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Microhardness under strain, 4. Reversible microhardness in polyblock thermoplastic elastomers with poly(butylene terephthalate) as hard segments
Author(s) -
Calleja Francisco J. Baltá,
Boneva Daniela,
Krumova Marina,
Fakirov Stoyko
Publication year - 1998
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/(sici)1521-3935(19981001)199:10<2217::aid-macp2217>3.0.co;2-#
Subject(s) - indentation hardness , thermoplastic elastomer , elastomer , materials science , composite material , polymer chemistry , thermoplastic , polymer science , polymer , copolymer , microstructure
The microhardness ( H ) technique was recently applied to poly(butylene terephthalate) (PBT) and its multiblock copolymers for examination of the stress‐induced polymorphic transition. Following these investigations the present study attempts to observe the reversible variation of microhardness under strain. For this purpose bristles of drawn and annealed (at 160°C in vacuum) poly(ether ester) (PEE) were characterized with respect to their microhardness at various stages of tensile deformation. H was measured under and after loading (σ) in deformation steps of 5% each. In accordance with previous results on PBT and PEE, H values at σ ≠ 0 show a sharp drop (by 40%) in a relatively narrow deformation interval (ε = 10–15%), owing to the stress‐induced α ⇔ β polymorphic transition. The hardness measurements at σ = 0 show a continuous decrease of H with a remaining strain. H values at σ = 0, corresponding to plastic deformation up to 5%, are much higher than the corresponding ones taken under stress at an overall deformation between 10 and 25%. The higher H values are explained by the regeneration of the starting α modification. Results reveal that in materials characterized by high and reversible deformability it is possible to observe a reversible microhardness behaviour, provided the strain–induced structural changes are reversible.