰值和总热释放量分别降低 70.9%和58.2%，残炭增加1565.2%。ED-0.5/DDM环氧固化树脂可通过捕获猝灭自由基，产生大量不燃气体，形成致密炭层，发挥气相和凝聚相协同阻燃作用。Abstract: Commercial epoxy resin is mainly made from non renewable petroleum-based raw materials, and it has the problem of flammability and non self extinguishing, which limits its widespread application in fields such as electronics, electrical engineering, and rail transit. Therefore, a novel epoxy oligomer with magnolol phosphaphenanthrene (ED-0.5) was successfully synthesized with biomass compound magnolol, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and epichlorohydrin, and then a high flame retardant epoxy resin (ED-0.5/DDM) was prepared by using 4,4'- diaminodiphenylmethane (DDM) as the epoxy curing agent. The chemical structure was characterized by FTIR and NMR, and the curing kinetics and thermal stability of epoxy resin were studied by DSC and TGA. The flame retardancy of epoxy resin was investigated by limiting oxygen index, vertical combustion, and cone calorimeter. The thermal decomposition gas phase composition of the cured resin and the morphology of the carbon layer after combustion of the epoxy resin were analyzed by TG-FTIR and SEM, respectively, to study its flame retardancy mechanism. The results showed that the thermal stability and thermal mechanical properties of ED-0.5/DDM epoxy resin were better than traditional bisphenol A epoxy resin, but the activating energy of the curing reaction was higher. The limiting oxygen index (LOI) of ED-0.5/DDM epoxy cured resin can reach 52.5%, passing the V-0 level of UL-94, reducing the peak heat release rate and total heat release by 70.9% and 58.2% respectively, and increasing the residual carbon by 1565.2%. ED-0.5/DDM epoxy resin can capture and quenching active radicals, generate a large amount of non-burning gases, form a dense carbon layer, and exert the synergistic flame retardant effect of gas phase and condensed phase.
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Key words:
- epoxy oligomer /
- magnolol /
- phosphaphenanthrene /
- flame retardancy /
- mechanism
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图 1 磷杂菲-厚朴酚基环氧低聚物(ED-0.5)合成路线
Figure 1. Synthesis route of epoxy oligomer with Magnolol and phosphaphenanthrene (ED-0.5)
图 2 DOPO-M，E-DBP 和 ED-0.5 在不同波数范围内的红外谱图；(a) 4000-500 cm−1，(b) 1700- 1400 cm−1 和(c) 1400-600 cm−1
Figure 2. FTIR spectra of DOPO-M, E-DBP and ED-0.5 at various wavenumber ranges: (a) 4000-500 cm−1 , (b) 1700-1400 cm−1 , and (c) 1400-600 cm−1,(b) 1700-1400 cm−1 , and (c) 1400-600 cm−1
图 4 (a) DGEBA/DDM 和 ED-0.5/DDM在10 K·min−1 的 DSC 曲线；(b) DGEBA/DDM 和(c) ED-0.5/DDM 在不同升温速率下的 DSC 曲线
Figure 4. DSC curves of DGEBA/DDM and ED-0.5/DDM at 10 K·min−1 (a); DSC curves of (b) DGEBA/DDM and (c) ED-0.5/DDM at different heating rates
图 5 (a) DGEBA/DDM 和 ED-0.5/DDM体系固化树脂的DSC曲线；(b) DMA 测试中 DGEBA/DDM和ED-0.5 DDM体系固化树脂的储能模量和Tanδ随着温度的变化图
Figure 5. (a) DSC curves of DGEBA/DDM and ED-0.5/DDM system cured resins; (b) DMA spectra for the storage modulus and Tan δ against temperature of DGEBA/DDM and ED-0.5/DDM system cured resins.
图 6 氮气氛围中 DGEBA/DDM 和 ED-0.5/DDM体系固化树脂的TGA(a)和DTG 曲线(b)
Figure 6. TGA (a) and DTG (b) curves of DGEBA/DDM and ED-0.5/DDM system cured resins (N2 atmosphere)
图 7 UL-94 测试的数码照片；(a)DGEBA/DDM，(b)ED-0.5/DDM
Figure 7. Digital photographs of UL-94: (a) DGEBA/DDM, (b) ED-0.5/DDM
图 8 在45%氧气浓度的条件下(a) DGEBA/DDM，(g) ED-0.5/DDM的LOI测试数码照片
Figure 8. Digital photographs of LOI test at 45% oxygen atmosphere: (a) DGEBA/DDM, (b) ED-0.5/DDM
图 9 锥形量热测试的 DGEBA/DDM 和 ED-0.5/DDM固化树脂的HRR(a)，THR(b)，和RCY(c) 随时间的变化曲线
Figure 9. HRR (a), THR (b), and RCY (c) versus time curves form CC tests for cured DGEBA/DDM and ED-0.5/DDM
图 10 DGEBA/DDM(a)和 ED-0.5/DDM(b)的碎片产物的实时红外谱图
Figure 10. Real-time FTIR spectra of volatile products for DGEBA/DDM (a) and ED-0.5/DDM (b)
图 11 残炭的数码照片；(a)DGEBA/DDM，(b)ED-0.5/DDM，
Figure 11. Digital photographs of the residual char: (a) DGEBA/DDM and (b) ED-0.5/DDM
图 12 (a) E51-DDM 残炭的 SEM 图像；(b) ED-0.5/DDM残炭外层的 SEM 图像(c) ED-0.5/DDM残炭内层的 SEM 图像
Figure 12. SEM images of char for DGEBA/DDM (a), SEM image of residual carbon in the outer layer of ED- 0.5/DDM and residual carbon in the inner layer of ED-0.5/DDM(c)
图 13 DGEBA/DDM和ED-0.5/DDM固化树脂残炭的红外谱图
Figure 13. FTIR spectra of char for DGEBA/DDM and ED-0.5/DDM cured resins
表 1 环氧固化树脂的组成
Table 1. Formulations of flame-retardant epoxy thermoset
Sample Components /wt% Phosphorus/
wt%Gel
content/%Resin DDM DGEBA/DDM 79.8 20.2 - 99.4 ED-0.5/DDM 90.2 9.8 3.1 97.6 Notes：DGEBA-Bisphenol A epoxy resin; DDM-4,4 '-diaminodiphenylmethane; Phosphorus-Theoretical content calculated according to the phosphorus content of the resin; Gel content-insoluble gel fraction as a result of inter-molecule cross-linking formation. 
