You can, in fact, cast sugar in PR resin. The simpliest way that I have found is to start with sugar cubes stuck together with spray adhesive. Then, either make a mold or find one that will allow you to stack the cubes into the mold in "brick laying" patterns. Put as much sugar as you pack into the mold.
Make sure to line your work bench with poly painters drops or waxed paper. Then mix the resin and any translucent dyes that you choose. Add double the catalyst that you normally use. (for example, for regular mica pearl casting, I use 3 drops per oz. For sugar, jelly, etc, I use 6 drops per)
Be ready to immediately pressurize or vacuum. The hot resin does, in fact, melt the sugar and cause it to sink to the bottom of the mold (hence the need to "pack" the mold with as much sugar as possible).
The last time I cast sugar (jelly, actually), it took 6 days to fully harden and not be sticky. For the obvious problem with bugs, be prepared to seal the mold in a air tight container as soon as it comes out of pressure.
With all that said, sugar can be cast but doesn't produce a beautiful blank.....white beach sand, on the other hand looks great.
Be