Biodegradable, injection moldable, suitable for making plastic films, PLA is an amazing polymer

The PLA polymer or more technically called polylactic acid is a biodegradable polyester that we do not find in nature, but which is made by sintering sugar through industrial procedures.

In fact, by fermenting the sugar, a phase of transformation of the raw material into lactic acid takes place and, in the intermediate phase of the process, the polymerization is carried out in PLA.

The polymer thus obtained is transparent, crystalline, rigid and has excellent mechanical resistance , making it suitable for the production of many objects.

Furthermore, PLA is one of the most used polymers for making products through the use of 3D printers, useful not only for production in series of identical objects, but also for rapid prototyping processes in many engineering fields.

How the PLA production phases take place

To make the PLA biodegradable polymer, the following work steps of the raw material are required, mainly composed of sugar, molasses and whey and, alternatively, using Bacillus Coagulans:

- Processing of starch through the separation of fibers and gluten

- Saccharification and liquefaction of starch

- Fermentation of the protein part of starch

- Treatment of lactic acid salt solutions

- Polymerization

The polymer thus obtained has a density of 1.25 g. /c3, with a tensile strength of 70 Mpa and an elastic modulus of 3600 Mpa.

What are the main characteristics of the PLA polymer

The main characteristics of the polymer can be summarized in rheological, mechanical and biodegradability.

The rheological characteristics are expressed in an elasticity of the melt lower than that of olefins.

The mechanical characteristics are between those of an amorphous and a semi-crystalline polymer and, in particular, they approach those between a PET and a Polystyrene.

If we talk about the glass transition temperature of PLA we can say that it is higher than the ambient temperature. Allowing to obtain transparent compounds.

As regards biodegradability it is necessary to pay attention to the meaning of the word "biodegradable", as it is important to know that, despite the PLA is defined as a biodegradable polymer, it is not unless certain fundamental conditions are met.

The biodegradability is triggered if the PLA is subjected to hydrolysis, in the presence of temperatures above 60 °C and with a humidity rate greater than 20%.

The biodegradation times are very variable depending on the environmental conditions in which the object produced with PLA is located, in any case we can indicate them in a time between 1 and 4 years, which, compared to the traditional plastic it uses, based on the conditions in which it is found, from 100 years upwards, is considered short.

What are the advantages of PLA polymer?

- If burned it does not release harmful fumes such as toxic gases or heavy metals

- If accidentally dispersed at sea, the combination of the sun, water and wind reduce it to microplastics. These will not be toxic to fish or humans through the food chain

- Reduces dependence on oil

What are the disadvantages of PLA polymer?

- Contrary to what the word "biodegradable" expresses, it cannot be used to make domestic compost, as, as previously mentioned, it needs to undergo an industrial biodegradation process.

- If thrown into a landfill mixed with other waste, it does not accelerate the decomposition processes compared to traditional plastic, as it is not supported by sunlight, using in decomposition the same times as other types of plastics.

- It cannot be mixed with other plastics in the recycling stages, which is very important when separating waste in separate collection. A small amount of PLA can contaminate a waste stream composed of traditional plastics, compromising their recycling.

- From an environmental point of view, to produce the PLA raw material, it is necessary to use land that could be taken away from crops for the food chain or, worse, deforestation could be increased to try to have more land available to cultivate.

How to recycle PLA

As we have seen, PLA is a recyclable polymer, but must be separated from other plastic waste at the source due to material incompatibility issues.

Once the correct PLA waste flow has been created, the material follows the same operational activities as a plastic waste that comes from post-consumption, therefore from separate collection.

In fact, after careful selection, in which we are certain that we only deal with PLA, it is ground, washed in slow-flow decantation tanks, dried and subsequently bagged , if sold as ground, or it will pass to the extrusion phase if you want to make a PLA in granules.

Machine translation. We apologize for any inaccuracies. Original article in Italian.