Influence of Semicrystalline Morphology on the Glass Transition of Poly(<scp>L</scp>‐lactic acid)

Wang, Yaming; Funari, Sérgio S.; Mano, João F.

doi:10.1002/macp.200600114

Cited by 99 publications

(83 citation statements)

References 52 publications

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“…We assume that this change is related to the contribution of the geometrical restrictions of the amorphous segments-that is, the physical confinement of the MAP. 45,54,55,56 Similar results are obtained after UCW and SEQ drawings even if the cooperativity length is slightly higher ( T = 2.0 nm). These results are supported by previous ones obtained with drawn PET, 49,57,58,59 showing that drawing can also induce high heterogeneities in molecular dynamics.…”

Section: Thermal Analysis and Molecular Mobilitysupporting

confidence: 77%

Structural Dependence of the Molecular Mobility in the Amorphous Fractions of Polylactide

et al. 2014

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Fragilityindex and cooperativity length characterizing the molecular mobility in the amorphous phase are for the first time calculated in drawn polylactide (PLA). The microstructure of the samples is investigated from wide-angle X-ray scattering (WAXS) whereas the amorphous phase dynamics are revealed from broadband dielectric spectroscopy (BDS) and temperature-modulated differential scanning calorimetry (TMDSC). The drawing processes induce the decrease of both cooperativity and fragility with the orientation of the macromolecules. Post-drawing annealing reveals an unusual absence of correlation between the evolutions of cooperativity length and fragility. The cooperativity length remains the same compared to the drawn sample while a huge increase of the fragility index is recorded. By splitting the fragility index in a volume contribution and an energetic contribution, it is revealed that the amorphous phase in annealed samples exhibits a high energetic parameter, even exceeding the amorphous matrix value. It is assumed that the relaxation process is driven in such a way that the volume hindrance caused by the thermomechanical constraint is compensated by the acceleration of segmental motions linked to the increase of degrees of freedom. This result should also contribute to the understanding of the constraint slackening in the amorphous phase during annealing of drawn PLA, which causes among others the decrease of its barrier properties.

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Section: Thermal Analysis and Molecular Mobilitysupporting

confidence: 77%

Structural Dependence of the Molecular Mobility in the Amorphous Fractions of Polylactide

et al. 2014

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“…The occurrence of bimodal melting behavior of PLA and its composites was reported by several researchers. [40][41][42][43][44] This phenomenon was linked to various reasons: [45][46][47][48][49][50][51][52] (i) The effect of melting the original crystals, recrystallization, and remelting the recrystallized crystals during the heating scan; (ii) the presence of different lamellae morphologies formed prior to the heating scan; (iii) the existence of more than one crystal structure (polymorphism); (iv) processing conditions or molecular weight distribution; and (v) the effect of low crystallization temperature which caused the formation of the disordered alpha phase of PLA.…”

Section: Thermal Analysismentioning

confidence: 99%

“…[42,45,47,51] These changes in endothermic peaks were also attributed to the existence of different crystalline structures (i.e., variation in lamella thickness) being formed during processing or in the DSC scans. [41][42][43][44] For the PLA/SG2 composites, the peak shape and the intensity of the prominent endothermic peak correspond- …”

Section: Thermal Analysismentioning

confidence: 99%

Poly(lactic acid)/Aluminum Oxide Composites Fabricated by Sol‐Gel and Melt Compounding Processes

Yüzay

Auras

Selke

2010

Macro Materials & Eng

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Aluminum‐oxide‐coated PLA pellets, particles derived from aluminum oxide sol‐gel, and calcinated α‐Al2O3 powders were used to fabricate PLA/AlOx composites. The formation of aluminum oxide was confirmed by FTIR and EDS. SEM images suggested the melt compounding system provided a fairly homogeneous dispersion of AlOx particles in the PLA matrix. XRD analysis showed PLA and PLA/AlOx composites were both amorphous. The incorporation of AlOx particles did not alter the melting temperature of PLA. However, the shape and intensity of the melting endotherms was significantly changed, suggesting bimodal melting behavior. UV‐Vis transmission spectra suggested that PLA/AlOx composites may act as a better UV barrier than neat PLA.magnified image

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“…The a-form is yielded at crystallization temperatures higher than 120°C, between both temperatures, mixtures are obtained [14]. With regards to the amorphous phase, PLA has been described with the help of the three-phase model [15][16][17][18][19], considering besides the crystalline phase two fractions of the amorphous phase, the mobile amorphous fraction (MAF) and the rigid amorphous fraction (RAF). The latter does not relax at the glass transition temperature, because molecules are partially trapped in the crystalline lamellae [20].…”

Section: Introductionmentioning

confidence: 99%

Impact of crystallinity of poly(lactide) on helium and oxygen barrier properties

Guinault¹,

Sollogoub²,

Ducruet³

et al. 2012

European Polymer Journal

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is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible.This is an author-deposited version published in: http://sam.ensam.eu Handle ID: .http://hdl.handle.net/10985/10118 To cite this version :A GUINAULT, C SOLLOGOUB, Violette DUCRUET, Sandra DOMENEK -Impact of crystallinity of poly(lactide) on helium and oxygen barrier properties -European Polymer Journal -Vol. 48, p.779-788 -2012 Any correspondence concerning this service should be sent to the repository The helium and oxygen gas barrier properties of poly(lactide) were investigated as a function of stereochemistry and crystallinity degree. Poly(L-lactide) and poly(D,L-lactide) films were obtained by extrusion and thermally cold crystallized in either a 0 -or a-crystalline form with increasing crystallinity degree. Annealing of the films at low temperatures yielded to a 0 -crystals as well as the creation of a rigid amorphous fraction in the amorphous phase. Unexpectedly, the quantity of the rigid amorphous fraction was highest in poly(L-lactide) crystallized under a 0 -form. Unexpectedly, the gas permeability increased with increasing quantity of a 0 -crystals in poly(L-lactide) and remained constant with increasing quantity of a 0 -crystals in poly(D,L-lactide). A gain in gas barrier properties was obtained upon crystallization at higher temperatures yielding a-crystals. The analysis of the oxygen transport parameters, in particular the diffusion and the solubility coefficient showed that the diffusion was accelerated upon crystallization, while the solubility coefficient decreased in an expected manner which led to conclude that it remained constant in the amorphous phase. The acceleration of the diffusion seems to be correlated to the occurrence of the rigid amorphous fraction, which holds larger free volume. To conclude, for optimization of poly(lactide) gas barrier properties by focussing on the decrease of the diffusion coefficient it can be suggested to work with poly(D,L-lactide) and to aim a crystallization in a-form avoiding the formation of a rigid amorphous fraction.

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Influence of Semicrystalline Morphology on the Glass Transition of Poly(L‐lactic acid)

Cited by 99 publications

References 52 publications

Structural Dependence of the Molecular Mobility in the Amorphous Fractions of Polylactide

Structural Dependence of the Molecular Mobility in the Amorphous Fractions of Polylactide

Poly(lactic acid)/Aluminum Oxide Composites Fabricated by Sol‐Gel and Melt Compounding Processes

Impact of crystallinity of poly(lactide) on helium and oxygen barrier properties

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