Degradable plastic---polylactic acid (PLA)

Degradable plastic---polylactic acid (PLA)

Polylactic acid (hereinafter referred to as PLA) is known as the most commercially promising biodegradable material and is also known as the "king of degradable materials". According to statistics from the European Bioplastics Association, global PLA production capacity will account for approximately 40.2% of the total global biodegradable plastic production capacity in 2022. This proportion is expected to increase to 67.1% by 2027, and the corresponding global production capacity is expected to increase from 459,000 tons to 2.384 million tons. It is a well-deserved main force.

Polylactic acid, also known as polylactide or PLA, is a polyester polymer polymerized with lactic acid as the main raw material. It is a new type of biodegradable material.

PLA is a thermoplastic aliphatic polyester, because there is one chiral carbon atom and two optical isomers in the lactic acid molecule. Therefore, PLA can be divided into poly-L-lactic acid (PLLA), poly-D-lactic acid (PDLA) and poly-racemic lactic acid (PDLLA). Among them, PLLA is a partially crystalline polymer with a hard texture; while PDLLA is an amorphous transparent polymer because the two isomers in the molecular chain cannot be arranged into an orderly crystal structure.

PLA has good thermal stability and the processing temperature is 170~230℃.

1) It has good solvent resistance and can be processed in a variety of ways, such as extrusion, spinning, biaxial stretching, injection, blow molding, etc.

2) In addition to being biodegradable, products made of PLA have good mechanical properties, biocompatibility, gloss, transparency, feel and heat resistance.

3) When PLA is incinerated, its combustion calorific value is the same as that of incinerated paper, which is half of that of incinerated traditional plastics (such as polyethylene), and incinerated PLA will never release toxic gases such as nitrogen compounds and sulfides. The human body also contains lactic acid in a monomeric form, which indicates the safety of this decomposable product.

Preparation method of PLA

1. Direct polycondensation method (one-step method)

Direct condensation of lactic acid monomers is also called one-step polymerization. In the presence of a dehydrating agent, the hydroxyl and carboxyl groups in the lactic acid molecule are heated and dehydrated, and are directly condensed to form oligomers. Add a catalyst and continue to raise the temperature, and the polylactic acid with a low relative molecular weight will polymerize into a polylactic acid with a higher relative molecular weight.

2. Two-step method

Lactic acid is converted into a cyclic dimer lactide, which is then ring-opened and condensed into polylactic acid. This technology is relatively mature. The main process is that the raw materials are fermented by microorganisms to obtain lactic acid, and then undergo refining, dehydration and oligomerization, high-temperature pyrolysis, and finally polymerization into polylactic acid.

3. Preparation of high molecular weight polylactic acid by reaction extrusion

Using a combination of a batch stirring reactor and a twin-screw extruder to conduct continuous melt polymerization experiments, polylactic acid with a molecular weight of 150,000 can be obtained from lactic acid through continuous melt polycondensation. A twin-screw extruder is used to further polycondensate the low molar mass lactic acid prepolymer on the extruder to prepare higher molar mass polylactic acid.

sale02@sdzlplastic.com

https://www.sdzlplastic.com/pvc-film/