Polypropylene is a thermoplastic filament, often abbreviated as PP. It is one of the most commonly used plastic materials in the world, due to its chemical-resistant properties, temperature resistance, and durability. However, although it is a common material, it actually isn’t the most popular filament option in 3D printing. This is because it can be challenging to work with.
Pros of Polypropylene
Despite being difficult to work with, polypropylene can be quite rewarding for those who take the time to learn to use the material. It is a flexible and lightweight filament frequently used to make living hinges like the ones on the caps of ketchup bottles.
It Can Be Formed for Precise Measurements
Nobody will claim that it is easy, but it is very practical to use polypropylene to print out parts with precise dimensions. It is actually possible to machine polypropylene down to several thousandths of an inch. This definitely requires attention to detail and quite a bit of handiwork.
Still, if you are going to work on a project that is exceptionally precise in nature, polypropylene is an excellent candidate as a material.
For professionals looking for a durable and flexible filament, the benefits of PP outweigh the negatives. A quick search for PP filament reveals the most popular choices as:
It Does Not Break Easily
Polypropylene does not break easily when it is bent. For this reason, many of the most common household products are actually made from polypropylene. This includes many electric components, food containers, furniture, and automotive parts among a host of other products in and around the home.
In the world of 3D printing, polypropylene is considered the go-to material for both prototyping and end-use products. This material is favored for use in living hinges, which are used in products like plastic bottles; you probably use living hinges every day without even realizing it!
Chemical-Resistance & Versatility
Polypropylene is resistant to many chemicals, which makes it suitable for a wide range of purposes. For this reason, PP is well-suited for printing products that will be used to hold food or for objects that will spend a lot of time outdoors baking in the sun.
Polypropylene is one of few plastics that can withstand exposure to a large number of chemical agents:
- Boric Acid
- Hydrochloric Acid
- Nickel Carbonate
- Nickel Sulfamate
- Many other acids, alkalis, and organic solvents
More Bendable Than PLA
Polypropylene turns out to be more bendable than polylactic acid (PLA) and is better at resisting deformation under a load. This is why PP is commonly used to make plastic storage containers with living hinges for easy opening and closing.
Of all the plastics commonly used in the manufacturing industry, polypropylene reportedly has the lowest density. The characteristic low density of polypropylene means that any object made from it will be easier to carry than any item of the same size made from the other plastics on the market.
The low density of PP also leads to cost savings when you are trying to print out a bunch of different mechanical parts. If these same components were to be molded from PLA filament, they would be bulky, and it would take more filament to print them to equivalent dimensions.
Cons of Polypropylene
Some limiting factors can make polypropylene challenging to work with compared to other filaments.
Rapid Shrinkage Rate
Polypropylene filament has the unfortunate characteristic of shrinking very fast due to the crystallization rate. The rate of crystallization is defined as the speed at which the different layers of filament can bond to each other. This is a bad thing because it could lead to the final print product becoming deformed or mispositioned.
However, the shrinkage rate of PP can be brought under control via the use of additives. Previous research suggests that blends of calcium carbonate and petroleum resin are the best at reducing shrinkage rate.
Of course, there are several other reasons that PP composites are a common alternative to pure polypropylene in 3D printing. Research has shown that carbon and glass fibers are effective in addressing material strength concerns. Calcium carbonate may also be added for fireproofing purposes.
Either way, it is clear that additives are often necessary to make polypropylene an easier material to work with in 3D printing.
Poor Bed Adhesion
Although polypropylene is known for crystallizing rapidly, the filament can actually be relatively poor at being able to adhere to the printer bed. Even if the bed happens to be heated, you will still have trouble getting the print job to stick. You can achieve better results if you apply scotch tape directly to the print bed and then clean the print bed after you have completed your job.
Low Melting Point
Even though polypropylene is both flexible and durable, it certainly cannot hold its shape under heat in the way that ABS materials can. Polypropylene has a relatively low melting point of 320 degrees Fahrenheit. This means that you wouldn’t be able to use this material for oven or stovetop applications.
Despite its status as a go-to plastic for mechanical components, you would never want to expose polypropylene to conditions where it may be exposed to the extreme heat referenced above.
Not as Common in Filament Form as PLA or ABS
Both polylactic acid (PLA) and ABS are among the most used filaments. As such, they are widely available. You should have no trouble finding a PLA or ABS filament that best fits your needs. Unfortunately, polypropylene is not as common and may come at a higher price range.
3D-printing services will generally charge more for polypropylene prints than many other materials in the industry. This higher rate is evidenced in this price sheet for UMass-Amherst, which charges $0.30/gram for polypropylene. The more affordable options cost just $0.15 per gram.
About ABS Filament
ABS is actually a conglomerate of several chemicals: acrylonitrile butadiene styrene. This is a popular thermoplastic designed to provide a balance of both strength and flexibility. It is a reasonably-priced filament built for post-processing activities, thanks to its solubility in acetone.
Pros of ABS
There are many advantages that ABS have to offer to users. Besides being affordable, ABS is also able to withstand high temperatures. It doesn’t degrade due to heat in the same way that polypropylene does. The properties of this filament also make it an excellent choice for mechanical parts, including automobile components.
ABS filament is reasonably-priced, particularly when you consider the benefits that ABS offers for users looking for a filament that is compatible with all sorts of post-processing activities. A quick search of ABS reveals just how inexpensive this filament is.
Some of the most popular ABS filaments include:
You can also get a sense of how inexpensive ABS filament is by looking at UMass-Amherst’s 3D print service rates. ABS is priced at $0.15/gram, while polypropylene is priced at $0.30/gram.
