Toughening of a dicyandiamide-cured epoxy resin: Influence of cure conditions on different rubber modifications,Polymer Engineering and Science

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Toughening of a dicyandiamide-cured epoxy resin: Influence of cure conditions on different rubber modifications
Polymer Engineering and Science ( IF 3.2 ) Pub Date : 2021-08-21 , DOI: 10.1002/pen.25770
Jan‐Pierre Schneider ₁ , Hauke Lengsfeld ₁

Affiliation

Cure kinetics of modified epoxy resins cured with dicyandiamide are studied. The influence of different heating rates in the curing process, such as curing behavior, morphology, and thermo-mechanical properties, is studied. Additionally, three different post-cure cycles at 180°C are employed. Two butadiene-based toughening agents are used, a carboxyl-terminated polybutadiene-co-acrylonitril (CTBN) prepolymer and a functionalized block copolymer of polytetrahydrofuran and hydroxyl-terminated polybutadiene. The amphiphilic block copolymer enables investigations with a bimodal particle size morphology. All results are contrasted with those of the neat resin and butadiene-free block polymer. Faster curing processes result in smaller average particle sizes and better fracture toughness of the modified epoxy resins. Further improvements are achieved with additional post-cure cycles at 180°C. An increased interfacial adhesion between the particles and the epoxy matrix is considered to be the main mechanism. Optimized lengths of the post-cure process can be determined with the butadiene-based toughening agents indicating a competing thermal degradation. Longer post-cures than 40 min lead to lower fracture toughness in the butadiene-based modified materials. In general, similar influences of the curing and post-curing process on the bimodal and unimodal distributed system can be observed differing in more intense dependencies of the bimodal system.

中文翻译：

双氰胺固化环氧树脂的增韧：固化条件对不同橡胶改性的影响

研究了用双氰胺固化的改性环氧树脂的固化动力学。研究了固化过程中不同加热速率的影响，如固化行为、形态和热机械性能。此外，在 180°C 下采用了三个不同的后固化循环。使用了两种基于丁二烯的增韧剂，一种是羧基封端的聚丁二烯-共聚丙烯腈 (CTBN) 预聚物和一种聚四氢呋喃和羟基封端的聚丁二烯的官能化嵌段共聚物。两亲性嵌段共聚物能够以双峰粒径形态进行研究。所有结果都与纯树脂和不含丁二烯的嵌段聚合物的结果形成对比。更快的固化过程导致更小的平均粒径和更好的改性环氧树脂的断裂韧性。通过在 180°C 下进行额外的后固化循环，可以实现进一步的改进。颗粒和环氧树脂基体之间增加的界面粘附被认为是主要机制。后固化过程的优化长度可以用丁二烯基增韧剂确定，表明竞争性热降解。超过 40 分钟的后固化时间会导致丁二烯基改性材料的断裂韧性降低。通常，可以观察到固化和后固化过程对双峰和单峰分布式系统的类似影响，但双峰系统的依赖性更强。后固化过程的优化长度可以用丁二烯基增韧剂确定，表明竞争性热降解。超过 40 分钟的后固化时间会导致丁二烯基改性材料的断裂韧性降低。通常，可以观察到固化和后固化过程对双峰和单峰分布式系统的类似影响，但双峰系统的依赖性更强。后固化过程的优化长度可以用丁二烯基增韧剂确定，表明竞争性热降解。超过 40 分钟的后固化时间会导致丁二烯基改性材料的断裂韧性降低。通常，可以观察到固化和后固化过程对双峰和单峰分布式系统的类似影响，但双峰系统的依赖性更强。

更新日期：2021-10-01

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