Polymer Structure and Main Characteristics

Because of the presence of two chiral centers, lactic acid is a chiral molecule, and therefore it has two stereoisomers L- and D-lactic acid. These two optical isomers can be produced in different ways they can be synthesized biologically or chemically [31]. 

In the biological synthesis, lactic acid is obtained by fermentation of carbohydrates by lactic bacteria belonging mainly to the genus Lactobacillus, or fungi [32,33]. This kind of synthesis leads mainly to poly(L-lactic acid). On the other hand, the chemical synthesis could lead to various ratios of L- and D-lactic acid. 

The properties of PLA depend on their structure and molecular characteristics. The main factors affecting its behavior are crystallinity, morphology, crystalline thickness, degree of chain orientation and spherulite size [34]. 

Because D and L monomers are optically active, the polymers derived from them are semicrystalline. Meanwhile, the optically inactive monomer D,L-PLA is amorphous, which enhanced a homogenuous dispersion of the biological active substance within a monophasic matrix, and for this reason it is applied in drug delivery developments [35]. 

Polylactic acid shows great potential among biopolyesters, particularly for packaging [36-38] and medical applications, and the reason for this fact is its large availability on the market and its relatively low price [34,36-39]. 

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