From a Three-Phase Model to a Continuous Description of Molecular Mobility in Semicrystalline Poly(hydroxybutyrate-co-hydroxyvalerate)

Abstract

In most cases, a three-phase model consisting of crystalline domains surrounded by rigid amorphous areas dispersed in the mobile amorphous phase is required and eventually sufficient to accurately describe the microstructure of semicrystalline polymers. This work shows that the microstructure developed by poly(hydroxybutyrate-co-hydroxyvalerate) by cold crystallization is better described by a complex two-phase model in which the boundaries of the crystalline domains and the surrounding amorphous environment form a “continuum of mobility”. This concept can be extended to a wide range of semicrystalline polymers. When the crystalline and the amorphous phases are strongly coupled, the rigid and mobile amorphous fractions are hardly fractionated, and the whole noncrystalline phase should be rather depicted as continuum with a broad distribution of the relaxation times associated with the glass transition. Such a depiction of the amorphous phase allows taking into account any modification of the mobility landscape with time, which can be evidenced as the progressive spreading of the relaxation functions. From a practical point of view, the rigidification of the “continuum of mobility” upon storage in conditions of cold crystallization could be considered as a cause of the progressive embrittlement sometimes observed in semicrystalline materials during physical aging and would be explained by a redistribution of the relaxation times translated in terms of relaxation temperatures

Biodegradable PLA/PBS multinanolayer membrane with enhanced barrier performances

“…In FSC, the high heating/cooling rates (1000 � C/s) that are used, allow obtaining thermal signatures characteristics of the sample initial microstructure by preventing reorganization [45], and eventually amorphizing the polymer. The first analyze (Fig.…”

Structure and Barrier Properties of Multinanolayered Biodegradable PLA/PBSA Films: Confinement Effect via Forced Assembly Coextrusion

“…18,19,20 The change in crystalline phase can accordingly have an impact on the amorphous phase through a stiffening of a part of macromolecular chains. Recently, it has been emphasized a relation between changes in barrier performances with the occurrence of a Rigid Amorphous Fraction (RAF), as an intermediate phase between crystalline and amorphous phases, 21 in PBSA monolayer films, 22 although not contributing to the heat capacity increment of the glass transition. Moreover, faced with the reduction of the fossil resources and because of the environmental challenge, a great attention is focused on eco-friendly materials, especially biodegradable polymers used for packaging applications.…”

Study of the Compatibilization Effect of Different Reactive Agents in PHB/Natural Fiber-Based Composites

“…It could be hypothesized that more voluminous RDGE and TGIC disrupt the pseudo-order in the rigid amorphous phase region. This is not observed in PHB/HMDI compounds, probably because of the small and linear geometry of the HMDI molecule, which does not prevent the rearrangements of the amorphous phase that take place during physical aging [ 16 , 17 , 43 , 48 ].…”

“…PHB is a semicrystalline polymer that is capable of a high degree of crystallinity but has a relatively low crystallization rate. Hence, PHB suffers an appreciable embrittlement with time due to secondary crystallization and physical aging [ 14 , 15 , 16 , 17 ], and its long-term mechanical properties are characterized by low ductility and toughness. Indeed, the processing temperature window of PHB is very narrow: the lower limit is relatively high due to its high crystallinity, and the upper limit is relatively low because of its poor thermal stability in molten state (the degradation temperature is close to the melting temperature [ 7 ]).…”