Doesn’t Degrade Easily
ABS is a thermoplastic polymer that can be melted and crystallized multiple times without degrading too much. It is like PLA (Polylactic Acid) filament in this regard, but it does have a much higher melting temperature than PLA. Noticeable deformation will not set in until the surrounding temperature reaches approximately 208 degrees Fahrenheit.
This is where ABS really holds an advantage over polypropylene, which is known for becoming deformed easily. You would not want to melt and crystallize polypropylene multiple times, out of fear that the end product would not be usable.
Soluble in Acetone
Filaments that are soluble in acetone allow for many adjustments after the object has been printed, and ABS just so happens to have this ability. This will give you a chance to smooth prints or connect multiple printed parts together with ease.
Acetone is often simply marketed as nail polish remover. This product is suitable for careful use with print jobs and will certainly give you plenty of opportunities to do all the post-processing you want to do with your prototype or end product.
Good for Mechanical Parts
ABS is frequently used to print automotive parts and other mechanical components. This is because ABS prints have more “give” to them than prints made using other filaments. Parts made using ABS are durable due to the ductile properties of this filament.
If a component is more ductile, this means that it can be formed into a wire easily. Knowing this, you can imagine how advantageous it would be to use ABS as an automotive part. Mechanical parts are required to meet shape and dimension requirements.
Cons of ABS
There are some unfortunate aspects to ABS filament, including a foul odor. The properties of this filament are such that it is best printed in a heated chamber. This is because it can become deformed under the influence of thermal contraction.
Unfortunately, ABS does produce what is considered to be unpleasant. If you are going to use ABS filament, you may consider placing your printer in an isolated location where others will not be exposed to the print. Proper ventilation will also greatly assist in ensuring that the fumes do not linger in your workspace.
You are encouraged to print within the confines of an enclosed chamber anyways. Besides serving the function of keeping the foul odor in check, the enclosed room will also ensure that the print does not become deformed. Keeping the printer’s interior heated to 122 degrees Fahrenheit will help keep pieces 8 inches in height from becoming deformed.
Enclosed chambers are kept at a constant temperature, sometimes in the territory of 175 degrees, with this avid user reporting success at 134 degrees Fahrenheit. These printer chambers can often be simplistic in nature.
This 3D printing expert at the University of Washington has improvised with enclosed chambers made from:
- Removable polycarbonate screens with weatherstripping added
- Windshield sun visor with spray adhesive affixed to hold everything together
- Long bolts can be used to connect everything together
You will find all kinds of resources for making improvised enclosed chambers. Still, you will have no problem finding manufactured heat enclosures like this one if you don’t want to have to go through all the trial and error associated with a DIY heat chamber.
You will likely find that it is difficult to print large objects with ABS filament. Even if your printer has a heated bed, you will still find it challenging to keep the print from lifting off the build plate and warping.
The edges and corners of the print job begin curling off the print bed in a process that is commonly known as warping. This problem can even render the print model unusable. ABS parts have a tendency to shrink as soon as it gets into contact with the surrounding air.
But the entire printed piece doesn’t shrink or contract evenly. The print’s outer layers stay stuck to the build plate while the other layers start to contract. Eventually, the bottom layer of the print begins to buckle upwards, causing deformities.
Thermal contraction can be avoided if steps are taken to ensure that contracting forces are held back. Through experience, savvy operators have found a way to print with ABS filament successfully. The answer is “ABS juice,” an additive that you can make with products that may already be lying around:
To make ABS juice, you will need:
You will want a 1:1 concentration of ABS and acetone in the solution. This is made possible by the fact that the ABS filament will dissolve in the acetone. Start by pouring at least ⅛ cup of acetone into the Pyrex container and then dissolve enough ABS filament so that there is ¼ cup of the solution in the container. You will then mix the solution thoroughly and spread a thin film on top of the Kapton tape that you have stuck to the print bed.
You Will Need a Heated Platform
If you are going to print with ABS filaments, you will definitely need to get a printer that has a heated platform. A cold build plate can result in a print that has trouble adhering to the plate. This results in deformities, where the printed object begins warping or curling upwards.
Getting a heated build plate is advantageous because it will allow you to work with more filaments. Heated build plates are encouraged for those printing PLA and several other filaments. It is of absolute necessity if you are going to achieve professional-level quality.
Heated beds for 3D printers include popular options like:
Should I Use Polypropylene or ABS?
Although they are both popular thermoplastics, ABS and polypropylene do differ enough for there to be a clear favorite in your specific circumstances.
ABS is used more frequently in 3D printing primarily because of its solubility in acetone. This characteristic allows users to give ABS products a smoother appearance; this means that art pieces, like this user’s project, will have a visually-appealing glossy finish.
Polypropylene is popular for engineers and manufacturers thanks to its tough and rigid characteristics.
If you’re still not sure which filament is best for you, consider their common uses:
Common uses for Polypropylene filament include:
- Medicine containers
- Vehicle bumpers
- Packaging such as milk jugs
- Living hinges like the ones on ketchup bottle caps
- Food containers
Common uses for ABS filament include:
- Electrical components
- Mechanical components, including automotive parts
- Items with a smooth finish
- Products that need to withstand high temperatures
ABS and polypropylene are both thermoplastic filaments widely used in 3D printing. They can both be challenging to work with, but can be rewarding for those who learn to work with them. If you are looking for a filament that can be printed to precise dimensions, you’d be hard-pressed to find an option better than polypropylene. On the other hand, ABS is soluble in acetone, allowing for more post-processing opportunities and can withstand high temperatures.