PLA belongs to the bioplastics. This designation stands for plastics that are produced from renewable raw materials - i.e. are biobased - as well as for those that are biodegradable or compostable. The latter can also be produced in part from fossil raw materials. In the case of PLA, both properties apply. The material consists of a renewable raw material and is at the same time compostable according to DIN EN 13432.
PLA is the short form for polylactides (from the English word polylactic acid), which are colloquially called polylactic acids. In order to obtain these lactic acids, it requires starch, which develops in plants such as corn, potatoes or beets through photosynthesis. If the starch extracted from the plant - in the case of PLA mainly from the corn plant - ferments, lactic acids are formed. These synthetic polymers can be formed into granules, which are necessary for plastic products, in further steps through the process of polymerization.
CPLA is obtained in the same way. However, 20 to 30 percent talc powder is added. This causes the PLA to crystallise, which explains why the "C" also stands for "crystallized PLA". As a reaction to the talc powder, the material becomes opaque, harder and more heat resistant. In this state it can also be cast and is therefore used for disposable cutlery, for example.
PLA is the most important bioplastic in the packaging market because it is available in large quantities and can be easily processed. It belongs to the polyester family and scores with its high transparency and strength. It is also permeable to water vapour, which preserves the flavour of food for longer. The range and use of PLA packaging is correspondingly diverse. It ranges from the coating of a coffee cup to viewing windows for take-away packaging or cake cartons to carrier bags. As already mentioned, the CPLA variant does not offer transparency, but is heat-resistant up to + 85°C. It is therefore used to make cutlery or lids for hot beverage cups, for example.
For various reasons, bioplastics are considered to be sustainable packaging materials. On the one hand, it is manufactured from renewable raw materials and thus offers a possibility to conserve fossil - non-renewable - raw materials and to become independent of them. It is true that the basis for the bioplastics is corn. But industrial corn is used, not food. It is usually grown on land that is not suitable for food corn. In addition, only about 0.02 percent of global corn cultivation is currently used for PLA.
On the other hand, PLA scores with a good CO2 balance - even during production, because the emission of carbon dioxide is lower than that of other plastics such as PET or PP. If the material is incinerated during disposal, only the amount of CO2 that the plant absorbed while growing is returned to the atmosphere.
Last but not least, PLA is compostable and, under certain conditions, decomposes to CO2 and water alone - without toxic residues. However, you will find out what needs to be taken into account in this decomposition process in the following section.
PLA can be disposed of in various ways. As already mentioned, it is compostable according to DIN EN 13432. This standard states that the material has decomposed in an industrial composting plant under certain temperature, oxygen and humidity conditions in three months in such a way that when sieved through a 2 mm sieve no more than 10 percent residue remains. As described, PLA does not produce any toxic residues. Such certification does not mean, however, that the bioplastics decompose in your own garden compost or in nature or that humus or nutrients can be extracted from it. In addition, conventional biowaste rots in less time than bioplastics. As PLA is currently being fed in very small quantities into industrial composting plants, it is therefore not economical for operators to separate the bioplastics from other plastics and waste and to have them composted for longer.
The same applies to the recycling of PLA. Since the quantities are currently still too small, this processing is not worthwhile. Accordingly, there are no sorting and recycling processes in the plants, although the material is promising for recycling. The most worthwhile disposal at present is therefore incineration. With thermal recycling, part of the energy used for production can be reused. As mentioned above, only the amount of CO2 that the plant has absorbed during growth is emitted, which also reduces greenhouse gases.
PLA achieves an even better ecological balance in recycling. With higher production and thus waste quantities, this may be the optimal disposal in the future, especially since sorting - and separation from other plastics - is technically possible. Tests at the Fraunhofer IAP as well as by the research association of Fraunhofer UMSICHT have shown that the recycled plastic can replace virgin material or, at a certain processing stage, even has the quality of virgin material. If already produced PLA is reused, the cultivation, fertilization and harvesting of crops is no longer necessary, which further improves the ecological balance of the material. Thus PLA proves to be a material with a sustainable future prospect!