RepRap: Blog

Inspired by Fernando Muñiz over on the RepRap Builder's blog and by meeting Norman Frost of Sustainable Composites Ltd. (who kindly donated a sample of their UV-cure resin to me) I have been experimenting with thermosets. (There is plenty of time between my tweaking the parameters of my new Darwin as it makes a splodge of polycaprolactone almost resembling a cube.)

The idea is to mix the resin with a glass filler like this stuff from Tomps to make a paste, and then put that in the paste extruder with a ring of UV LEDs round its nozzle to set the stuff after it's been laid down.

Norman said that the ideal cure wavelength is 365nm.

The first thing I discovered is that cheapo vanilla 400nm LEDs won't touch the stuff. It just sits there and stays sticky for hours. So then I got some NSHU550A LEDs that emit at 370nm. The picture above shows one of these zapping a drop of resin about 5mm underneath it using a forward-bias current of 20mA. That forms a thick skin at 10 minutes, and is solid to the touch in 15.

Now. All we need is for each layer to be mechanically rigid enough to support the next, so that should be fine. And, of course, layers underneath will be further hardened as the layers above are laid down, because the UV will percolate down through the resin and the glass.

As you know, we've been working on using polylactic acid in RepRap because it's a plant-source thermoplastic that can be home-made, and when it's finished with it can be locally composted. Widespread use would take CO₂ out of the atmosphere then put it back, and so would be carbon neutral.

But Sustainable Composites' thermosets are plant-derived too. So using that resin to make stuff that gets thrown in landfill rather than recycled would be even better. Thermosets are very stable underground (think amber), so widespread takeup of them in replicating RepRaps would be carbon-positive...

Labels: CO2, LED, resin, thermoset, UV