Preparation and performance of flame-retardant epoxy resin composite containing phosphorus and nitrogen
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摘要: 为改善环氧树脂的阻燃性，成功合成了一种含苯砜基和磷杂菲杂环的阻燃添加剂(FRASP)。采用傅里叶变换衰减全反射红外光谱法(ATR-FTIR)、核磁共振(NMR)和元素分析等手段对FRASP的化学结构进行表征。将FRASP添加到双酚A型环氧树脂(DGEBA)中，经4,4’-二氨基二苯甲烷(DDM)固化后，制备出DGEBA-FRASP复合树脂。FRASP质量分数为9wt%的DGEBA-FRASP复合树脂的极限氧指数(LOI)达到35.9%，垂直燃烧(UL94)的等级为V-0级。残炭的形貌和激光拉曼光谱(LRS)分析显示，FRASP促进膨胀、致密、高石墨化程度的多孔炭层的生成。热重分析表明，FRASP改变了DGEBA-FRASP复合树脂的热降解过程，促进了DGEBA-FRASP复合树脂提前热分解，使最大失重率降低，并提高了残炭量。热裂解分析显示，DGEBA-FRASP复合树脂裂解过程中产生了含磷分子和不可燃气体，可稀释O2并抑制燃烧过程中自由基链式反应。FRASP分子中P、N和S的协同作用，改善了DGEBA-FRASP复合树脂的阻燃性能。Abstract: A flame retardant additive with sulfone and phosphaphenanthrene groups (FRASP) was successfully synthesized for improving the flame retardancy of diglycidyl ether of bisphenol A type epoxy resins (DGEBA). The chemical structure of FRASP was characterized by attenuated total internal reflectance Fourier transform infrared spectroscopy (ATR-FTIR), nuclear magnetic resonance (NMR) and elemental analysis. FRASP was added into DGEBA, and the flame-retardant DGEBA-FRASP composite resins were prepared via thermal curing reaction between 4,4’-diaminodiphenyl methane (DDM) and the mixed DGEBA. When the mass fraction of FRASP is 9wt%, the limiting oxygen index (LOI) reaches 35.9%, and V-0 rating under the vertical combustion (UL94) test is achieved. The morphology and Laser Raman spectroscopy (LRS) analysis of char residues after UL94 test indicate that the addition of FRASP favor the generation of an intumescent, tight and high-graphitization degree char layer with porous structure inside. The thermosgravimetric analysis results reveal that FRASP changes the thermal degradation process of DGEBA-FRASP composite resins and the maximum mass loss rate decreases, which results in a higher residual char. Pyrolysis-gas chromatography/mass spectrometry analysis shows that the phosphorus fragments and nonflammable gas release during DGEBA-FRASP composite resins thermal decomposition, which can dilute the O2 and act as free radical inhibitors in combustion. Owing to the synergistic effect of P, N and S in condensed and gas phase, the DGEBA-FRASP composite resins display improved flame-retardancy.
