Sign up

Thermal characterization and morphological study of polyphenylene sulfide-polycarbonate blends.
Abstract:
The thermal behavior and phase morphology of binary blends of poly(phenylene sulfide) (PPS) with polycarbonate (PC) have been investigated. Differential scanning calorimetry and dynamic mechanical thermal analysis indicate the blends are immiscible, but the glass transition temperature of PC in the blends was found to be decreased due to the degradation of the PC. The PC degradation was investigated by measuring the molecular weight of PC extracted from the blends. Rheological properties of the blends were also studied using a rheodynamic spectrometer. An inversion of the phase morphology was observed from the scanning electron microscopy and dynamic mechanical thermal analysis. The increase of crystallinity of the PPS in the blends was found from a DSC study.

Subject:
Plastics (Mixing)
Polyphenylene sulphide (Research)
Polycarbonates (Research)
Authors:
Lim, Soonho
Kim, Junkyung
Park, Min
Choe, Chul-Rim
Lee, Jeongmin
Kim, Daeheum
Pub Date:
10/01/1996
Publication:
Name: Polymer Engineering and Science Publisher: Society of Plastics Engineers, Inc. Audience: Academic Format: Magazine/Journal Subject: Engineering and manufacturing industries; Science and technology Copyright: COPYRIGHT 1996 Society of Plastics Engineers, Inc. ISSN: 0032-3888
Issue:
Date: Oct, 1996 Source Volume: v36 Source Issue: n20
Accession Number:
18915711
Full Text:
INTRODUCTION

Poly(phenylene sulfide) (PPS) is a high performance engineering thermoplastic with outstanding chemical resistance and thermal stability (1-3). PPS is generally known to be insoluble in any solvent below 200 [degrees] C. It has a high degree of crystallinity and good retention of physical properties at elevated temperatures, so it is widely used for applications including electrical and electronics.

There are several methods to overcome the marginal properties of PPS including improving impact strength and high heat distortion temperature. One approach is to manufacture the filled PPS resin as a glass fiber or glass/mineral filled resin. Another approach is to increase the glass transition temperature by increasing the molecular weight of PPS resin. But this method is quite expensive compared with blending or alloying resins.

Blending of PPS with thermoplastic polymers has been widely investigated in various patents (4-11) and recently published in the open literature (12-19). Yoon and White (13) have measured the interfacial tension between PPS and various polymer melts. PPS and polysulfone (PSF) blends are considered by Cheung (14-16) and Mai (17), PPS-polyarylate (PAR) blends by Golovoy (18), PPS-polyetherimide (PEI) blends by Scobbo (19), PPS - high density polyethylene (HDPE) blends by Chen (20), and PPS-poly(ethylene terephthalate) (PET) blends by Nadkarni (21). PPS-PC blends are considered in the patent by Bailey (4).

In our study, we characterize the thermal behavior and phase morphology of blends containing PPS and PC using differential scanning calorimeter (DSC) and dynamic mechanical thermal analyzer (DMTA). Polycarbonate resin was chosen since this polymer shows high toughness and has a high glass transition temperature. Thermal properties such as melting temperature, crystallization temperature, heat of fusion, and other properties were measured. Also we investigated the degradation of polycarbonate in blends during processing.

EXPERIMENT

Materials

The PPS polymer used in this investigation was Ryton E2480 manufactured by Phillips Petroleum Co. Shape of the PPS polymer was white colored granular type. Glass transition temperature of PPS is [approximately equal to] 90 [degrees] C and melting temperature is around 285 [degrees] C. The Ryton E2480 PPS is a linear crystalline polymer. The general properties of the PPS polymer are listed in Table 1.

The polycarbonate resin used in this study was General Electric Plastics' Lexan 141L, a medium-viscosity material most commonly used for injection molding. The PC polymer has a glass transition temperature of [approximately equal to] 150 [degrees] C. The general properties of the polycarbonate are listed in Table 1.

Blending and Injection Molding

PPS and PC were dried at 150 [degrees] C under vacuum for 3 h and then were dry blended. The weight ratios of PPS/PC blend were 80/20, 70/30, 60/40, 50/50, 40/60, 30/70, 20/80 and the dry blended materials were melt blended using a ZSK-30 W & P co-rotating twin screw extruder. This twin screw extruder is a modular intermeshing type and has a screw diameter of 30.7 mm and a screw length of 880 mm. The temperature was 280 [degrees] C for barrels and 300 [degrees] C near a die. The screw rotation speed was 150 rpm.

