Thermal Characterization and Morphological Studies of Binary and

Chapter 26

Downloaded by PURDUE UNIVERSITY on July 20, 2013 | http://pubs.acs.org Publication Date: September 29, 2005 | doi: 10.1021/bk-2005-0916.ch026

Thermal Characterization and Morphological Studies of Binary and Ternary Polymeric Blends of Polycarbonate, Brominated Polystyrene, and Poly(2,6-dimethyl-1,4-phenylene oxide) 1

2

A. Z . Aroguz , Z. Misirli , and Β. M . Baysal

3,4,*

1

Department of Chemistry, Faculty of Engineering, University of Istanbul, 34850, Avcilar, Istanbul, Turkey AdvancedTechnologies R&D Center, Bogazici University, 80815, Bebek, Istanbul, Turkey Department of Chemical Engineering, Bogazici University, 80815, Bebek, Istanbul, Turkey TUBITAK Marmara Research Center, P.O. Box 21, 41470 Gebze, Turkey 2

3

4

The thermal behaviors of binary blends of polycarbonate (PC)/brominated polystyrene (PBrS) and ternary blends of PC/PBrS/poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) were investigated. The compatibilizing effect of PPO on the miscibility of the PC/PBrS blends was examined. The miscibility of binary and ternary blends was studied by using differential scanning calorimeter (DSC). The results of DSC indicate that the binary blends of PC/PBrS are immiscible but ternary blends of PC/PBrS/PPO in certain limits are miscible. The microstructural properties of the blends was characterized by environmental scanning electron microscope (ESEM) where the properties are determined in the natural state of the structural role of individual phases (PC/PBrS/PPO) and their effect on the overall microstructure of the products. DSC and ESEM results were supported by FT-IR measurements.

351 In New Polymeric Materials; Korugic-Karasz, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005.


352 Poly(2,6-dimethyl-1,4-phenylene oxide)(PPO) an engineering plastic is miscible in all proportion with a commodity plastic polystyrene (1-6), due to the favorable specific interactions of the repeat units of these polymers (7,8). Mixtures of PPO and PS give amorphous blends of significant commercial importance (9). Limited compatibility was observed for the blends of PPO and halogene-substituted-polystyrenes (9). The phase behavior of PS, PPO, and brominated-polystyrenes was studied (7). The mean field theory of phase behavior was used to discuss, in detail, the interactions and compatibility in polymeric/copolymer systems of these blends (8,10,11). In an earlier work, we studied the miscibility of the two binary polymeric systems: PS/brominated PS, and PPO/brominated PS. Only limited miscibility was observed for a binary PPO/brominated PS blends. The blends of PS/brominated PS are immiscible in all compositions (12). However, compatible compositions of ternary blends of PPO/PS/brominated PS were obtained due to the compatibilizing effect of PPO in this system. In this work, first we studied the thermal behaviors of binary blends of an engineering plastic polycarbonate (PC) and brominated polystyrene (PBrS). Limited miscibility was observed for binary PC/PBrS blends. We have also studied the ternary blends of PC/PBrS/PPO and we examined the compatibilizing effect of Poly(2,6-dimethyl-1,4-phenylene oxide) on the miscibility of PC/PBrS blends.

Experimental Materials The polymers used in this study were obtained from commercial sources. PPO was purchased from Polysciences, Inc. (Warrington,PA; M =50xl0 g mol' ; M =20xl0 g mol* ; high softening point, 90 °C). PBrS was also purchased from Polysciences, Inc. Gel permeation results obtained for PBrS were M =63xl0 g mol" ; M =19xl0 g mol' . The structural characterization of this polymer was performed using IR, NMR and chemical analysis. We found that pendant phenyl groups of the PS backbone chain contain, on avarage, 2.66 Br atoms (i.e., two of each three pendant phenyl groups were ortho-para-tnbromo whereas the remaining one was dibromosubstituted). PC was purchased from Bayer AG. The molecular weights of PC are M =45xl0 g mol" ; M =25xl0 g mol" . AU materials were dried at least 4h at 80°C under vacuum. 3

w

1

3

1

n

3

1

w

3

1

n

9

3

w

1

3

1

n

Formulas of polymers used in this work

In New Polymeric Materials; Korugic-Karasz, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005.

353

Polycarbonate(PC): Tg=140°C

•o-tib-f α

4-0-

Brominated polystyrene (PBrS):

- 6 - c H — otj-ur


Tg=177°C

2.66

Br

Poly(2,6-dimethyl-1,4-phenylene oxide)(PPO): Tg=216°C

Methods of Characterizations

Preparation of the Blends Nine binary blends of PC/PBrS were prepared by dissolving in chloroform with PC weightfractionsof 90,80,70,60,50,40,30,20,10 at room temperature for DSC analysis. The solutions were clear for all blend compositions. In order to examine the compatibilizing effect of PPO on the miscibility of PC/PBrS blends, ternary blends were prepared in different compositions. It was known that the binary blends of PPO/PC (9,13) and PPO/PBrS (12) are partly miscible. The compositions of ternary blends PC/PBrS/PPO were 40/20/40, 40/40/20, 20/40/40. The polymer concentration in the solution was kept below 2 wt % to obtain uniform mixing. The polymer solution was coprecipitated in acetone drop by drop with vigorous agitation and the white precipitates were repeatedly washed with acetone. The blends were dried under vacuum at 50°C for 2-3 days and used for DSC analysis.