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Keywords:
- thermosetting resin /
- thermal analysis /
- flame retardant /
- epoxy resin /
- synergism
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环氧树脂因其优良的特性被广泛用于电子电气、涂层和建筑材料等领域[1-3]，但其易燃性具有潜在的火灾隐患[4-8]。通过添加阻燃剂可提高环氧树脂的阻燃性能。自欧盟颁布限制使用部分含卤化合物(持久性有机污染物(POPs))的环境法案以来，含磷类阻燃剂因其良好的阻燃性及环保性近年来得到广泛关注[9-11]。9,10-二氢-9-氧杂-10-磷杂菲-10-氧化物(DOPO)作为一种含磷中间体，分子中P—H键具有活泼的反应性，可与多种缺电子化合物(如亚胺)发生加成反应，制备出具有阻燃性的含DOPO基团的化合物[12-14]。通过合理的分子结构设计，还可引入多种其他元素，从而形成协同效应[6,15-18]。
本研究通过分子结构设计，以对二氨基二苯基砜(DDS)为含氮供体，DOPO为含磷供体，制备出含P、N和S的无卤的含苯砜基和磷杂菲杂环的阻燃添加剂(FRASP)，并用于双酚A型环氧树脂(DGEBA)-FRASP复合阻燃环氧树脂的制备。采用红外、核磁和元素分析等手段对FRASP分子结构进行表征，应用垂直燃烧(UL94)测试和极限氧指数(LOI)测试对DGEBA-FRASP复合树脂的阻燃性能进行评价，利用SEM和拉曼光谱分析研究了残炭形貌和石墨化程度，并对DGEBA-FRASP复合树脂的热稳定性和裂解行为进行分析。
1. 实验材料及方法
1.1 原材料
9,10-二氢-9-氧杂-10-磷杂菲-10-氧化物(DOPO)，在乙醇中重结晶后使用，上海诺泰化工有限公司；4,4’-二氨基二苯砜(DDS，97%)、对苯二甲醛(98%)，Aladdin；无水乙醇、4,4’-二氨基二苯甲烷(DDM，99%)、二甲基甲酰胺(DMF)，均为AR，国药化学试剂；双酚A型环氧树脂(DGEBA)，商品名：E-44，昆山绿循化工。
1.2 含苯砜基和磷杂菲杂环的阻燃添加剂(FRASP)的合成
FRASP的合成过程：(1) 对苯二甲醛与DDS通过缩合反应生成中间体亚胺(DP)，在配有磁力搅拌和回流装置的四口烧瓶中加入DDS和乙醇，N2保护下搅拌加热至70℃，缓慢滴加对苯二甲醛的乙醇溶液，保温2 h后，加入2滴冰醋酸，升温至乙醇回流温度, 保温反应6 h。将混合物自然冷却至室温，过滤、洗涤后，真空烘干(60℃，24 h)，得到橙红色固体DP，产率为90.5%；(2) DP与DOPO进行加成反应生成产物FRASP，取定量DP，DOPO加入到装有磁力搅拌和回流装置的三口烧瓶中，加入N,N-二甲基甲酰胺(DMF)，搅拌下加热至回流温度，保温反应24 h后，冷却至室温，过滤洗涤后，真空烘干(80℃，24 h)，得白色固体FRASP，产率为91.4%。FRASP的合成路线如图1所示。
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图 1 含苯砜基和磷杂菲杂环的阻燃添加剂(FRASP)的合成路线Figure 1. Synthetic routes of flame retardant additive with sulfone and phosphaphenanthrene groups (FRASP)DP—N-phenylsulfonyl dibenzimide; DMF—N,N-dimethylformamide1.3 DGEBA-FRASP复合树脂的制备
定量的DDM与FRASP混合后，加入到带有搅拌器的三口圆底烧瓶中，油浴中加热至80℃，待混合物变均匀、透明后，保温15 min，加入定量的DGEBA，快速搅拌5 min，随后将混合物倒入到垂直燃烧(UL94)、极限氧指数(LOI)和拉伸性能测试所需样品尺寸(分别依据UL94垂直燃烧实验方法、ASTM D2863—19[19]和ASTM D638—08[20])的模具中，转移至烘箱，在120℃下保温固化2 h后，升温至160℃保温固化2 h。自然冷却至室温后，从模具中取出，得到不同FRASP质量分数的DGEBA-FRASP复合树脂，各成分组成及FRASP质量分数如表1所示。