The melt blended pellets were vacuum dried at 130 [degrees] C for 2 h and injection molding was performed using a Mini-max molder (Custom Scientific Instruments Inc., CS-183 MMX). The mold temperature was kept at 70 [degrees] C and the shape of the mold was rectangular.

Measurement of Rheological Properties

Rheological properties of the pure resins and the blends were measured using a rheodynamic spectrometer (RDS, Rheometrics Inc. 7700) with a parallel plate type. The range of frequency was from 0.01 to 500 rad/s. The gap distance of the parallel plates was 1.2 mm and all experiments were carried at 300 [degrees] C and in a nitrogen environment.

Observation of Morphology

Scanning electron microscopy was used for morphological observation of the PPS/PC blends. A Hitachi [TABULAR DATA FOR TABLE 1 OMITTED] (Model S-2500) scanning electron microscope was used. The samples were obtained by fracturing the extrudates in liquid nitrogen. The magnification was 3000.

Thermal Characterization

Differential scanning calorimetry (DSC, Model 8230) and dynamic mechanical thermal analyzer (DMTA, Polymer Laboratories) were used in order to characterize the thermal properties of the PPS/PC blend system. For the DSC experiment, scanning rate was 10 [degrees] C/min, the weight of samples was [approximately equal to]10 mg, and the scanning temperature range was from room temperature to 320 [degrees] C. For analyzing the crystallization behavior, the samples scanned to 320 [degrees] C were rapidly cooled using liquid nitrogen and re-scanned to 320 [degrees] C. DMTA analysis was performed to measure the bending modulus and tan [Delta] of the PPS/PC blend.

Measurement of Solution Viscosity

Solution viscosity of polycarbonate in blends was measured in order to calculate the molecular weight of polycarbonate in the blends. Polycarbonate was extracted from the blends using a soxhlet equipment for 24 h and dichloromethane was used as a solvent. Solution viscosity was obtained from a one-point method (22) using an Ostwald viscometer at 25 [degrees] C with the concentration of polycarbonate solution of 0.005 g/ml.

RESULTS AND DISCUSSION

Melt viscosity of pure polymers and blends was measured as a function of shear rate using a RDS. Figure 1 shows the viscosity change for various ratios of PPS/PC blends. Melt viscosity of pure PPS and PC was [approximately equal to]220 and 420 Pa [center dot] s at 300 [degrees] C and a range of melt viscosity of PPS/PC blend was from 10 to 50 Pa [center dot] s. Melt viscosity of PPS / PC blends severely decreased as a small amount of PPS was added to the PC polymer. This is a very interesting phenomenon, which implies the better processibility of the PPS/PC blends due to the reduced viscosity. Actually, this blend can be processed at 250 [degrees] C using a twin screw extruder. Melt viscosity of the blends gradually increased as the content of PPS was increased in the blend.

A morphological study was carried out using a scanning electron microscopy (SEM). The fracture of the blend shown in Fig. 2 represents the incompatibility of the PPS/PC blend. When the content of PC is up to 40 wt%, the PC domain has the spherical shape. The domain shape changes from sphere to rod between 60/40 and 50/50 of PPS/PC blends, which shows that the phase is converted from PC domain to PPS domain. This phenomenon was confirmed in the experiment of dynamic mechanical thermal analysis [ILLUSTRATION FOR FIGURES 2 AND 4 OMITTED].

