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

Abstract

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/m 2 ), 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.

Role of Inorganic Fillers on the Physical Aging and Toughness Loss of PLLA/BaSO4 Composites

“…7,8 Due to the semicrystalline nature of PLLA, it is possible to tune its mechanical properties by adjusting the crystalline fraction and structure. 9,10 Specifically, the stiffness of PLLA fits within the elastic modulus range of the trabecular bone, with Young's moduli of 2−3 and 1−10 GPa, respectively. 11,12 Furthermore, it is a bioabsorbable polymer with no harmful agents for the body that can be derived upon its degradation.…”

In‐situ generation of biodegradable poly(lactic acid)/poly(butylene succinate) nanofibrillar composites via a facile and cost‐effective strategy of pressure‐induced flow processing

“…Finally, the specimens were cut into rectangular prisms (length × width × thickness, 60 × 10 × 2 mm 3 , 30 × 10 × 4 mm 3 , 20 × 10 × 6 mm 3 , 15 × 10 × 8 mm 3 , and 12 × 10 × 10 mm 3 ). The prisms were placed at the PIF device as depicted in our previous work 30 . The device was heated from room temperature to a processing temperature of 100°C (slightly below the T m of PBS) which was held for 4 min.…”

“…It is a novel solid‐state processing approach in which the solid polymer matrix is forced to flow and deform along the flow direction and constrained in the other directions under high pressure and temperature below the melting point 28 . Previous studies showed that PIF processing in the solid state could produce an ordered lamellar structure in some polymeric materials which achieved self‐reinforcing and self‐toughening 29–31 . Kuang et al 32 reported that a chain‐like interlocking shish‐kebab crystal structure in PLA with 0.5 wt% self‐assembly nucleation agent that acted as a shish was obtained through PIF processing.…”

“…28 Previous studies showed that PIF processing in the solid state could produce an ordered lamellar structure in some polymeric materials which achieved self-reinforcing and self-toughening. [29][30][31] Kuang et al 32 reported that a chain-like interlocking shish-kebab crystal structure in PLA with 0.5 wt% self-assembly nucleation agent that acted as a shish was obtained through PIF processing. It was found that the chain-like interlocking shish-kebab structure significantly improved the strength, ductility, and impact strength of the material.…”

“…The prisms were placed at the PIF device as depicted in our previous work. 30 The device was heated from room temperature to a processing temperature of 100 C (slightly below the T m of PBS) which was held for 4 min. Subsequently, the stress was applied by a hydraulic pump-controlled piston to ensure the internal pressure of 180 MPa and kept for 10 min.…”