Common modification methods of polylactic acid

Polylactic acid (PLA) is a polymer polymerized with lactic acid produced by biological fermentation as the main raw material. There are two preparation methods: lactide ring opening polymerization and direct polycondensation. Among them, lactide ring opening polymerization is the most widely used method in industry. PLA has sufficient raw materials and can be regenerated. The production process is pollution-free, and the products can be biodegraded. When the temperature is higher than 55 ° C or the oxygen is enriched and the microbial action is reduced, it can be decomposed into carbon dioxide and water, so as to realize the material circulation in the nature and have no impact on the environment.

PLA is an early developed commercial biodegradable material with high strength and modulus, but its brittleness, toughness and heat resistance are poor, which greatly limits its application. Therefore, at present, the modification of PLA mainly focuses on heat resistance and toughening.

1、 Heat resistance modification

The basic reason for the poor heat resistance of PLA is its slow crystallization rate. The products obtained by extrusion and injection molding are almost amorphous. The heat-resistant modification methods of PLA mainly include: improving the crystallinity of PLA, blending with other materials with good heat resistance, crosslinking with other monomers or polymers, fiber reinforcement, etc. At present, the widely used modification methods are improving crystallinity and fiber reinforcement.

Improve crystallinity

The effective method to improve the crystallinity is annealing treatment or adding nucleating agents. The nucleating agents applied to PLA include organic modified montmorillonite, organic bentonite, mica, starch, polyglycolic acid, dihydrazide compounds (such as tmc-300), amide compounds (such as tmc-328), etc.

Fiber reinforced

The fibers used in PLA include ramie fiber, short basalt fiber, glass fiber, plant fiber, etc.

2、 Toughening modification

The toughening methods of PLA include plasticizing, blending with other materials with good toughness, copolymerization, etc. at present, the main methods are plasticizing or blending.

Plasticizing

The plasticizers used in PLA include glycerol, glyceryl citrate, polyethylene glycol 400, epoxy soybean oil, acetyl butyl citrate and other organic molecules.

Blending

The polymers used in PLA blending include: PCL, PBAT, PBS, ABS, NR, PU, SBS, ACR, etc.

PLA is a hot topic in the research of renewable green materials at present. Its broad application prospect has attracted numerous scientific researchers. As the application of PLA is more and more extensive, and the performance requirements are higher and higher, the research direction of PLA will be more and more, not only in heat resistance and toughening, but also in other aspects, such as flame retardancy, conductivity and heat conduction.