Production Methods of pla material

Production Methods of pla material

  There are several industrial ways to produce usable PLA with a high molecular rate. Lactic acid and the cyclic di-ester, lactide are the two main monomers used for this.

  The most common method of creating PLA is ring-opening polymerisation of lactide with various metal catalysts (typically tin octoate) either in a solution or as a suspension. The metal-catalysed reaction tends to lead to recemisation of the PLA, which reduces stereoregularity when compared to the biomass starting material.

  It is also possible to produce PLA through the direct condensation of lactic acid monomers. This process is carried out at temperatures under 200 °C, at which point an entropically favoured lactide monomer is generated. This process generates water equivalent to each esterification step. The water needs to be removed either by using a vacuum or through azeotropic distillation to promote polycondensation and attain a high molecular rate. Even higher molecular rates can be achieved by crystallising the crude polymer from the melt. This concentrates carbolyxic acid and alcohol end groups in the amorphous region of the solid polymer, reacting to achieve molecular weights of 128–152 kDa.

  By polymerising a racemic mixture of L- and D-lactides, it is possible to synthesise the amorphous poly-DL-lactide (PDLLA). Stereospecific catalysts can lead to heterotactic PLA, that has been known to show crystallinity. The degree of this crystallinity is controlled by the ratio of D to L enantiomers that are used, as well as by the type of catalyst that is used. The five-membered cyclic compound lactic acid O-carboxyanhydride (lac-OCA) has also been used in academic surroundings instead of lactic acid and lactide. This compound doesn’t produce water as a co-product and is more reactive than lactide. PLA has also been directly biosynthesised while lactic acid has also been contacted with a zeolite, creating a one-step process that takes place at a temperature that is around 100 °C lower.