Preparation and Characterization of NR/wax/CNT Shape Memory Nanocomposites

Autor: Guo, Geng-Luen, 郭耕綸
Rok vydání: 2018
Druh dokumentu: 學位論文 ; thesis
Popis: 106
In this study, we investigated the shape memory properties of small molecule-filled natural rubber. Previously, we have used natural rubber and paraffin wax at proportional (8:2, 6:4 and 4:6) and vulcanized with sulfur/accelerators to prepare composite blends (S-NR/PW). Based on the DMA (Dynamic mechanical analyzer) test, the shape fixity ratio and shape recovery ratio of the S-NR/PW 4:6 blend reached up to 99.4 % and 99.3% in the third thermomechanical cycle. However, the blends can have higher mechanical properties at the lower wax content. Thus, we choose the natural rubber and wax at 6:4. Herein, beeswax was used to prepare biodegradable composite blends (S-NR/BW) at similar ratios with good shape memory performance as well. In the one-way test, the shape fixity ratios for S-NR/BW 6:4 blends only reach 66.1 %. With the addition of multi-walled carbon nanotube (CNT), we found that the crystallinity of the S-NR/BW blend increased, which led to S-NR/BW-CNT nanocomposites with higher shape memory performance at the lower wax content. The shape fixing ratios of the S-NR/BW 6:4-0.5 CNT could reach up to 73.5 %. We want to endow the sample with multi-shape memory ability, so we use carnauba wax which has a higher melting point (Tm) at 81.8 oC. In the one-way test, the shape fixing ratios for S-NR/CW 6:4 blends could reach 85.2 % in the third thermomechanical cycle, respectively. With the addition of CNT, we also found that the crystallinity of the S-NR/CW blend increased as S-NR/BW blend, which led to S-NR/CW-CNT nanocomposites with higher shape memory performance at the lower wax content. The shape fixing ratios of the S-NR/CW 6:4-0.5 CNT could reach up to 94.9 %, which was the best one-way shape memory efficacy in S-NR/Wax 6:4/MWCNT system. Moreover, CNT can not only enhance the mechanical properties but also selectively and remotely heated by irradiation with the near-infrared to trigger shape memory process in a very short time. To the authors’ best knowledge, this is the first small molecule-filled NR/CW nanocomposites with remotely triggered shape memory properties. In the multi-shape memory process for S-NR/(C7B3)-0.5 CNT blends, the shape fixing ratios of Rf (C→B) and Rf (B→A) could reach 51.3 % and 94.6 %, respectively, and the shape recovery ratios of Rr (A→B) and Rr (B→C) could also reach 77.6 % and 88.0 %. In this system, the carnauba wax with higher crystallization temperature (73.4 oC) and melting temperature (79.4 oC) served the switching role in the first fixing stage. In addition, the beeswax with lower crystallization temperature (61.3 oC) and melting temperature (60.4 oC) played the switching role in the second fixing stage. Finally, the vapor-induced two-way shape memory behavior using THF was demonstrated via the simple melt-blending process for the first time in the literature.
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