Sample preparation

2.2.1 Silica/epoxy nanocomposite

In this research, the weight ratio of silica in the nanocomposite is selected by 10wt%.

Due to F400 is containing 40wt% epoxy functional silica in a DGEBA epoxy, F400 needed to be diluted with C1532 (DGEBA), and then, the quantity of silica contained in the DGEBA would become 10wt%. First, the mixture (F400 and C1532) was stirred by the mechanical stirrer (YEONG-SHIN Co., Ltd) at 200 rpm for 10 min at room temperature (Fig 2.1). In order to let silica disperse well in the DGEBA, the sonicator (Sonicator 3000, Misonix, Inc,) played an important role after the mechanical stirrer was finished (Fig 2.2). In this research, the sonicator was programmed to run ten consecutive cycles of 120 s of total sonication per cycle. Each cycle included 60 s of sonication pulse (90~120 W power output) followed by a pulse off period of 60 s. High temperature would generate in the mixture solution after using the sonicator. Therefore, in order to avoid changing of chemistry of the DGEBA system which was caused by high temperature, the beaker was cooled by ice-cubes around it. After sonication, DGEBA mixture solution was subsequently degassed for 20 minutes at room temperature in order to remove little bubbles which were caused by the sonication. Then, a stoichiometric amount of curing agent H-100 was added to DGEBA mixture solution at room temperature and mixed under mechanical stirring at 200 rpm for 10 min. After mechanical stirring, bubbles might be generated again; therefore, followed by degassing at room temperature for 30 minutes. After degasification, the solution was quickly poured into the

mold and then thermally cured in an oven. The curing cycle was shown in the Fig 2.3.

2.2.2 CTBN/epoxy nanocomposite

In this research, the weight ratio of CTBN in the CTBN/epoxy nanocomposite was selected by 10wt% and 30wt%. First, CTBN was added into C1532 and the mixture solution was stirred by the mechanical stirrer at 200 rpm for 10 minutes at room temperature. Then, the solution was equipped with the mechanical stirrer at 200 rpm and thermocouple with a temperature controller (preheated to 80℃) maintained at 80℃ for 6 hrs (Fig 2.4). After mechanical stirring, bubbles were generated; therefore, followed by degassing at 80℃ for 20 minutes in an oven (preheated to 80℃). After degasification, the beaker was placed into a cup of water to cool down the mixture solution to room temperature. Then, a stoichiometric amount of curing agent H-100 was added to the mixture solution at room temperature and mixed under mechanical stirring at 200 rpm for 10 minutes, followed by degassing at room temperature for 30 minutes. After degasification, the solution was quickly poured into the mold and then thermally cured in an oven. The curing cycle was shown in the Fig 2.3.

2.2.3 Silica/CTBN/epoxy nanocomposite

In this research, silica/CTBN/epoxy nanocomposite materials were fabricated; the weight ratio of silica and CTBN in the nanocomposite was selected by 10wt%, respectively. First, F400 was diluted with C1532, and then, the quantity of silica contained in the epoxy would finally become 10wt%. Then, the mixture solution was stirred by the mechanical stirrer at 200 rpm for 10 minutes at room temperature. After mechanical stirring, in order to let silica particles disperse well in the DGEBA, the sonicator (Sonicator 3000, Misonix, Inc) was programmed to run ten consecutive cycles of 120 s of total sonication per cycle. Each cycle included 60 s of sonication pulse (90~120 W power output) followed by a pulse off period of 60 s. After sonication, DGEBA mixture solution was subsequently degassed for 20 minutes

at room temperature in an oven for removing little bubbles which were caused by the sonication. Next, CTBN was added into above mixture solution; and the solution equipped with the mechanical stirrer at 200 rpm and thermocouple with a temperature controller (preheated to 80℃) maintained at 80℃ for 6 hrs. After mechanical stirring, the mixture solution was followed by degassing at 80℃ for 20 minutes in an oven (preheated to 80℃).

After degasification, the beaker was placed into a cup of water to cool down the mixture solution to room temperature. Then, a stoichiometric amount of curing agent H-100 was added to DGEBA mixture solution at room temperature and mixed under mechanical stirring at 200 rpm for 10 minutes. After mechanical stirring, the solution was followed by degassing at room temperature for 30 minutes. Finally, the solution was quickly poured into the mold and then thermally cured in an oven. The curing cycle was shown in the Fig 2.3.

2.2.4 CSR/epoxy nanocomposite

In this research, the weight ratio of CSR in the nanocomposite is selected by 10wt%.

First, CSR powder was added into C1532 and the mixture solution was stirred by the mechanical stirrer at 200 rpm for 10 minutes at room temperature. In order to let nano-particles disperse well in the DGEBA, the sonicator was programmed to run ten consecutive cycles of 240 s of total sonication per cycle. Each cycle included 60 s of sonication pulse (90~120 W power output) followed by a pulse off period of 60 s. After sonication, DGEBA mixture solution was subsequently degassed for 20 minutes at room temperature. Next, the solution was equipped with the mechanical stirrer at 200 rpm and thermocouple with a temperature controller (preheated to 80℃) maintained at 80℃ for 2 hrs.

