ABSTRACT Natural fibers and particularly flax fibers have a great potential to replace glass fibers in composite materials. However, the interaction between these fibers and thermoset matrices remains unclear and results in a weak interface affecting the mechanical properties of the composite. This study was carried out to investigate the impact of natural fibers on the chemical reaction between the resin and the hardener, studying the interaction of fibers with each component separately to understand more precisely the phenomena involved. The results show that the contact with the fibers involves a change of the matrix properties that has been attributed to the water absorbed on their surface. On the one hand, water could modify amine functions of the hardener leading to a decrease of 40°C of matrix glass transition temperature (Tg). This issue could be corrected by adding a 16% excess of hardener. On the other hand, the water added to the resin could also accelerate the epoxide/amine reaction increasing slightly the Tg of the matrix and also generating weaker distinct networks of lower Tg by post-modification of the hardener. Therefore, the control of the water content in flax fibers is a crucial parameter for composite manufacturing.

中文翻译：

---

亚麻纤维对DGEBA/DETA基质网络形成的影响

摘要 天然纤维，尤其是亚麻纤维在复合材料中具有替代玻璃纤维的巨大潜力。然而，这些纤维和热固性基质之间的相互作用仍不清楚，并导致影响复合材料机械性能的弱界面。本研究旨在研究天然纤维对树脂和固化剂之间化学反应的影响，分别研究纤维与每种成分的相互作用，以更准确地了解所涉及的现象。结果表明，与纤维的接触涉及基质特性的变化，这归因于其表面吸收的水。一方面，水可以改变硬化剂的胺官能团，导致基质玻璃化转变温度 (Tg) 降低 40°C。这个问题可以通过添加 16% 过量的固化剂来解决。另一方面，添加到树脂中的水也可以加速环氧化物/胺反应，略微增加基体的 Tg 并通过硬化剂的后改性产生较低 Tg 的较弱的明显网络。因此，控制亚麻纤维中的水含量是复合材料制造的关键参数。