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表 2 关于ED-0.5的1H-NMR和环氧值滴定的数据
Table 2. The date of H-NMR spectrum and epoxy value titration about ED-0.5.
Sample D(——)P(——)
(1H-NMR)Epoxy value titration Average
quality/gAverage
volume/mLAverage epoxy
value /(mol·100g−1Average molecular
weight /(g·mol−1)D (——)P(——)
(Calculate)DGEBA - 0.41 21.97±0.1 0.536±0.002 373.1±2.6 0.10±0.1 ED-0.5 0.52±0.1 0.60 12.90±0.1 0.215±0.001 930.2±4.3 0.51±0.1 Notes：D(——)P(——)(1H-NMR)-average degree of polymerization measured by 1H-NMR; D(——)P(——) (Calculate)-average degree of polymerization calculated by epoxy titration.
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表 3 环氧固化树脂的非等温固化动力学参数
Table 3. Non-isothermal curing kinetics parameters of the cured resins
Sample Peak Temperature (TP)/(K·min−1) Ec(K)/
(kJ·mol−1)Ec (O)/
(kJ·mol−1)Gel Content/% 5 10 15 20 25 DGEBA/DDM 420.7 438.9 450.1 458.2 466.5 50.7 55.2 99.4 ED-0.5/DDM 397.2 412.2 422.2 427.8 436.9 52.8 56.8 97.6 Notes: Ec(K)-activation energy of reaction calculated by Kissinger equation; Ec (O)-activation energy of reaction calculated by Ozawa equation.
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表 4 DGEBA/DDM和ED-0.5/DDM体系固化树脂的热分析数据
Table 4. Thermal analysis data of DGEBA/DDM and ED-0.5/DDM system cured resins
Sample DGEBA/DDM ED-0.5/DDM Tg /℃ DSC 150.6 167.5 DMA 167.1 185.6 Storage modulus at 30℃/MPa Value 850.4 2072.5 Increase - +143.7% Storage modulus at Tg-DMA +30 K/MPa 11.44 153.47 Content of Biphenyl structure/% - 44.8 Content of benzene ring/% 52.4 52.3 ve × 103/(mol·m−3) 0.98 12.59 Thermal decomposition temperature /℃ Td5% 367.3 396.2 The temperature of the maximum thermal decomposition rate /℃ Tmax1 385.1 415.8 Tmax2 - 483.6 Char yield at 700℃/% Value 20.2 41.2 Note: Tg-glass-transition temperature; ve -Crosslinking density.
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表 5 DGEBA/DDM和ED-0.5/DDM固化树脂阻燃性能参数
Table 5. Flame-retardant property of DGEBA/DDM and ED-0.5/DDM cured resins.
Sample UL-94 LOI/% t1/s t2/s Dripping Rating DGEBA/DDM 124+ - YES NO Rating 26.0 ED-0.5/DDM 0.8 0.8 NO V-0 52.5 Notes: t1- Average combustion times after the first applications of the flame; t2 - Average combustion times after the second applications of the flame: LOI-Limiting Oxygen Index.
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表 6 DGEBA/DDM 和 ED-0.5/DDM固化树脂的锥形量热测试的数据
Table 6. Cone calorimetric data of the DGEBA/DDM and the ED-0.5/DDM cured resins.
Sample DGEBA/DDM ED-0.5/DDM Max-relative value TTI/s 46 29 − pHRR/(kW·m−2) 1629.4 474.4 −70.9% THR/(MJ·m−2) 141.3 59.0 −58.2% Av-EHC/(MJ·kg) 32.7 25.9 −20.8% RCY/% 2.3 38.3 +1565.2% Notes: TTI-Time to ignition; pHRR-Peak heat release rate; THR-Total heat release; av-EHC-Average effective heat combustion; RCY-Residue char yield.
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