3D printing polyethylene has its challenges, but these can be mitigated with the right print settings.
There are many types of 3D printing filament out there: from your everyday PLA, to hardy ABS, to flexible TPU. One material that often comes up in conversations about 3D printing, particularly FDM, is polyethylene (PE). And why shouldn’t it: the plastic group is among the most ubiquitous in the world. But 3D printing polyethylene isn’t quite as simple as turning the raw thermoplastic into a filament and feeding into your extruder. The unique characteristics of the material present certain challenges for 3D printer users. In this article, we’re exploring how to 3D print polyethylene and some of its most common types, including HDPE, PET, and PETG.
Polyethylene (PE) is a group of synthetic polymers in the polyolefin class. Used in the production of plastic bottles, bags, and food packaging, the material is the most widely produced and used plastic in the world. In terms of properties, the thermoplastic is known for its high ductility, flexibility, good impact strength, toughness, and chemical resistance. The material is also very lightweight.
PE is a highly versatile plastic, and many commonly used polymers are derived from it, including polyethylene terephthalate (PET) and high-density polyethylene (HDPE). While PE itself is not particularly well suited to 3D printing, PET, PETG, and HDPE can be 3D printed, bringing the benefits of the world’s most popular plastic to 3D printing applications.
High-density polyethylene (HDPE) is a linear version of polyethylene that has superior durability and thermal resistance to pure PE. The polymer has a dense chemical structure and is highly crystalline. These characteristics translate to properties like high strength and a substantially higher melting point than low-density polyethylene. Crucially, HDPE can withstand temperatures of up to 120 °C, which means it can be subjected to high temperatures for sterilization. HDPE is also UV resistant and resistant to most chemicals.
You’ve almost certainly come across HDPE: the thermoplastic is used to produce plastic piping, as well as containers for cleaning products, milk bottles, recycling bins, shampoo bottles, plastic toys, and much more. Its relative stiffness and durability are key to these applications, as is the fact that it isn’t known to leach chemicals into water or food. The material is also highly recyclable, which makes it a good option for disposable products.
Today, the most popular production processes used to transform raw HDPE into plastic products are die extrusion, injection molding, blow molding, and compression molding. It is possible to 3D print HDPE using Fused Deposition Modeling (FDM), but the material can be a challenge. For this reason, it has not become a widespread material for the production of prototypes or printed parts.
On the positive side of things, HDPE offers makers a low-cost, lightweight, and durable plastic. HDPE is also FDA approved for food contact and is fully recyclable, which can take the sting out of a failed print. Makers can buy HDPE filament from a small number of filament manufacturers, or take it upon themselves to produce their own filament using shredded HDPE (from bottles or used prints) and a filament extruder.
If you do decide to 3D print HDPE, there are a number of challenges you should be aware of. For starters, the material is highly prone to warping on the print bed. It is possible to carefully tune and monitor print settings and temperatures to minimize warping, but it is a much more likely phenomenon than with other 3D printing filaments like polylactic acid (PLA) and acrylonitrile butadiene (ABS).
HDPE filaments also suffer from poor adhesion. And this is on all fronts: it can be difficult to ensure a strong first layer adhesion bond to the build surface as well as between printed layers of the polymer.
To sum it up, here are the pros and cons of 3D printing HDPE
Pros of 3D printing HDPE
Cons of 3D printing HDPE
Good strength-to-density ratio
Highly prone to warping
Water and chemical resistant
Highly prone to shrinkage
FDA approved for food contact
Poor bed adhesion
Poor inter-layer adhesion
Low cost filament
Not widely sold
HDPE is a tough material to 3D print, but there are ways of improving the odds of a successful print using specific print settings. Here’s how:
Preheat your 3D printer’s print bed to between 100–130 °C. A heated bed will help to slow the material’s cooling rate, which can mitigate the effects of shrinkage.