The dynamic mechanical thermal analysis for PPS/PC blend as molded was performed to investigate the glass transition temperature of each component. The DMTA results of all blends were represented In one figure to compare the transition temperature, where 1 Hz was chosen. Figure 3 shows the storage bending modulus and Fig. 4 shows the tan [Delta] of PPS/PC blends. These Figures demonstrate that the glass transition temperature of the PPS did not change regardless of the composition of the blends but the glass transition temperature of the polycarbonate was decreased from 150 to 120 [degrees] C as the PPS was added. This is due to the degradation of the polycarbonate during blending in the twin screw extruder. The molecular weight of the PC in the blends were measured using an Ostwald viscometer, which is listed in Table 2. The molecular weight was severely decreased from 30,400 to 4,900 as the PPS was added. The molecular weight-glass transition temperature relations were confirmed from Cowie's work where he studied the relationship between MW and [T.sub.g] (23). Also, we can see that the bending modulus of the blends shows a different trend at high temperature range [ILLUSTRATION FOR FIGURE 3 OMITTED]. For the low content of PC (less than 40%), the modulus of the blends changes very slowly at the high temperature range but for the high content of the PC (more than 50%), the modulus rapidly decreased. This phenomenon is related to the property of the matrix in the blends. The blends with PPS matrix show little change in modulus above the glass transition temperature due to the crystalline region but the blends with the PC matrix show a rapid change in modulus above the glass transition temperature. So we can expect that the phases are inverted between 60/40 and 50/50 of PPS/PC blends. For the low content of PC (less than 40%), the modulus is slightly increased around 110 [degrees] C, which is due to the crystallization of the PPS. This phenomenon is also observed in Fig. 4, where the tan [Delta] of the pure PPS shows a peak near 110 [degrees] C. The pure PPS (100/0) shows a large drop of the modulus above the glass transition temperature comparing with the PPS/PC blends. This is due to the lower crystallinity of the pure PPS than the PPS/PC blends since the molecular motion of the blends is easier than that of pure PPS due to the reduced viscosity of the blends.



[TABULAR DATA FOR TABLE 3 OMITTED]

Differential scanning calorimeter was used to measure the crystallinity of the PPS in the blends. The samples were scanned up to 320 [degrees] C at the rate of 10 [degrees] C/min after quenching from 320 [degrees] C. Figure 5 shows the DSC thermograms of the PPS/PC blends. The glass transition temperature of the PPS was observed near 90 [degrees] C but it's difficult to observe the [T.sub.g] of PC in the blends by DSC. We can see that the [T.sub.g] of the PPS, crystallization temperature of the PPS, and Tm of the PPS do not change regardless of composition. The results of the DSC thermogram are summarized in Table 3. The heat of fusion obtained experimentally was normalized with respect to PPS content in the blends. The crystallinity of the blends becomes a little bit higher than the pure PPS due to the reduced viscosity of the blends and the nucleating ability of PC in the interface between PPS and PC.

[TABULAR DATA FOR TABLE 4 OMITTED]

A transition temperature change of PPS after annealing was reported by Cheung (14). This transition is attributed to the glass transition of the amorphous phase of crystallized PPS. This phenomenon is common to many semicrystalline polymers and has been reviewed by Struik (24). Figures 6 and 7 show the results of dynamic mechanical thermal analysis for the annealed PPS/PC blends. Since the [T.sub.g] of PC in the blends occurs at temperatures between 120 and 150 [degrees] C, the annealing condition should be carefully chosen. After annealing at 130 [degrees] C and 2h, a surface of the blends bulged out and many voids were formed inside the specimens. The annealing condition of 110 [degrees] C and 4 h was chosen for annealing the PPS/PC blends from several annealing experiments. The storage bending modulus of the annealed PPS/PC blends is represented in Fig. 6 and the tan [Delta] is represented in Fig. 7. The glass transition temperature of the pure PPS was increased from 94 to 119 [degrees] C after the PPS was annealed. For the annealed blends it was difficult to observe the glass transition temperature of the PPS in the blends because of the high crystallinity of the PPS after annealing. The glass transition temperature of the PC in the blends was decreased from 152 to 116 [degrees] C after annealing the blends. This is the same trend as the unannealed blends. We can clearly observe the different shape of the modulus change above the glass transition temperature of the PC in the blends from Fig. 6, which represents the phase inversion between 50/50 and 60/40 of the PPS/PC blends. The glass transition temperature of the PPS and the PC is summarized in Table 4 from the results of the dynamic mechanical thermal analyzer. [T.sub.[g.sub.1]] represents the glass transition temperature of the PPS in the blends and [T.sub.[g.sub.2]] represents the glass transition temperature of the PC in the blends. The glass transition temperature of the PPS in the blends shows almost the same temperature regardless of composition but after annealing the [T.sub.g] of the PPS was increased to around 118 [degrees] C. The glass transition temperature of the PC in the annealed blends shows a large decrease when the PPS was added to the PC, which represents the degradation of the PC in the blends during processing. This severe degradation of PC occurred when the PC was blended with PPS, which means the PC molecules are easily broken down by the PPS molecules in the molten state. This phenomenon is more severe for the crosslinking type PPS which has a lower molecular weight than the linear type PPS.

