Jeevananthan Velusamy, Shanmugan Swaminathan
Department of Chemistry, Faculty of Engineering and Technology, SRM Institute of Science and Technology Kattankulathur 603203 Tamil Nadu India
RSC Adv. 2022 Aug 16;12(36):23322-23336. doi: 10.1039/d2ra02586h.
The development of halogen-free flame retardants as environmentally friendly and renewable materials for heat and fire-resistant applications in the field of electronics is important to ensure safety measures. In this regard, we have proposed a simple and halogen-free strategy for the synthesis of flame retardant LDH-PN materials to decrease the fire hazards of epoxy resin (EP), a co-precipitation reaction between Mg(NO) and Al(NO) and the subsequent incorporation of different cyclotriphosphazene (PN) carboxylate anions. The cyclotriphosphazene-based di, tetra and hexacarboxylate-intercalated layered double hydroxides are designated as LDH-PN-DC, LDH-PN-TC and LDH-PN-HC, respectively. Furthermore, the intercalation of cyclotriphosphazene carboxylate anions into the LDH layers was confirmed by PXRD, FT-IR, TGA, solid-state P NMR, nitrogen adsorption and desorption analysis (BET), HR-SEM and XPS. Evaluation of the flame retardant (vertical burning test and limiting oxygen index) properties was demonstrated by formulating the LDH-PN materials with epoxy resin (EP) in different ratios coated on wood substrates to achieve the desired behaviour of the EP/LDH-PN composites. Structure-property analysis reveals that EP/LDH-PN-TC-20 wt% and EP/LDH-PN-HC-20 wt% achieved a rating in the UL-94 V test and achieved higher LOI values (27.7 vol% for EP/LDH-PN-TC-20 wt% and 29 vol% for EP/LDH-PN-HC-20 wt%) compared to the epoxy-coated wood substrate (23.2 vol%), whereas EP/LDH-PN-DC failed in the vertical burning test for various weight percentages of LDH-PN-DC from 5 wt% to 20 wt% in the composites, with a lower LOI value of 22.1 vol%. Excellent flame retardancy was observed for EP/LDH-PN-TC and EP/LDH-PN-HC due to the presence of more binding sites of carboxylate anions in the LDH layers and less or no spiro groups in cyclotriphosphazene compared to that in EP/LDH-PN-DC. In addition, the synergistic flame retardant effect of the combination of LDH and cyclotriphosphazene on the epoxy resin composites remains very effective in creating a non-volatile protective film on the surface of the wood substrate to shelter it from air, absorb the heat and increase the ignition time, which prevents the supply of oxygen during the combustion process. The results of this study show that the proposed strategy for designing flame-retardant properties represents the state-of-the-art, competent coating of inorganic materials for the protection and functionalization of wood substrates.
开发无卤阻燃剂作为电子领域中用于耐热和防火应用的环保可再生材料对于确保安全措施至关重要。在这方面，我们提出了一种简单的无卤策略来合成阻燃剂LDH-PN材料，以降低环氧树脂（EP）的火灾隐患，即Mg(NO)和Al(NO)之间的共沉淀反应以及随后引入不同的环三磷腈（PN）羧酸盐阴离子。基于环三磷腈的二羧酸、四羧酸和六羧酸插层层状双氢氧化物分别命名为LDH-PN-DC、LDH-PN-TC和LDH-PN-HC。此外，通过PXRD、FT-IR、TGA、固态P NMR、氮吸附和解吸分析（BET）、HR-SEM和XPS证实了环三磷腈羧酸盐阴离子插入到LDH层中。通过将不同比例的LDH-PN材料与环氧树脂（EP）配制成涂层涂覆在木材基材上，以实现EP/LDH-PN复合材料的理想性能，从而对阻燃性能（垂直燃烧试验和极限氧指数）进行了评估。结构-性能分析表明，EP/LDH-PN-TC-20 wt%和EP/LDH-PN-HC-20 wt%在UL-94 V试验中达到了 等级，并且与环氧涂层木材基材（23.2 vol%）相比，实现了更高的LOI值（EP/LDH-PN-TC-20 wt%为27.7 vol%，EP/LDH-PN-HC-20 wt%为29 vol%），而EP/LDH-PN-DC在复合材料中5 wt%至20 wt%的各种LDH-PN-DC重量百分比下的垂直燃烧试验中失败，其LOI值较低，为22.1 vol%。与EP/LDH-PN-DC相比，由于LDH层中羧酸根阴离子的结合位点更多，环三磷腈中的螺环基团更少或没有，因此观察到EP/LDH-PN-TC和EP/LDH-PN-HC具有优异的阻燃性。此外，LDH和环三磷腈组合对环氧树脂复合材料的协同阻燃作用在木材基材表面形成非挥发性保护膜以使其与空气隔绝、吸收热量并延长着火时间方面仍然非常有效，这在燃烧过程中阻止了氧气的供应。这项研究的结果表明，所提出的设计阻燃性能的策略代表了用于木材基材保护和功能化的无机材料的最新、有效的涂层技术。
