Currently, there are two common methods to improve the toughness of PLA:
(1) Graft flexible molecular chains into PLA as block or graft copolymers to improve the ductility of the PLA matrix.
(2) Physical blending method. Blend PLA with materials such as elastomers, inorganic fillers or plasticizers to improve the toughness of PLA. The physical modification method is simple and convenient, and has become the most commonly used modification method in industrial production.
1. Blended with elastomer
Blending PLA with elastomers is an effective way to toughen PLA. When impacted by an external force, the elastomer will produce streaks or shear bands, which can absorb the energy from the outside and improve the impact strength of the material. But this method will reduce the strength and modulus of PLA. Therefore, researchers focus on developing high-performance elastomers. Blending elastomers with PLA can improve toughness without reducing strength and modulus.
Xi Lifeng and others used discrete metallocene catalysis technology to develop propylene-based elastomer (PBE) and toughened and modified PLA to obtain high-toughness PLA/PBE melt-blown nonwoven materials. The results show that as the PBE content increases, the stress of PLA/PBE melt-blown nonwoven materials increases, and the elongation at break increases accordingly. When the PBE addition amount is 20%, the elongation at break and tensile strength of PLA/PBE melt-blown nonwoven materials increase by 455% and 25% respectively, the filtration efficiency increases by about 1.1 times, and the filtration performance of the material is enhanced.
Researchers use the superior thermoplasticity and high elasticity of elastomers to toughen PLA so that the blends exhibit excellent toughness. However, as the toughener content increases, the tensile strength and modulus of PLA blends are affected. In addition, currently commonly used elastomers are all petroleum-based, and their extensive use causes serious pollution to the environment and affects the degradation performance of PLA. Therefore, the development of bio-based/degradable elastomers is a research hotspot for elastomer-toughened PLA.
2. Blended with flexible polymers
2.1 Flexible biodegradable polymers
In order to maintain the biodegradability and compostability of PLA, polycaprolactone (PCL), starch, polybutylene adipate-terephthalate (PBAT), and polybutylene succinate (PBS) are usually used Toughened PLA with biodegradable polymers such as polyhydroxyalkanoate (PHA) to prepare a variety of biodegradable polymers.
