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Dual glassy relaxations in physically aged semi‐crystalline poly( L ‐lactic acid)
Author(s) -
Shieh YeongTarng,
Jho JiaCing,
Wang TzongLiu,
Yang ChienHsin,
Su CheanCheng
Publication year - 2011
Publication title -
polymer international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.592
H-Index - 105
eISSN - 1097-0126
pISSN - 0959-8103
DOI - 10.1002/pi.3045
Subject(s) - crystallinity , differential scanning calorimetry , amorphous solid , endotherm , glass transition , crystallization , enthalpy , materials science , phase (matter) , atmospheric temperature range , thermodynamics , crystallography , chemical engineering , polymer chemistry , analytical chemistry (journal) , chemistry , polymer , composite material , organic chemistry , physics , engineering
Semi‐crystalline poly( L ‐lactic acid) (PLLA) was physically aged below the glass transition temperature for various times to investigate its amorphous phase behavior. During a differential scanning calorimetry heating scan, dual enthalpy recovery endotherms were found to appear in the glass transition region of PLLA, aged at 52 °C, of a particular degree of crystallinity ( X c ) within a definite range. Below the lower X c limit, only the low endotherm corresponding to the free amorphous phase was observed; above the upper X c limit, only the high endotherm corresponding to the constrained amorphous phase was observed. Dual tan δ peaks in dynamic mechanical analysis confirmed the coexistence of the dual amorphous phases. Both lower and upper limits of the X c range increased with an increase in isothermal crystallization temperature from the melt. Long‐term physical aging at 52 °C, which did not affect X c , allowed the evolution of the free amorphous phase to the constrained amorphous phase in PLLA with X c within the definite range. The effects of physical aging at various temperatures on the enthalpy recovery endotherms were also investigated. Copyright © 2011 Society of Chemical Industry