Supertough and Transparent Poly(lactic acid) Nanostructure Blends with Minimal Stiffness Loss

Zhaoxin Li; Shuwen Shi; Fei Yang; Dafu Cao; Kunyu Zhang; Bin Wang; Zhe Ma; Li Pan; Yuesheng Li

doi:10.1021/acsomega.0c01165

Supertough and Transparent Poly(lactic acid) Nanostructure Blends with Minimal Stiffness Loss

ACS Omega. 2020 May 26;5(22):13148-13157. doi: 10.1021/acsomega.0c01165. eCollection 2020 Jun 9.

Authors

Zhaoxin Li¹, Shuwen Shi¹, Fei Yang¹, Dafu Cao¹, Kunyu Zhang², Bin Wang¹, Zhe Ma¹, Li Pan¹, Yuesheng Li^{1

3}

Affiliations

¹ Tianjin Key Lab of Composite & Functional Materials, School of Materials Science and Engineering, Tianjin University, Tianjin 300072, China.
² School of Chemical Engineering and Technology, Tianjin University, Tianjin 300350, China.
³ Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072, China.

Abstract

This contribution is an attempt to explore the effectiveness of a series of newly obtained thermoplastic elastomers (TPEs) as a toughening agent for modifying poly(lactic acid) (PLA). The TPEs, including ionically modified isotactic polypropylene-graft-PLA (iPP-g-PLA) copolymers with explicit graft length, graft density, and ionic group content, and an iPP-g-PLA copolymer with a very high molecular weight and explicit graft density, were elaborately designed and synthesized. The semicrystal or rubbery copolymer backbone originated from iPP was designed to improve the toughness and maintain a relatively high strength, while the grafted PLA side chain was to ensure a high level of compatibility with the PLA matrix. To obtain further enhancement in interfacial reinforcement, the imidazolium-based ionic group was also added during graft onto reaction. All of these graft copolymers were identified with randomly distributed PLA branches, bearing a very high molecular weight ((33-398) × 10⁴) and very high PLA content (57.3-89.3 wt %). Unprecedentedly, with a very small amount of newly designed TPE, the modified PLA blends exhibited a significantly increased elongation at break (up to about 190%) and simultaneously retained the very high stiffness and excellent transparency. The nanometer-scale phase-separated particles with good compatibility and refractive index matching to the PLA matrix were demonstrated to play a crucial role in the excellent performance. The findings suggested that the newly designed iPP-g-PLA copolymers are very economic, promising, and effective modifying agents for developing highly transparent and tough PLA-based sustainable materials.