Unexpected observation of highly thermostable transcrystallinity of poly(lactic acid) induced by aligned carbon nanotubes

• We established the first instance of highly aligned CNTs in melt-spun PLA fibers.
• Oriented CNTs activated the nucleation of PLA even at extremely high temperatures near the melting point of PLA.
• Unprecedented thermal stability was observed for CNTs-induced transcrystallinity occurring at high temperatures.

Developing poly(lactic acid) (PLA) based biopolymers has long been perceived as a promising strategy for revitalizing the polymer technology and industry. Its poor crystallization ability caused by the inherent molecular characters, however, undesirably restricts the enhancement of physical properties of PLA products, and largely limits the potential applications. The melt-crystallization kinetics, in principle, is of paramount importance to alter the ultimate crystallization morphology of PLA submitted to normal polymer processing. Inspired by the extremely high specific surface energy and rich nucleation sites of carbon nanotubes (CNTs), we exploited PLA fibers containing highly oriented CNTs to enhance the nucleation kinetics of PLA, especially at ultrahigh crystallization temperatures. Furthermore, flexible poly(ethylene glycol) (PEG) chains were introduced to promote chain mobility of PLA and thus boost crystal growth rates. It was of great interest to observe that effective nucleation of PLA at temperatures up to 150 °C was established using aligned CNTs as the nucleating template, resulting in the formation of symmetrically developed transcrystallinity. A distinguished feature has been moreover revealed that the transcrystallinity developed at higher crystallization temperature presented higher thermal stability. Unexpectedly, the transcrystallinity fostered at 150 °C could be largely preserved even at the melting temperature of the bulk matrix.

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