Hybrid rocket engine with acrylic and gaseous oxygen

I built a small rocket engine for demonstration purposes. The engine is built from a 2 diameter acrylic rod through which I drilled a 0. 5 hole. The oxygen at 80 psi or less is passed through the hole and then is forced through a convergentdivergent nozzle at the tail end. The nozzle s throat is about 0. 25 and expands to 0. 625. I lit the engine by inserting a burning cotton swab (with wooden stick) while a small amount of oxygen was flowing. The acrylic catches fire very easily in a pure oxygen environm