College of Materials Science and Engineering, Hebei University of Engineering, Handan City, Hebei Province, 056038, China.
Hebei Province Technology Institute of Green Chemical Industry, Hebei University of Technology, Tianjin, 300130, China.
J Mol Graph Model. 2019 Jan;86:192-198. doi: 10.1016/j.jmgm.2018.10.018. Epub 2018 Oct 23.
The epoxy resin coating is a fundamental species with epoxy resins used as main components to form the final film. Unexpectedly, bulky CO bubbles that occasionally appeared during the curing process of epoxy resin coatings might destroy the final film properties. With an attempt to thoroughly understand the formation mechanism of CO bubbles and further propose countermeasures to control them, Density Function Theory (DFT) in this paper was employed to calculate the absorption process, the curing reaction and the formation mechanism of CO bubbles. The gas phase basicity (GB) values and pK values of common amine curing agents were calculated. The total Gibbs free energies difference of the curing reactions between polluted curing agents and epoxy resins were calculated according to a thermodynamic cycle. Whether in gas phase or resin phase, the energetically negative ΔG indicated that the curing reactions might occur spontaneously and CO molecules would be separated and released from amine molecules. The total Gibbs free energy calculations also revealed that the re-absorption of CO by the curing system was energetically unfavorable. Thus, the formation mechanism of CO bubbles of epoxy resin coatings could be summarize in three steps: (1) Carbon dioxide pollutes accidentally the curing agents. (2) CO molecules are gradually released as the curing process occurs. (3) CO molecules are collected to form big bubbles which can lead to seriously surface and/or internal defects. Finally, based on practical experiences three tips were proposed to control CO bubbles. The present results not only evidenced the nature of the unexpected bubbles of epoxy resin coatings, but also additionally paved to the way to full utilization of the formation mechanism to improve the epoxy coatings' properties.
环氧树脂涂层是一种基本的品种，其以环氧树脂作为主要成分来形成最终的膜。出乎意料的是，环氧树脂涂层在固化过程中偶尔会出现体积庞大的 CO 气泡，这些气泡可能会破坏最终的膜性能。为了彻底了解 CO 气泡的形成机制，并进一步提出控制它们的对策，本文采用密度泛函理论（DFT）计算 CO 气泡的吸收过程、固化反应和形成机制。计算了常见胺固化剂的气相碱度（GB）值和 pK 值。根据热力学循环，计算了污染固化剂与环氧树脂之间固化反应的总吉布斯自由能差。无论是在气相还是树脂相中，能量上为负的 ΔG 表明固化反应可能自发发生，CO 分子将从胺分子中分离并释放出来。总吉布斯自由能计算还表明，固化体系对 CO 的再吸收在能量上是不利的。因此，环氧树脂涂层 CO 气泡的形成机制可以概括为三个步骤：（1）二氧化碳意外污染固化剂。（2）随着固化过程的进行，CO 分子逐渐释放。（3）CO 分子被收集形成大气泡，这可能导致严重的表面和/或内部缺陷。最后，根据实际经验提出了控制 CO 气泡的三个技巧。本研究结果不仅证明了环氧树脂涂层中意外气泡的性质，而且还为充分利用形成机制来改善环氧树脂涂层的性能铺平了道路。
