Polylactic Acid, most commonly known as PLA, is a polymer made from renewable resources. Contrary to other thermoplastics which are petroleum-based, some of the raw materials used for PLA’s production include corn starch, tapioca roots, or sugarcane. Its properties, however, are comparable to other plastics in the industry. These characteristics and consumers’ desire to use a less impactful material have triggered its rapid entrance to the plastic market as a competitive commodity.
In this article, we will focus on PLA plastic itself, its composition, benefits, drawbacks, and production methods among others. If you are interested in reading directly about PLA filament for 3D printing check our article below out.
PLA is a polyester produced by fermentation under controlled conditions of a carbohydrate source like corn starch or sugarcane. Its building blocks can either be lactic acid or lactide monomers. They will later be polymerized into PLA.
Initially, corn goes through wet milling. Here’s were the starch gets separated. The starch is then mixed with acid or enzymes and heated. This process “breaks” starch into dextrose (D-glucose), or corn sugar. Finally, fermentation of glucose produces L-Lactic acid, which will be the basic constituent of PLA.
Two methods for manufacturing PLA plastic from lactic acid are applied. The first one uses lactide as an intermediate state, which results in greater molecular weight. The second method consists in the direct polymerization of lactic acid.
PLA is a pseudoplastic, non-Newtonian fluid. This means that its viscosity (resistance to flow) will change depending on the stress that it is subjected to. Specifically, PLA is a shear-thinning material, which means that the viscosity decreases with applied stress.
PLA plastic has good mechanical properties compared to traditional polymers like polypropylene, polystyrene, and polyurethane. Especially when it comes to Young’s modulus (the ability to tolerate elongation under tension or compression), tensile strength (force needed to pull something), and flexural strength (stress needed to start plastic deformation).
Even though its thermal properties depend on its molecular weights, PLA can be classified as a semi-crystalline polymer. Its glass transition temperature at ~55°C and melting temperature at ~180°C are comparatively low, for example when thinking of other thermoplastics such as ABS. And, just like oil-based plastics, PLA can burn. Precautions should be taken.
All of the varieties of PLA share that they are made up of lactic acid (C3H6O3). Their difference, despite having the same molecular formula is the orientation of their atoms in space. They include poly L-lactide (PLLA), poly D-lactide (PLDA), and poly-DL-lactide (PDLLA).
Note that PLA is a nomenclature that does not agree with the IUPAC, as it is a polyester rather than a polyacid.
The answer to this question depends strictly on where on Earth it is asked. In the gross sense, yes, PLA plastic is sustainable. It comes from renewable resources that absorb CO2 and convert it into glucose. This will later be processed to obtain a nearly carbon-free product. After PLA material is ready to be disposed of by the consumer, it can be biodegraded.
However, this last point is dependent on where its useful life ends. Proper disposal of PLA plastic requires very specific conditions, and mixing it with other plastics can affect the whole recycling process. The waste PLA plastic needs to be sorted apart and sent to an industrial composting facility. This implies an environmental cost for transportation. Later, the bioplastic is to be heated to around 60°C and exposed to special microbes, which will digest the material and decompose it.
Yet, many cities do not have the facilities to carry this process. And even if they did, PLA plastic would need a strict separation process that cannot always be ensured. As a consequence, most of the PLA plastic waste will end up in landfills or in the oceans.
Read more about PLA plastic biodegradability:
Great news, PLA is not toxic! In fact, it is used in the medical industry in implants, which can be biodegraded in the body over time. Note that this statement is only true for when PLA is in its solid form.
The poor to no ventilation available in some house or office 3D printers has been reported as a source of risk. Even though the chemicals emitted by PLA have been claimed to be harmless, the release of nanoparticles can potentially pose a health threat.
The methods for processing PLA plastic are no different than those applied to other commercial polymers, such as PS and PET. Of special importance during industrial production is controlling PLA’s humidity: A high concentration of moisture can result in a failed piece. Additionally, production at high temperatures may result in PLA degradation.
Before the actual production, it is recommended to store PLA in its original package at ambient conditions. Pre-drying the material is also a good idea, given the fast moisture uptake of this thermoplastic.
According to Bioplastic news, the largest PLA plastic producers are:
PLA is an awesome development that offers amazing possibilities for replacing petroleum-based plastics. The bio-based and biodegradable principles promise this thermoplastic will have increasing application in the medical and food industries, among others. However, much has to be overcome to ensure actual sustainability. Two main points in PLA research to be overcome are:
So, even though we are keen to see its development in the years to come, a broader reach, stronger waste disposal and enhancement of the mechanical properties are essential in order to take over the non-renewable plastics currently dominating the industry. We are happy to wait for such improvements in the near future.
License: The text of "PLA Plastic / Material: All You Need to Know in 2019" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.