Crystallisation and spherulite morphology of polylactide stereocomplex

Shyr, Tien-Wei; Ko, Huan-Chieh; Wu, Tzu-Ming; Wu, Tzong‐Ming

doi:10.1002/pi.5708

Cited by 14 publications

(10 citation statements)

References 48 publications

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“…A single exothermic peak of L C and D C in the cooling curve was approximately 100 °C, which was contributed by the homocrystallization of PLLA and PDLA (Figure 5a,i). A broad exothermic peak was observed in all LD C chips during cooling, possibly mixing the formation of homocrystals and stereocomplex crystals (Figure 5b–h) [5,19,20,21]. The crystallization enthalpy of the LD C chips during cooling was significantly higher than that of the L C and D C .…”

Section: Resultsmentioning

confidence: 99%

“…The crystallization enthalpy of the LD C chips during cooling was significantly higher than that of the L C and D C . This is because the stereocomplex crystal of the LD C chips that formed beforehand acted as nucleating agents, and the crystallization temperature periods of the homocrystals and stereocomplex crystals overlapped [5]. When the as-spun and hot-draw fibers were heated to 290 °C, which was higher than the equilibrant melting temperature of stereocomplex crystals at 279 °C [22], and then cooled, the crystallization enthalpy of all the as-spun and hot-drawn fibers during cooling was significantly higher than that of the corresponding chip.…”

Section: Resultsmentioning

confidence: 99%

“…The stereocomplex crystals present in the blend served as a nucleating agent, significantly increasing the number of PLLA spherulites per unit of area or volume and enabling the acceleration of the overall PLLA crystallization. Shyr et al [5] also reported that a single endothermic peak related to stereocomplex crystals could be obtained after remelting and recrystallization of PLLA:PDLA in a 1:1 weight ratio. The regime II→III transition of the stereocomplex crystals in the poly( l- lactide)/poly( d -lactide) (LD) blends was determined to be 165 °C.…”

Section: Introductionmentioning

confidence: 99%

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Homocrystallization and Stereocomplex Crystallization Behaviors of As-Spun and Hot-Drawn Poly(l-lactide)/Poly(d-lactide) Blended Fibers During Heating

Shyr

Chen

2019

Polymers

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A series of poly(l-lactide)/poly(d-lactide) blended chips (LDC), as-spun LD fibers (LDA) and hot-drawn LD fibers (LDH) were prepared for investigating the homocrystallization and stereocomplex crystallization behaviors of LDA and LDH fibers during heating. Modulated differential scanning calorimetry (MDSC), hot stage polarized microscopy (HSPM), and real-time wide-angle X-ray diffraction (WAXD) were used for studying the crystallization and melting behaviors, fiber morphology, and crystalline structure evolution of the LDA and LDH fibers’ homocrystals and stereocomplex crystals during heating. The molecular chain orientations of the LDA and LDH fibers were obtained through spinning and improved through the hot drawing processes. When the molecular chain was oriented on the fiber axis, the homocrystals and stereocomplex crystals of the fibers began to form in turn as the heating temperature exceeded the glass transition temperature of the fiber. The side-by-side packing of the molecular chains was promoted by mixing the molecular chains with the extrusion screw during the spinning process, facilitating stereocomplex crystallization. When the LDA fiber was heated above the glass transition temperature of the fiber, movement of the fiber molecular chain—including molecular chain orientation and relaxation, as well as crystallization, melting, and recrystallization of homocrystals and stereocomplex crystals—were investigated through HSPM. MDSC and real-time WAXD were used to observe the molecular chains of the melted poly(l-lactide) and poly(d-lactide) homocrystals of the fibers rearranging and transiting to form stereocomplex crystals during heating.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Homocrystallization and Stereocomplex Crystallization Behaviors of As-Spun and Hot-Drawn Poly(l-lactide)/Poly(d-lactide) Blended Fibers During Heating

Shyr

Chen

2019

Polymers

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“…This finding is consistent with studies on NCC with PHBV as well as studies on NCC with other semicrystalline polymers. [21,42] Comparison of the various PHBV/NCC ratios clearly demonstrates the nucleating effect of NCC in PHBV crystallization. With the addition of NCC from 0 to 1%, the spherulite density is dramatically increased from 100 to 1680 spherulites/cm 2 , respectively.…”

