Poly lactic acid

Polylactic acid (PLA) is a 100% biobased polymer obtained by transforming lactic acid, which is currently produced from the fermentation of edible sugars from corn, beet, tapioca and sugar cane. This polymer is also biodegradable under certain conditions, notably in industrial compost.

PLA has taken off against a backdrop of dwindling natural resources and a desire to optimize waste processing. PLA degradation ultimately generates lactic acid, a natural product that can be assimilated by the human body, and even carbon dioxide and water if assimilated by micro-organisms. As a result, PLA is mainly used in the manufacture of food packaging and disposable tableware. This use is facilitated by PLA's rigidity and naturally shiny, highly transparent appearance.

However, PLA also has other interesting characteristics, enabling it to be used in a wide range of applications. Its high rigidity, for example, means it can be used to reduce the thickness of certain types of packaging, and helps to increase the elastic modulus of blends with other polymers. PLA is also highly permeable to water, which is appreciated in applications such as sports textiles, to reduce the dampness caused by sweat, or films for packaging fresh fruit and vegetables.

PLA's good dimensional stability and "non-toxic" character have made it the main material used for melt-filament 3D printing. These characteristics also make it a material of choice for the manufacture of biocompatible and resorbable implants or prostheses, notably in the form of a copolymer with glycolic acid, enabling the speed of degradation in the human body to be controlled.

Other unique features of PLA include excellent chemical reactivity, and bacteriostatic and piezoelectric properties obtained under certain conditions.

These attractive properties are combined with a low crystallization rate and relatively low glass transition temperature (55-60°C). This has the effect of limiting the use of PLA for certain applications requiring temperature resistance. However, solutions do exist, such as adding nucleation additives or modifying transformation processes or parameters to enable PLA crystallization.

This article provides an overview of PLA, from its synthesis and structures to its properties. It also describes the various conversion processes used to obtain finished products for a wide variety of applications. An important part is also dedicated to the different end-of-life options for PLA, and its place in the biopolymer market in the current context of saving and optimizing natural resources.

As is customary in the profession, the compositions given in the text are, unless otherwise specified, by mass....