The plastic in most 3D printers starts life as fermented corn or sugarcane
PLA, the most common filament in desktop 3D printers, is a plastic made from plants. Starch from corn, cassava, sugarcane or beet pulp is fermented into lactic acid, which is linked into long chains. In 2022 it was the world's most consumed bioplastic, with about 26% of demand.
Despite the everyday name polylactic acid, chemists point out it is not really an acid but a polyester. The usual industrial route first converts lactic acid into lactide, a ring made of two units, then opens the rings with a metal catalyst, typically a tin compound, to form the polymer. Joining lactic acid directly also works, but must stay below 200 °C and needs the water given off at each step removed, by vacuum or distillation, to build long chains.
Lactic acid comes in left- and right-handed mirror forms, and the mix matters. A random blend gives a glassy, shapeless plastic, while controlling the ratio tunes how crystalline the result is. Blending the left-handed polymer with its right-handed twin locks them into a very regular structure, raising the melting point by 40 to 50 °C and the temperature at which it sags under load from around 60 °C to as high as 190 °C.
For printing, PLA melts easily, expands little on cooling and sticks well between layers, although untreated parts soften in heat unless annealed. Its stiffness and strength sit between polystyrene and PET, but it is brittle, stretching less than 10% before it snaps. Mixing it with other bio-based materials and a plasticiser has pushed that figure from 6% to between 140 and 190% in lab composites, which interests food-packaging makers.
Whether PLA breaks down or lasts depends on how it is made and what is added, so it can be engineered either to compost or to endure.
Source: Polylactic acid
