Is PLA Microwave Safe?
No, polylactic acid, a common component for 3D printing, is not safe in the microwave or in any other situation in which it might come into contact with heat. Microwaves heat their inside by agitating water molecules, as well as different types of particles. This agitation causes heat for people who have not thought about chemistry in a few years.
PLA products may or may not contain water molecules, depending on how they were made. Some PLA products are cooled in a water bath immediately after being printed, which allows the product to absorb some of those water molecules. Even without the water bath, PLA is porous and quickly absorbs moisture from the air.
The fact that PLA holds water molecules means that PLA products will soften or melt in high temperatures because the water molecules will boil and convert into steam. Without diving into the advanced chemistry of the process, know that this robs the PLA product of its rigidity and essentially melts it.
For people who have considered making parts for their microwave with convenient 3D printing, the general consensus is to reconsider. While making mechanical components is very appealing with 3D printing, it would be better to use a different base filament instead of PLA. PLA is not designed to be used in heated environments.
What Is PLA Made Of?
Polylactic acid is what is known as a bioplastic, or a plastic that can be melted down into a substance that is safe for the earth. That biodegradability has made it very appealing to manufacturers and 3D printers. It is made by fermenting something like corn that is full of carbohydrates. That starch contains the lactic acid that is used in polylactic acid.
As you might have guessed, pure PLA is safe to eat, in the same way, that corn, starch, and the glucose, or corn syrup, derived from it is. However, the PLA filament used in 3D printing needs to go through a long process during production. As a renewable resource, PLA is highly desired for its ease of production and manipulation.
As explained above, the heat melts PLA, but it does not destroy it. While that property makes PLA products problematic for microwaving, it does mean that it is easy to reshape and reuse PLA. For people who are continually looking for recyclable resources, PLA checks that box. This property is known as thermoplasticity.
It should also be noted that PLA is often mixed with other types of plastic or additives to dye it a certain color, to make it more durable and less brittle, or for further enhancements, either aesthetic or mechanical. You should never assume that your PLA filaments for 3D printing are pure PLA or food-safe unless specifically marked on the packaging.
Can PLA Burn?
PLA is quite capable of burning and has a much lower melting point than most other types of 3D printing filaments. For those who are very cautious, even boiling liquids like coffee and tea might be enough to start melting your PLA products. However, you would need a higher temperature to start the burning process.
If you have been considering 3D printing objects like ashtrays, candle holders, candle snuffers, or other products that might come into contact with heat, you should keep in mind that PLA has a low melting point and can easily catch fire. If you are curious and have a safe place outside, you can take a strand of PLA filament and light it on fire.
In addition to burning and releasing possibly toxic fumes, the plastic melts very quickly and starts to drip off the filament strand. In doing this, be sure to wear gloves and keep the strand far away from your body and anything that is not easily cleaned or disposed of because once the plastic reforms, it will stick to whatever it dripped onto.
Pure PLA does not produce inherently toxic fumes. In fact, PLA has been rated as one of the safer filaments available for 3D printing. Most people notice that PLA fumes smell sweet like the corn syrup it was made from. In small bursts, these fumes are not toxic and should not pose a problem, even for children and more sensitive adults.
If the PLA starts to burn from use in a microwave, a stove, an oven, or another heating device, you should use a gas mask or open windows and try to ventilate the area. PLA products can release fumes that may be toxic to inhale for an extended period while it is burning. Any kind of intense smell for a long time can make you lightheaded!
These same precautions should be used during the 3D printing process as well, as it is better to be safe than sorry. It is not recommended to leave a 3D printer running for hours on end in a room without proper ventilation, no matter what kind of filaments are being used.
Is PLA Food Safe?
There is some debate over whether containers made from PLA filaments are food safe at all, regardless of whether you heat the meal. While pure PLA would be food-safe, products made from a 3D printer often contain other additives that make the filaments unsafe for contact with food. You can see on the packaging if the manufacturer deems it safe for food.
Additionally, PLA products are porous, as mentioned above, and can accumulate bacteria from old food particles in between meals. Because they can’t be subjected to heat, that rules out putting them in the dishwasher, and even the toughest hand-scrubbing is not enough to get rid of everything. Single-use PLA products are much safer than reusable ones for this reason.
It is also essential to consider the 3D printer itself. For example, certain types of nozzles, like brass, used in the printing process may contain lead and other toxic chemicals unrelated to the filament you are using for printing. These chemicals may make your 3D printed products unsafe for consumption, even if you use FDA approved filaments.
For people who want to make multiple dish sets or many utensils, investing in stainless steel nozzles is highly recommended. Stainless steel is considered safe for printing products that will come into contact with food, and you can rest easy knowing that your food will not be spending time sitting on a plate made with excessive amounts of lead.
Although PLA products that have been 3D printed are not microwave safe, there are plenty of other upsides to them, including holding room-temperature food. PLA is usually rated as safe for contact with food, according to the FDA. However, you should always check the packaging to see if the manufacturer has complied with federal regulations.