Mesophase formation and its thermal transition in the stretched glassy polylactide revealed by infrared spectroscopy

Lv, Ruihua; Na, Bing; Tian, Na; Zou, Shufen; Li, Zhujun; Jiang, Shichun

doi:10.1016/j.polymer.2011.08.023

Cited by 71 publications

(60 citation statements)

References 39 publications

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“…34 It is confirmed by the orientation degree of the amorphous phase of PLA drawn at different temperatures. 34,37,39 A characteristic band at about 918 cm −1 in the FTIR spectrum, corresponding to the chain conformation, was found for the mesocrystal appearance. 6.…”

Section: In Situ Saxs and Waxs Analysis Of Pla Stretched At Differentmentioning

confidence: 97%

“…The orientation degree of the amorphous phase at higher temperatures is lower than that at lower temperatures with the same strain, as shown in Fig. 34,37,39 Stoclet et al determined a specific melting enthalpy ΔH meso m of about 70 J g −1 and a "melting" point of about 75°C for the PLA mesocrystal. Therefore, a higher initial strain is required for amorphous segments to gain enough orientation to form the mesocrystal at a higher drawing temperature.…”

Section: In Situ Saxs and Waxs Analysis Of Pla Stretched At Differentmentioning

confidence: 97%

“…Fig. 34,39,41 Moreover, with increasing drawing temperature, the post-T g endothermic peak becomes much sharper and shifts to higher temperatures, indicating that the mesocrystal with higher thermal stability and cohesive strength could be formed at a higher drawing temperature. For the undrawn PLA sample, a typical step change of glass transition is observed.…”

Section: Thermal Properties Of the Deformed Pla Samplesmentioning

confidence: 97%

“…Zhang et al 37 identified the existence of the mesophase with a characteristic band at 918 cm −1 in PLA samples drawn at 65°C by means of FTIR. [34][35][36][39][40][41][42][43] Stoclet et al [34][35][36] and Na et al 39 reported a sharp post-T g endothermic peak in the DSC traces of PLA drawn near T g and it could be assigned to the melting of the mesophase. 38 Furthermore, the evolution of a mesophase has significant influence on the final structure formation and properties of PLA.…”

Section: Introductionmentioning

confidence: 98%

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Deformation and structure evolution of glassy poly(lactic acid) below the glass transition temperature

Zhou

Zhang

et al. 2015

CrystEngComm

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Poly(lactic acid) (PLA) is a bio-based and compostable thermoplastic polyester that has rapidly evolved into a competitive commodity material over the last decade. One key bottleneck in expanding the field of application of PLA is the control of its structure and properties. Therefore, in situ investigations under cooling are necessary for understanding the relationship between them. The most intriguing feature of a supercooled liquid is its dramatic rise in viscosity as it is cooled toward the glass transition temperature (T g ) though accompanied by very little change in the structural features observable by typical X-ray experiments. The deformation behaviors and structure evolution of glassy PLA during uniaxially stretching below T g were investigated in situ by synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) techniques. The stretched samples were measured by differential scanning calorimetry (DSC). The obtained results showed that the deformation and yield stress of glassy PLA are strongly dependent on the stretching temperatures together with the transition from mesophase to mesocrystal and the formation of cavities. With the increase in drawing temperature, the onset of the mesocrystal formation is delayed to a higher strain value, whereas corresponding to the same critical orientation degree of amorphous chains (f am ≈ 0.45). The DSC results indicated that the post-T g endothermic peak corresponding to the melting of mesocrystal appears and shifts to a higher temperature with increasing stretching temperature, followed by the down-shifts (to a lower temperature) of the exothermic peak of cold crystallization of PLA. The appearance of a small exothermic peak just before the melting peak related to the transition of the α′ to α crystal implies the formation of an α′ crystal during cold crystallization in the drawn PLA samples. The structure evolution of glassy PLA stretched below T g was discussed in details.

