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Skin/core crystallinity of injection-molded poly (butylene terephthalate) as revealed by microfocus X-ray diffraction and fast scanning chip calorimetry

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Abstract

The semicrystalline morphology of a poly (butylene terephthalate) was formed under the shear, pressure, and thermal gradients of the injection-molding process, and subsequently studied regarding the crystallinity of the skin layer and the core using fast scanning chip calorimetry (FSC) and microfocus X-ray diffraction. Test bars of 3 mm thickness were molded via a broad tab gate at one end of the part, designed to facilitate a linear flow path and to minimize shearing of the polymer as it passes through the gate. Simulation of the injection-molding process suggests a gradient in the cooling rate through the test part that varies from 50 K s−1 100 µm below the surface to 10 K s−1 in the core, at the temperature of crystallization after the cessation of flow. Analysis of the crystallinity reveals skin and core crystallinities of 35 and 46 %, respectively, near the gate, while there were observed values of 42 and 48 % at the end of fill; XRD data consistently confirmed the crystallinity difference between skin and core, and between the near and far gate positions. The observed cooling-rate-controlled crystallinity values are in excellent agreement with data of the degree and kinetics of quiescent melt-crystallization obtained in a former study. For the first time, the reliability of FSC data obtained during first heating, in order to gain thermal-history/processing-controlled structure information, is demonstrated.

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Acknowledgements

The authors wish to thank General Motors Corporation and Beaumont Technologies for partial funding and encouragement of the described research. RA gratefully acknowledges financial support by the Deutsche Forschungsgemeinschaft (DFG) (Grant AN 212/18).

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Authors and Affiliations

  1. Behrend College, School of Engineering, Pennsylvania State University, 4701 College Drive, Erie, PA, 16563, USA

    Alicyn Marie Rhoades & Jason Louis Williams

  2. Materials Characterization Laboratory, Pennsylvania State University, N-003 Millenium Science Complex, University Park, PA, 16802, USA

    Nichole Wonderling

  3. Center of Engineering Sciences, Martin Luther University Halle-Wittenberg, 06099, Halle/Saale, Germany

    René Androsch

  4. Mondelēz International, 200 Deforest Ave, East Hanover, NJ, 07936, USA

    Jiaxi Guo

Authors
  1. Alicyn Marie Rhoades
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  2. Jason Louis Williams
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  4. René Androsch
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  5. Jiaxi Guo
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Correspondence to Alicyn Marie Rhoades.

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Rhoades, A.M., Williams, J.L., Wonderling, N. et al. Skin/core crystallinity of injection-molded poly (butylene terephthalate) as revealed by microfocus X-ray diffraction and fast scanning chip calorimetry. J Therm Anal Calorim 127, 939–946 (2017). https://doi.org/10.1007/s10973-016-5793-z

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  • DOI: https://doi.org/10.1007/s10973-016-5793-z

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