Deformation and failure kinetics of iPP polymorphs. Issue 9 (8th March 2017)

• Record Type: Journal Article
• Authors: Caelers, Harm J. M.; Parodi, Emanuele; Cavallo, Dario; Peters, Gerrit W. M.; Govaert, Leon E.
• Is Part Of: Journal of polymer science. Volume 55:Issue 9(2017)
• Page Start: 729
• Page End: 747
• Publication Date: 2017-03-08
• Subjects: α‐, β‐ and γ‐iPP -- iPP‐polymorphism -- Mechanical behavior -- Intrinsic properties -- Yield kinetics -- Lifetime predictions -- Failure kinetics; 547
• DOI: 10.1002/polb.24325
• Languages: English
• ISSNs: 0887-6266

Abstract

ABSTRACT: In this study, the mechanical performance of the different polymorphs of isotactic polypropylene, typically present in iPP crystallized under industrial processing conditions, is assessed. Different preparation strategies were used to obtain samples consisting of almost solely α, β, or γ crystals. X‐Ray measurements were used to validate that the desired phase was obtained. The intrinsic true stress ‐ true strain response of all individual phases was measured in uniaxial compression at several strain rates (deformation kinetics). Moreover, measurements were performed over a wide temperature range, covering the window in between the glass transition and the melting temperature. The relation between obtained yield stress and the strain rate is described with a modification of the Ree‐Eyring model. Differences and similarities in the deformation kinetics of the different phases are presented and discussed. Furthermore, the presence of three deformation processes, acting in parallel, is revealed. The Ree‐Eyring equation enables lifetime prediction for given thermal and mechanical conditions. These predictions were experimentally validated using constant load tests in uniaxial compression. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2017, 55, 729–747 Abstract : The mechanical performance of the different polymorphs of isotactic polypropylene is assessed. The intrinsic true stress–true strain response of all individual phases is measured in uniaxial compression at various strain rate and temperatures. The deformation kinetics give evidence of three molecular deformation processes contributing to the yield stress. The processes are discussed and their contributions compared for the different polymorphs. The deformation kinetics are subsequently extended to provide a tool for lifetime prediction under static load.