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Shanghai, China

Huang W.,Ningbo Institute of Materials Technology and Engineering | Huang W.,Ningbo University | Luo X.-Z.,Ningbo Institute of Materials Technology and Engineering | Wang B.-J.,Ningbo Institute of Materials Technology and Engineering | And 6 more authors.
Macromolecular Chemistry and Physics | Year: 2015

Nanostructures of stereocomplex polylactide (sc-PLA) are obtained and studied in poly(l-lactide) (PLLA) doped with a low amount of poly(d-lactide) (PDLA) during successive melt-quenching, extrusion, spinning, and drawing processes corresponding to quiescent, shear flow, elongational flow, and tensioned annealing conditions, respectively. Nanogranules of predominantly sc-PLA are initially formed with rapid quenching in quiescent and shear flow, which developed into microspheres with slow quenching and uniform nanofibrils in elongational flow. While only amorphous or the α′-form PLLA is formed with the quenched melts and macroscopic fibers, the embedded nanogranules and nanofibrils are highly crystallized with the coexistence of sc-PLA and the α-crystals. A 1D coalescence of nascent sc-nuclei into nanofibrils in elongational flow is preliminarily proposed to explain the structure evolution and the minor reinforcement of the nanofibrils on the macroscopic fibers. Nanostructures of predominantly stereocomplex polylactide (sc-PLA), including nanogranules and nanofibrils, are obtained during direct melt process of poly(l-lactide) doped with poly(d-lactide). The nanostructures take diverse, but well-defined, morphologies and substructures, as governed by thermal and flow conditions. This opens up a facile and scalable route toward either all-PLA nanocomposites or nanofibrils and membranes of sc-PLA. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Xiong Z.,Beijing Institute of Fashion Technology | Xiong Z.,CAS Beijing National Laboratory for Molecular | Zhang X.,Beijing Institute of Fashion Technology | Wang R.,Beijing Institute of Fashion Technology | And 4 more authors.
Polymer (United Kingdom) | Year: 2015

An aryl amide derivative (TMB-5) was used to nucleate the poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) blend for the first time. The effect of TMB-5 nucleating agent on the crystallization behavior of PLLA/PDLA blend was systematically investigated. The selective nucleation of stereocomplex (sc) crystals by incorporation of TMB-5 was realized under appropriate crystallization conditions. During the cooling process, various morphology of TMB-5 due to its partial or complete dissolution in the PLLA/PDLA blend melt was observed. Furthermore, an sc crystals layer on the lateral surface of TMB-5 was found. Upon cooling a PLLA/PDLA blend from 260 °C at rates between 2 and 100 °C/min, 0.5 wt% addition of TMB-5 induced a single melting peak of sc crystals and no homocrystallization was observed in the subsequent DSC heating scan. The melting temperature of the sc crystals was found to decrease in the presence of TMB-5 from 230 to ca. 200 °C, which is still 20 °C higher than that of PLLA homopolymer. The results suggest that the supramolecular structure of the nucleating agent plays an important role in the crystallization of the PLLA/PDLA blend. The difference in solubility and recrystallization ability of TMB-5 in polymer melt results in the variation of crystallization behavior of PLLA/PDLA blend, which is correlated with the concentration of TMB-5 and crystallization conditions including the final melting temperature, annealing time and cooling rate. © 2015 Elsevier Ltd. All rights reserved. Source


Song Y.,CAS Beijing National Laboratory for Molecular | Zhang X.,Beijing Institute of Fashion Technology | Yin Y.,CAS Beijing National Laboratory for Molecular | Zhang C.,CAS Beijing National Laboratory for Molecular | And 5 more authors.
European Polymer Journal | Year: 2016

The isothermal crystallization behavior of a 1:1 poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) mixture under pulsed shear was investigated by in-situ polarized light optical microscopy (POM) and wide angle X-ray scattering (WAXS). The effects of shear rate and temperature were studied. The results showed that application of shear flow increased the nucleation density, crystallization rate and degree of orientation for both stereocomplex crystals (SC) and α crystals. Interestingly, when the crystallization temperature was below the melting temperature of α crystals, the phase content of SC increased with shear rate, while the α content displayed a bell-shaped curve with regard to shear rate. The structure formation in this system was closely related to the shear-induced nucleation, phase mixing and chain mobility. © 2015 Elsevier Ltd. All rights reserved. Source


Yin Y.,CAS Beijing National Laboratory for Molecular | Song Y.,CAS Beijing National Laboratory for Molecular | Xiong Z.,CAS Beijing National Laboratory for Molecular | Zhang X.,Beijing Institute of Fashion Technology | And 5 more authors.
Journal of Applied Polymer Science | Year: 2016

The effect of the final melting temperature (Tf) on the crystallization of poly(l-lactide) (PLLA)/poly(d-lactide) (PDLA) was studied via a combination of differential scanning calorimetry, wide-angle X-ray scattering, polarized optical microscopy, and Fourier transform infrared (FTIR) spectroscopy. We observed that a residual stereocomplex (SC) crystal induced the formation of SC crystals during cooling from a Tf (230°C) just above the melting peak of the SC crystals. On cooling from a Tf (240°C) just above the endset temperature of SC crystal melting [Tm(S)(E)], the possible order structure and the strong interchain interaction promoted the preferential crystallization of SC crystals; this enhanced the formation of α crystals. During cooling from a Tf (≥250°C) far above Tm(S)(E), the crystallization peaks of α and SC crystals converged. The FTIR results indicated that the residual SC crystals, possible ordered structure, and interchain interactions in the melt might have been the key factors for the different crystallization of PLLA/PDLA. © 2015 Wiley Periodicals, Inc. Source


Yin Y.,CAS Beijing National Laboratory for Molecular | Yin Y.,University of Chinese Academy of Sciences | Liu G.,CAS Beijing National Laboratory for Molecular | Song Y.,CAS Beijing National Laboratory for Molecular | And 7 more authors.
European Polymer Journal | Year: 2016

The formation of stereocomplex (SC) in enantiomeric poly(lactide)s via recrystallization of homocrystals was investigated by using simultaneous wide-angle and small-angle X-ray scattering. When the symmetric blend of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) was heated from the glassy state at a slow heating rate (5 °C/min), predominant homocrystals were formed during heating (cold crystallization). Melting of homocrystals and crystallization of stereocomplex occurred almost simultaneously. In this case, the diffusion of PLLA and PDLA chains played an important role in determining the maximum attainable SC crystallinity. The crystallization behavior during annealing at different temperatures (185 °C, 195 °C and 225 °C) and subsequent cooling was further investigated to understand the effectiveness of annealing on the formation of stereocomplex. The stereocomplex content was unchanged during annealing at 185 °C and kept constant during cooling to room temperature. The SC crystallinity increased slightly during annealing at 195 °C and subsequently cooling. On the other hand, the content of SC increased during annealing at 225 °C and increased remarkably during cooling. A possible mechanism considering the diffusion of PLLA and PDLA chains was proposed. © 2016 Elsevier Ltd Source

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