Morphology and Properties of Epoxy/Polycaprolactone@CNF Microsphere/CNF Composite Foams

Solid‐state blends containing epoxy resin, polycaprolactone@carbon nanofiber microspheres, and carbon nanofiber (EP/PCL@CNF/CNF) are mechanically mixed and then subjected to the free‐foaming (Free foam) and limited‐foaming (Limited foam) process, respectively. Owing to the low melt viscosity of PCL, typically large bubbles appear in PCL domains while small bubbles form in EP matrix, constructing the bimodal‐cell structure. A higher proportion of semi‐interpenetrating network morphology exists in Limited foam as opposed to Free foam, ascribing to that the compressed gas in Limited foam promotes more PCL chains to diffuse into the EP networks. The PCL@CNF combined with the CNF in EP matrix effectively constructs the conductive networks when the content of microspheres reaches 5 wt%. At this time, the positive temperature coefficient and negative temperature coefficient intensity of 2.17 and 2.03, respectively, are obtained in Limited foam, which are much higher than those of Free foam. In addition, an obvious anisotropy in electromagnetic interference shielding effectiveness (SE H /SE v = 1.41) and compressive strength ( σ v / σ H = 1.13) in Limited foam with 2.5 wt% of microspheres is achieved while those values, respectively, decrease to 1.07 (SE H /SE v ) and 0.91 ( σ v / σ H ) when 20 wt% of microspheres is added, relating to the CNF orientation and cell morphology.