As a thermoplastic polyester (or polyhydroxyalkanoate) it has the backbone formula (C3H4O2)n or [–C(CH3)HC(=O)O–]n. PLA is formally obtained by condensation of lactic acid C(CH3)(OH)HCOOH with loss of water (hence its name).

[9] The monomer is typically made from fermented plant starch such as from corn, cassava, sugarcane or sugar beet pulp.

The most common route to PLA is the ring-opening polymerization of lactide with various metal catalysts (typically tin ethylhexanoate) in solution or as a suspension.

The condensation reaction is reversible and subject to equilibrium, so removal of water is required to generate high molecular weight species.

Carboxylic acid and alcohol end groups are thus concentrated in the amorphous region of the solid polymer, and so they can react.

The degree of crystallinity, and hence many important properties, is largely controlled by the ratio of D to L enantiomers used, and to a lesser extent on the type of catalyst used.

Although PLA performs mechanically similar to PET for properties of tensile strength and elastic modulus, the material is very brittle and results in less than 10% elongation at break.

By mixing PLLA with poly (3-hydroxy butyrate) (PHB), cellulose nano crystal (CNC) and a plasticizer (TBC), a drastic improvement of mechanical properties were shown.

Several technologies such as annealing,[23][24][25] adding nucleating agents, forming composites with fibers or nano-particles,[26][27][28] chain extending[29][30] and introducing crosslink structures have been used to enhance the mechanical properties of PLA polymers.

In one study, increasing the duration of annealing directly affected thermal conductivity, density, and the glass transition temperature.

It has also been demonstrated that the addition of a PLA-based, cross-linked nucleating agent improved the degree of crystallinity of the final PLA material.

[7] Alongside the use of the nucleating agent, annealing was shown to further improve the degree of crystallinity and, therefore, the toughness and flexural modulus of the material.

[34] Furthermore, the branched PLA experiences much longer relaxation times at low shear rates, contributing to higher viscosity than the linear grade.

Understanding properties such as these are crucial when determining optimal processing conditions for materials, and that simple changes to the structure can alter its behavior dramatically.

[38] PLA objects can be fabricated by 3D printing, casting, injection moulding, extrusion, machining, and solvent welding.

[42] PLA-printed solids can be encased in plaster-like moulding materials, then burned out in a furnace, so that the resulting void can be filled with molten metal.

[44] PLA is used in a large variety of consumer products such as disposable tableware, cutlery, housings for kitchen appliances and electronics such as laptops and handheld devices, and microwavable trays.

In the form of nonwoven fabrics, it is used for upholstery, disposable garments, awnings, feminine hygiene products, and diapers.

Its heat resistance and durability are inferior to the widely used polypropylene (PP), but its properties are improved by means such as capping of the end groups to reduce hydrolysis.

[45] PLA can degrade into innocuous lactic acid, making it suitable for use as medical implants in the form of anchors, screws, plates, pins, rods, and mesh.

The composite blend of poly(L-lactide-co-D,L-lactide) (PLDLLA) with tricalcium phosphate (TCP) is used as PLDLLA/TCP scaffolds for bone engineering.

[47][48] Poly-L-lactic acid (PLLA) is the main ingredient in Sculptra, a facial volume enhancer used for treating lipoatrophy of the cheeks.

[49][50] PLLA is under investigation as a scaffold that can generate a small amount of electric current via the piezoelectric effect that stimulates the growth of mechanically robust cartilage in multiple animal models.

[56] Pure PLA foams are selectively hydrolysed in Dulbecco's modified Eagle's medium (DMEM) supplemented with fetal bovine serum (FBS) (a solution mimicking body fluid).

[57] PLA samples of various molecular weights were degraded into methyl lactate (a green solvent) by using a metal complex catalyst.