表 1 双酚A型环氧树脂(DGEBA)-FRASP复合树脂的配方及FRASP的质量分数Table 1. Formulas of diglycidyl ether of bisphenol A(DGEBA)-FRASP composite reins and mass fraction of FRASPSample Composition/g MFRASP/wt% DGEBA DDM FRASP Neat DGEBA 100 22 0 0 DGEBA-FRASP3 100 22 3.77 3 DGEBA-FRASP6 100 22 7.79 6 DGEBA-FRASP9 100 22 12.07 9 Notes: DDM—4,4-diaminodiphenyl methane; MFRASP—Mass fraction of FRASP in DGEBA-FRASP composite resins. 1.4 测试与表征
采用珀金埃尔默Spectrum Two (USA)对样品的傅里叶变换衰减全反射红外光谱进行测试；采用布鲁克Avance spectrometer (400 MHz)核磁共振仪对样品进行1H-Nuclear Magnetic Resonance(NMR)和31P-NMR测试，测试溶剂为氘代二甲基亚砜(DMSO-d6)，四甲基硅烷(TMS)为标准参照物，将10.0 mg左右聚合物样品完全溶解于核磁样品管中；采用美国Leeman Prodigy 型电感耦合等离子体原子发射仪对样品进元素分析，对产物中C、H、N、P元素进行含量分析；采用德国NETZSCH公司的TG 209 F1 thermal analyzer对样品进行热重分析(TGA)，N2和空气氛围下，升温速率为10℃/min，测试温度为室温至800℃；采用意大利ATS FAAR公司Oxygen Index Flammability Gauge对样品的LOI进行测试，样品尺寸为130 mm×6.5 mm×3 mm；样品的燃烧性能测试尺寸为130 mm×12.7 mm×3 mm；采用日本的Hitachi公司TM-1000型SEM观察UL94测试后残炭的微观形貌，电压为20 kV，放大倍数为300倍；残炭形貌(N2氛围中热降解)：将固定尺寸(12.7 mm×12.7 mm×3.0 mm，从UL94测试样条上截取)的环氧树脂置于上海升利公司SLG40型气氛炉中，在N2氛围下以10℃/min的升温速度升温600℃，随后自然降温至室温，取出观察形貌并用数码相机记录。采用SPEX-1430型激光拉曼光谱仪(SPEX，USA)对残炭进行拉曼光谱分析，激光光源为633 nm氩激光器，扫描范围为500~2500 cm−1。根据ASTM D638—08[20]，1BA型样条，总长为75 mm，标距为25 mm，厚度为2.1 mm，采用英国Housfield公司的H5K-S型万能材料测试仪进行拉伸性能测试。
2. 结果与讨论
2.1 FRASP的微观结构
图2为对苯二甲醛、DDS、DP和 FRASP的FTIR图谱。可以发现，第一步合成产物DP在1699 cm−1处出现亚胺键—N=C—的吸收峰，说明DDS与对苯二甲醛发生亚胺化反应。在FRASP的FTIR图谱中，1594 cm−1和1477 cm−1 处出现苯环上P—CAr键的伸缩振动峰，在1330 cm−1处出现—C—N—键的振动吸收峰，在1285 cm−1和1230 cm−1处出现P=O的伸缩振动峰，在924 m−1和751 m−1处出现P—O—CAr 的伸缩振动峰[21-22]，且在2436 cm−1处未发现P—H键的伸缩振动峰[23]，说明DOPO已与DP进行加成反应，形成了FRASP。
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图 2 对苯二甲醛、4,4’-二氨基二苯砜(DDS)、亚胺(DP)和FRASP的FTIR图谱Figure 2. FTIR spectra of 1,4-Phthalaldehyde, 4,4’-diaminodiphenylsulfon (DDS), N-phenylsulfonyl dibenzimide (DP) and FRASP图3为FRASP的31P-NMR and 1H-NMR图谱。由图3(a)可以看到，化学位移为5.22×10–6~5.32×10–6处发现P—C—H基团中H的特征吸收峰，化学位移为5.68×10–6~5.82×10–6处观测到—NH—基团中的H吸收峰；化学位移为6.01×10–6处观测到CAr—NH2基团的H吸收峰，化学位移为6.56×10–6~8.21×10–6处观测到苯环上H吸收峰，与FRASP分子结构一致。
由图3(b)可以看到，在化学位移为30.95×10–6和28.44×10–6处出现两个吸收峰，对应FRASP分子中重复单元的P原子。这是由于芳砜基的强吸电子作用和刚性DOPO基团产生的空间位阻效应导致FRASP分子中P原子在31P-NMR上的化学位移偏离，而产生这种双峰现象[24-26]。
