Poly lactic acid PLA is a biodegradable polymer derived from renewable resources like corn starch or sugar cane. It has gained significant attention due to its biodegradability, biocompatibility, and environmentally friendly nature. The synthesis pathway of PLA involves two main steps: 1 production of lactic acid and 2 polymerization of lactic acid to form PLA.1. Production of Lactic Acid:Lactic acid can be produced through two main routes: fermentation and chemical synthesis. Fermentation is the most common method, where microorganisms e.g., bacteria or fungi convert carbohydrates e.g., glucose or starch into lactic acid under anaerobic conditions. The lactic acid produced can be either L-lactic acid or D-lactic acid, depending on the microorganism used. After fermentation, the lactic acid is purified through filtration, evaporation, and crystallization processes.2. Polymerization of Lactic Acid:There are two primary methods for the polymerization of lactic acid to form PLA: polycondensation and ring-opening polymerization ROP .a. Polycondensation: In this method, lactic acid molecules undergo a condensation reaction, where water is eliminated, and ester bonds are formed between the lactic acid monomers. This process requires high temperatures and low pressure to remove the water formed during the reaction. However, polycondensation often results in low molecular weight PLA due to the reversibility of the reaction and the presence of water.b. Ring-Opening Polymerization ROP : This method involves the synthesis of cyclic lactide monomers from lactic acid, followed by their polymerization. Lactic acid is first converted to its dimer, lactide, through a process called backbiting. Lactide exists in three forms: L-lactide, D-lactide, and meso-lactide. The ring-opening polymerization of lactide is initiated by a catalyst e.g., tin II 2-ethylhexanoate and involves the opening of the lactide ring and the formation of ester bonds between the monomers. ROP results in PLA with higher molecular weight and more controlled properties compared to polycondensation.Factors affecting PLA properties and biodegradability:1. Molecular weight: Higher molecular weight PLA has better mechanical properties but slower degradation rates due to the reduced accessibility of the polymer chains for hydrolysis.2. Stereochemistry: The ratio of L-lactic acid and D-lactic acid units in PLA affects its crystallinity, mechanical properties, and degradation rate. PLLA Poly-L-lactic acid is more crystalline and has slower degradation rates compared to PDLLA Poly-DL-lactic acid , which is amorphous.3. Crystallinity: The degree of crystallinity in PLA affects its mechanical properties, thermal stability, and degradation rate. Higher crystallinity leads to increased mechanical strength and slower degradation rates.4. Processing conditions: The processing conditions, such as temperature, pressure, and catalyst type, can influence the molecular weight, stereochemistry, and crystallinity of PLA, which in turn affect its properties and biodegradability.5. Presence of additives: The addition of plasticizers, fillers, or other polymers can modify the properties of PLA, such as its flexibility, toughness, and degradation rate.6. Environmental factors: The degradation rate of PLA depends on factors like temperature, humidity, and the presence of microorganisms. Higher temperature and humidity accelerate the hydrolytic degradation of PLA, while the presence of microorganisms can enhance its biodegradation through enzymatic processes.