Hi everyone, 
I want to create a box of cellulose acetate butyrate (CAB) in Material Studio. For this purpose, I create the cellulose structure, attach butyryl and acetate groups to this structure, optimize CAB with Forcite-Geometry optimization, and finally create a CAB box with Amorphous cell calculation. The final system is attached. I don't understand why this happens! 
I would appreciate it if someone can help me.