The crystallization behaviour of poly (p-phenylene sulfide) (PPS) has been studied. lsothermal rates of bulk crystallization, spherulitic radial growth rates, and nucleation densities were analyzed as functions of molecular weight of PPS, branching agent concentration, and chemical nature of the endgroup counter-atom. The overall rate of bulk crystallization was described by an Avrami equation with exponent ~3. As molecular weight increased in the 24,000-63,000 range, the rates of spherulitic growth and bulk crystallization decreased by a factor of 4. The nucleation density of PPS with <M<sub>w</sub>>=24,000 was 32-fold lower than those of the higher molecular weight polymers. Introduction of 0.2% by weight of branching agent trichlorobenzene in the synthesis vessel reduced the spherulitic growth rate to 1/2, and the rate of bulk crystallization and the nucleation density to 1/4 of those of the linear polymer of the same molecular weight. The decreasing order of crystal growth rates for the endgroup counter-atoms is Ca>H>Zn>Na with calcium providing growth rates two·foId higher than the sodium counter-atom. The rates of overall bulk crystallization (K) followed the decreasing trend H>Zn>Ca>Na. For hydrogen, K was 17-fold higher than that of sodium counter-atom. The nucleation densities presented a different trend, H> Na>Zn>Ca.
The spherulitic growth rates were analyzed in terms of equations proposed to explain the molecular weight dependence. The logarithm of the crystal growth rate followed a linear function of the logarithm of the number average molecular weight proposed by Cheng and Wunderlich.
Since most processing operations occur under non-isothermal conditions, the non-isothermal crystallization of PPS was also studied. Differential scanning calorimetry data folIowed a model proposed by Ozawa for non-isothermal kinetics of crystallization. This model allowed the determination of the Avrami exponent under non-isothermal conditions. The values of the Avrami exponent obtained were in good agreement with values determined isothermally.
The morphological textures of semicrystalline poly (p-phenylene sulfide) (PPS) were investigated utilizing two etching techniques to enhance the finer details. One technique was based on the partial attack of chromic acid solutions at high temperature (100°C), whereas the other used suspensions of anhydrous aluminum chloride at lower temperature (35°C). The aluminum chloride approach was shown to be more appropriate and successful in enhancing the fine details in textures of PPS. This reagent selectively attacked amorphous PPS enhancing the crystalline textures to a greater extent than the chromic acid approach. This technique allowed the observation of the spherulitic growth habit and the “interconnectivity” between impinged spherulites.
The morphology of PPS in composite materials containing few carbon fibers was analyzed. Low crystallization temperatures, slow cooling rates, low molecular weight polymer and local orientation favored the nucleation of transcrystallinity at the carbon fiber surface. T300U carbon fibers were the most effective in nucleating transcrystallinity. Fiber anodization in H₂SO₄ and NaOH electrolytes decreased the nucleating ability of the fibers possibly due to an increase of polarity at the fiber surface. Utilization of the aluminum chloride etching technique in conjunction with scanning electron microscopy conürmed that PPS was nucleating at the fiber surface and showed the radial growth habit and cylindrical symmetry of the transcrystalline regions. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/54316 |
| Date | January 1987 |
| Creators | López, Leonardo C. |
| Contributors | Materials Engineering Science, Wilkes, Garth L., Ward, Thomas C., McGrath, James E., Wightman, James P., Henneke, Edmund G. |
| Publisher | Virginia Polytechnic Institute and State University |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | xiv, 218 leaves, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 17685681 |
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