Polylactic acid or polylactide (PLA

Polylactic acid or polylactide (PLA) is a biodegradable thermoplastic polyester. Compared with other polyesters, it has attracted attention due to its potential to replace traditional petrochemical polymers. Good processability, sustainability and environmental protection characteristics Make PLA a favorable biopolymer, so it has gained traction in the fields of packaging, textiles, automotive composites and biomedical applications.PLA is synthesized by direct polycondensation of lactic acid (LA) or ring-opening polymerization (ROP) of lactide cyclic dimer (called lactide). Lactic acid is a naturally occurring organic acid that can be produced by chemical synthesis or fermentation. Due to environmental friendliness and the prospect of using renewable resources to replace petrochemical products, people's interest in the production of lactic acid by fermentation has increased. The carbon source for microbial production of lactic acid can be molasses, bagasse or whey. In the polycondensation process, the LA monomers are joined together by the reaction between the -OH and -COOH groups that remove the by-products to produce low molecular weight polymers.Ring-opening polymerization (ROP) of lactide is used to produce high molecular weight PLA. First, the water is removed in the continuous condensation reaction of the aqueous LA to produce a low molecular weight prepolymer. Through internal transesterification, the prepolymer is then catalytically converted to lactide and purified through a "bite-back" reaction. Three potential forms of cyclolactide: D,D-lactide (called D-lactide), L,L-lactide (called L-lactide) and L,D- or D, L-lactide (called meso-lactide). The proportion and sequence of D and L-lactic acid units in the final polymer can be controlled according to the monomers used and the control reaction conditions.However, PLA has some disadvantages, such as poor toughness, slow crystallization rate and low heat distortion temperature. If PLA's performance is enhanced to achieve suitable performance, its applications may be very extensive. Various methods have been proposed, for example, mixing with other polymers, plasticizers, micron (natural fibers, particles) and nano-sized (nanoclays, carbon nanotubes, nanoparticles or nanocrystals) reinforcement materials. This review mainly focuses on blending PLA with polymers, such as PHA, PLA/polybutylene succinate (PBS) and other polymers, which will be discussed further in the following sections.