Structural evolution of poly(lactic acid) upon uniaxial stretching investigated by in situ infrared spectroscopy

Zhuo, Ranran; Zhang, Yanyan; Li, Guili; Shao, Chunguang; Wang, Yaming; Liu, Chuntai; Li, Qian; Cao, Wei; Shen, Changyu

doi:10.1016/j.vibspec.2016.08.001

Cited by 17 publications

(17 citation statements)

References 38 publications

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“…As a consequence, polarization appears in a direction perpendicular to the plane of applied stress. Therefore, this processing provokes the transformation into β polymorph, in order to induce the required molecular orientation besides increasing the degree of crystallinity [ 20 , 21 , 22 , 23 ].…”

Section: Introductionmentioning

confidence: 99%

“…Up to the best of our knowledge, there are research works published dealing with the seeking of optimal electrospinning parameters to obtain uniaxially oriented PLA fibers or directly studies based on aligned PLA electrospun fibers for biomedical applications [ 14 , 24 , 25 ]. There are also studies based on the development of the β-crystalline phase on PLA films and very few on electrospun fibers, but with the required posterior drawing and/or annealing step as already mentioned [ 21 , 22 , 23 ]. Our intention with this work is to eliminate the need for such a post-processing step in order to facilitate the scale-up of this material, which might be industrially relevant.…”

Section: Introductionmentioning

confidence: 99%

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Development of Highly Crystalline Polylactic Acid with β-Crystalline Phase from the Induced Alignment of Electrospun Fibers

et al. 2021

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Polylactic acid (PLA) is one of the known synthetic polymers with potential piezoelectric activity but this property is directly related to both the crystalline structure and crystalline degree. Depending on the process conditions, PLA can crystallize in three different forms: α-, β-, and γ- form, with β-crystalline phase being the piezoelectric one. To obtain this crystalline structure, transformation of α to β is required. To do so, the strategies followed so far consisted in annealing or/and stretching of previously obtained PLA in the form of films or fibers, that is, additional post-processing steps. In this work, we are able to obtain PLA fibers with high macromolecular alignment, as demonstrated by SEM, and in the β polymorph, as detected by X-ray diffraction (XRD) without the requirement of post-processing. For that, PLA fibers were prepared by using an electrospinning coupled to a drum collector. This set up and the optimization of the parameters (voltage flow-rate, and drum collector speed) induced molecular stretching giving rise to uniaxially oriented and highly aligned fibers.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Development of Highly Crystalline Polylactic Acid with β-Crystalline Phase from the Induced Alignment of Electrospun Fibers

et al. 2021

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“…The slow R ( t ) variation during the de‐aging is reported in the left side of Figure (B). Indeed, in PLLA, the temperature range for the de‐aging is very narrow since it has been observed that thermal treatment few degrees above the glass transition brought about a partial polymer crystallization, possibly favored by the formation in the physical aging of ordered structures that acts as crystallization nuclei or a mesophase promoting the crystallization . In fact, it has been reported that annealing at 75 °C for 2 min or at 78 °C for 5 min have brought about partial crystallization.…”

Section: Resultsmentioning

confidence: 99%

“…In fact, it has been reported that annealing at 75 °C for 2 min or at 78 °C for 5 min have brought about partial crystallization. Zhuo et al have reported a critical cold crystallization temperature located between 63 and 68 °C . Moreover, it has been observed that a 20 min annealing at 70 °C of the strain‐induced mesophase led to crystallization; meanwhile, at 60 °C in the same time period, no crystallization occurred .…”

Section: Resultsmentioning

confidence: 99%

Effects of annealing above T_g on the physical aging of quenched PLLA studied by modulated temperature FTIR

Lisio

Sturabotti

Francolini

et al. 2018

J Polym Sci B Polym Phys

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The effect of the annealing few degrees above the glass transition temperature (T da = 62 C) on the physical aging (T pa = 51 C) of amorphous quenched poly(L-lactide) is investigated by an implementation of variable temperature Fourier transform infrared (FTIR). By using a temperature program composed of a linear heating ramp superimposed to a temperature modulation (modulated temperature FTIR), the reversing and nonreversing intensity variation of selected bands, related to high-energy gg and low-energy gt conformers, is investigated. It is observed that the annealing above T g changes irreversibly the conformation distribution of the liquid polymer. The glasses obtained from annealed and nonannealed liquids behave differently, evolving in the physical aging toward their own liquid state and retaining the memory of their original condition before the vitrification. The recovery through T g of the relaxation occurred in the physical aging depends not only from aging conditions but also by the thermal history of the sample above the T g .