FT-IR Measurements In general, the miscibility in polymeric blends arises from specific interactions between the two polymers. Infrared spectroscopy can be used to In New Polymeric Materials; Korugic-Karasz, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005.

354 establish the nature and the level of interactions in polymer blends. Fourier transform infrared (Mattson 1000 FT-IR spectrometer) spectra of samples were recorded in the range 400-4000 cm" with KBr pellet as IR transmitting material. Spectra were obtained at 8 cm' resolution. 1

1


Thermal Properties The thermal properties of all samples were measured calorimetrically using Shimadzu Differential Scanning Calorimeter Computerized Thermal Analysis System 40-1 Model. Blend samples were heated from 298 to 532 Κ at a heating rate of 20 Κ min" under stream of nitrogen with a sample size between 15 and 25 mg using standard aluminum sample pans. The DSC curves taken for analysis were obtained from the second run and glass transition temperature was taken as the initial onset of the change of slope in DSC curve. Temperature calibration was performed using indium (T ^lSé.^CHe^S.SJg ) 1

m

1

Characterization of Microstructural Behavior by ESEM Binary and ternary polymer films were prepared by solution casting for morphologic analysis at ESEM. The polymer mixtures were dissolved in a given compositions in chloroform at room temperature (3.0 w/v solution) for at least 2 days. Blends were cast on glass plates and all film samples were dried under vacuum for 15 days at room temperatures before use. The surface morphology of the solution cast films was examined by ESEMFEG/EDAX. The samples werefracturedby immersing them in liquid nitrogen and then breaking them between two grips while at low temperature and then the sections should be free from dust or loose particles, were then stained with osmium tetroxide vapor for eight hours at room temperature. These surfaces were examined in their natural, uncoated state at low vacuum around 0.2-0.8 torr and 10 KeV. ESEM micrographs were obtained by secondary (SE) or backscattered electrons (BE) or mixed (SE+BE) images for effectively indicated at each phase detail of interest.

RESULTS AND DISCUSSION

FT-IR Characterization Figure 1 shows die full FT-IR spectra of polymers, PC, PBrS, and PPO used in this work, respectively. Figure 2 shows the FT-IR spectra of the binary blend of PC/PBrS (50/50). In New Polymeric Materials; Korugic-Karasz, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005.


355

3000

2000 *AV?NUM3ER

1O00 (cf-tî

Figure 1. FT-IR spectra of pure polymers a)PC, b)PBrS, c)PPO



356

Figure 2. FT-IR spectra of binary blend PC/PBrS (50/50)


357 1

Carbonyl (C=0) adsorption peak is seen 1776 cm* in pure PC. Since the carbonylfrequencyshift is very small this results emphasizes the weakness of the interactions, leading to thermodynamic miscibility in these blends. This peak was splitted at 10 wt% and 20 wt% of PC in the blend compositions as 1776 cm" , 1730 cm" and 1776 cm" ,1741cm" . C-Br aromatic peaks were seen at 1038 cm" . This peak is shifted to lower wavenumbers as the composition of PC increased to 50wt%. Aliphatic C-H streching is seen in pure PBrS at 2923 cm" . It changes from this value to 2934 cm" when adding PC to the blend. This peak is splitted at PC 50 wt% in the blend compositions as 2963 and 2934 cm' . FT-IR spectra of ternary blends of PC/PBrS/PPO, 40/20/40, 40/40/20 are also seen in Figure 3. In the ternary blends of (PC/PBrS/PPO) (40/40/20) aliphatic C-H streching peaks are shifted at 2980 and 2940 cm ' . If we compare PC/PBrS (50/50) and PC/PBrS/PPO (40/40/20) carbonyl peak were shifted from 1776 to 1788 cm' . 1

1

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1

1

1


1

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Thermal Characterization Figure 4 shows the composition dependence of glass transition temperature of PC/PBrS binary blends. The glass transition temperature of PC was decreased from 140 °C to 129 °C as PBrS was added. This is due to the degradation of PC. When each of the polymer weightfractionin binary blend is very high (80 wt% or more ) they are miscible otherwise immiscible. From the DSC thermographs it can be seen that the ternary blends of PC/PBrS/PPO in the compositions of40/40/20,40/20/40, 20/40/40 are miscible (Figure5).

