How to improve the flexibility of polylactic acid?

PLA has high strength and rigidity, but poor flexibility and impact resistance. It is a hard and brittle material at room temperature, so it needs to be toughened and plasticized.

1、 Copolymerization modification

By introducing another molecular chain onto the PLA molecular chain through copolymerization, the regularity of the PLA polymer chain is reduced, resulting in a decrease or even complete loss of crystallization ability, or weakening of polymer interactions, reducing the glass transition temperature, melting point, and viscous flow temperature, and improving the toughness of PLA. Both direct condensation and ring opening polymerization can be used to prepare copolymers.

2、 Blending modification

PLA can be blended with elastomers, tough polymers, fillers, or plasticizers. Elastic materials such as ABS, SEBS, PVC modifiers, MBS, and tough polymers such as PC and PE.

If the original biodegradability of polylactic acid is maintained, biodegradable resins such as PBS and PBAT are added to the PLA system. Blending modification can effectively improve the flexibility of PLA, but often causes PLA to lose its transparency.

1. Non biodegradable resin blending toughening

Commonly used impact modifiers for PVC or nylon. Although it does not have biodegradability, blending with PLA can significantly improve its impact resistance.

Plastics with high flexibility, such as PC and PE, can also improve the toughness of PLA through melt blending. The key issue is to ensure that the dispersed phase is evenly and finely dispersed in the matrix of PLA through their compatibility with PLA.

2. Blending and toughening of biodegradable resin

On the premise of not damaging the biodegradability of PLA, PLA is blended with biodegradable polymers for modification. By changing the amount added, the balance between the rigidity and toughness of the modified PLA material can be adjusted.

① PLA/PCL blend system

PCL has good flexibility, but poor strength, with a glass transition temperature of only -60 ℃ and a melting point of only 60 ℃. When blended with PLA, high-strength materials can be obtained. To improve the compatibility of the blend, pre synthesized block copolymers such as PLA co PCL and PCL-b-PEG can be added as compatibilizers for the blend system.

② PLA/PBS blend system

The melting points of PBS and PBSA are 114 ℃ and 94 ℃, respectively, and the glass transition temperatures are -32 ℃ and -45 ℃, respectively. They have high tensile strength, but low bending modulus, which means they have both toughness and elasticity.

The purpose of blending PBS and PLA is usually to improve the toughness, elongation at break, and processability of PLA. The tensile yield strength and modulus of PLA/PBSA blend decrease with increasing PBSA content, the elongation increases with increasing PBSA content, and the impact strength increases with increasing PBSA content.

③ PLA/PBAT blend system

PBAT is a completely biodegradable aliphatic aromatic polyester with a glass transition temperature and melting point of -29 ℃ and 115 ℃, respectively. With the increase of PBAT content, the tensile strength and modulus of PLA/PBAT blend decrease, but the elongation and toughness significantly increase.

PLA and PBAT are incompatible, and adding a compatibilizer can further improve the mechanical properties of the blend.