Preparation of poly(lactic acid) with excellent comprehensive properties via simple deformation or microfibrillation of spherulites

• Published in: Journal of applied polymer science 2022-01, Vol.139 (4), p.n/a
• Main Authors: Xiang, Pei, Fan, Lijun, Li, Shen, Cao, Nuo, Wan, Chao, Bi, Siwen, Chen, Xuhang, Yu, Peng
• Format: Article
• Language: English
• Subjects: Deformation; Elongation; Glass transition temperature; Heat resistance; Impact strength; Materials science; Mechanical properties; mechanical property; microfibrillation; Mud; poly(lactic acid); Polylactic acid; Polymers; pressure‐induced‐flow processing; Sandwich structures; spherulite; Spherulites; Stiffness; Storage modulus; Tensile strength; Thermal resistance
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/app.51539

Our work overcomes the long‐standing challenge to achieve comprehensive improvements in thermo/mechanical properties of poly(lactic acid) (PLA), especially for impact toughness, strength, ductility, stiffness, and heat resistance. Simple deformation or microfibrillation of spherulites can create excellent thermo/mechanical properties making PLA compete against conventional petrochemical‐based polymers. It was performed by pressure‐induced‐flow (PIF) processing, and produced typical deformed spherulite structure and brick‐mud structure. It was found that the critical deformation degree of spherulites was around 2.7, beyond which spherulites would fragment. Through three transition stages of spherulite structures, deformed spherulite structures, and brick‐mud structure, PLA exhibited an enhancement of orientation, storage modulus and glass transition temperature. And a substantial increase was proved in impact strength (105.6 kJ/m2), tensile strength (148.4 MPa) and elongation at break (107.7%), which can be comparable to most engineering plastics. Both the deformed spherulite structures and the brick‐mud structures can enhance the impact toughness of PLA by increasing the fracture path of cracks. Besides, the evolution of the microstructure for a sandwich structure during PIF‐processing was proposed. By simple deformation or microfibrillation of PLA spherulites, PLA achieves considerable improvements in overall properties, including impact toughness, tensile strength, ductility, stiffness, and heat resistance. This method gets rid of the dilemma that the above properties are mutually exclusive. Deformed spherulites are a transition between normal spherulites and microfiber structure, and their deformation behavior is predicted and a good agreement with actual situation is obtained.