FRASP元素分析测试结果为：C含量为67.51wt%，H含量为4.16wt%，N含量为3.84wt%，P含量为7.57wt%。根据 FRASP的分子结构，计算不同重复单元数n下C、H、N、P等元素的含量，当n为5时，FRASP理论分子量为4 474.34，理论分子式为C252H185N12O35P11S6，各元素理论含量计算值为：C含量为67.64wt%，H含量为4.18wt%，N含量为3.75wt%，P含量为7.61wt%，测试值与n为5时的理论值相近。
因此，根据红外、核磁和元素分析结果可知，FRASP被成功合成，产物中主要以重复单元数n为5的FRASP分子。
2.2 DGEBA和DGEBA-FRASP树脂的阻燃性能
表2为DGEBA及DGEBA-FRASP树脂的UL94和LOI测试结果。可知，DGEBA树脂的LOI为24.8%，在第一次点火后，持续燃烧并燃尽。添加FRASP后，DGEBA-FRASP复合树脂的LOI随FRASP质量分数的增加而逐渐增大，由DGEBA-FRASP3复合树脂的33.7%增大至DGEBA-FRASP9复合树脂的35.9%，UL94测试中第一次点火后的自熄灭时间和第二次点火后的自熄灭时间(t1+t2)由DGEBA-FRASP3复合树脂的(6.1+6.3) s降低到DGEBA-FRASP9复合树脂的(2.3+1.9) s，并达到V-0级。
表 2 DGEBA和DGEBA-FRASP树脂的垂直燃烧(UL94)和极限氧指数(LOI)测试结果Table 2. Vertical combustion (UL94) and limiting oxygen index (LOI) test results of DGEBA and DGEBA-FRASP resinsSample LOI/% t1 +t2/s Dripping Rating DGEBA 24.8 NR Yes No rating DGEBA-FRASP3 33.7 6.1+6.3 No V-1 DGEBA-FRASP6 34.5 4.3+3.0 No V-0 DGEBA-FRASP9 35.9 2.3+1.9 No V-0 Notes: t1—Self-extinguishing time after the first ignition, take the average value of 2 sets of samples; t2—Self-extinguishing time after the second ignition, take the average value of 2 sets of samples; NR—No ranking. 图4为DGEBA和DGEBA-FRASP树脂在UL94测试时的图片。可以发现，添加FRASP后，DGEBA-FRASP复合树脂的燃烧行为明显减缓。一般认为，含磷阻燃剂主要在凝聚相起到阻燃作用，而含氮和硫类阻燃剂主要在气相中发挥阻燃作用。FRASP分子结构中的DOPO基团及含硫和含氮基团在燃烧过程中能促进成炭，形成致密、多孔的炭层，在凝聚相发挥阻燃作用；同时通过生成的含磷分子(自由基)和含硫、氮不可燃气体在气相中发挥阻燃作用[27-29]。在UL94测试过程中，发现有气体从试样内部冲出，吹灭火焰，这可能是由于当足够量的不可燃气体在因燃烧产生的致密炭层下集聚后最终冲出炭层时，因O2稀释将炭层外正在燃烧的火焰吹灭，形成“吹熄”效应[30]。FRASP的复合提高了DGEBA-FRASP复合树脂的阻燃性能。
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图 4 DGEBA和DGEBA-FRASP树脂在UL94测试时的图片Figure 4. Digital photographs of DGEBA and DGEBA-FRASP resins in UL94 test2.3 DGEBA和DGEBA-FRASP树脂燃烧后的残炭形貌
图5为UL94测试后DGEBA和DGEBA-FRASP树脂残炭形貌的图片及其圆形标注区域相应位置的SEM图像。从图5(a)可以观察到，UL94测试后，纯DGEBA树脂的残炭呈收缩形貌，而添加FRASP后的DGEBA-FRASP复合树脂的残炭基本保持长方体三维结构，且在试样上观测到山丘状的凸起物(图5(a)中方框标注)，部分凸起物上有破裂的大气孔，也正是在这些位置发现了气体冲出并吹熄火焰的现象。由图5(b)可以发现，纯DGEBA树脂的结构松散，而DGEBA-FRASP复合树脂具有紧密而膨胀的丘壑状外观；由图5(c)可以看到，纯DGEBA树脂的残炭不连续且带有裂纹，而DGEBA-FRASP复合树脂具有光滑而多孔的结构，这种膨胀、多孔的残炭在燃烧过程中可起到保护层的作用，隔绝热源对试样的传热，从而在凝聚相起到提高阻燃性的作用。
