Radiation from UV rays are known for its ability to cause photochemical effects in a polymer structure. This can be a blessing when it comes to resin based 3D printers (SLA) that uses UV laser to print.
On the other hand it can also cause degradation in plastics. If you are building any model that will be for external day time use and want it to be resilient to UV and sunlight, then this article will shed some light (sorry) on which materials are best to qualify this purpose.
PLA isn’t UV resistant and will be negatively affected by sunlight over a long period of time. ABS has better UV resistant qualities, but one of the most UV resistant filament is ASA, which is an alternative from ABS. Not only is it easier to print with than ABS, but it is more durable overall.
Let’s get into more details and also look into the effects of UV and sunlight on the popular printing materials like PLA, ABS and PETG.
UV & Sun Resistance of Each Material
PLA (Polylactic Acid)
PLA is a biodegradable plastic that is made from renewable resources such as sugar cane or starch of corn.
Just because it is biodegradable, doesn’t necessarily mean it won’t fair well outside in the sun. It may start to become more brittle and lose its rigidity, but for the most part it will keep its main form and strength as long as it’s not functional.
Basically meaning you can leave PLA out in the sun for visual, aesthetic pieces, but not for let’s say a handle or mount.
The video below by Makers Muse shows the effects of PLA being left out in the sun for a year, with some cool UV-color changing PLA.
Check out my article on Why Does PLA Filament Get Brittle & Snap, which goes into some about this phenomenon.
PLA is more prone to weathering compared to other plastics used for 3D printing as it is biodegradable. It is found that exposure of PLA towards UVC for 30 to 90 minutes can shorten it’s time of degradation.
If you are wondering what UVC is, it is the most powerful UV radiation and it is used as a germicidal in water purifiers.
This exposure can also cause slow destruction of the coloring pigments present in the material and create a chalky appearance on the surface. PLA in its purest form is more resistant to UV.
If the purchased filament of PLA contains impurities like poly carbonates or coloring agent added in it, this can lead to faster degradation when exposed to UV from sunlight. The physical characteristics won’t be so much affected, more so on a chemical breakdown level.
To truly breakdown PLA, it requires very specific conditions such as extremely high temperatures and physical pressure. There are specialized plants that do this, so don’t count on the sun being able to do anything close to that. Keeping PLA in a compost bin with high heat and pressure takes several months to break down.
You’d want to avoid using any dark colored PLA because they attract heat and will turn soft. Even more surprising is, since PLA is made of organic products, some animals have been known to actually try to eat PLA objects so definitely keep that in mind!
Even though it is the most popular and economic 3D printing material, it is often advised to use PLA plastic indoors or for mild outdoor use only.
ABS (Acrylonitrile Butadiene Styrene)
ABS plastic has many advantages compared to PLA when it comes to outdoor use. The main reason is due to the fact that it is a non-biodegradable plastic compared to PLA.
ABS can withstand sunlight for longer time as it is much more temperature resistant than PLA. Due to its rigidity and good tensile strength, it is a good option for short term outdoor use.
Exposing it for longer time under the sun can have degrading effects on it. ABS in its purest form won’t absorb energy from UV radiation to create free radicals.
Longer periods of exposure towards UV and sunlight can speed up the process of weathering on ABS. Moreover, the exposure of ABS under sunlight for long time can cause the model to warp due to changing temperature.
The degradation of this material can be observed as similar symptoms to that of PLA on degradation. ABS on long exposure can lose its color and become pale. A white chalky substance appears on its surface, which can often precipitate on mechanical force.
The plastic slowly starts to lose its rigidity and strength and starts becoming brittle. Still, ABS can be used for outdoors for much longer period compared to PLA. ABS holds its structural integrity a lot better, but has been known to fade quicker.
Since the main culprit of negative effects are from heat, ABS holds up a lot better to sunlight and UV rays due to its high temperature resistance.
The usual way to give your outdoor 3D printed materials UV protection is to apply some lacquer to the outside. You can get UV protecting varnishes easily to solve this problem.
The UV-resistant varnish I would use is the Krylon Clear Coatings Aerosol (11-Ounce) from Amazon. It not only dries in minutes, but is moisture-resistant and has a non-yellowing permanent coating. Very affordable and useful!
ABS is actually used for outdoor applications like long boards which are exposed to sunlight for long periods of time.
Of all the three commonly used materials for 3D printing, PETG is the most durable one under long exposure towards UV radiation. PETG is a Glycol modified version of normal PET (Polyethylene Terephthalate).
The lack of additives and color pigment in natural PETG means that it’s more available in pure form in the market for UV resistance.
As discussed in the above sections, purer forms of any plastic is less affected by UV.
It is a less rigid and more flexible material compared to ABS plastic. The flexibility of the material allows it to expand and contract according to the temperature conditions under long exposure to outdoor.
PETG’s smooth finish helps it to reflect most of the radiation falling on the surface and its transparent appearance does not hold any heat energy from the radiation.
These properties give it much more endurance from UV compared to PLA and ABS. Even though it is more durable under UV and sunlight; it is more prone to wear when used outdoors due to its soft surface.
Many forms of PETG are used specially for outdoor use, so depending on the manufacturer it can be a great choice for you.
If you’re looking for a great white PETG to use for outdoor purposes, go for Overture PETG Filament 1KG 1.75mm (White). They are a high quality, trusted filament manufacturer and it also surprisingly comes with a 200 x 200mm build surface!
Which Material is the Most Durable in the Sunlight?
Even though we found that PETG is more durable under UV exposure, it is not the ultimate solution for outdoors due to other downsides it suffers from.
It would be very nice to have a print material that is UV resistant as well as holds the properties possessed by ABS like its strength and rigidity. Well don’t get disappointed as there is one.
ASA (Acrylic Styrene Acrylonitrile)
This is a plastic that has the best of both. It has the strength as well as the durability under UV radiation.
It is the best known 3D printable plastic for harsh weather. ASA was actually developed as an alternative to ABS plastic. Even though it is a tough material to print and an expensive one, it has many advantages.
Along with being UV resistant, it is also wear-resistant, temperature resistant and has a high impact resistance.
Due to these properties, some common applications of ASA plastic is for outdoor electronic housing, exterior parts for vehicles and for outdoor signage.
You would think ASA comes at a massive premium, but the pricing isn’t actually too bad. Check out the price of Polymaker PolyLite ASA (White) 1KG 1.75mm on Amazon.
This filament is explicitly UV resistant and weather resistant so for any projects that you are using outdoors, this is your go-to filament.
You can easily purchase filament specially designed for outdoor use and that aren’t sensitive to UV rays or temperature changes. Check out Maker Shop 3D’s Filament Outdoor Use Section for a wide range of colors and materials.
What Material Should I Use For Car Parts?
If you are printing or prototyping materials for the interior of the automobile, it is best advised to stick with the good old ABS as it is cheap and not prone to weathering.
When you are using 3D printed materials to make small exterior parts for the automobile, the best choice would be to stick with the above mentioned ASA to be more durable under UV and sunlight.
If you have a light weight and strong prototype idea for automobiles, then the best option would be to use materials with carbon fiber composite like ABS infused with carbon fiber.
Carbon fiber is used in most of the high performance automobiles for its aerodynamic parts and body. It is even used to build extreme lightweight and strong chassis for super cars by companies like McLaren and Alfa Romeo.