It May Be Time To Abandon PLA For 3D Printing

A big pile of PLA scraps that must be dealt with [Source: Fabbaloo]

I’m now considering whether PLA should be the default 3D printing material for desktop equipment.

Filament History in 3D Printing

Filament has a straightforward history in desktop 3D printing: initial devices built in 2008-9 had to decide on a commonly available material as there was simply no materials industry dedicated to 3D printing at the time aside from commercial providers for industrial equipment.

The choice was ABS, as it was often easily found everywhere in the form of “ABS welding wire”. This rudimentary filament type was how these machines began operation. However, there were a number of problems, not the least of which was that the consistency of the diameter of the filament was pretty low.

Also, ABS itself was not chemically designed for 3D printing. ABS was first patented way back in 1948, and was intended for use with injection molding equipment.

Since it was not designed for 3D printing, it is subject to several key challenges: first, it warps significantly. Hot ABS is somewhat larger in volume and thus when it cools the parts often distort. That’s not a good property when you’re trying to accurately produce objects. Even worse, it caused 3D printer manufacturers to develop heated print surfaces, heated build chambers and a lot of print tuning to achieve successful ABS 3D printing.

ABS also smells terrible when it’s printed.

Introduction Of PLA To 3D Printing

Enter PLA, which at the time, was revolutionary for the market. It offers minimal warping, and thus led to a much higher ratio of successful 3D prints. It was even possible to offer 3D printers with no heated print surface and they occasionally worked properly.

Finally, PLA had a bit of an eco-brand: it was said to be produced with organic materials, was recyclable and would biodegrade if abandoned. The market quickly shifted towards PLA and many new suppliers of PLA and variants appeared around the world.

Using PLA, we felt good because not only did our 3D print jobs work, but we were apparently doing something good for the environment at the same time.

But were we really?

PLA Benefits Re-Examined

Let’s take a look at these characteristics:

More Successful 3D Printing (than ABS): This is true; ABS is far trickier to successfully use, primarily due to the difference in warping. With the introduction of mildly-heated print surfaces, most desktop 3D printers are easily able to 3D print PLA.

Made With Organic Materials: This is true. Much PLA is made from corn — as is a surprising number of other common products you might use. The organic source material is fermented to produce lactic acid, which is then converted into proper PLA with the application of 200C heat. Here’s a video of the process:

However, you’ll see the process involves many steps.

Recyclable: PLA is indeed recyclable, as it is a thermoplastic. You simply heat it up and re-extrude it into a fresh filament.

But while that is technically possible, it is far more difficult to do in practice. This is because few people own a filament recycling unit like those from 3DEVO, and thus most people simply trash their leftover PLA scraps.

A major issue in recycling PLA is that there are now many different variants. These might be different colors, but also could involve additives like ceramics, metals, wood or other materials. There are also PLAs mixed with PHA to offer slightly different engineering properties. The problem is that if you were to mix these scraps together to recycle these scraps into filament you’d get a Frankenstein’s material with unknown properties.

Biodegradable: This is where there is a problem. When we’re told that PLA can biodegrade it may be technically true, but is not true in real-life situations. It turns out to actually break down PLA there is specialized equipment required that is quite rare.

One fellow tested PLA’s biodegradability by burying a print outside in dirt for two years, and compared the results with outdoor exposure and a two-year immersion in water:

The results were startling: none of these multi-year exposures caused ANY degradation in the print samples, and it’s clear that PLA would survive in a landfill just as easily as ABS.

There was an initiative to properly recycle PLA, Project PLA, but the site now seems abandoned, effectively demonstrating that it is not financially feasible to recycle PLA with normal civic recycling programs.

I’m now wondering what I will ever do with my box of PLA scraps.

So PLA is not really biodegradable.

And recycling is challenging.

And finally, objects 3D printed in PLA have one terrible property: they have very low heat resistance. PLA objects will begin to soften at temperatures as low as 50C, and certainly at 60C. These are temperatures you will frequently encounter in day-to-day situations, placing significant constraints on how you can use parts made in PLA.

Switch To PETG?

Recently I’ve been 3D printing in PETG and it seems to have some notable advantages over PLA. It has a higher thermal resistance and appears to be easily recyclable. I don’t know about you, but I’ve found PETG to be remarkably more reliable when 3D printing than PLA and certainly ABS. The prints look good and I’m trying hard to remember the last time I had a PETG print job fail.

So tell me why again are we using PLA?

Should PLA be the default 3D print material? Aside from ultra-low-cost non-heated 3D printers, I’m now thinking it should not, and perhaps PETG should be the de facto standard material most people use.

What do you think? Have you switched from PLA to PETG already?

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