Flax fibers are particularly relevant in composite fabrication due to natural availability and mechanical properties close to glass fibers. We explore flax fiber-containing epoxy-amine (DGEBA/DETA) polymers with wide industrial applicability. Flax fibers impact the glass transition temperature (DSC), with a T_g drop of 67 °C at 30 wt% loading. For deeper insight, we develop here an original mixing calorimetry approach to follow in situ DGEBA/fibers and DETA/fibers interphases. DGEBA does not interact quantitatively with flax fibers while DETA/fibers interaction is significantly exothermic and directly related to fibers content. DETA/water interaction only accounts for 25% of total heat effect. Experiments run by contacting DETA with each of the main components of flax fibers (cellulose, hemicelluloses, lignin) point out systematic exothermic effects. Considering their mean proportion in flax fibers, the sum of enthalpy contributions agrees well with the overall effect measured with entire fibers. The main contribution (58%) arises from cellulose. XRD analyses and literature considerations allow concluding on the direct implication of DETA molecules with cellulose chains, resulting in T_g decrease. This work clarifies the chemical role of flax fibers in DGEBA/DETA thermosets, down to the molecular-scale, and highlights that mixing calorimetry is a powerful tool to follow interphase formation in situ.

由于天然可用性和接近玻璃纤维的机械性能，亚麻纤维在复合材料制造中尤为重要。我们探索具有广泛工业适用性的含亚麻纤维的环氧胺 (DGEBA/DETA) 聚合物。亚麻纤维会影响玻璃化转变温度 (DSC)，在 30 wt% 的负载下， T _g下降 67 °C。为了更深入地了解，我们在这里开发了一种原始的混合量热方法，可以原位遵循DGEBA/纤维和 DETA/纤维界面。DGEBA 不与亚麻纤维定量相互作用，而 DETA/纤维相互作用显着放热并与纤维含量直接相关。DETA/水相互作用仅占总热效应的 25%。通过将 DETA 与亚麻纤维的主要成分（纤维素、半纤维素、木质素）中的每一种接触进行的实验指出了系统的放热效应。考虑到它们在亚麻纤维中的平均比例，焓贡献的总和与用整个纤维测量的整体效果非常吻合。主要贡献（58%）来自纤维素。XRD 分析和文献考虑允许得出 DETA 分子与纤维素链的直接含义，从而导致T _g减少。这项工作阐明了亚麻纤维在 DGEBA/DETA 热固性塑料中的化学作用，直至分子尺度，并强调混合量热法是跟踪原位界面形成的有力工具。