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TitleGlass transition of semi-crystalline PLLA with different morphologies as studied by dynamic mechanical analysis
Author(s)Picchioci, R.
Yang, Y.
Rodriguez-Perez, M. A.
Alves, N. M.
Mano, J. F.
Confined glass transition
Semi-crystalline polymers
Glass transition dynamics
Issue date2007
JournalColloid & Polymer Science
Abstract(s)Poly(L-lactic acid) was crystallized from the glassy state at different temperatures to produce fully transformed semi-crystalline specimens exhibiting different lamellar morphologies. The materials were tested by dynamic mechanical analysis, where a Tg decrease was found with an increasing crystallization temperature. Considering a three-phase model, this tendency was related to the corresponding increase in the thickness of the rigid amorphous phase. It is suggested that this phase could, in some extent, accommodate through local translational/ rotational motions the cooperative motions taking place within the mobile amorphous phase. This could be due to the non-compact structure of the cooperatively rearranging regions, which can present a string-like or fractal structure in their edges. The width of the loss factor peak associated to the glass transition increases with increasing crystallization temperature, suggesting an increase in the broadness of the distribution of relaxation times. The drop in the storage modulus across Tg varies systematically with the crystallization temperature in the different materials and could be correlated with the crystalline content. Above Tg, the loss factor exhibits a plateau-like behaviour at significantly high values, which seems to be a rather general behaviour in semi-crystalline systems that could be related to the contribution of pure irreversible flow in the overall viscoelastic behaviour.
AccessOpen access
Appears in Collections:3B’s - Artigos em revistas/Papers in scientific journals

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