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Polymers 2016, 8(12), 431; doi:10.3390/polym8120431

The Effect of Thermal History on the Fast Crystallization of Poly(l-Lactide) with Soluble-Type Nucleators and Shear Flow

The Key Laboratory of Food Colloids and Biotechnology, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, 1800 Lihu Road, Wuxi 214122, China
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Academic Editors: Alexander Böker and Frank Wiesbrock
Received: 14 October 2016 / Revised: 24 November 2016 / Accepted: 1 December 2016 / Published: 10 December 2016
(This article belongs to the Special Issue Young Talents in Polymer Science)
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Abstract

The N1,N1ʹ-(ethane-1,2-diyl)bis(N2-phenyloxalamide) (OXA) is a soluble-type nucleator with a dissolving temperature of 230 °C in poly(l-lactic acid) (PLLA) matrix. The effect of thermal history and shear flow on the crystallization behavior of the PLLA/OXA samples was investigated by rheometry, polarized optical microscopy (POM), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), and scanning electron microscopy (SEM). The crystallization process of the PLLA/OXA-240 sample (i.e., pre-melted at 240 °C) was significantly promoted by applying a shear flow, e.g., the onset crystallization time (tonset) of the PLLA at 155 °C was reduced from 1600 to 200 s after shearing at 0.4 rad/s for even as short as 1.0 s, while the crystallinity (Xc) was increased to 40%. Moreover, the tonset of the PLLA/OXA-240 sample is 60%–80% lower than that of the PLLA/OXA-200 sample (i.e., pre-melted at 200 °C) with a total shear angle of 2 rad, indicating a much higher crystallization rate of the PLLA/OXA-240 sample. A better organization and uniformity of OXA fibrils can be obtained due to a complete pre-dissolution in the PLLA matrix followed by shear and oscillation treatments. The well dispersed OXA fibrils and flow-induced chain orientation are mainly responsible for the fast crystallization of the PLLA/OXA-240 samples. In addition, the shear flow created some disordered α′-form crystals in the PLLA/OXA samples regardless of the thermal history (200 or 240 °C). View Full-Text
Keywords: poly (l-lactide); crystallization; soluble-type nucleator; shear flow; melting process poly (l-lactide); crystallization; soluble-type nucleator; shear flow; melting process
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Shen, T.; Ma, P.; Yu, Q.; Dong, W.; Chen, M. The Effect of Thermal History on the Fast Crystallization of Poly(l-Lactide) with Soluble-Type Nucleators and Shear Flow. Polymers 2016, 8, 431.

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