附录B：外文文献翻译 obtained by self-emulsification in water after being neutralized with tertiary amine. However, the hydrophilic nature of ionic groups or water-soluble segments of waterborne type polyurethanes inevitably poses some problems associated with poor water resistance and mechanical property. This problem can more or less be reduced by hybridization techniques, such as the latexes blending[9], polymerization of composite emulsion[10], emulsion copolymerization[11], latex interpenetrating polymer network [12,13], and WPU/inorganic-clay hybridization[14–25].
In this paper, the WPU was synthesized from poly (tetramethylene glycol), 4,4-diphenyl-methane diisocyanate, dimethylol butanic acid, and neutralized by triethylamine. The WPU/AT nanocomposites have been prepared by direct emulsion blending. The structure and properties of the nanocomposites have been characterized by scanning electron microscopy (SEM), FTIR, dynamic mechanical analysis (DMA), thermal gravimetricanalysis (TGA) and tensile test.
2 Experimental
2.1 Materials
Poly (tetramethylene) glycol (PTMG) was purchased from Mitsubishi Chemical, which was dried for 4 h at 110 ℃ under vacuum to eliminate moisture before use. 4, 4-Diphenylmethane diisoccyanate (MDI) were acquired from Yantai wanhua Co.China. Dimethylol butanic acid (DMBA) was purchased from Sam Wing International Ltd. Methyl ethyl ketone (MEK), triethylamine (TEA), hydrogen chloride (HCl) were purchased from Shanghai Chemistry Reagent Company. All chemicals were used as received. Attapulgite (AT) with purity greater than 90% was provided by Jiangsu Junda Attapulgite Material Co. Ltd China. The received AT sample was first dispersed in a 0.15 M HCl solution and was stirred for 12 h. Then, the AT suspension was filtered and wished by deionized water until no Cl-1was checked out by AgNO3. The purified AT was dried at 80 ℃ under vacuum for at least 24 h before being used.
2.2 Preparation of WPU
Synthesis of WPU was carried out in a 3000 ml three-neck round-bottom flask equipped with mechanical stirrer, reflux condenser, thermometer, and heating mantle under nitrogen atmosphere. First, 113.6 g of MDI, 300 g of PTMG were fed into the flask. The reaction was carried out at 80 ℃ for 2 h to obtain NCO-terminated prepolymer. Then 44.4 g of DMBA were added into the system to react for another 1.5 h. In this process, 500 g MEK was added to reduce the viscosity of the reaction mixture. Then the system was neutralized by 30.3 g of TEA at 60 ℃, and 1450 g deionized water was added into the system to form an emulsion under vigorous stirring. WPU with a solid content of about 25% was obtained after removal of MEK by distilling at 55 ℃ under vacuum using a rotation evaporation equipment. The molecular weight of WPU, measured by GPC (Waters 1515 GPC instrument, using styragel-1000 columns and tetrahydrofuran as a mobile phase at a flow rate of 1 mL/min), is Mn = 2.07×105, Mw = 6.61×105, respectively, and the Mw/Mn is 3.19.
2.3 Preparation of WPU/AT nanocomposites
AT was first dispersed in a diluent WPU dispersion (ca. 1 wt%) under ultrasonic vibration, and then
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附录B：外文文献翻译 the dispersion was blend with WPU dispersion at room under mechanical stirring for 3 h. AT content W (wt%) was calculated according to Eq.(1) W (wt%)= Wa×100% (1) Wa?WpWhere Wa and Wp represent the weight of AT and solid WPU, respectively. The samples with different AT contents were numbered as WPU/AT0, WPU/AT0.5, WPU/AT1, WPU/AT2, corresponding to AT contents of 0%, 0.5%, 1% and 2%, respectively. 2.4 Measurements SEM measurement was conducted on a JEOL JSM-5610LV SEM equipment. The film samples were fractured in liquid nitrogen, and then were sputter-coated with a thin layer of gold palladium alloy prior to SEM observation. FTIR measurements were carried out by a NEXUS-670 FTIR spectrometer. The samples for FTIR measurements were prepared by casting the dispersions on glass plates and maintaining at ambient temperature for 48hr and then at 40 ℃ under vacuum for 24 h. Dynamic mechanical properties of the nanocomposites were investigated by a Netzsch DMA 242 instrument, with a tensile mode at a heating rate of 3 ℃/min from -150 ℃ to +150 ℃. The testing frequency was 1 Hz. Tensile mechanical measurement was performed at 25℃ using a universal mechanical testing machine made by Shanghai Tuolong electronic technology Ltd. Co. The conditions of tensile measurement were as follows: sample size was 20 mm×5 mm×0.4 mm; Sample length between jaws was 10 mm; crosshead speed was 50 mm/min. At least 5 samples were tested for each type of sample and the data were averaged. Thermal gravity analysis (TGA) was carried out using a Perkin–Elmer instrument in air at a heating rate of 20 ℃/min from room temperature to 600 ℃.
3 Results and discussion
3.1 Preparation of WPU/AT nanocomposites
In this study, the WPU/AT nanocomposites were prepared by latex blending. The AT used here is a type of natural fibrillar clay with a theoretical half unit-cell formula Mg5Si8O20(OH)2(OH2)4.4H2O. It contains many hydroxyl groups on the surfaces. Fig. 1 is the SEM photography of AT.
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附录B：外文文献翻译
It resolves as a randomly oriented network of densely packed fibers with the diameter of a single fiber less than 100 nm and the length of a fiber from several hundred nanometers to several micrometers. We found that AT can be separated into dispersed units under shear or ultrasonic vibration. However, the dispersed units tend to agglomerate in the dispersion due to their huge surface area. In order to get nanocomposites with more uniform dispersion of AT, a pre-treatment route was adopted in our experiment. AT was first dispersed in a 1 wt% diluent WPU dispersion under ultrasonic vibration, and then the dispersion was blended with the WPU dispersion at room for 3 h. Fig. 2 shows the SEM photography of the fractured section of the pristine WPU and WPU/AT nanocomposites. Photographs of fractured section of pristine WPU and WPU/AT nanocomposites (a) WPU/AT0, (b) WPU/AT1, (c) WPU/AT2.
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附录B：外文文献翻译
It can be seen that the fractured section of pristine WPU is smooth, while those of WPU/AT samples show many irregularly distributed nano-sized AT fibril. In addition, the interface between AT and the WPU matrix is not so clear. Most AT fibrils were fractured and only a few fibrils were pulled out from the WPU matrix. This implies that the adhesion between AT and the WPU matrix is well.
3.2 FTIR analysis
The FTIR spectra of the pristine WPU and WPU/AT nanocomposites are shown in Fig.3.
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附录B：外文文献翻译 .
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There are four characteristic absorbance peaks seen in the spectra of pristine WPU, the 1110 cm1peak corresponding to the stretching vibration of ether C–O–C, the 1700-1730 cm-1 peak due to the stretching vibration of urethane carbonyl group (C＝O), the 2940-2862 cm1peaks due to the asymmetric and
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symmetric stretching vibration of C–H and the 3330 cm-1 peak resulting from the stretching vibration of N–H group in hydrogen bonding [14, 20, 26]. It is found that the main features of various bond vibrations and hydrogen bonding of the WPU/AT nanocomposites remain the same as those of the pristine WPU. This result indicates that there are no major chemical structural changes in WPU matrix with the addition of a small amount of AT.
3.3 Dynamic mechanical analysis
The plots of loss factor, tand, versus temperature for the WPU/AT samples are shown in Fig. 4.
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