Biodegradable polyesters

Biodegradable polyester as new varieties of plastics,it has the function of environmental protection and developing fastly,now entering into the practical stage. Biodegradable polyester can be eventually decomposed into carbon dioxide and water and return to nature,by the enzyme that widely exist in nature microorganisms or plants and animals,and the degradation of intermediate products is harmless to the environment.This kind of polyester has aliphatic structure unit connected by the ester bond,which can be prepared by microorganism fermentation or by chemical synthesis method.Compared with the natural macromolecules such as starch, cellulose,etc,this kind of polyester have better mechanical properties,processability and water resistance,meanwhile,by adjusting chemical structure,can realize controllable degradation.at present,the research of biodegradable polyester mostly focus on following categories:PBS,PHA,PLA,PCL.

Polylactic acid (PLA) is a new type of degradable plastics that developing very fastly in recent years,with corn starch as the main raw material,its strength pressure, buffer resistance,moisture-proof,oil resistance and impermeability are all better than PE and PP,non-toxic harmless to human body,is considered by industry line as the most promising new environmental protection packaging materials.PLA is suitable for all kinds of processing methods,such as blow molding, thermoforming, application is very extensive.

PLA performance is stable at room temperature,over 55℃ or in rich oxygen condition,it can automatically microbes decompose,so abandoned after completely degradation by microorganism in the nature,the resulting carbon dioxide and water in the soil,won't cause pollution to the environment,the future is expected to replace polyethylene,polypropylene and polystyrene material for plastic products,wide prospect of application.

The raw material of PLA is lactic acid,the traditional production is lactic acid fermentation,with starch as raw materials,now USA,Japan and other countries has been researching utilization of agricultural and sideline products as raw materials,to produce lactic acid.as there is only L-lactic acid metabolism enzymes in the human body,if intaking D-lactic acid excessively,can cause metabolic disorders and even acidosis, therefore,PLA for package,major in L-lactic acid as raw materials.

Currently the most advanced production technology both at home and abroad, is using corn grains as carbon source,producing L-lactic acid by the production method of bacteria fermentation.while domestic mostly use the technial of rice roots enzyme fermentation,with starch as carbon source,controlled by calcium carbonate neutralization agent,and then use sulfuric acid neutralization,this approach will cause a large amount of calcium sulfate precipitation,make the process complex,and also bring into a large number of impurities and bacteria,product purity is low.Rice roots enzyme fermentation is aerobic fermentation,high energy consumption,the conversion rate is only 80%.

America LLC process for PLA:corn starch hydrolyzed to glucose,then lactobacilli anaerobic fermentation,Fermentation process using liquid alkali neutralization,fermented liquid after purified by electrodialysis process,made into L-lactic acid of 99.5% purity.

By Steven