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Effect of different nanofillers on the phase morphology of polycarbonate/acrylonitrile-butadiene-styrene polymer blends materials R. Sulcis, F. Marinello, G. Marino, M . Balbo CIVEN (Coord inamento Interuniversitario VEneto per le Nanotecnologie) Via delle Industrie 5, Parco scientifico e Tecnologico Vega, 30175 Venezia-Marghera Italia Presented results regard the preparation and the morphology characterizat ion of different polycarbonate/acrylonitrile-butadiene-styrene blend nanocomposites. In dependence of the nanofiller used (alumina, fu med silica or silicate layers), different phase distributions are obtained; this observation was mainly attributed to the variation of the interfacial tension between the phases. 1. Introduction The polymer industry‘s demand for new applications with minimal capital investment and turnaround time has led to the concept of blending two or more different existing polymers rather than synthesizing comp letely new poly mers. Poly mer b lends are, in the majority, mu ltiphase systems for thermodynamic reasons, i.e., they phase separate to form a heterogeneous mixture with a unique morphology. The design and control of such morphology can lead to ’tailor-made” blends with desired mechanical, physical, and/or rheological properties. Blends of bisphenol-A-polycarbonate/acrylonitrile - butadiene-styrene have shown extensive growth since their first commercialization. Applications in the automotive industry and electronic housings have shown tremendous growth. The PC/ABS blend gained popularity in the polymer compounding sector because of its unique combination of properties provided by the constituent polymers. The addition of a minor amount of ABS to PC leads to ease of processing, enhancement in notch impact strength, and a reduction in the base material cost. On the other hand, a minor amount of PC in ABS leads to improvement in impact strength and heat resistance. A synergistic property in PC/ABS blends is not observed because of the limited thermodynamic miscib ility. An appropriate compatibilizer could be utilized to enhance adhesion between PC and ABS, and at the same t ime reduce the minor phase domain size by lo wering the interfacial tension between the phases. The interface of a polymer b lend plays a crucial role in controlling the b lend’s mechanical and physical properties. In this work the effect of different nanosized fillers (three fumed silica, an alu mina and two d ifferent organic modified layered silicates) on the phase distribution of a 70/30 PC/A BS b lend obtained by melt blend ing was evaluated by optical microscopy observations. 2. Experime ntal 2.1 Materials A polycarbonate (PC) (Calibre TM 201-22, Dow Plastics) with density 1.20 g/cm3 and melt flo w rate 22 300°C/1.2Kg (g/10’) according with the data sheet was used. The acrylonitrile -butadiene-styrene used was a MagnumTM 3616 supplied by Dow Plastics, with density 1.05 g/cm3 and melt flo w rate 5.5 220°C/10Kg (g/10’). The -alu mina used for the preparation of the nanocomposites was characterized by a mean particle size of 150 n m, superficial area of 5-15 m2 /g and purity of 99.97%, according with the producer (J.T. Baker). Nanoscale silica materials Aerosil R972 (16 n m), Aerosil R812 (7 n m) and Aerosil R805 (12 n m) were provided by Degussa co. These fumed silica are organo-silica obtained by the superficial treat ment with different silane coupling agents and in particular with dimethyldichlorosilane, hexamethyldisilo xane and octylsilane, respectively. The characteristics of the three Aerosil are reported in Table 1. Table 1. Characteristics of the different fumed silica. Aerosil Aerosil Aerosil Property R972 R812 R805 Superficial treat ment Dimethyldichlorosilane hexamethyld isilo xane octylsilane Specific surface area 110±20 260±30 150±25 (m2 /g) Carbon content 0.6-1.2 2.0-3.0 4.5-6.5 (wt%) Average primary 16 7 12 particle size (n m) The silicate layers were organophilic bentonites, Dellite 72T and Dellite CW 9, kindly provided by Laviosa Chimica M ineraria SpA, Livorno, Italy. The organic modified clays were obtained by cation-exchange of sodium with dimethyl-dihydrogenated tallow ammon iu m ions (tallow is composed predominantly of octadecyl chains with smaller amounts of lower ho mologues). The characteristics of the two clays are summarized in Table 2. Table 2. Characteristics of the investigated organo-modified silicate layers. Property Dellite 72T Dellite CW9 Hu mid ity (wt%)a 3 3 Weight decrease on ignition (wt%)a 36-38 43-48 Particle dimension (µm)a 7-9 15-20 Interlayer spacing (Å)b 25.6 32.7 a From technical sheet b From X-Ray diffraction analysis 2.2 Nanocomposite preparati on Nanocomposites of PC/ABS and different nanofillers were prepared by melt compounding at 240 ° C in a Brabender Plastograph ® with a 50 ml mixing chamber, using a screw speed of 40 rp m and a mixing time of 15 min in all cases. The PC/ABS weight ratio was 70:30 and the different nanofiller were added at 7% by weight with respect to the polymer b lend. In order to reduce the degradation of the blend, 0.1% by weight of a mixture 1:1 of Irgano x 1010 and Irgafos 168 (both provided from Ciba) was added at the nanocomposite materials during melt b lending. 