Effect of gamma ray on isothermal crystallization kinetics of syndiotactic polystyrene
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Tinh Nguyen Tinh Nguyen Scientific Consulting, Inc., Gaithersburg, Maryland 20878
Chen-Ti Hu Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 300, Taiwan
Chia-Chieh Chen Institute of Nuclear Energy Research, Longtan, Taoyuan 32546, Taiwan
Sanboh Leea) Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 300, Taiwan (Received 27 August 2013; accepted 4 October 2013)
Isothermal crystallization kinetics of gamma-irradiated syndiotactic polystyrene (sPS) has been investigated by differential scanning calorimetry. Amorphous sPS samples were irradiated in air with gamma ray at various doses from 0 to 800 kGy, at a rate of 30 kGy/h, and melt-crystallized at different temperatures and times. Kinetics parameters were determined using Avrami’s model with Gaussian functions and a modified Arrhenius equation. Isothermally crystallized sPS irradiated in air with gamma ray exhibited multiple endothermic melting peaks corresponding to various crystalline forms, and the radiation dose had a strong effect on their melting enthalpies, crystallinities, and crystallization kinetic parameters. The amount of the a-crystalline form increased with increasing crystallization time and those of the b- and b9 forms had an opposite trend. Both crystallization half time and crystallization activation energy of the a form in gamma-irradiated sPS increased with increasing radiation dose.
I. INTRODUCTION
Syndiotactic polystyrene (sPS) has received a great deal of interest because of its high melting temperature, high crystallization rate, low dielectric constant, good chemical resistance, and good irradiation resistance. The structure, quantity, and form of crystalline materials in an sPS material are complex and vary greatly depending on the thermal history and solvent treatment.1–16 Both a- and b-crystalline forms are obtained by cooling from the melt,1 whereas c and d are induced by a solvent.2 a and b crystals exist mainly between limit disordered (a9 and b9) and limit ordered (a0 and b0). The a form has a hexagonal structure,3,4 whereas the b form possesses an orthorhombic shape.2,6 Guerra et al.2 observed that the crystalline structure of sPS that is produced by cooling from the melting point consists of both a0 and b9 forms. The multiple endothermic peak phenomenon frequently observed for sPS cooling from the melt has also been investigated. Woo et al.,7 Lin and Woo,8 and Hong et al.9 identified the high, intermediate, and low melting a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.309 J. Mater. Res., Vol. 28, No. 21, Nov 14, 2013
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peak temperatures correspond to b9, a, and b forms, respectively. Wang et al.10 agreed the low and intermediate melting peaks correspond to b and a forms, respectively, but they believed that the high melting peak is a mixture of a and b. For isothermal crystallization of sPS, Zhou et al.11 and Rosa et al.12 found that the crystalliz
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