Li Liang, Cai Zaisheng
College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai 201620, China.
School of Pharmacy, Yancheng Polytechnic College, Yancheng 224005, China.
Polymers (Basel). 2020 Feb 4;12(2):317. doi: 10.3390/polym12020317.
In this study, a flame-retardant additive with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) groups denoted DSD was successfully synthesized from DOPO, 4,4'-diaminodiphenyl sulfone (DDS), and salicylaldehyde. The chemical structure of DSD was characterized by FTIR-ATR, NMR, and elemental analysis. DSD was used as an amine curing agent, and the transparent, tensile strength-enhanced epoxy resins named EP-DSD were prepared via thermal curing reactions among the diglycidyl ether of bisphenol A (DGEBA), 4,4'-diaminodiphenylmethane (DDM), and DSD. The flame-retardancy of composites was studied by the limiting oxygen index (LOI) and UL-94 test. The LOI values of EP-DSD composites increased from 30.7% for a content of 3 wt % to 35.4% for a content of 9 wt %. When the content of DSD reached 6 wt %, a V-0 rating under the UL-94 vertical test was achieved. SEM photographs of char residues after the UL-94 test indicate that an intumescent and tight char layer with a porous structure inside was formed. The TGA results revealed that EP-DSD thermosets decomposed ahead of time. The graphitization degree of the residual chars was also investigated by laser Raman spectroscopy. The measurement of tensile strength at breaking point shows that the loading of DSD increases the tensile strength of epoxy thermosets. Py-GC/MS analysis shows the presence of phosphorus fragments released during EP-DSD thermal decomposition, which could act as free radical inhibitors in the gas phase. Owing to the promotion of the formation of intumescent and compact char residues in the condensed phase and nonflammable phosphorus fragments formed from the decomposition of DOPO groups, EP-DSD composites displayed obvious flame-retardancy.
在本研究中，由9,10 - 二氢 - 9 - 氧杂 - 10 - 磷杂菲 - 10 - 氧化物（DOPO）、4,4'-二氨基二苯砜（DDS）和水杨醛成功合成了一种带有DOPO基团的阻燃添加剂，记为DSD。通过傅里叶变换红外光谱 - 衰减全反射（FTIR - ATR）、核磁共振（NMR）和元素分析对DSD的化学结构进行了表征。DSD用作胺类固化剂，通过双酚A二缩水甘油醚（DGEBA）、4,4'-二氨基二苯甲烷（DDM）和DSD之间的热固化反应制备了名为EP - DSD的透明且拉伸强度增强的环氧树脂。通过极限氧指数（LOI）和UL - 94测试研究了复合材料的阻燃性能。EP - DSD复合材料的LOI值从3 wt%含量时的30.7%增加到9 wt%含量时的35.4%。当DSD含量达到6 wt%时，在UL - 94垂直测试中达到了V - 0等级。UL - 94测试后残炭的扫描电子显微镜（SEM）照片表明形成了内部具有多孔结构的膨胀且致密的炭层。热重分析（TGA）结果显示EP - DSD热固性材料提前分解。还通过激光拉曼光谱研究了残余炭的石墨化程度。断裂点拉伸强度的测量表明，DSD的加入提高了环氧热固性材料的拉伸强度。热解气相色谱 - 质谱联用（Py - GC/MS）分析表明，EP - DSD热分解过程中释放出磷碎片，这些磷碎片可在气相中作为自由基抑制剂。由于在凝聚相中促进了膨胀且致密的残炭形成以及DOPO基团分解形成不可燃的磷碎片，EP - DSD复合材料表现出明显 的阻燃性。
