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Most of the properties of epoxy resins are tied to their degree of cross-linking, making understanding the reactivity of different epoxy systems a crucial aspect of their utilization. Here, epoxy-amine reactivity is studied with density functional theory (DFT) at various cut-off levels to explore the suitability of the method for estimating the reactivity of specific epoxy systems. Although it is common to use minimal structures in DFT to reduce computational cost, the results of this study highlight the important role of hydrogen bonding and other noncovalent interactions in the reactivity. This is a promising result for differentiating the most probable reactive paths for different resin systems. The significance of amine groups as a potential source of catalyzing H-bonds was also explored and, while not quite as effective as a catalyst as a hydroxyl group, a clear catalyzing effect was observed in the transition state energies. Unfortunately, the added complexity of a more representative reactive system also results in increased computational cost, highlighting the need for proper selection of structural cutoffs. publishedVersion

Currently, the vast majority of composite waste is either landfilled or incinerated, causing a massive burden on the environment and resulting in the loss of potentially valuable raw material. Here, conventional pyrolysis and reactive pyrolysis were used to reclaim carbon fibers from aeronautical scrap material, and to evaluate the feasibility of using reclaimed carbon fibers in structural components for the automotive sector. The need for fiber sizing was investigated as well as the behavior of the fiber material in macroscopic impact testing. The fibers were characterized with the single fiber tensile test, scanning electron microscopy, and the microbond test. Critical fiber length was estimated in both polypropylene and polyamide matrices. Tensile strength of the fiber material was better preserved with the reactive pyrolysis compared to the conventional pyrolysis, but in both cases the interfacial shear strength was retained or even improved. The impact testing revealed that the components made of these fibers fulfilled all required deformation limits set for the components with virgin fibers. These results indicate that recycled carbon fibers can be a viable option even in structural components, resulting in lower production costs and greener composites This research was partly funded by FINNISH CULTURAL FOUNDATION, grant number 00210821, and EU H2020-IND-CE project “FiberEUse” (grant agreement number 730323).