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图 5 DGEBA和DGEBA-FRASP树脂残炭的照片和SEM图像Figure 5. Digital photographs and SEM images of char residue of DGEBA and DGEBA-FRASP resins图6为N2氛围下DGEBA和DGEBA-FRASP树脂热降解前、残炭外部和残炭内部的图片。从图6(a)可以看到，添加FRASP后，改变了环氧树脂的光学性质，DGEBA-FRASP复合树脂颜色随着FRASP添加量的增加而加深，呈黄棕色，未见明显的聚集现象，FRASP在DGEBA-FRASP树脂中分布均匀，呈半透明外观。由图6(b)可以看到，纯DGEBA树脂为片状结构，而DGEBA-FRASP复合树脂呈膨胀的立体结构，体积远远大于热解前的体积。由图6(c)可以看到，切开残炭，发现残炭内部为空心结构，这是在热降解过程中，内部产生大量热降解气体充斥在炭层中，形成了内部空心的膨胀立体结构，与SEM图像中观测到残炭紧密而多孔的形貌一致，表明FRASP促进了环氧树脂在降解过程中产生紧密而多孔的炭层。
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图 6 N2氛围下DGEBA和DGEBA-FRASP树脂热降解前(a)、残炭外部(b)和残炭内部(c)的图片Figure 6. Digital photographs of DGEBA and DGEBA-FRASP resins before degradation(a) and exterior(b) and interior(c) of char residue after degradation in N2图7为N2氛围下DGEBA和DGEBA-FRASP树脂热降解后残炭的拉曼散射图谱。可知，1352 cm−1附近的峰(D峰)对应C原子晶体的缺陷，表示分子无序排列，1574 cm−1附近的峰(G峰)对应C原子sp2杂化的面内伸缩振动，与石墨化性质有关[31]。D峰与G峰的强度比(ID/IG)可以用对应的峰面积比值计算，ID/IG越大表明残炭的无序化，ID/IG越小表明残炭的有序度高，石墨化程度越高[32-34]。通过对DGEBA 和DGEBA-FRASP树脂残炭的拉曼散射曲线的分峰拟合，计算得到DGEBA残炭的ID/IG为1.65，而DGEBA-FRASP9复合树脂残炭的ID/IG为1.31，说明DGEBA-FRASP复合树脂的残炭石墨化程度更高，排列更有序，在热降解过程中，更紧密的炭层能起到更好的保护和隔绝作用。
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图 7 DGEBA和DGEBA-FRASP树脂残碳的拉曼图谱Figure 7. Raman spectra of char residue of DGEBA and DGEBA-FRASP resins2.4 DGEBA-FRASP复合树脂的热稳定性
图8为FRASP、DGEBA和DGEBA-FRASP树脂在空气下的TG和DTG曲线。图9为FRASP、DGEBA和DGEBA-FRASP树脂在N2下的TG和DTG曲线。表3为FRASP、DGEBA和DGEBA-FRASP树脂在空气下的TGA数据。表4为FRASP、DGEBA和DGEBA-FRASP树脂在N2下的TGA数据。
表 3 FRASP、DGEBA和DGEBA-FRASP树脂在空气下的TGA数据Table 3. TGA data of FRASP, DGEBA and DGEBA-FRASP resins in air atmosphereSample T5%/℃ Tmax/℃ Vmax/(%·℃–1) CY700/% DGEBA 362.2 384.7 –1.45 1.90 FRASP 292.1 361.4 –0.46 43.41 DGEBA-FRASP3 343.8 374.6 –1.26 2.85 DGEBA-FRASP6 339.1 368.3 –1.14 3.72 DGEBA-FRASP9 332.4 363.2 –1.13 5.74 Notes: T5%―Temperature at 5% mass loss; Tmax―Temperature at the maximum mass loss rate; Vmax―Maximum mass loss rate; CY700―Char yield at 700℃. 表 4 FRASP、DGEBA和DGEBA-FRASP树脂在N2下的TGA数据Table 4. TGA data of FRASP, DGEBA and DGEBA-FRASP resins in N2 atmosphereSample T5%/℃ Tmax/℃ Vmax/(%·℃–1) CY700/% DGEBA 367.9 387.2 –1.76 16.58 FRASP 310.1 365.3 –0.81 33.40 DGEBA-FRASP3 357.8 382.1 –1.25 19.48 DGEBA-FRASP6 353.9 379.6 –1.19 21.27 DGEBA-FRASP9 341.3 377.1 –1.16 22.96 ![]()
