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17Sulcis

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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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