Microstructural Examinations As shown in typical ESEM Figures (6a-6i) morphology studies of these binary and ternary multiphase polymer blends have been concerned with controlling the size and shape of dispersed phase. These morphological structures were basically described as being composed of a matrix ( PC is a continuous phase) and second phase (PBrS is a dispersed phase). The dispersed and continuous phases can be seen in all compositions of die blends in different sizes as shown in the micrographs. The mean sizes of different phases were measured by atomatic image analysis using software program and results were given in Table I and Table II. Figure 6a shows the internal structure of the pure PC. The surface morphology migrograph of the binary blend Pd/PBrS (80/20) was given in Figure 6b. The spherical PBrS particles are dispersed and adherent to the matrix. Dispersed phase becomes elongated. This phenomenon was confirmed by the



358

Figure 3. FT-IR spectra of ternary blends a)PC/PBrS/PPO (40/20/40), b)PC/PBrS/PPO (40/20/40)



i 20

'·

1 90

1 160 TEMPERATURE [fc]

1 230

1 230

Figure 4. DSC Thermograms of binary blends of PC/PBrS.



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Figure 5. DSC Thermograms of ternary blends of PC/PBrS/PPO.



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Table I . Statistical results of dispersed spherical particles. The sizes* of various binary blends given as μιη. PCiwt%) 10 Size 0.14

20 15

30 60

40 525

50 88

60 837

70 256

80 1175

90 1180

*mean size of dispersed phases was taken in cross-sectional view

Table II. Statistical results of dispersed spherical particles. The sizes* of various ternary blends given as μπι. Dispersed phases

PPO PBrS

PC/PBrS/PPO 40/20/40 0.9 20

Compositions PC/PBrS/PPO 40/40/20 3 24

PC/PBrS/PPO 20/40/40 3 34

"'mean size of dispersed phases was taken in cross-sectional view



362

Figure 6a. SEM micrograph of pure PC surface morphology.

Figure 6b. SEM micrograph of surface morphology of PC/PBrS (80/20).



363

Figure 6c. SEM micrograph of surface morphology of PC/PBrS (50/50).

Figure 6d. SEM micrograph of surface morphology and surface detail of PC/PBrS (40/60). In New Polymeric Materials; Korugic-Karasz, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005.


364

Figure 6e. SEM micrograph of surface morphology and surface detail of PC/PBrS (30/70).

Figure 6f. SEM micrograph of surfece morphology of PC/PBrS (20/80). In New Polymeric Materials; Korugic-Karasz, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005.


365

Figure 6g. SEM micrograph of surface morphology of PC/PBrS/PPO (40/20/40).

Figure 6h. SEM micrograph of surface morphology of PC/PBrS/PPO (40/40/20). In New Polymeric Materials; Korugic-Karasz, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005.


366

Figure 6i. SEM micrograph of surface morphology of PC/PBrS/PPO (20/40/40).


367 DSC results in which a single T was obtained for this composition. Figure 6c shows the surface morphology of PC/PBrS (50/50) blend. The particle size becomes larger over the surface. Surface and surface-detail were investigated for another blend, PC/PBrS (40/60) (Figure 6d). Excessively big particles can be observed. These migrographs show that the domain-sizes of the dispersed phase becomes larger and the dispersed phase is pulled inside of the matrix (wetting). Increasing the PBrS content in the blend causes the nonwetting behavior, PC/PBrS (30/70) (Figure 6e). There are holes around of the spherical particles. These holes indicate that interfacial adhesion between two polymers was poor. This is due to the limited compatibility between two polymers. Gel structures were observed inside the holes (insert micrograph in Figure 6e). Figure 6f shows the surface morphology of PC/PBrS (20/80) blend. The big particles are pulled inside the matrix. Homogenous morphology was found. DSC results also verify that this blend composition is miscible. Figures 6g-6i show PC/PBrS/PPO ternary blends migrographs in different compositions. As seen from Figure 6g, a homogenous structure of PC/PBrS/PPO (40/20/40) is present. PBrS and PPO particles are distributed in the PC matrix. The size of the spherical particles in the ternary blend of PC/PBrS PPO (40/40/20) is heterogeneous but the distribution of these particles is homogenous (Figure 6h). Figure 6i shows PC/PBrS/PPO (20/40/40) ternary blend morphology. Again a homogenous structure can be seen. Extremely big particles are mostly eliminated. Big particle-dimensions decreased from 500 μτη to 104 μπι. A dimpling effect can be seen. If the binary and ternary blends morphologies are compared, it can be observed that the spheres are pulled out of matrix to the surface in the binary blends. However, in the ternary blends the spheres are inside of the matrix.


g

Conclusions DSC studies show that the binary blends of PC/PBrS are incompatible and show two T values. However, blends containing small amounts of second components indicate a single T . DSC results of ternary blends studied in this work indicate a single T value for each composition. Morphological studies by scanning electron microscope support the above observations and provide additional information on the structures of the blends studied in this work. g

g

g


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Acknowledgment This work was supported by Research Foundation of the University of Istanbul Contract Grant Number .1081/031297, B.MBaysal acknowledges support from TUBA-Turkish Academy ofSciences.


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Thermal Characterization and Morphological Studies of Binary and

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