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Section: In Situ Saxs and Waxs Analysis Of Pla Stretched At Differentmentioning

confidence: 97%

Section: In Situ Saxs and Waxs Analysis Of Pla Stretched At Differentmentioning

confidence: 97%

Section: Thermal Properties Of the Deformed Pla Samplesmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 98%

See 2 more Smart Citations

Deformation and structure evolution of glassy poly(lactic acid) below the glass transition temperature

Zhou

Zhang

et al. 2015

CrystEngComm

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“…In our study, this behavior is only observed for the as-spun fibers of neat PLA so the existence of the second peak could be related to the presence of mesophase previously revealed by WAXS. Indeed it has been reported that the "melting" of the mesophase in oriented PLA often occurs in the glass transition temperature range when its thermal stability is low [18,48]. According to Lv et al [48], when the formation of the mesophase is not followed by a subsequent crystallization (which provides a good representation of the microstructure of as-spun fibers), the molecular ordering induced by the process is completely destroyed above T g due to the conformational rearrangements of the macromolecules that become possible with the sudden gain of molecular mobility.…”

Section: Tablementioning

confidence: 99%

Molecular dynamics in electrospun amorphous plasticized polylactide fibers

Monnier

Delpouve

Basson

et al. 2015

Polymer

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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. The molecular dynamics in the amorphous phase of electrospun fibers of polylactide (PLA) has been investigated using the cooperative rearranging region concept. An unusual and significant increase of the cooperativity length at the glass transition induced by the electrospinning has been observed. This behavior is attributed to the singularity of the amorphous phase organization. Electrospun PLA fibers rearrange in a pre-ordered metastable state which is characterized by highly oriented but non-crystalline polymer chains, and the presence of highly cohesive mesophase which plays the role of an anchoring point in the amorphous phase. The successful processing of electrospun fibers of plasticized polylactide is also demonstrated. It is shown that the plasticizer remains in the polymer matrix of the nanofiber after electrospinning. When PLA is plasticized, the loosening of the macromolecules prevails over the preferential orientation of the chains; therefore no mesophase is formed during the electrospinning and the cooperativity length remains the same. When the content of plasticizer increases, the inter-chain characteristic distances estimated from wide angle X-ray scattering (WAXS) are redistributed, suggesting a change in the level of interactions between macromolecules. It is assumed that the resulting decrease of the cooperativity length is driven by the progressive reduction of the number of inter-chain weak bonds. It is shown that in a non-confined environment, the number of structural entities involved in the alpha relaxation is strongly dependent on the level of physical interactions in the amorphous phase.

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New insight into the mechanism of enhanced crystallization of PLA in PLLA/PDLA mixture

Zhou

et al. 2017

J of Applied Polymer Sci

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Poly(lactic acid) (PLA) is a bio-based and compostable polymer that has quickly developed into a competitive material, but the control of crystallinity is a bottleneck in extended utilization. The crystallization of PLA has been a rich topic because of the existence of two enantiomeric forms of poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) can form stereocomplex (SC) crystal with high melting point that can be used to control the crystallization behaviors. The SC crystal was regarded as an effective nucleating agent for promoting the crystallization rate and crystallinity of PLA. We investigated cold crystallization of PLLA/PDLA (1:1) mixture with in situ WAXS measurements and found that the homo-crystal of PLA formed earlier than the SC-crystal in the mixture within the measured temperature range, which is different from the melting crystallization. The final crystalline structures are in correspondence with the melting and cold crystallization temperature, and the transition of homo-PLA (d to a) is not altered by the crystallization procedure. The SC-crystal can be detected in both cold and melting crystallization of the mixture at the temperatures lower than 150 8C, which is conflict with the reported results. A new crystallization mechanism of the mixture was proposed to understand the crystallization behaviors in PLLA/PDLA mixtures.

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Mesophase formation and its thermal transition in the stretched glassy polylactide revealed by infrared spectroscopy

Cited by 71 publications

References 39 publications

Deformation and structure evolution of glassy poly(lactic acid) below the glass transition temperature

Deformation and structure evolution of glassy poly(lactic acid) below the glass transition temperature

Molecular dynamics in electrospun amorphous plasticized polylactide fibers

New insight into the mechanism of enhanced crystallization of PLA in PLLA/PDLA mixture

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