Deformation-induced phase transitions in iPP polymorphs

Harm J.M. Caelers, Enrico M. Troisi, Leon E. Govaert, Gerrit W.M. Peters

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Abstract

This detailed study reveals the relation between structural evolution and the mechanical response of α-, β- and γ-iPP. Uni-axial compression experiments, combined with in situ WAXD measurements, allowed for the identification of the evolution phenomena in terms of phase composition. Tensile experiments in combination with SAXS revealed orientation and voiding phenomena, as well as structural evolution in the thickness of the lamellae and amorphous layers. On the level of the crystallographic unit cell, the WAXD experiments provided insight into the early stages of deformation. Moreover, transitions in the crystal phases taking place in the larger deformation range and the orientation of crystal planes were monitored. At all stretching temperatures, the crystallinity decreases upon deformation, and depending on the temperature, different new structures are formed. Stretching at low temperatures leads to crystal destruction and the formation of the oriented mesophase, independent of the initial polymorph. At high temperatures, above Tαc, all polymorphs transform into oriented a-iPP. Small quantities of the initial structures remain present in the material. The compression experiments, where localization phenomena are excluded, show that these transformations take place at similar strains for all polymorphs. For the post yield response, the strain hardening modulus is decisive for the mechanical behavior, as well as for the orientation of lamellae and the evolution of void fraction and dimensions. β-iPP shows by far the most intense voiding in the entire experimental temperature range. The macroscopic localization behavior and strain at which the transition from disk-like void shapes, oriented with the normal in tensile direction, into fibrillar structures takes place is directly correlated with the strain hardening modulus.

Original languageEnglish
Article number547
JournalPolymers
Volume9
Issue number10
DOIs
Publication statusPublished - 24 Oct 2017

Fingerprint

Polymorphism
Phase transitions
Strain hardening
Crystals
Stretching
Temperature
Experiments
Axial compression
Void fraction
Phase composition
Crystal orientation
Compaction

Keywords

  • Cavitation
  • Deformation
  • In situ X-ray
  • Isotactic polypropylene
  • Phase transitions
  • Polymorphism
  • Temperature
  • Uniaxial compression
  • Uniaxial tensile deformation

Cite this

Caelers, H. J. M., Troisi, E. M., Govaert, L. E., & Peters, G. W. M. (2017). Deformation-induced phase transitions in iPP polymorphs. Polymers, 9(10), [547]. https://doi.org/10.3390/polym9100547
Caelers, Harm J.M. ; Troisi, Enrico M. ; Govaert, Leon E. ; Peters, Gerrit W.M. / Deformation-induced phase transitions in iPP polymorphs. In: Polymers. 2017 ; Vol. 9, No. 10.
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Deformation-induced phase transitions in iPP polymorphs. / Caelers, Harm J.M.; Troisi, Enrico M.; Govaert, Leon E.; Peters, Gerrit W.M.

In: Polymers, Vol. 9, No. 10, 547, 24.10.2017.

Research output: Contribution to journalArticleAcademicpeer-review

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KW - Deformation

KW - In situ X-ray

KW - Isotactic polypropylene

KW - Phase transitions

KW - Polymorphism

KW - Temperature

KW - Uniaxial compression

KW - Uniaxial tensile deformation

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JO - Polymers

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