Set your nozzle temperature to between 230–260 °C to ensure the material flows smoothly through the extruder.
If possible, use an enclosed build chamber to further slow the cooling process and minimize warpage.
Implement rafts or brims in your slicer software to improve first layer adhesion.
You can also apply polypropylene (PP) tape to your build plate to improve adhesion, since HDPE bonds well with PP.
Finally, don’t print too fast: a slower printing speed of 20 mm/s can improve the quality of an HDPE print.
Interestingly, there are efforts underway to improve HDPE’s printability. For example, in a study published in 2021, researchers found that adding natural fibers to an HDPE matrix to create a composite helped to reduce warping significantly.
Despite the challenges of 3D printing HDPE, one of the main reasons the additive manufacturing world is so interested in pursuing the material is its recyclability. Technically, all 3D printing thermoplastics are recyclable. This is because thermoplastics by nature soften and melt when exposed to high temperatures and then resolidify when cooled. Thermoplastics can therefore be melted and reprocessed to make pellets, filament, or other products.
What sets HDPE apart from other common filaments is how easy it is to recycle. Common filaments like ABS and PLA can be recycled, but they require a special facility to be processed. These 3D printing materials are characterized as Type 7 plastics, which are not often accepted at local recycling centers. HDPE on the other hand, is a Type 2 plastic, which is collected by municipal recycling programs and can be transformed into new products, like detergent bottles, piping systems, and more.
The recycling process for HDPE is simple: once the recycled products have been properly sorted and cleaned, the HDPE scrap is shredded, melted, and turned into pellets. From there, it can be made into filament, or used in other production processes to make new products. With the right equipment and tools, it is possible to recycle HDPE at home and make new filament for 3D printing at a low cost.
Recommended reading: HDPE 3D printing: applications, advantages, alternatives
Before we wrap up, we also want to address another question that comes up when talking about 3D printing polyethylene: what is the difference between HDPE, PET, and PETG?
PET and PETG are both polyethylene blends: PET integrates a terephthalate monomer, while PETG also includes a glycol monomer. PET is used to produce over 70% of bottles for water and other beverages. The material is transparent and also highly recyclable. In the context of 3D printing, PET filament is known for its high rigidity and brittleness. The material also requires higher printing temperatures.
The added glycol in PETG filament offers a bit more flexibility, which improves the material’s impact strength. In addition to this, PETG has several beneficial material properties, including good thermal resistance, as well as superior durability and adhesion compared to PET. It can also be sterilized.
Perhaps the most important distinction to make when comparing the three polyethylene printer filaments is that PETG is engineered for easier processing and is less prone to warpage. The material also has good adhesion. Sometimes it can even bond too much to the print surface, particularly if you are using a glass build plate in the printing process. If you are having trouble with PETG sticking too much to the print bed, we covered the issue here.
Recommended reading: PETG print settings: Adjusting temperature, speed & retraction to improve printing
Polyethylene is the most widely used polymer globally, but as we’ve seen, it’s not the best suited for 3D printing technologies. High-density polyethylene (HDPE) can be printed, however it is prone to shrinking and warping and does not have good adhesion. PETG, a PE blend with terephthalate and glycol monomers, is significantly easier to print using FDM/FFF processes.
Here’s a quick summary of what we covered:
PE is a thermoplastic known for its light weight, high ductility, flexibility, good impact strength, and chemical resistance. It is the most commonly used polymer today.
High-density polyethylene (HDPE) is a linear PE that boasts superior durability and thermal resistance to regular PE. It is used to produce containers for cleaning products, milk bottles, drainage pipes, and more.
HDPE is also easily recycled: most municipal recycling centers collect the material to be recycled.
HDPE can be 3D printed, however it comes with its challenges, including warping and poor adhesion.
For the best print results, HDPE requires a heated print bed with enclosure and a high-temp nozzle.
Using rafts or brims can help to improve adhesion, as can printing at a slow speed.
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