2.3 Characterizati on X-ray diffraction (XRD) was carried out onto silicate nanocomposites and onto the silicate layers by using a Siemens Kristalloflex 810 diffracto meter D 500/501 (CuKα1 radiation, with = 0.154178 n m) at roo m temperature. The diffractograms were collected over 2θ ranges from 1.5 to 15, where the basal reflection of the interlayer d- spacing appears, at a scanning rate of 0.016 ◦s −1 . The nanocomposites and the fillers were analy zed as pressed films and as powders, respectively. For the optical microscopy observations an optical microscope LOM DM 6000M (Leica) was used. The samples where first embedded in an epoxy resin, then polished and finally etched with a K2 Cr2 O7 /H2 SO4 solution at 80 °C for 30 s in order to remove selectively the ABS phase (according with O. Charoen et al.) and washed in an ultrasonic batch with distilled water. 3. Results and Discussion In Figure 1 the phase morphology of the PC/ABS blend, obtained with optical microscopy observations is reported. The ABS is present as dispersed phase in a form of discrete droplets with dimentions below 20 micron of diameter in the PC matrix. Fig. 1. Phase morphology of the 70:30 PC/ABS blend obtained with optical microscopy. For all the composites the nanoparticles are almost dispersed in the ABS phase, in agree with what obsreved by Zong et al. Moreover, in dependance of the filler type, the form of the dispersed phase markedly changes, as reported in Figure 2. The composite with -alu mina is characterized by having the dispersed phase in a pseudo-spherical form, with dimensions of ca. 10-25 micron. The two silicate layers induce an elongated form suggesting a low dispersion of the nanofillers, especially Dellite CW9. This is in agree with XRD analyses (Figure 3), showing no marked difference in the position of the (001) diffraction peak even at low Dellite amount (2% by weight), which indicates the formation of a phase separated traditional microco mposite. This is probably due to the low compatibility between the alky l ammon iu m cation of the organoclays and the polymer blend. Instead, all the three aerosil cause the formation of a more distributed dispersed phase. The better efficiency of Aerosil R812 and Aerosil 805 in the reductio n of the dispersed phase dimentions can be exp lained by the higher co mpatibility between the hexamethyld isilo xane and octylsilane coating with respect to dimethyldich lorosilane one with the polymer blend. However, for all the fumed silica, a variation in the viscosity and of the tension at the interf ace between the two phases can be supposed . Moreover, the increase in the interface in all these materials can suggest in this case better mechanical performances for these materials. a) b) c) d) e) f) Fig. 2. Phase morphology of the 70:30 PC/ABS blend with -alumina (a), Dellite 72T (b), Dellite CW9 (c) Aerosil R972 (d), Aerosil R812 (e), Aerosil R805 (f) obtained with optical microscopy. PC/ABS CW9(7%) 5 Dellite 72T 4 PC/ABS CW9(2%) PC/ABS 72T(7%) CW9 3,45 PC/ABS 72T(2%) 4 2,7 3 intensità (counts/s) intensità (counts/s) 3 2 2 2,9 2,8 1 2,7 2,9 1 0 0 0 2 4 6 8 10 12 0 2 4 6 8 10 12 2 2 Fig. 3. X-Ray diffraction of Dellite 72T, PC/ABS blend with 2 and 7 %wt of Dellite 72T (left) and Dellite CW9, PC/ABS blend with 2 and 7%wt of Dellite CW9 (right). 4. Conclusions The interface of a polymer blend plays a crucial role in controlling the blend’s mechanical and physical properties. In this work, different PC/ABS nanocomposites with different nanofillers were prepared by melt blending. The effect of alu mina, silicate layers and different fu med silica on the phase distribution of a 70/30 PC/ABS blend was evaluated by optical microscopy observations. In dependence of the nature of the filler or of the superficial treat ment different morphologies where obtained. A fine dispersion of ABS phase in the PC matrix was obtained with fumed silica with hexamethyld isilo xane and octylsilane surface treat ment. 3. References O-Charoen N., Leong Y.W., Hamada H., 2008, Poly m. Eng. Sci. 48, 786. Tanpaiboonkul P., Lerdwijit jarud W., Sirivat A., Larson R.G., 2007, Poly mer 48, 3822. Yang K., Lee S.-H., Oh J.-M., 1999, Po ly m. Eng. Sci. 39, 1667. Zong R., Hu Y., Liu N., Wang S., Liao G., 2005, Poly m. Adv. Technol. 16, 725.
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