Study on the impact of CNT or graphene reinforced interlaminar region in composites
Abstract: The interlaminar region is a contributing factor to the limited electrical conductivity of carbon ﬁber/epoxy composites. Consisting of electrically insulating epoxy matrix between conductive layers of carbon ﬁber, the interlaminar region prevents electrical interaction between the carbon ﬁber layers and electrical conduction in the through thickness direction.The interlaminar region in thin [0,0] carbon ﬁber/epoxy composites has been reinforced by carbon nanotubes (CNT) by two methods. First by aligned CNT forests from N12 Technologies and secondly by self-produced Buckypapers, porous CNT ﬁlms, of diﬀerent areal densitites. Two batches of laminates modiﬁed by aligned CNTs, having diﬀerent curing conditions, and laminates modiﬁed with Buckypapers were manufactured. The laminates were evaluated by their electrical conductivity and electromagnetic interference shielding eﬃciency (EMI SE). The addition of external pressure to the laminates during curing brought an increase in longitudinal conductivity, a consequence of higher ﬁber packing. Also, both reinforcement methods increased the longitudinal conductivity through improved electrical interaction between the carbon ﬁber layers. However, only the Buckypaper reinforcement augmented the transversal conductivity signiﬁcantly, acting as a highly conductive route in the interlaminar region. Both batches of aligned CNT modiﬁed laminates exhibited equal EMI SE, questioning the inﬂuence of the conductivity of the laminate on its EMI SE. Also, the increase in EMI SE brought by the aligned CNT forests were negligible compared to the reference. However, the reinforcement by Buckypapers proved successful, reaching -45/-50 dB at 1000 MHz, improving from 30 dB of the unmodiﬁed reference at the same frequency.
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