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document updated 3 months ago, on Feb 21, 2023

PCL plastic being pulled out of boiling water

Fabrication techniques for polycaprolactone

Fabrication techniques for polycaprolactone

Polycaprolactone (PCL) is a hand-moldable plastic that softens when placed in hot water. It's sold under brand names such as Polymorph, Friendly Plastic, PlastiMake, InstaMorph, Thermoworx, and ShapeLock.



Heating methods

Cutting tools

Adhering to other materials

Thermal staking of plastic

PCL plastic will stick to nearly everything when it's hot — except for parchment paper. The importance of parchment paper when shaping PCL plastic can not be overstated.

(Side note — The vast majority of tapes refuse to adhere to parchment paper. One of the few that does stick is 3M Nexcare "pain-free removal" medical tape, also known as "3M Micropore S Surgical Tape". It's available at your local pharmacy. I believe this is very similar to other silicone medical tape, but I don't have experience with others yet.)

A list of materials that will stick to PCL when hot, but won't stick very well once the plastic has cooled:

If you want PCL to adhere strongly to a dissimilar material, consider using plastic staking. [2]

Making sheets

squishing PCL plastic between two glass plates

The quickest way to make sheets, if having a precise thickness doesn't matter as much, is to squish PCL between two plates of glass. Amazon and kitchen stores sell glass cutting boards. Hot PCL will stick to the glass, so it's good to wrap the glass with parchment paper, and secure the parchment on the back side with silicone medical tape.

(Pro-tip: just before putting away your PCL, it's good to squish all unused thick pieces into thin pancakes. This allows the eventual re-heating to go much quicker.)

To get sheets of a consistent thickness, use a rolling pin or pasta machine. Rolling pin depth guides can help, and there are two kinds — rings that go around each end of the rolling pin and linear guides that go along the sides of the "dough".

Lastly, flat sheets of PCL and similar thermoplastics are available ready from the manufacturer.

Small revisions

It is very useful to provide localized heating to a specific area of your part, so that you can make revisions to that area only, leaving the rest of the piece unmodified. This allows you to iteratively refine the shape over several steps.

Having a tub of cold water available speeds up the hot ⇒ cold ⇒ hot cycle enormously.

When you're working on refining thicker structures, those can be pretty tricky to make small revisions to. Here are some approaches you might think of trying:

  1. Hand-hold half of the piece above water. Unfortunately, thicker structures require multiple minutes to soften completely through, and my arm starts to hurt when holding it out for more than 60 seconds.
  2. Jury-rig a mechanism to hang half the piece above the water. This does work, but it might be time-consuming to rig up each time.
  3. I recommend creating separate sub-pieces of the structure, each small enough that it's okay to reheat the entire sub-piece. Then use a heat gun to adhere all the sub-pieces together.

Mold-making / casting

(TODO — maybe recreate part of this image for use in this section?)

Similar articles — one, two, three, four.

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  1. The reason that thick pieces are challenging to fully heat through is because of plastic's low thermal conductivity.
  2. Here's how to view a microwave's standing waves at home. Also, here's a computer visualization of a microwave's standing waves.
  3. This inexpensive thermometer can read down to -50°C, and is well-reviewed by HVAC professionals: UEi Test Instruments PDT650.

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† I haven't yet been able to verify this information either via personal experience or via multiple reliable sources. Take with a big grain of salt. TODO — Verify these.