Engineering Putty: Microwavable Instamorph/Shapelock/Polymorph (PCL)

Instamorph, Shapelock, and Polymorph are all brand names for pelletized PCL (polycaprolactone), a relatively tough, non-toxic polymer with a melting temperature around 60C. PCL is easily worked by hand when molten and can be shaped into a variety of useful objects, used to repair broken parts, or can be used as an adhesive for 3D printed parts. Typically, in order to use PCL, you must heat the pellets with hot water, then extract them, consolidate them, re-heat the resulting mass, and then you're ready to use the material. In this instructable, I'll show you how to add a microwave susceptor, such as graphite or iron oxide, to PCL to enable direct heating with microwaves, rapidly reducing the time it takes to heat the material and making it much easier to use.

NOTE: by enabling direct heating of the PCL with microwaves, the material can become significantly hotter than the 100C maximum possible when heating with boiling water. Be careful when using this method to not microwave the material too long and take care when handling.

Materials:

• Instamorph (Amazon)
• Graphite Powder (Amazon)
• Iron Oxide (eBay)

Before we can directly heat the PCL with microwaves, we have to melt a quantity in order to incorporate the graphite. Ratios do not need to be terribly precise, but I've had good luck with 50:1 ratios of PCL to graphite and 50:4 ratios of PCL to Fe3O4 (black Iron oxide), which both equate to about 1/3 cup PCL to 1 tsp susceptor. Melt the PCL by submerging it in water and microwaving it until the pellets turn clear. If you would like to verify that neat PCL does not absorb microwaves, include a vessel with dry pellets at this step.

Once the pellets are clear, extract them from the water (careful, as the water will be hot) and gently work the pellets into a cohesive mass, begin careful to squeeze excess water and air out of the mass. If necessary, place the mass back in the hot water and microwave a bit more to keep it pliable. I like to spread it into a high surface area sheet when reheating to quicken the process. Once the mass is clear, pliable, and relatively bubble free, move on the the next step to add the susceptor.

Note: while this technique makes PCL remarkably easy to work with, it also allows it to get significantly (and potentially dangerously) hotter than when it is heated with water (where its maximum possible temperature is always 100C). Take care using this method.

(Gloves are optional as none of these materials are toxic) Spread the melted PCL into a sheet and pour the susceptor into the middle of the sheet. Again, the ratio of PCL to graphite is 50:1 by weight and the ratio for PCL to Iron oxide is about 50:4 by weight. Carefully fold the sheet over the powder and seal it around the edges, trapping the powder in the molten PCL. Gently stretch and fold the sheet repeatedly to knead the powder into the PCL, reheating as necessary with water and the microwave. Once the material is fully incorporated, it's time to verify that the new heating method works.

Take the rod of susceptor-loaded PCL and place it in the microwave. 10-20 seconds should render the majority of the material pliable, though placement with respect to the individual microwave's hot spots may result in variation within the material. To address this, I usually place the material at the edge of the rotting tray to maximize the number of potential hotspots that it passes through in a given rotation.

I like to form 20g quantities of the loaded material into small pucks the size and shape of river stones that I can keep in my pocket for quick fixes. Iron oxide-loaded PCL has a higher heat capacity, can be worked longer, and the resulting material is magnetic, while the graphite-loaded PCL cools a bit more quickly. There are several other common microwave susceptors, such as Silicon carbide, and Aluminum and Copper powders will likely work as well.

Why does this work?

The answer is quite material dependent (see here for a survey of specific heating mechanisms), but generally Joule heating is responsible for most of the heating. When microwaves strike a somewhat conductive material, they cause electrons to oscillate within the material, generating heat in the same way that passing current through a material generates heat.

Some quick tips and applications:

• great for welding PLA printed parts togethercan be molded around various leadscrews to make a quick custom drive nut
• can be used to join two non-absorbing pieces of material in a structural, but reconfigurable manner
• great for mounting screens, electronics, and other small devices temporarily

I like to form 20g quantities of the doped material into small pucks the size and shape of river stones that I can keep in my pocket for quick fixes. Iron oxide-loaded PCL has a higher heat capacity, can be worked longer, and the resulting material is magnetic, while the graphiteloaded PCL cools a bit more quickly.

Some quick tips and applications:

• great for welding PLA printed parts together
• can be molded around various leadscrews to make a quick custom drive nut
• can be used to join two non-absorbing pieces of material in a structural, but reconfigurable manner
• great for mounting screens, electronics, and other small devices temporarily