Curing kinetics and thermomechanical properties of latent epoxy/carbon fiber composites

37th Risø International Symposium on Materials Science

Vacche, S. Dalle^1 ; Michaud, V.^1 ; Demierre, M.^1 ; Bourban, P.-E.^1 ; Månson, J.-A.E.^1

Laboratoire de Technologie des Composites et Polymères, Ecole Polytechnique Fédérale de Lausanne, Station 12, Lausanne

CH-1015, Switzerland^1

关键词: Diglycidyl ether of bisphenol-A;    Dynamic mechanical analysis (DMA);    Flexural properties;    Impregnation quality;    Long term stability;    Temperature changes;    Thermomechanical properties;    Three-point bending test;   

Others  :  https://iopscience.iop.org/article/10.1088/1757-899X/139/1/012049/pdf
DOI  :  10.1088/1757-899X/139/1/012049

来源: IOP

【 摘 要 】

In this work, resins based on diglycidyl ether of bisphenol A (DGEBA) epoxy and a latent hardener, dicyandiamide (DICY), as well as carbon fiber (CF) composites based on them, were prepared with three commercial accelerators: a methylene bis (phenyl dimethyl urea), a cycloaliphatic substituted urea, and a modified polyamine. The curing kinetics of the three DGEBA/DICY/accelerator systems were investigated by chemorheology and differential scanning calorimetry (DSC), in isothermal and over temperature change conditions. Differences in the reaction onset temperature, and in the glass transition temperature (Tg) were highlighted. For curing of thick resin samples, a slow curing cycle at the lowest possible temperature was used, followed by high temperature (160 - 180 °C) post-curing. Indeed, fast curing at higher temperatures caused the formation of hot spots and led to local burning of the samples. The obtained thermomechanical properties, assessed by ultimate tensile testing and dynamic mechanical analysis (DMA) in single cantilever configuration, were all in the expected range for epoxy resins, with tensile moduli close to 3 GPa and Tg> 140 °C. The longterm stability of these resins at room temperature was verified by DSC. Composite samples were prepared by hand lay-up by manually impregnating four layers of 5-harness satin CF textile, and curing in vacuum bag. Impregnation quality and void content were assessed by optical microscopy. The flexural properties of the post-cured composites were assessed by three-point bending test at room temperature and showed no relevant differences, all composites having bending moduli of 45 - 50 GPa. Finally, composites cured with a faster high temperature curing cycle (20 min at 140 °C) were prepared with the DGEBA/DICY/ methylene bis (phenyl dimethyl urea) system, obtaining similar properties as with the slower curing cycle, showing that the prepreg system allowed more flexibility in terms of curing cycle than the bulk resin samples.