图 8 FRASP、DGEBA和DGEBA-FRASP树脂在空气下的TG和DTG曲线Figure 8. TG and DTG curves of FRASP, DGEBA and DGEBA-FRASP resins in air atmosphere![]()
图 9 FRASP、DGEBA和DGEBA-FRASP树脂在N2下的TG和DTG曲线Figure 9. TG and DTG curves of FRASP, DGEBA and DGEBA-FRASP resins in N2 atmosphere由图8和表3可知，在空气中，DGEBA和DGEBA-FRASP树脂的TG曲线均出现两次快速降解过程，与DTG曲线中两个波谷一致。与纯DGEBA相比，添加FRASP后，DGEBA-FRASP复合树脂初始降解温度下降，失重率为5%时的温度T5%由DGEBA的362.2℃下降到DGEBA-FRASP9复合树脂的332.4℃，表明FRASP使环氧树脂的热降解提前，热稳定性下降，有利于在降解初始阶段快速成炭，降低热流的传递效率。这种热降解提前的现象是含磷裂解产物在材料表面脱水炭化形成的炭化层导致的。最大失重速率温度Tmax也随着FRASP添加量的增加由DGEBA的384.7℃降低到DGEBA-FRASP9复合树脂的363.2℃；最大失重速率Vmax由DGEBA的1.45%·℃−1减小到DGEBA-FRASP9复合树脂的1.13%·℃−1，失重速率下降，促进了残炭量的增加，700℃时的残炭率CY700由DGEBA的1.90%增大到DGEBA-FRASP9复合树脂的5.74%。FRASP作为含P、N和S的阻燃剂，改变了DGEBA-FRASP复合树脂的热降解过程，使其提前热分解形成残炭保护层，并在炭层中通过—P—O—P—等含磷基团的交联作用生成更致密、热稳定更好的聚芳香结构的网状化合物[35]，同时分子中S可进一步增强复合树脂的成炭[28]，提高炭层对火焰的隔绝作用和稳定性，改善DGEBA-FRASP复合树脂的阻燃性能。
由图9和表4可知，与在空气中不同，在N2中环氧树脂的降解只出现一次快速降解过程，对应DTG曲线中的一个波谷。与在O2中一致的是，FRASP降低了DGEBA-FRASP复合树脂的T5%、Tmax和Vmax，提高了700℃时的残炭率，700℃时的残炭率由DGEBA的16.58%增加到DGEBA-FRASP9复合树脂的22.96%。FRASP与DGEBA的复合使环氧树脂的热降解提前，在降解初始阶段迅速脱水成炭，形成炭化层，保护树脂基体进一步热降解，降低了热失重速率，残炭率增大，从而提高DGEBA-FRASP复合树脂的阻燃性能。
2.5 DGEBA-FRASP复合树脂的热裂解
图10为FRASP的热裂解图谱。图11为DGEBA和DGEBA-FRASP树脂的热裂解图谱。由图10可见，FRASP的裂解产物主要为苯胺、邻苯基苯酚、联苯和二苯并呋喃，峰面积占比分别为27.8%、4.82%、5.28%和45.61%，还有少量的SO2气体(峰面积占比为1.49%)。根据这些产物的结构和FRASP分子特征，推测FRASP的分解主要是在C—N键和C—P键的断裂。其中，二苯并呋喃是FRASP分子中DOPO基团的C—P键和P—O键断裂释放出含磷分子而形成的产物[27,36]。FRASP的裂解分析表明，在热裂解过程中，含磷自由基和SO2等不可燃气体的产生可在气相起到阻燃作用。
由图11可以发现，DGEBA与DGEBA-FRASP9复合树脂的裂解产物大致相同，但产物的相对面积发生明显变化。在DGEBA-FRASP9复合树脂的裂解产物中发现二苯并呋喃、联苯和邻苯基苯酚，这些裂解产物也出现在FRASP的裂解产物中。依据Schartel等和Zhang等[36-37]的建议，二苯并呋喃、联苯和邻苯基苯酚是FRASP分子中P—C键和P—O键受热断裂释放出含磷分子而形成的产物，在DGEBA的裂解产物中未发现，表明在DGEBA-FRASP9复合树脂的裂解过程中有含磷分子(主要是含磷自由基)产生。在燃烧过程中，这些含磷分子可以捕捉火焰中的H和HO自由基，抑制燃烧的自由基链式反应，阻止火焰的传播，从而使燃烧区的火焰密度下降，燃烧速度下降，直至燃烧终止；同时，DGEBA-FRASP9复合树脂在裂解过程中产生了少量的SO2和含氮气体，这些不可燃气体可以起到稀释O2的作用，与含磷分子一起在气相起到阻燃作用。产物中还发现了具有长碳链的烷烃(如图11中所示的产物A)，在DGEBA中未发现，说明FRASP改变了DGEBA-FRASP复合树脂的裂解过程，促进了大分子裂解产物的形成，在一定程度上可降低DGEBA-FRASP复合树脂热降解速率，延缓火焰燃烧速度，提高DGEBA-FRASP复合树脂的阻燃性能。