CONCLUSIONS

The melt viscosity of the PPS/PC blends was largely decreased as the PC was added to the PPS polymer. This seems to be due to the degradation of the PC during blending in the twin screw extruder. The phenomenon was confirmed by measuring the molecular weight of the PC in the blends. The molecular weight of the PC was severely decreased from 30,400 to 4900 as the PPS was added. The phases are inverted between 60/40 and 50/50 of the PPS/PC blends, which was observed from the SEM pictures and the results of the dynamic mechanical thermal analysis. The glass transition temperature of the PPS in the blends did not change regardless of composition but the [T.sub.g] of the PC in the blends decreased from 150 to 120 [degrees] C, which is due to the degradation of the PC in the blends. The degradation of the PC becomes severe when the PC is blended with PPS. The blends with a high content of PPS have a little higher crystallinity than the pure PPS because of the reduced viscosity of the blends and the nucleating ability of PC in the interface between PPS and PC.

REFERENCES

1. H. W. Hill, Jr., and D. G. Brady, Polym. Eng. Sci., 16, 832 (1976).

2. L. C. Lopez and G. L. Wilkes, JMS-Rev. Macromol. Chem. Phy., 29, 83 (1989).

3. C. C. Martin, J. E. O'Connor, and A. Y. Lou, SAMPE Q., 12 (1984).

4. F. W. Bailey, U.S. patent 4,021,596 (1977).

5. R. T. Alvarez, U.S. patent 4,017,555 (1977).

6. S. Adelmann, D. Margotte, J. Merten, and H. Vernaleken, U.S. patent 4,046,836 (1977).

7. G. Salee, U.S. patent 4,211,687 (1980).

8. H. F. Giles, U.S. patent 4,455,410 (1984).

9. R. A. Garcia and R. J. Martinovich, U.S. patent 4,451,607 (1984).

10. B. D. Dean, U.S. patent 4,497,928 (1985).

11. Y. F. Liang, U.S. patent 4,708,983 (1987).

12. C. J. T. Landry and D. M. Teegarden, J. Polym. Sci. (B), 32, 1285 (1994).

13. P. J. Yoon and J. L. White, J. Appl. Polym. Sci., 51, 1515 (1994).

14. M. F. Cheung, A. Golovoy, H. K. Plummer, and H. van Oene, Polymer, 31, 2299 (1990).

15. M. F. Cheung, A. Golovoy, and H. van Oene, Polymer, 31, 2307 (1990).

16. M. F. Cheung, A. Golovoy, V. E. Mindroiu, H. K. Plummer, Jr., and H. van Oene, Polymer, 34, 3809 (1993).

17. K. Mai, M. Zhang, H. Zeng, and S. Qi, J. Appl. Polym. Sci., 51, 57 (1994).

18. A. Golovoy, M. F. Cheung, and M. Zinbo, Polym. Commun., 30, 322 (1989).

19. J. J. Scobbo, Jr., SPE ANTEC Tech. Papers, 38, 605 (1992).

20. T. H. Chen and A. C. Su, Polymer, 34, 4826 (1993).

21. V. L. Shingankuli, J. P. Jog. and V. M. Nadkarni, J. Appl. Polym. Sci., 51, 1463 (1994).

22. O. F. Solomon and I. Z. Ciuta, J. Appl. Polym. Sci., 6, 683 (1962).

23. J. M. G. Cowie, Eur. Polym. J., 11, 297 (1975).

24. L. C. E. Struik, Polymer, 28, 1521 (1987).
Table 2. Solution Viscosity of PC Extracted From the PPS/PC Blends.

PPS/PC (by wt%)   [M.sub.v]

0/100              30,400
20/80              20,900
30/70              14,700
40/60              12,400
50/50                9600
70/30                4900
Gale Copyright:
Copyright 1996 Gale, Cengage Learning. All rights reserved.