Polylactic acid/Manufacturing Instructions

Lactic acid fermentation

Lactic acid production by microorganism fermentation can be performed by many different organisms and conducted in a variety of anaerobic growth conditions. Optimized production instructions will be produced for microorganisms utilized by collaborators based upon their experience. It is currently proposed to use Bacillus coagulans in a bioreactor for a variety of advantages and high yield.

Lactic acid purification

A protocol for lactic acid purification from the fermentation process is still being explored.

Two-step polymerization

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 protonic acid solvent and tin catalyst under vacuum dehydration to produce moderate weight polylactic acid by melt polycondensation. A finishing step uses the addition of a second small amount of the protonic acid. The process is expected to yield polymers of 100+ kDa. The product will most likely need to be mixed with a plasticizer, such as glycerol, and can then be thermomolded.

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 temperature 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 (wt%) 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 through the condenser and a medium weight (50 kDa) product is obtained.

Second step solid polycondensation

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