TY - JOUR
T1 - Hydration, Refinement, and Dissolution of the Crystalline Phase in Polyamide 6 Polymorphs for Ultimate Thermomechanical Properties
AU - Gardeniers, Milo
AU - Mani, Mohanraj
AU - de Boer, Ele
AU - Hermida-Merino, Daniel
AU - Graf, Robert
AU - Rastogi, Sanjay
AU - Harings, Jules A. W.
N1 - KAUST Repository Item: Exported on 2022-06-17
Acknowledgements: The authors acknowledge the Province of Limburg, Sappi (The Netherlands), and NWO (Nederlandse Organisatie voor Wetenschappelijk Onderzoek) for providing financial support (project number 731.017.418). We wish to express gratitude to NWO and ESRF for granting beamtime. Dr. Varun Srinivas, Dr. Gijs de Kort, and the DUBBLE (Dutch Belgian beamline) staff are acknowledged for supporting the X-ray experiments.
PY - 2022/6/13
Y1 - 2022/6/13
N2 - Timescales of polyamide 6 melt-shaping technologies, relative to the dynamics of conformational rearrangements upon crystallization, challenge the formation of the most thermodynamically favorable chain packing and thus optimum performance. In this publication, we make use of the mediation of hydrogen bonding by water molecules in the superheated state of water, i.e., above 100 °C in a closed environment, in the structural refinement of polyamide 6 for enhanced thermomechanical performance. The paper addresses dissolution and (re)crystallization of different polyamide 6 polymorphs in the superheated state of water by time-resolved simultaneous small- and wide-angle X-ray scattering and solid-state 1H NMR spectroscopy and the effect on mechanical properties. The experiments reveal that upon heating in the superheated state of water, the pseudo-hexagonal phase dissolves at relatively low temperature and instantly crystallizes in a defected monoclinic phase that successively refines to a perfected monoclinic structure. The dissolution temperature of the pseudo-hexagonal phase of polyamide 6 is found to be dependent on the degree of crystal perfection originating from conformational disorder and misalignment of hydrogen bonding in the lattice, retrospectively, to the Brill transition temperature. The perfected monoclinic phase below the dissolution temperature can be preserved upon cooling but is plasticized by hydration of the amide moieties in the crystalline phase. The removal of water from the hydrated crystals, in the proximity of Brill transition temperature, strengthening the hydrogen bonding, occurs. Retrospectively, the most thermodynamically stable crystallographic phase is preserved and renders an increase in mechanical properties and dimensional stability of the product. The insight obtained on the influence of superheated water on the structural refinement of imperfected crystallographic states assists in polyamide 6 postprocessing strategies for enhanced performance.
AB - Timescales of polyamide 6 melt-shaping technologies, relative to the dynamics of conformational rearrangements upon crystallization, challenge the formation of the most thermodynamically favorable chain packing and thus optimum performance. In this publication, we make use of the mediation of hydrogen bonding by water molecules in the superheated state of water, i.e., above 100 °C in a closed environment, in the structural refinement of polyamide 6 for enhanced thermomechanical performance. The paper addresses dissolution and (re)crystallization of different polyamide 6 polymorphs in the superheated state of water by time-resolved simultaneous small- and wide-angle X-ray scattering and solid-state 1H NMR spectroscopy and the effect on mechanical properties. The experiments reveal that upon heating in the superheated state of water, the pseudo-hexagonal phase dissolves at relatively low temperature and instantly crystallizes in a defected monoclinic phase that successively refines to a perfected monoclinic structure. The dissolution temperature of the pseudo-hexagonal phase of polyamide 6 is found to be dependent on the degree of crystal perfection originating from conformational disorder and misalignment of hydrogen bonding in the lattice, retrospectively, to the Brill transition temperature. The perfected monoclinic phase below the dissolution temperature can be preserved upon cooling but is plasticized by hydration of the amide moieties in the crystalline phase. The removal of water from the hydrated crystals, in the proximity of Brill transition temperature, strengthening the hydrogen bonding, occurs. Retrospectively, the most thermodynamically stable crystallographic phase is preserved and renders an increase in mechanical properties and dimensional stability of the product. The insight obtained on the influence of superheated water on the structural refinement of imperfected crystallographic states assists in polyamide 6 postprocessing strategies for enhanced performance.
UR - http://hdl.handle.net/10754/679052
UR - https://pubs.acs.org/doi/10.1021/acs.macromol.2c00211
U2 - 10.1021/acs.macromol.2c00211
DO - 10.1021/acs.macromol.2c00211
M3 - Article
C2 - 35784656
SN - 0024-9297
JO - Macromolecules
JF - Macromolecules
ER -