Then, the solution was degassed for at 100℃ for 2 hrs. After the solution was cool down to room temperature, a stoichiometric amount of curing agent H-100 was added to DGEBA mixture solution at room temperature and mixed under mechanical stirring at 200 rpm for 10 minutes. After mechanical stirring, the solution was followed by degassing at room

temperature for 30 minutes. Finally, the solution was quickly poured into the mold and then thermally cured in an oven. The curing cycle was shown in the Fig 2.3.

2.2.5 Silica/CSR/epoxy nanocomposite

In this research, the weight ratio of silica and CSR in the nanocomposite is selected by 10wt%, respectively. First, F400 was diluted with C1532 and then CSR powder was added into the mixture solution. The solution was stirred by the mechanical stirrer at 200 rpm for 10 minutes at room temperature. In order to let nano-particles disperse well in the DGEBA, the sonicator was programmed to run ten consecutive cycles of 240 s of total sonication per cycle. Each cycle included 60 s of sonication pulse (90~120 W power output) followed by a pulse off period of 60 s. After sonication, DGEBA mixture solution was subsequently degassed for 20 minutes at room temperature. Next, the solution was equipped with the mechanical stirrer at 200 rpm and thermocouple with a temperature controller (preheated to 80℃) maintained at 80℃ for 2 hrs. Then, the solution was degassed at 100℃ for 2 hrs.

After the solution was cool down to room temperature, a stoichiometric amount of curing agent H-100 was added to DGEBA mixture solution at room temperature and mixed under mechanical stirring at 200 rpm for 10 minutes. After mechanical stirring, the solution was followed by degassing at room temperature for 30 minutes. Finally, the solution was quickly poured into the mold and then thermally cured in an oven. The curing cycle was shown in the Fig 2.3.

2.2.6 Organoclay/epoxy nanocomposite

In this research, the weight ratio of organoclay in the nanocomposite is selected by 10wt%. First, organoclay powder was added into C1532 and the mixture solution was stirred by the mechanical stirrer at 150 rpm for 10 minutes at room temperature. Then, the solution was equipped with the mechanical stirrer at 800 rpm and thermocouple with a

temperature controller (preheated to 80℃) maintained at 80℃ for 4 hrs. In order to let the layer structure of clay platelet completely separate to each other and disperse well in the DGEBA, the sonicator was programmed to run ten consecutive cycles of 1 hr of total sonication per cycle. Each cycle included 60 s of sonication pulse (90~120 W power output) followed by a pulse off period of 60 s. Next, DGEBA mixture solution was subsequently degassed for 20 minutes at room temperature. After the solution was cool down to room temperature, a stoichiometric amount of curing agent H-100 was added to DGEBA mixture solution at room temperature and mixed under mechanical stirring at 200 rpm for 10 minutes.

After mechanical stirring, the solution was followed by degassing at room temperature for 30 minutes. Finally, the solution was quickly poured into the mold and then thermally cured in an oven. The curing cycle was shown in the Fig 2.3.

After the remove of above nanocomposite plate from the mold, the dimension of the original nanocomposite plate is, 240 mm in length, 80 mm in width and 3.5 mm in thickness.

Subsequently this specimen was cut by diamond saws with appropriate dimension. The corresponding width, length, and thickness of the vibration test specimen are 15, 235, and 3 mm, respectively. Moreover, at least three specimens were prepared for each particulate nanocomposite. The corresponding width, length, and thickness of the DMA test specimen are 5, 40, and 3 mm, respectively; one or two specimens were prepared for each particulate nanocomposite.

2.2.7 Nanocomposite sandwich structures

The sandwich nanocomposite structures were fabricated in this research. There were eight kinds of sandwich nanocomposite structures which were interleaved in different core materials. This sandwich specimen consists of CFA graphite/epoxy laminates and nanocomposites. The stacking sequence of sandwich specimen is [03/d/03], where d is the particulate nanocomposite which was manufactured from the above section. The stacking

sequence of specimen is also presented in Fig 2.5. The upper and lower surfaces of the particulate nanocomposite were adhered to the [03] laminates which consisted of the CFA-05624E19 unidirectional prepreg tapes. Accordingly, the sandwich nanocomposite laminates plate was produced in a hot press machine (Fig 2.6) with the following layup:

vacuum bag, backing tray, cotton patch (five pieces), released fabric, sandwich nanocomposite laminates, released fabric, cotton patch (three pieces), cellophane, and backing tray. The stacking sequence of those materials is setup in Fig 2.7. Those materials were cured at the suggested temperature profile: at 100 ℃ for 40 minutes and at 150 ℃ for 50 minutes under an applied pressure of 13.6 kg/cm², i.e. 16 Psi, with vacuum conditions. The vacuum is essential for forming nanocomposites since it can facilitate the removal of tiny bubbles trapped in the nanocomposites during the process.

After the remove of above sandwich structure from the hot press machine, the specimen was cut by diamond saws with appropriate dimension. The corresponding width, length, and thickness of the test specimen are 10, 185, and 2.3 mm, respectively. At least three specimens were prepared for each sandwich specimen. Furthermore, the uniformity of thickness in sandwich specimen could be found in Fig 2.8 by using an optical microscope.

In Fig 2.8, the specimen was separated by four parts in the length direction; each part had an image in 100 magnification photograph. It can be shown that the uniformity of core material is quite well. From observing Fig 2.8, the core thickness is around 1.55 mm; each face sheet thickness is around 0.375 mm. In addition, a schematic of the dimensions in sandwich nanocomposite structure is shown in Fig 2.9.