Right, but there you're either putting the acrylic in an extra structural tube, or you're using an acrylic tube which is hugely thicker than necessary so you can leave a substantial unburned shell there as the structure.
The outer part which is acting as structure cannot be burned as fuel because it's necessary as structure, and if you let the burn continue too long, it would cause the rocket to fail. When the burn ends, there's a lot of unburned acrylic still there.
This design allows a given piece of tube to first serve as structure, and then later serve as fuel, ostensibly ending the burn having consumed the whole tube with no structure left behind except perhaps a bit stuck in the feed mechanism. That's novel.
The outer part which is acting as structure cannot be burned as fuel because it's necessary as structure, and if you let the burn continue too long, it would cause the rocket to fail. When the burn ends, there's a lot of unburned acrylic still there.
This design allows a given piece of tube to first serve as structure, and then later serve as fuel, ostensibly ending the burn having consumed the whole tube with no structure left behind except perhaps a bit stuck in the feed mechanism. That's novel.