In the latest of our series looking at FDM 3D printing materials, it seemed like a change of tone or direction was needed. So, rather than look at a specific material individually, let's take a look at some of the additives that can be mixed into PLA to change both its makeup and uses.
Just as a reminder, PLA (Polylactic Acid) is the go-to material for most users due to its ease-of-use, dimensional accuracy and wide availability. Most beginners in 3D printing use PLA for these exact same reasons and the range of colours and different types within the PLA genre is mind blowing.
Standard PLA is the most common but you can also find PLA+, silk, matt, rainbow, glow-in -the-dark and even colour changing PLA to name but a few. PLA Has a low melting point so to become workable for 3D printing, you need a nozzle temperature of between 190-220ºC and a hot bed temperature of around 50-60ºC.
PLA with Additives
There are also variants of PLA where a particular additive has been included which changes the consistency and performance of standard PLA.
PLA is used in such cases as its relatively cheap and easy to produce so adding what might be a more expensive material to it will keep costs manageable. Using PLA as the base material also keeps it fairly easy to use but it can obviously change the working parameters and uses of the material.
You will also find additive based ABS in some cases but the use of this material is less common.
Let's then look at some of the additive based PLA filaments that are currently on the market.
Carbon Fibre Filled
Carbon fibre filaments contain short fibres that are infused into th PLA base material to help increase strength and rigidity. This makes them a strong but lightweight alternative to using metals.
Carbon fibre is often used in the automotive industry due to its strength and weight but also as it's much easier to fabricate than metals. In 3D printing terms therefore, the uses are numerous and its an ideal material for making small automotive parts and also for prototyping of carbon fibre based machinery and bodywork.
Wood filaments combine a PLA base material with cork, wood dust or other derivatives giving the models a real wooden look and feel. Some wood filled filaments can also give off the actual aroma of the wood itself which is pleasant but dissipates over time. Don’t however confuse wood filled filaments with “wood effect” filaments as these will only give a similar look to real wood but are just wood coloured PLA.
It's worth also looking at the percentage of wood that's used in the filament. A minimum of 20% is standard but higher quality wood based filaments will have higher percentages. Obviously though the percentage of PLA needs to remain high and the dominant material otherwise it won't work as a 3D printing filament.
Metal filled filaments are made in a similar way to carbon fibre filaments by mixing a fine metal powder into a base material, providing a unique metallic finish. They also have increased strength and durability.
However, the added weight may not be suitable in all applications such as those where carbon fibre has the advantage. The material is also more difficult to work with as the metal additive will increase the temperatures at which the PLA becomes workable. In terms of home use 3D printing therefore, it will limit the type of machine that could be used.
The term PLA+ covers a wider range of additives where the basic PLA has been enhanced to either make the material easier to work with or to produce higher quality 3D prints. The materials mentioned above would technically fall under the PLA+ heading but aren't usually named as such due to the very specific material additive used.
The material additive in general PLA+ is usually a copolymer or melt viscosity modifier. As you can imagine, naming a product "PLA with Melt Viscosity Modifier" doesn't really roll off the tongue so it's easier to call these filaments PLA+.
The advantage of adding a copolymer will increase the strength and durability of standard PLA while also giving better print quality. A melt viscosity modifier changes the molecular structure of the PLA to make it easier to work with and flow better through the nozzle. This will then lead to better adhesion of l;ayers and in turn, better quality prints.
Pros and Cons
The pros and cons of using these filaments is varied as you can imagine and would be determined by the particular additive that's been included with the base PLA. Let's just then remind ourselves of the pros and cons of basic PLA and see how they adapt to additive based PLA.
Easy to work with: Low printing temperatures and easy to cut and sand in post processing
Rigid and relatively strong: Can withstand a certain degree of impact
Good dimensional accuracy: Good quality PLA will be +/- 0.02mm or better
Long shelf life: If stored correctly, PLA will last as long as you need it
Low heat resistance: The low working temperature has a disadvantage when it comes to heat exposure when printed
Blockages occur regularly: The low melting point again plays a part at slow printing speeds
Requires cooling fans: Somewhere between a pro and con for this as most printers have fans anyway
Filament can get brittle and break: If not stored correctly, the filament will harden and break. Vacuum storage is suggested and possibly the use of a filament dryer
Not suitable for outdoor use: PLA is vulnerable to water and UV light so won’t react well to being outdoors
These pros and cons will change somewhat when using certain of the additive based PLA. For instance, carbon fibre and metal filled PLA will have much better strength and durability and will be possible to use in outdoor conditions. The heat resistance will also be improved as will the quality of the print.
In contrast, the pros will also change with these materials as they will be harder to work with, particularly in post processing. Different nozzles will need to be used as well as the standard brass nozzle will wear quickly. A tungsten nozzle is recommended but this will increase the cost of the overall 3D print.
PLA filaments with additives are a great way to adapt the FDM 3D printing technology and almost bring it in sync with factory production line processes. The uses of such materials are generally best suited to the more "serious" side of FDM 3D printing such as prototyping and the actual manufacture of usable parts. You'd therefore not really find additive based PLA used for model making or other items printed for fun.
Additive based FDM 3D printing filaments are therefore an interesting type of material with which to 3D print and their uses and value shouldn't be underestimated.