TIT# Structure formation in poly(ethylene terephthalate) upon annealing as revealed
     by microindentation hardness and X-ray scattering
AUT# Flores, A.; Pieruccini, M.; Stribeck, N.; Funari, S. S.; Bosch, E.;
     Baltá Calleja, F. J.
SOU# Polymer (2005), 46(22), 9404-9410
LOC# xv097 @ xv097.pdf
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COM#
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ABS# The micromechanical properties (microindentation hardness, H, elastic
     modulus, E) of poly(ethylene terephthalate) (PET), isothermally
     crystallized at various temperatures (Ta) from the glassy state are
     determined to establish correlations with thermal properties and
     nanostructure. Analysis of melting temperature and crystal thickness
     derived from the interface distribution function analysis of SAXS data
     reveals that for Ta<190 °C the occurrence of two lamellar stack
     populations prevails whereas for samples annealed at Ta>190 °C a
     population of lamellar stacks with a unimodal thickness distribution
     emerges. The H and E-values exhibit a tendency to increase with the
     degree of crystallinity. The results support a correlation E/H ~ 20 in
     accordance with other previously reported data. The changes of
     microhardness with annealing temperature are discussed in terms of the
     crystallinity and crystalline lamellar thickness variation. Unusually
     high hardness values obtained for PET samples crystallized at Ta=190 °C
     are discussed in terms of the role of the rigid amorphous phase which
     offers for the hardness of amorphous layers constrained between lamellar
     stacks a value of Ha ~ 150 MPa. On the other hand, for Ta=240 °C the
     decreasing H-tendency could be connected with the chemical degradation of
     the material at high temperature.