Abstract The temperature of epoxy curing reaction and the change of amino reactivity for the amine curing agent have an effect on the three-dimensional network structure of the product, which in turn affect the performance of the epoxy resin. The study on the reactivity and kinetics of primary and secondary amines in epoxy curing process is of great significance to deeply understand the curing mechanism and realize the control of product quality. In this paper, an effective method for studying the reactivity and kinetics of primary and secondary amines in epoxy curing process by near-infrared (NIR) spectroscopy combined with multivariate analysis was proposed. The curing system of bisphenol A epoxy resin (E51) and M-xylylenediamine (MXDA) was studied, and the resins were isothermally prepared at 50, 60, 70, 80, 90 °C, respectively. The NIR spectra of the system for each curing reaction process were continuously collected online. The characteristic absorption bands of the primary and secondary amines overlap heavily in the wavenumber range of 6700–6330 cm−1. The wavelet-based second derivative together with multivariate curve resolution(MCR) were employed to resolve their respective absorption peaks. Then, the curves of conversion and conversion rate for primary and secondary amines were obtained. The study shows that the kinetics of the curing reaction follows the self-catalytic Kamal model in the early stage, and it follows the revised model of incorporating the diffusion factor after vitrification, in which the hydroxyl group plays a self-catalytic role in the reaction process; the reactivity of primary and secondary amines is different during epoxy curing process. There is a competitive reaction between them, and its competitiveness can be expressed by k2(SA)/k2(PA); the reactivity of primary and secondary amines varies with curing temperature, and k2(SA)/k2(PA) increases significantly when curing temperature exceeds 60 °C, which has a significant influence on the formed resin network structure.

中文翻译：

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近红外光谱结合多元分析研究环氧固化过程中伯胺和仲胺的反应性和动力学

摘要 环氧固化反应温度和胺类固化剂氨基反应性的变化对产物的三维网络结构有影响，进而影响环氧树脂的性能。研究环氧固化过程中伯胺和仲胺的反应活性和动力学，对于深入了解固化机理，实现产品质量控制具有重要意义。本文提出了一种利用近红外 (NIR) 光谱结合多元分析研究环氧固化过程中伯胺和仲胺反应活性和动力学的有效方法。研究了双酚A环氧树脂（E51）和间苯二甲胺（MXDA）的固化体系，分别在50、60、70、80、90℃等温下制备了树脂。在线连续收集系统每个固化反应过程的近红外光谱。伯胺和仲胺的特征吸收带在 6700-6330 cm-1 的波数范围内严重重叠。采用基于小波的二阶导数和多元曲线分辨率(MCR)来解析它们各自的吸收峰。然后，得到伯胺和仲胺的转化率和转化率曲线。研究表明，固化反应的动力学早期遵循自催化Kamal模型，玻璃化后遵循加入扩散因子的修正模型，其中羟基在反应中起自催化作用。过程; 环氧固化过程中伯胺和仲胺的反应性不同。它们之间存在竞争反应，其竞争力可以用k2(SA)/k2(PA)表示；伯胺和仲胺的反应性随固化温度而变化，固化温度超过60℃时k2(SA)/k2(PA)显着增加，对形成的树脂网络结构有显着影响。