3. 结 论
(1)成功合成了一种含苯砜基和磷杂菲杂环的阻燃添加剂(FRASP)，并对其化学结构进行表征。
(2) FRASP用于双酚A型环氧树脂(DGEBA)的复合，提高了DGEBA-FRASP复合树脂的阻燃性能。当FRASP质量分数为9wt%时，DGEBA-FRASP复合树脂的极限氧指数(LOI)为35.9%，垂直燃烧(UL94)的等级为V-0级。
(3) FRASP降低了DGEBA-FRASP复合树脂失重5%时的温度、最大失重速率温度和最大失重速率，当FRASP质量分数为9wt%时，DGEBA-FRASP复合树脂的残炭率在空气和N2气氛下分别为5.74%和22.96%；DGEBA-FRASP复合树脂在燃烧过程中形成了致密、膨胀、多孔的炭层，可在凝聚相发挥阻燃作用。
(4) DGEBA-FRASP复合树脂在热裂解过程中能形成含磷分子和不可燃气体，可在气相中发挥阻燃作用。
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图 1 含苯砜基和磷杂菲杂环的阻燃添加剂(FRASP)的合成路线
Figure 1. Synthetic routes of flame retardant additive with sulfone and phosphaphenanthrene groups (FRASP)
DP—N-phenylsulfonyl dibenzimide; DMF—N,N-dimethylformamide
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图 2 对苯二甲醛、4,4’-二氨基二苯砜(DDS)、亚胺(DP)和FRASP的FTIR图谱
Figure 2. FTIR spectra of 1,4-Phthalaldehyde, 4,4’-diaminodiphenylsulfon (DDS), N-phenylsulfonyl dibenzimide (DP) and FRASP
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图 4 DGEBA和DGEBA-FRASP树脂在UL94测试时的图片
Figure 4. Digital photographs of DGEBA and DGEBA-FRASP resins in UL94 test
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图 5 DGEBA和DGEBA-FRASP树脂残炭的照片和SEM图像
Figure 5. Digital photographs and SEM images of char residue of DGEBA and DGEBA-FRASP resins
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图 6 N2氛围下DGEBA和DGEBA-FRASP树脂热降解前(a)、残炭外部(b)和残炭内部(c)的图片
Figure 6. Digital photographs of DGEBA and DGEBA-FRASP resins before degradation(a) and exterior(b) and interior(c) of char residue after degradation in N2
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图 7 DGEBA和DGEBA-FRASP树脂残碳的拉曼图谱
Figure 7. Raman spectra of char residue of DGEBA and DGEBA-FRASP resins
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图 8 FRASP、DGEBA和DGEBA-FRASP树脂在空气下的TG和DTG曲线
Figure 8. TG and DTG curves of FRASP, DGEBA and DGEBA-FRASP resins in air atmosphere
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图 9 FRASP、DGEBA和DGEBA-FRASP树脂在N2下的TG和DTG曲线
