洛阳理工学院毕业设计论文
The
organophilic
montmorillonite
(OMT)
was
prepared
from
montmorillonite (MMT) by ion exchange reaction using hexadecyl trimethyl ammonium bromide (C16) in water according to the reported method [13].
Preparation of ABS/OMT/La2O3 nanocomposites
The OMT, La2O3 and ABS were dried under vacuum at 80°C for overnight before use. All the samples were meltmixed in a twin-roller mill (KX-160, Jiangsu, China) for 10 min. The temperature of the mill was maintained at 180°C and the roller speed was 100 rpm for the preparation of all the samples listed in Table 2.
Vacuum
carbonization
and
purification
of
ABS/OMT/La2O3
nanocomposites
The prepared sample of ABS/5wt%OMT/3wt%La2O3 was put into a quartz tube, charged pure nitrogen in it and then vacuumized by a vacuum pump, finally sealed the tube immediately. The pressure of the hermetic vacuum
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洛阳理工学院毕业设计论文
system was less than 0.01 atm. The hermetic vacuum system was heated to 600°C and last for a period of 2 h. The obtained carbonization products were purified with hydrofluoric acid and nitric acid and then dried under vacuum at 80°C.
Characterization
X-ray diffraction (XRD) patterns were performed on the 1 mm thick films with a Japan Rigaku D/Max-Ra rotating anode X-ray diffractometer equipped with a Cu-Ka tube and Ni filter (λ=0.1542 nm).
Transmission electron microscopy (TEM) images were obtained on a Jeol JEM-100SX transmission electron microscope with an acceleration voltage of 100 kV. The TEM specimens were cut at room temperature using an ultramicrotome (Ultracut-1, UK) with a diamond knife from an epoxy block with the films of the nanocomposite embedded. Thin specimens, 50–80 nm, were collected in a trough filled with water and placed on 200 mesh copper grids.
Fig. 1 XRD patterns of the ABS nanocomposites a MMT, b OMT,c ABS/5wt%OMT and d ABS/5wt%OMT/3wt%La2O3
Thermogravimetric analyses (TGA) were carried out using a TGA50H thermo- analyzer instrument from 25 to 700°C using a linear heating rate of 10°C/min under nitrogen flow. The nitrogen flow was 25 ml/min. Samples
33
洛阳理工学院毕业设计论文
were measured in an aluminum oxide pan with a mass of about 10 mg.
Laser Raman spectroscopy (LSR) measurements were carried out at room temperature with a SPEX-1403 laser Raman spectrometer (SPEX Co, USA) with excitation provided in back-scattering geometry by a 514.5 nm argon laser line.
High-resolution electron microscopy (HRTEM) images were obtained by JEOL 2010 with an acceleration voltage of 200 kV. Specimens for the HRTEM measurements were obtained by using an ultramicrotome (Ultracut-1, UK) with a diamond knife from an epoxy block with the films of the nanocomposite embedded or placing a drop of sample suspension prepared by ultrasonic dispersion on a carboncoated copper grid, and dried at room temperature.
Fig. 2 TEM image of ABS/5wt%OMT nanocomposites
Fig. 3 HRTEM image of ABS/5wt%OMT nanocomposites
Results and discussion
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洛阳理工学院毕业设计论文
Dispersibility of ABS/OMT nanocomposites
The XRD patterns of ABS/OMT nanocomposites are shown in Fig. 1. The maximum peaks correspond to the (001) plane reflection of the clays. The XRD patterns show that the interlayer spacing of the OMT is 2.39 nm compared to 1.51 nm of MMT, which means the molecules of CTAB intercalate into the gallery of MMT. The XRD pattern of ABS/5wt%OMT (Fig. 1c) shows that the average basal spacing of the silicate layers increases from 2.39 nm of the OMT to 3.43 nm meaning the formation of the intercalated morphology.
TEM (Fig. 2) and HRTEM (Fig. 3) images of ABS/OMT nanocomposites are used to further investigate the distribution of the silicate layers. Fig. 2 shows that the silicates disperse uniformly in ABS matrix, and it can be seen that some large intercalated tactoids are visible in the TEM.HRTEM image of ABS/OMT nanocomposites (Fig. 3) also reveals the distribution of the layers. Individual silicate layer, along with several stacks are dispersed in the polymer matrix. From Fig. 1c,d it can be observed that with the addition of La2O3, the d001 peak has almost no change. These indicate the loading of La2O3 has little influence on the formation of intercalated morphology.
Fig. 4 TGA curves of the ABS nanocomposites under nitrogen
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洛阳理工学院毕业设计论文
Thermal stability property of the ABS/OMT nanocomposites
The thermal properties of pure ABS and the ABS/ OMT nanocomposites are analyzed by TGA under nitrogen. The TGA curves are shown in Fig. 4. The 5% weight loss temperature (T-5wt%), the maximum decomposition temperature (Tmax) and the char residue at 700°C are listed in Table 3. The onset temperature degradation of ABS/5wt%OMT shows a little poorer thermal stability at a low temperature than that of pure ABS, and this mainly due to the thermal decomposition of the OMT which takes place at around 200°C and proceeds according to the Hofmann degradation mechanism [14, 15]. The weight loss of ABS/5wt%OMT is terminated after 500°C, and the char residue is mainly MgO, Al2O3, SiO2 and amorphous carbon and so on. From the Table 3 it can be observed that addition of OMT does not remarkably increase the thermal stability of ABS. With the addition of 5wt% OMT, the char residual only increases from 2.4 to 5.3wt% compare to that of pure ABS. The reasons may be that clay layers can act as a superior insulator and as a mass-transport barrier to the volatile products to increase the thermal stability of the matrix, but the alkylammonium cations in OMT has thermal instability and can degrade in advance. Furthermore, the alkylammonium cations in the OMT can suffer decomposition following the Hofmann elimination reaction [14, 15]. So the influence of OMT on ABS is not obvious.
With the addition of 3wt%La2O3, ABS/5wt%OMT shows few changes before 450°C, but has a decreased yield of volatile decomposed products and a notable increase of the insoluble char residue at 700°C. The charresidue yield can be up to 12.6wt% with 3wt% La2O3 in comparison to 2.4wt% of pure ABS.
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