Structural and Dynamic Heterogeneity in the Amorphous Phase of Poly(<scp>l</scp>,<scp>l</scp>-lactide) Confined at the Nanoscale by the Coextrusion Process

Nassar, Samira Fernandes; Domenek, Sandra; Guinault, Alain; Stoclet, Grégory; Delpouve, Nicolas; Sollogoub, Cyrille

doi:10.1021/acs.macromol.7b02188

Cited by 22 publications

(29 citation statements)

References 68 publications

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“…As crystallization proceeds, the organization of the crystal phase slightly improves, which can lead to a decrease in the X RAF / X C ratio in bulk PLLA, as also reported for poly(3-hydroxybutyrate). 64 It is worth noting that a different X RAF / X C evolution has been observed for nanoconfined PLLA, 65 which proves that the crystal/amorphous coupling strongly depends on the geometrical dimensions of the sample under investigation. The present results demonstrate that formation of rigid amorphous fraction is favored at lower crystallization temperatures.…”

Section: Results and Discussionmentioning

confidence: 95%

Constrained Amorphous Interphase in Poly(l-lactic acid): Estimation of the Tensile Elastic Modulus

et al. 2020

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The mechanical properties of semicrystalline PLLA containing exclusively α′- or α-crystals have been investigated. The connection between experimental elastic moduli and phase composition has been analyzed as a function of the polymorphic crystalline form. For a complete interpretation of the mechanical properties, the contribution of the crystalline regions and the constrained amorphous interphase or rigid amorphous fraction (RAF) has been quantified by a three-phase mechanical model. The mathematical approach allowed the simultaneous quantification of the elastic moduli of (i) the α′- and α-phases (11.2 and 14.8 GPa, respectively, in excellent agreement with experimental and theoretical data reported in the literature) and (ii) the rigid amorphous fractions linked to the α′- and α-forms (5.4 and 6.1 GPa, respectively). In parallel, the densities of the RAF connected with α′- and α-crystals have been measured (1.17 and 1.11 g/cm 3 , respectively). The slightly higher value of the elastic modulus of the RAF connected to the α-crystals and its lower density have been associated to a stronger chain coupling at the amorphous/crystal interface. Thus, the elastic moduli at T room of the crystalline ( E C ), mobile amorphous ( E MAF ), and rigid amorphous ( E RAF ) fractions of PLLA turned out to be quantitatively in the order of E MAF < E RAF < E C , with the experimental E MAF value equal to 3.6 GPa. These findings can allow a better tailoring of the properties of PLLA materials in relation to specific applications.

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Section: Results and Discussionmentioning

confidence: 95%

Constrained Amorphous Interphase in Poly(l-lactic acid): Estimation of the Tensile Elastic Modulus

et al. 2020

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“…They also reported that MAF dimensions are significantly higher than the characteristic length of the CRR [42], suggesting that the geometrical confinement is not the only cause for the decrease of the CRR size. Nassar et al [82] showed that crystallization of PLLA confined against polystyrene did not induce any variation in the cooperativity length when no RAF was formed, evidencing that the coupling between amorphous and crystal plays a major role in the cooperativity variations.…”

Section: Free Volume and Glass Transition Cooperative Dynamicsmentioning

confidence: 99%

“…The assumption of a confinement effect induced by the crystalline phase seems not satisfying either. Indeed, in the study of Nassar et al [82], the effects of crystallization and coupling have been separated. It has been shown that the crystallization does not systematically impact the cooperativity, whereas the rigidification of the amorphous phase strongly decreases ξ Τα .…”

Section: Free Volume and Glass Transition Cooperative Dynamicsmentioning

confidence: 99%

Amorphous rigidification and cooperativity drop in semi−crystalline plasticized polylactide

Varol

Delpouve

Araujo

et al. 2020

Polymer

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Plasticization of amorphous polylactide shifts the glass transition and extends its temperature range of crystallization to lower temperatures. In this work, we focus on how lowÀ temperature crystallization impacts the mobility of the amorphous phase. Plasticizer accumulates in the amorphous phase because it is excluded from the growing crystal. The formation of rigid amorphous fraction is favored by the low crystallization temperature. It reaches values up to 50% in plasticized polylactide. The increase in the content of rigid amorphous fraction coincides with both the increase of free volume quantified by positron annihilation lifetime spectroscopy, and the decrease in the cooperativity length obtained from the temperature fluctuation approach. The drop of cooperativity is interpreted in terms of mobility gradient due to the amorphous rigidification.

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“…As a consequence, geometrical limitations increase, which maximizes RAF formation. 4,42,47 Despite the uncertainties, it seems that the RAF development in PC/PLLA is independent from the PLLA layer thickness and that more RAF is created at lower temperature. This is the contrary to the results of the PS/PLLA system reported for the annealed 20 nm thick PLLA layers.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…The experimental setup consisted of two single screw extruders (Rheoscam Scamex, France) of 20 mm with gear pumps, a three-layer feed block (A-B-A), a series of layer-multiplying elements, a flat die, and chill rolls (Scamex, France), as described by our earlier work. 42 The layermultiplying elements cut the flow in half vertically and subsequently superpose, compress, and stretch it to its original width. A series of n elements leads thus to 2 n+1 +1 alternating layers.…”

Section: ■ Materials and Methodsmentioning

confidence: 99%

Impact of Nanoconfinement on Polylactide Crystallization and Gas Barrier Properties

Nassar

Delpouve

Sollogoub

et al. 2020

ACS Appl. Mater. Interfaces

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The barrier properties of poly(L-lactide) (PLLA) were investigated in multinanolayer systems, probing the effect of confinement, the compatibility between the confining and the confined polymer, crystal orientation, and amorphous phase properties. The multilayer coextrusion process was used to confine PLLA between two amorphous polymers (polystyrene, PS; and polycarbonate, PC), which have different chemical affinities with PLLA. Confined PLLA layers of approximately 20 nm thickness were obtained. The multinanolayer materials were annealed at different temperatures to obtain PLLA crystallites with distinct polymorphs. PLLA annealed in PC/PLLA films at 120°C afforded a crystallinity degree up to 65%, and PLLA annealed in PC/PLLA or PS/PLLA films at 85°C had a crystallinity degree of 45%. WAXS measurements evidenced that the PLLA lamellas between PS layers had a mixed in-plane and on-edge orientation. PLLA lamellas between PC layers were uniquely oriented in-plane. DMA results evidenced a shift of the PC glass transition toward lower temperature, suggesting the possible presence of an interphase. The development of the rigid amorphous fraction (RAF) in the amorphous phase during annealing was impacted by the confiner polymer. The RAF content of semicrystalline PLLA was about 15% in PC/ PLLA, whereas it was neglectable in PS/PLLA. The oxygen barrier properties appeared to be governed by RAF content, and no impact of the PLLA polymorph or the crystalline orientation was observed. This study shows that the confinement of PLLA on itself does not impact barrier properties but that the proper choice of the confiner polymer can lead to decrease the phase coupling which creates the RAF. It is the prevention of RAF that decreases permeability.

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Structural and Dynamic Heterogeneity in the Amorphous Phase of Poly(l,l-lactide) Confined at the Nanoscale by the Coextrusion Process

Cited by 22 publications

References 68 publications

Constrained Amorphous Interphase in Poly(l-lactic acid): Estimation of the Tensile Elastic Modulus

Constrained Amorphous Interphase in Poly(l-lactic acid): Estimation of the Tensile Elastic Modulus

Amorphous rigidification and cooperativity drop in semi−crystalline plasticized polylactide

Impact of Nanoconfinement on Polylactide Crystallization and Gas Barrier Properties

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