Significantly High Melting Temperature of Homopolymer Crystals Obtained in a Poly(l-Lactic Acid)/Poly(d-Lactic Acid) (50/50) Blend

Neimatallah Hosni Mohammed Mahmoud; Hideaki Takagi; Nobutaka Shimizu; Noriyuki Igarashi; Shinichi Sakurai

doi:10.1021/acsomega.3c05165

Significantly High Melting Temperature of Homopolymer Crystals Obtained in a Poly(l-Lactic Acid)/Poly(d-Lactic Acid) (50/50) Blend

ACS Omega. 2023 Oct 17;8(43):40482-40493. doi: 10.1021/acsomega.3c05165. eCollection 2023 Oct 31.

Authors

Neimatallah Hosni Mohammed Mahmoud¹, Hideaki Takagi², Nobutaka Shimizu², Noriyuki Igarashi², Shinichi Sakurai^{1

3}

Affiliations

¹ Department of Biobased Materials Science, Kyoto Institute of Technology, Kyoto 606-8585, Japan.
² High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan.
³ Indian Institute of Technology Guwahati, Guwahati, Assam 781015, India.

Abstract

The isothermal crystallization of a poly(l-lactic acid) (PLLA)/poly(d-lactic acid) (PDLA) (50/50) blend, neat PLLA, and neat PDLA, was studied at different crystallization temperatures (110 °C, 150 °C, 170 and 180 °C) for different durations (1-300 min) by means of differential scanning calorimetry (DSC), polarized optical microscope (POM) observations, and time-resolved wide-angle X-ray diffraction (WAXD). The effects of both the isothermal crystallization temperature and the duration of the isothermal crystallization were investigated for the blend specimens fully crystallized at these crystallization temperatures. The formation of homopolymer crystallites (HC) was confirmed at the isothermal crystallization temperature of 170 °C, which was previously considered too high for its formation, after 70 min had elapsed from the temperature stabilization. Moreover, the melting temperature of the formed HC was found to be significantly high (T_m = 187.5 °C) compared to the one obtained during the nonisothermal DSC measurement of the same specimen of the PLLA/PDLA (50/50) blend, as well as the neat PLLA and PDLA specimens. To the best of our knowledge, this extremely high T_m (=187.5 °C) for HC has never been reported before.