Rok 2019
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Browsing Rok 2019 by Author "Tran, Huu Nam"
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- ItemResearch and development of aligned multi-walled carbon nanotube sheets, their prepregs and composites(2019) Tran, Huu NamCarbon nanotubes (CNTs) have attracted great interest because of their outstanding mechanical, thermal, and electrical properties. Their excellent properties along with high aspect ratio, high surface area available for stress transfer, and low density make CNTs attractive as potential reinforcement agents for the next generation of high-performance structural materials. However, large-scale applications of individual CNTs remain challenging because of their poor processability and difficulty of structural control. To enable practical applications of CNTs, bulk CNT-reinforced polymer composites have been developed and assessed. Most have specifically addressed the development of randomly oriented and discontinuous CNTs dispersed in polymer matrices, which rely on unorganized CNT architectures. Therefore, the mechanical properties of such composites fall far short of the corresponding properties of high-performance composite materials. Organized CNT architectures with determined orientations such as vertically aligned CNT arrays have been demonstrated to be advantageous for the development of high-performance CNT composite structures. Vertically aligned and spinnable multi-walled CNT (MWCNT) arrays used in this habilitation thesis were grown on bare quartz substrate using chloride-mediated chemical vapor deposition (CVD) method. Solid-state drawing and winding techniques were applied to transform a vertically aligned MWCNT array into horizontally aligned and multiply MWCNT sheets. Highly aligned MWCNT sheets have been used to develop aligned MWCNT-reinforced polymer composites. The introduction of aligned MWCNTs in polymer matrices represents a novel direction for the development of high-performance composites. The aligned MWCNT-reinforced polymer composites are great interest because they are envisioned as a revolutionary advanced composite material for a host of demanding applications. Lightweight composites based on epoxy resin and differently aligned MWCNT sheets were developed using hot-melt prepreg processing method. The hot-melt prepreg processing maintained the alignment of MWCNTs during epoxy resin impregnation. The mechanical properties of the aligned MWCNT sheets, aligned vi MWCNT/epoxy prepregs and composites were studied. Although the composites made of epoxy resin and different MWCNT sheets contain aligned MWCNTs, their mechanical properties are low partly because of the waviness and poor packing of MWCNTs in the composites. Therefore, stretching and/or pressing of the aligned MWCNT sheets were conducted to reduce the wavy MWCNTs and to increase the dense packing of MWCNTs. The stretching and/or pressing of the MWCNT sheets improved the mechanical properties of aligned MWCNT sheets and their composites considerably. Particularly, application of both stretching and pressing is most effective to produce superior aligned MWCNT sheets for the development of high volume fraction MWCNT/epoxy composites with high strength and stiffness.