Introducing cryomilling for reliable determination of resin content and degree of cure in structural carbon fibre reinforced thermoset composites

A novel material preparation method is presented that facilitates accurate measurement of the degree of cure and resin content within carbon fibre reinforced polymer composites (CFRPs). When using conventional specimen preparation for standard thermal analysis, it is demonstrated that the experimentally-obtained enthalpy of reaction and resin content varies significantly between analyses. Measurement uncertainties arise because small specimen volumes are extracted from materials that exhibit both macroscopic inhomogeneity and physical discontinuities. To address this issue, representative sample volumes of aligned CFRPs were first cryogenically milled to develop a homogeneous powder before smaller specimens were extracted. The variation in obtained enthalpy of reaction between analyses was reduced from 23% (for conventional specimen extraction) to 1% following cryomilling. The accuracy in measurement of degree of cure for the compression moulding parts was improved 7 times. Further, subsequent FTIR analysis proved that cryomilling did not affect the final chemical structure of the cured material.