Determining paracrystallinity in mixed‐tacticity polyhydroxybutyrates

Van Opdenbosch, Daniel
Haslböck, Maria
Zollfrank, Cordt

DOI: https://doi.org/10.1107/S1600576720015794
Persistent URL: http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/8457
Van Opdenbosch, Daniel; Haslböck, Maria; Zollfrank, Cordt, 2021: Determining paracrystallinity in mixed‐tacticity polyhydroxybutyrates. In: Journal of Applied Crystallography, 54, 1, 217-227, DOI: https://doi.org/10.1107/S1600576720015794. 
 
Haslböck, Maria; 1Biogenic Polymers, Technical University of Munich, Campus Straubing for Biotechnology and Sustainability, Schulgasse 16, D-94315Straubing, Germany
Zollfrank, Cordt; 1Biogenic Polymers, Technical University of Munich, Campus Straubing for Biotechnology and Sustainability, Schulgasse 16, D-94315Straubing, Germany

Abstract

Recently, the authors reported on the development of crystallinity in mixed‐tacticity polyhydroxybutyrates. Comparable values reported in the literature vary depending on the manner of determination, the discrepancies being partially attributable to scattering from paracrystalline portions of the material. These portions can be qualified by peak profile fitting or quantified by allocation of scattered X‐ray intensities. However, the latter requires a good quality of the former, which in turn must additionally account for peak broadening inherent in the measurement setup, and due to limited crystallite sizes and the possible presence of microstrain. Since broadening due to microstrain and paracrystalline order both scale with scattering vector, they are easily confounded. In this work, a method to directionally discern these two influences on the peak shape in a Rietveld refinement is presented. Allocating intensities to amorphous, bulk and paracrystalline portions with changing tactic disturbance provided internal validations of the obtained directional numbers. In addition, the correlation between obtained thermal factors and Young's moduli, determined in earlier work, is discussed.


A method to robustly determine paracrystalline contents from Rietveld‐refined powder X‐ray data is presented and discussed for the example of mixed‐tacticity polyhydroxybutyrates. image