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“…The deformation behavior of PLLA was studied mostly in tensile deformation modesuniaxial [4,9,10,12,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] and biaxial drawing [13,14,[38][39][40][41][42], although other deformation modes, such as zone-drawing [43], die-drawing [44], solid-state extrusion [5][6][7]16,17] or plane-strain compression [18] were also explored. It was found that the deformation conditions, such as temperature of deformation, deformation rate, or final strain, seriously affect the structural evolution of PLLA and the resulting mechanical properties; for example, when deformation is performed at a temperature above T g , but below the cold crystallization temperature T cc (in this temperature range, the crystallization rate is too low to generate noticeable crystallinity in the time scale of the deformation experiment), the initially amorphous PLLA sample remains amorphous at low and moderate strains and then undergoes strain-induced crystallization when the strain increases [31,40] due to a decrease in conformational entropy associated with molecular orientation that grows gradually with increasing strain.…”

Section: Introductionmentioning

confidence: 99%

Deformation of Poly-l-lactid acid (PLLA) under Uniaxial Tension and Plane-Strain Compression

Vozniak

Bartczak

2021

Polymers

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The ability of PLLA, either amorphous or semicrystalline, to plastic deformation to large strain was investigated in a wide temperature range (Td = 70–140 °C). Active deformation mechanisms have been identified and compared for two different deformation modes—uniaxial drawing and plane-strain compression. The initially amorphous PLLA was capable of significant deformation in both tension and plane-strain compression. In contrast, the samples of crystallized PLLA were found brittle in tensile, whereas they proved to be ductile and capable of high-strain deformation when deformed in plane-strain compression. The main deformation mechanism identified in amorphous PLLA was the orientation of chains due to plastic flow, followed by strain-induced crystallization occurring at the true strain above e = 0.5. The oriented chains in amorphous phase were then transformed into oriented mesophase and/or oriented crystals. An upper temperature limit for mesophase formation was found below Td = 90 °C. The amount of mesophase formed in this process did not exceed 5 wt.%. An additional mesophase fraction was generated at high strains from crystals damaged by severe deformation. After the formation of the crystalline phase, further deformation followed the mechanisms characteristic for the semicrystalline polymer. Interlamellar slip supported by crystallographic chain slip has been identified as the major deformation mechanism in semicrystalline PLLA. It was found that the contribution of crystallographic slip increased notably with the increase in the deformation temperature. The most probable active crystallographic slip systems were (010)[001], (100)[001] or (110)[001] slip systems operating along the chain direction. At high temperatures (Td = 115–140 °C), the α→β crystal transformation was additionally observed, leading to the formation of a small fraction of β crystals.

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Structural evolution of poly(lactic acid) upon uniaxial stretching investigated by in situ infrared spectroscopy

Cited by 17 publications

References 38 publications

Development of Highly Crystalline Polylactic Acid with β-Crystalline Phase from the Induced Alignment of Electrospun Fibers

Development of Highly Crystalline Polylactic Acid with β-Crystalline Phase from the Induced Alignment of Electrospun Fibers

Effects of annealing above T_g on the physical aging of quenched PLLA studied by modulated temperature FTIR

Deformation of Poly-l-lactid acid (PLLA) under Uniaxial Tension and Plane-Strain Compression

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Structural evolution of poly(lactic acid) upon uniaxial stretching investigated by in situ infrared spectroscopy

Cited by 17 publications

References 38 publications

Development of Highly Crystalline Polylactic Acid with β-Crystalline Phase from the Induced Alignment of Electrospun Fibers

Development of Highly Crystalline Polylactic Acid with β-Crystalline Phase from the Induced Alignment of Electrospun Fibers

Effects of annealing above Tg on the physical aging of quenched PLLA studied by modulated temperature FTIR

Deformation of Poly-l-lactid acid (PLLA) under Uniaxial Tension and Plane-Strain Compression

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Effects of annealing above T_g on the physical aging of quenched PLLA studied by modulated temperature FTIR