Polylactic acid/Manufacturing Instructions

The improved method developed by Zhang and Wang will serve as a model for polylactic acid production due to its ability to produce high weight polymers, use of a limited number of relatively easily acquired materials, and detailed understanding of the physical process underway. The process first uses an aprotic solvent to and vacuum dehydration to produce Oligomeric lactic =Two-step polymerization=

Catalyst and reagents preparation
L(+)lactic acid may be filtered through 3-4 A sieves or distilled to remove water in preparation for direct polymerization.

Reactor configuration
1. The reactor is placed in an insulated steam jacket to control the reaction temperature

2. The reactor is connected to a reflux condenser and a vacuum pump.

Polymerization reaction protocol
First step melt polycondensation

1. The reactor is filled with 400 g 90% L(+)-lactic acid, and catalysts 0.5% SnCl2·2H2O and 0.4% p-toulenesulfonic acid monohydrate (TSA).

2. The reactor is heated to 150°C for 4 h, then 160°C for 4 h and the pressure is stepwise reduced to 500 Pa.

3. Water is removed and a medium weight (50 kDa) product is obtained.

Two step melt polycondensation

4. After the 8 hr melt polycondensation reaction is completed the reflux condensor is removed (as only a small amount of water is produced).

5. To complete the polymerization 0.4% wt (of starting lactic acid) TSA is added to the reactor. The temperature is further increased to 180 C and the pressure reduced to 300 Pa for 10 hrs.

6. The polymerization product is then dried under nitrogen.