Section: Phbv/ncc Crystallization Behaviormentioning

confidence: 99%

Comparison of nanocrystalline cellulose dispersion versus surface nucleation in poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) crystallization

Haham

Shen²,

Billington

et al. 2020

SPE Polymers

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Nanocrystalline cellulose (NCC), which is a known crystal nucleating agent, is utilized to improve poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) thermal properties. Since NCC aggregation in PHBV negatively affects composite properties and processability, NCC crystal nucleation effectiveness was examined at low concentrations (<1%) under isothermal and nonisothermal conditions. NCC was dispersed in PHBV solutions using a solvent exchange method and then cast into films. We found that NCC was an effective nucleating agent in amounts as low as 0.25%, resulting in an increase in PHBV crystallization rate by more than 50%. However, increasing to 1% NCC resulted in aggregation in PHBV, with the NCC becoming less effective compared to lower NCC concentrations. In an attempt to improve NCC dispersion, we added cellulose acetate (CA) or stearic acid (SA) to the casting solution, anticipating that CA or SA would preferentially adsorb on the NCC. With such pretreatment, dispersion was indeed improved but NCC became less effective as a PHBV nucleating agent. This work shows the advantage of using low NCC concentrations (<0.5%) for promoting PHBV crystallization, but the lack of improved nucleation upon addition of CA and SA supports the importance of NCC surface accessibility.

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“…The rate of lactide decomposition depends on the contact surface and temperature [ 10 ]. The formation of homocrystal and stereocomplex crystal in chips and fibers of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) of varying weight ratio has been investigated [ 11 , 12 ]. Because PLA can be hydrolyzed to obtain lactic acid under biological conditions, potential biomedical applications are concerned with the difference in hydrolytic activity between stereocomplex crystals with β-form 3 1 -helices and homocrystals with α-form 10 3 -helices.…”

Section: Introductionmentioning

confidence: 99%

Effect of Storage Conditions on the Thermal Stability and Crystallization Behaviors of Poly(L-Lactide)/Poly(D-Lactide)

Shyr

et al. 2021

Polymers

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Polylactide (PLA) is a biodegradable thermoplastic aliphatic polyester. The thermal stability and crystallization behavior of PLA are extremely sensitive to storage, processing, and usage conditions. This work systematically studied the thermal stability and crystallization behavior of poly(L-lactide) (PLLA), poly(D-lactide) (PDLA), and a PLLA/PDLA (LD) blend, which were stored under two sets of laboratory storage conditions: (1) stored in a vacuum-free desiccator and (2) stored in vacuum-sealed bags. Both were stored at room temperature for 3 years. Gel permeation chromatography results revealed that the PLLA, PDLA, and LD samples hydrolyzed slowly when stored in vacuum-sealed bags and degraded significantly when stored in a vacuum-free desiccator; this process significantly reduced the thermal stability of the samples stored in the vacuum-free desiccator. Owing to hydrolysis, the levorotation and dextrorotation (L- and D-) molecular chains were shortened; consequently, more nuclei were formed, and this caused the melting points of the PLLA, PDLA, and LD samples to decrease and the melting enthalpy of the crystals in these samples to increase. Wide-angle X-ray diffraction analysis revealed that when the L- and D- molecular chains were packed side by side to form stereocomplex crystals and the randomly arranged L- and D- molecular chains were easy hydrolyzed and degraded, this interfered with the formation of homocrystals in LD. When PLLA, PDLA, and LD samples are stored in a vacuum-free desiccator, they will be significantly hydrolyzed, resulting in the formation of only stereocomplex crystals, and no homocrystals are observed.

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Crystallisation and spherulite morphology of polylactide stereocomplex

Cited by 14 publications

References 48 publications

Homocrystallization and Stereocomplex Crystallization Behaviors of As-Spun and Hot-Drawn Poly(l-lactide)/Poly(d-lactide) Blended Fibers During Heating

Homocrystallization and Stereocomplex Crystallization Behaviors of As-Spun and Hot-Drawn Poly(l-lactide)/Poly(d-lactide) Blended Fibers During Heating

Comparison of nanocrystalline cellulose dispersion versus surface nucleation in poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) crystallization

Effect of Storage Conditions on the Thermal Stability and Crystallization Behaviors of Poly(L-Lactide)/Poly(D-Lactide)

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