Malik Muhammad Salman, Wolfahrt Markus, Schlögl Sandra
Polymer Competence Center Leoben Rossegerstraße 12 8700 Leoben Austria
RSC Adv. 2023 Oct 4;13(41):28993-29003. doi: 10.1039/d3ra05976f. eCollection 2023 Sep 26.
Frontal polymerization of epoxy-based thermosets is a promising curing technique for the production of carbon fiber reinforced composites (CFRCs). It exploits the exothermicity of polymerization reactions to convert liquid monomers to a solid 3D network. A self-sustaining curing reaction is triggered by heat or UV-radiation, resulting in a localized thermal reaction zone that propagates through the resin formulation. To date, frontal polymerization is limited to CFRCs with a low fiber volume percent as heat losses compromise on the propagation of the heat front, which is crucial for this autocatalytic curing mechanism. In addition, the choice of suitable epoxy monomers and thermal radical initiators is limited, as highly reactive cycloaliphatic epoxies as well as peroxides decarboxylate during radical induced cationic frontal polymerization. The resulting networks suffer from high defect rates and inferior mechanical properties. Herein, we overcome these shortcomings by introducing redox cationic frontal polymerization (RCFP) as a new frontal curing concept. In the first part of this study, the influence of stannous octoate (reducing agent) was studied on a frontally cured bisphenol A diglycidyl ether resin and mechanical and thermal properties were compared to a conventional anhydride cured counterpart. In a subsequent step, a quasi-isotropic CFRC with a fiber volume of >50 vol%, was successfully cured RCFP. The composite exhibited a glass transition temperature > 100 °C and a low number of defects. Finally, it was demonstrated that the redox agent effectively prevents decarboxylation during frontal polymerization of a cycloaliphatic epoxy, demonstrating the versatility of RCFP in future applications.
基于环氧树脂的热固性材料的前沿聚合是一种用于生产碳纤维增强复合材料（CFRC）的很有前景的固化技术。它利用聚合反应的放热性将液态单体转化为固态三维网络。通过热或紫外线辐射引发自持固化反应，产生一个局部热反应区，该反应区在树脂配方中传播。迄今为止，前沿聚合仅限于纤维体积百分比低的CFRC，因为热损失会影响热前沿的传播，而热前沿对于这种自催化固化机制至关重要。此外，合适的环氧单体和热自由基引发剂的选择有限，因为在自由基诱导的阳离子前沿聚合过程中，高反应性的脂环族环氧树脂以及过氧化物会发生脱羧反应。所得网络存在高缺陷率和较差的机械性能。在此，我们通过引入氧化还原阳离子前沿聚合（RCFP）作为一种新的前沿固化概念来克服这些缺点。在本研究的第一部分，研究了辛酸亚锡（还原剂）对前沿固化的双酚A二缩水甘油醚树脂的影响，并将其机械性能和热性能与传统酸酐固化的对应物进行了比较。在随后的步骤中，成功地通过RCFP固化了纤维体积大于50体积%的准各向同性CFRC。该复合材料表现出玻璃化转变温度>100°C且缺陷数量少。最后，证明了氧化还原剂有效地防止了脂环族环氧树脂前沿聚合过程中的脱羧反应，证明了RCFP在未来应用中的多功能性。