Figure 9. TG and DTG curves of FRASP, DGEBA and DGEBA-FRASP resins in N2 atmosphere
表 1 双酚A型环氧树脂(DGEBA)-FRASP复合树脂的配方及FRASP的质量分数
Table 1 Formulas of diglycidyl ether of bisphenol A(DGEBA)-FRASP composite reins and mass fraction of FRASP
Sample Composition/g MFRASP/wt% DGEBA DDM FRASP Neat DGEBA 100 22 0 0 DGEBA-FRASP3 100 22 3.77 3 DGEBA-FRASP6 100 22 7.79 6 DGEBA-FRASP9 100 22 12.07 9 Notes: DDM—4,4-diaminodiphenyl methane; MFRASP—Mass fraction of FRASP in DGEBA-FRASP composite resins. 
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表 2 DGEBA和DGEBA-FRASP树脂的垂直燃烧(UL94)和极限氧指数(LOI)测试结果
Table 2 Vertical combustion (UL94) and limiting oxygen index (LOI) test results of DGEBA and DGEBA-FRASP resins
Sample LOI/% t1 +t2/s Dripping Rating DGEBA 24.8 NR Yes No rating DGEBA-FRASP3 33.7 6.1+6.3 No V-1 DGEBA-FRASP6 34.5 4.3+3.0 No V-0 DGEBA-FRASP9 35.9 2.3+1.9 No V-0 Notes: t1—Self-extinguishing time after the first ignition, take the average value of 2 sets of samples; t2—Self-extinguishing time after the second ignition, take the average value of 2 sets of samples; NR—No ranking.
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表 3 FRASP、DGEBA和DGEBA-FRASP树脂在空气下的TGA数据
Table 3 TGA data of FRASP, DGEBA and DGEBA-FRASP resins in air atmosphere
Sample T5%/℃ Tmax/℃ Vmax/(%·℃–1) CY700/% DGEBA 362.2 384.7 –1.45 1.90 FRASP 292.1 361.4 –0.46 43.41 DGEBA-FRASP3 343.8 374.6 –1.26 2.85 DGEBA-FRASP6 339.1 368.3 –1.14 3.72 DGEBA-FRASP9 332.4 363.2 –1.13 5.74 Notes: T5%―Temperature at 5% mass loss; Tmax―Temperature at the maximum mass loss rate; Vmax―Maximum mass loss rate; CY700―Char yield at 700℃.
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表 4 FRASP、DGEBA和DGEBA-FRASP树脂在N2下的TGA数据
Table 4 TGA data of FRASP, DGEBA and DGEBA-FRASP resins in N2 atmosphere
Sample T5%/℃ Tmax/℃ Vmax/(%·℃–1) CY700/% DGEBA 367.9 387.2 –1.76 16.58 FRASP 310.1 365.3 –0.81 33.40 DGEBA-FRASP3 357.8 382.1 –1.25 19.48 DGEBA-FRASP6 353.9 379.6 –1.19 21.27 DGEBA-FRASP9 341.3 377.1 –1.16 22.96
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