Marco Liebscher

CNT-grafted glass fibers as a smart tool for epoxy cure monitoring, UV-sensing and thermal energy harvesting in model composites

A ‘hierarchical’ reinforcement of glass fibers (GFs) chemically grafted with multiwall carbon nanotubes (MWCNTs) has been utilized for epoxy cure monitoring, UV-sensing, and thermal energy harvesting in model composites. MWCNTs were covalently attached to the surface of glass fiber yarns (GF-yarns) in a dip-coating deposition process. Hereafter, the hybrid yarns are denoted as GF-CNT. Scanning electron microscopy (SEM) demonstrated a highly uniform CNT-layer covering the fiber surfaces. In turn, GF-CNT reached a maximum conductivity of 2060 S m−1, being of the same order of magnitude as the CNT-only bucky paper film. A GF-CNT in a uni-directional arrangement within a dog-bone shaped mould was employed for epoxy cure monitoring, recording the resistance changes during the curing process. In addition, three yarns connected in parallel highlighted the potential for detecting the resin position upon filling a mould. GF-CNT embedded in epoxy has been proposed also as an integrated non-invasive composite UV-sensor, allowing polymer matrix health monitoring. Besides, the semi-conductive nature of MWCNTs offered the opportunity of thermoelectric energy harvesting by the GF-CNT and its model composite when exposed to a temperature gradient. This work reports some new insights into and potential of fiber/CNT multi-scale reinforcements giving rise to multi-functional structural composites.

Mineral-Based Coating of Plasma-Treated Carbon Fibre Rovings for Carbon Concrete Composites with Enhanced Mechanical Performance

Surfaces of carbon fibre roving were modified by means of a low temperature plasma treatment to improve their bonding with mineral fines; the latter serving as an inorganic fibre coating for the improved mechanical performance of carbon reinforcement in concrete matrices. Variation of the plasma conditions, such as gas composition and treatment time, was accomplished to establish polar groups on the carbon fibres prior to contact with the suspension of mineral particles in water. Subsequently, the rovings were implemented in a fine concrete matrix and their pull-out performance was assessed. Every plasma treatment resulted in increased pull-out forces in comparison to the reference samples without plasma treatment, indicating a better bonding between the mineral coating material and the carbon fibres. Significant differences were found, depending on gas composition and treatment time. Microscopic investigations showed that the samples with the highest pull-out force exhibited carbon fibre surfaces with the largest areas of hydration products grown on them. Additionally, the coating material ingresses into the multifilament roving in these specimens, leading to better force transfer between individual carbon filaments and between the entire roving and surrounding matrix, thus explaining the superior mechanical performance of the specimens containing appropriately plasma-treated carbon roving.

Effect of Graphite Nanoplate Morphology on the Dispersion and Physical Properties of Polycarbonate Based Composites

The influence of the morphology of industrial graphite nanoplate (GNP) materials on their dispersion in polycarbonate (PC) is studied. Three GNP morphology types were identified, namely lamellar, fragmented or compact structure. The dispersion evolution of all GNP types in PC is similar with varying melt temperature, screw speed, or mixing time during melt mixing. Increased shear stress reduces the size of GNP primary structures, whereby the GNP aspect ratio decreases. A significant GNP exfoliation to individual or few graphene layers could not be achieved under the selected melt mixing conditions. The resulting GNP macrodispersion depends on the individual GNP morphology, particle sizes and bulk density and is clearly reflected in the composite’s electrical, thermal, mechanical, and gas barrier properties. Based on a comparison with carbon nanotubes (CNT) and carbon black (CB), CNT are recommended in regard to electrical conductivity, whereas, for thermal conductive or gas barrier application, GNP is preferred.

High-Strength, Strain-Hardening Cement-Based Composites (HS-SHCC) Made with Different High-Performance Polymer Fibers

This article presents an investigation on the tensile behavior of high-strength, strain-hardening cement-based composites (HS-SHCC) made with four different types of high-performance polymer microfibers. In particular, high-density polyethylene (HDPE), poly(p-phenylene-terephthalamide) (aramid), as-spun poly(p-phenylene-2,6-benzobisoxazole) (PBO), and high-modulus PBO fibers were examined in respect of their reinforcing effect in a high-strength, finely grained, cementitious matrix. Moreover, microscopic investigations were carried out to assess the fibers’ ability to be wetted and to explain their interaction with the cementitious matrix. It was shown that the HS-SHCC made with PBO and aramid fibers yielded increased first crack stress and tensile strength, but also a considerably reduced crack width compared to the HS-SHCC reinforced with HDPE fibers. This was traced back to the considerably higher wettability of these fibers compared to the hydrophobic HDPE fibers, ensuring a stronger interfacial bond with the cementitious matrix, but also to their superior mechanical properties, such as tensile strength and Young’s modulus.