Polylactic acid (PLA) is a high molecular compound, which is often used to prepare biodegradable plastics. The acidity of polylactic acid is usually not significant, which can be explained from the following aspects:

1. molecular structure: polylactic acid is a polymer compound formed by molecular polymerization of lactic acid. In the polymerization process, the carboxyl group (COOH) in lactic acid molecules is condensed with hydroxyl group (OH) to form polyester structure, so the carboxyl group in polylactic acid is not easy to react with water, which weakens its acidic characteristics.

2. Hydrolysis speed: PLA is a biodegradable polymer material. When polylactic acid comes into contact with water, it will undergo hydrolysis reaction to generate lactic acid monomer. Due to the structure of polylactic acid, it is difficult for water to enter the material, and the hydrolysis speed is slow, which leads to the slow release of acidity, so that polylactic acid is not acidic under certain conditions.

3.pH value: PLA is not acidic under neutral or weakly alkaline conditions. The acidity of lactic acid is mainly manifested by the decrease of pH value of the solution. In neutral or weakly alkaline solution, the acidity of lactic acid will be neutralized, and the acidity of polylactic acid will be weakened or not obvious.

To sum up, the lack of acidity of polylactic acid is mainly due to its molecular structure, which makes the carboxyl group in polylactic acid difficult to react with water, and its acidic characteristics are neutralized under neutral or weakly alkaline conditions.