Admittedly, “art” may be, ah, stretching it a bit, but hot-pulling scrap styrene model sprue over an open flame to make plastic rods of various thicknesses is a classic technique in plastic model-building. The resulting material can be as thin as a human hair, and commonly finds use in scale modelling as antenna aerials, wire, bolt heads, etc.
Flame-stretching is only the first of four creative reuses for leftover sprue from Peter Hall of Scale Model Guide, who also favors them for paint stirrers, internal bracing members, and temporary mounts for small parts during sculpting or painting.
You can also chop square sprue into model bricks, wooden logs, fence posts, and pipes.
Sprue that is otherwise unusable can be fed into a meat grinder (using a large screen) to quickly cut it into piles of rubble for war scenes, scrap yards, etc.