Delamination is a major drawback of carbon fiber reinforced plastics (CFRPs). Studies have reported that carbon nanofibers (CNFs) can improve the delamination toughness of various FRPs. However, lack of CNF alignment control caused substantial uncertainty in the improvements. In this study, a novel CNFs z-threaded CFRP (ZT-CFRP), which utilized z-aligned CNFs as long-range reinforcement threading through the packed carbon fiber bed, was manufactured. The mode-I delamination toughness (G IC) of the ZT-CFRPs was tested against both control CFRPs and unaligned CNF-modified CFRPs (UA-CFRPs). Through statistical comparison against control CFRPs, UA-CFRPs exhibited a relative change in mean G IC and coefficient of variation of +13.99% and +116.35%, respectively, whereas the ZT-CFRPs of equivalent CNF concentration exhibited a relative change in mean G IC and coefficient of variation of +28.93% and-12.33%, respectively. Accordingly, the CNF z-threads were found to play a positive role in toughening CFRPs, as supported by delamination experiments and microscopy analysis.

This study experimentally and analytically examined the influence of carbon nanofiber (CNF) z-threads on the through-thickness (i.e., z-direction) thermal conductivity of unidirectional carbon fiber reinforced plastics (CFRPs). It was hypothesized that a network of CNF z-threads within CFRPs would provide a thermally conductive microstructure throughout the sample thickness that would increase the through-thickness thermal conductivity. The experiments showed that the through-thickness thermal conductivity of the CNF z-threaded CFRPs (9.85 W/m-K) was approximately 7.53 times greater than that of the control CFRPs (1.31 W/m-K) and 2.73 times greater than that of the unaligned CNF-modified CFRPs (3.61 W/m-K). Accordingly, the CNF z-threads were found to play a substantial role in increasing the through-thickness thermal conductivity of CFRPs. To better understand the role of the CNF z-threads in through-thickness thermal transport, simple logical models of the CFRPs were constructed and then compared with the experimental results. Through these analyses, it was determined that CNF z-threads substantially enhance the through-thickness thermal conductivity by creating carbon fiber-CNF linkages throughout the CFRP laminate; these linkages allow the heat flow to largely bypass the resistive resin that envelops the carbon fibers. In addition, thermal infrared tests illustrated that the increased through-thickness thermal conductivity of the CNF z-threaded CFRP enabled the location and visualization of defects within the laminate, which was not possible with the control CFRP.

This research paper specifically focuses on experimentally characterizing and elaborating the effect of z-aligned carbon nanofibers (CNFs) on the through-thickness (i.e., z-direction) thermal conductivity of paraffin wax. The z-aligned CNF network present within the paraffin sample was hypothesized to provide a thermally-conductive nanostructure throughout the sample thickness, thereby increasing the thermal conductivity and the thermal energy charging/discharging capabilities of the paraffin wax. It was further hypothesized that the effectiveness of this thermally-conductive nanostructure was strongly related to both CNF alignment and CNF concentration. To experimentally analyze the respective impact of CNF concentration (measured as a percentage of sample weight) and CNF alignment on the through-thickness thermal conductivity, z-aligned CNF-modified paraffin wax samples with various CNF concentrations were manufactured and compared with unmodified (i.e. control) paraffin wax samples and unaligned CNF-modified paraffin wax samples; the concentration of CNF-reinforcement was tested at both 0.1wt.% and 0.3wt.%. The through-thickness thermal conductivities were characterized for all samples using a steady-state parallel plate testing device and the results were compared and discussed against the experimental parameters. It was found that both CNF alignment and concentration had a strong influence on the improvement of through-thickness thermal conductivity of paraffin wax.