Polylactic acid (PLA, Scheme 2), also known as polylactide, is produced from lactic acid, a naturally occurring α-hydroxycarboxylic acid constantly produced in living organisms. The market for PLA has grown significantly over the last 10 years so that over 400,000 metric tons are produced annually today. Lactic acid is manufactured by microbial fermentation of C5 or C6 sugars, typically glucose and sucrose, obtained from enzymatic hydrolysis (saccharification) of biomass such as sugar cane, corn, and beet. The method generates optically pure isomers (L-lactic acid in most cases) and the products account for approximately 90% of all lactic acid industrially produced. However, preparing bio-based lactic acid economically is challenging. Improvements in the yield and optical purity of lactic acid as well as maximizing the utilization of biomass have long been the goals of most research efforts. More recent research has focused on increasing fermentation efficiency by strain selection and mutagenesis of lactic acid bacteria, by optimization of biomass hydrolysate composition, and by finding sustainable fermentation substrates, such as food wastes, milk whey, and paper mill sludge. Scheme 2. Polylactic acid Polylactic acid prepared from bio-based optically pure lactic acid is highly crystalline and thus has good mechanical strength comparable to some fossil-based plastics. It is therefore considered one of the most promising bioplastics. PLA has also been the most widely used material for 3D printing, primarily due to the low printing temperature enabled by its low melting point. However, PLA's high crystallinity also results in poor impact resistance; its potential for high temperature applications is also limited by the low melting point. As with starch, PLA is frequently formulated with toughening additives or used in blends with other polymers. Polyhydroxyalkanoates (PHAs) are bio-based polyesters that can be produced directly from biomass via them to produce copious amounts of PHA as an energy reserve. The polymer beads are then isolated from the cells typically by extraction and precipitation. The composition of the obtained polymer is dependent on the bacterial strain and carbon substrate used, as well as on the fermentation conditions. Besides packaging, PHAs have been used in medical and surgical applications due to their biocompatibility. Further expansion of their applications, however, has been limited due to their nonoptimal thermal and mechanical properties, and high cost of production. Although thermal and mechanical properties can be tailored by modifying the monomer composition and side chain lengths, an optimum balance between mechanical hardness, toughness and thermal processability is difficult to attain. Again, blending with other bio-based or fossil-based polymers is considered necessary for PHAs' adoption as structural plastics. Still, high manufacturing cost due to low yields and/or cost of separation from fermentation broth is the major obstacle to the replacement of oil-based plastics by PHA which are produced today at about 40,000 metric tons per year. While continuous progress has been achieved in improving fermentation yield and efficiency using biological tools, PHAs differ from other fermentation-derived chemicals in that the polymers' structures and molecular weights are sensitive to the fermentation substrate. Manufacturers thus depend on stable supplies of feedstocks to maintain consistent product quality, making the utilization of biowaste substrates with varying compositions a challenge. Efforts to solve the problem by integrating PHA production facilities into food manufacturing plants or wastewater treatment facilities, to take advantage of their continuous access to consistent organic waste streams, have been reported.