Sealing a particle board subfloor
Honestly I wouldn't use it as flooring, even sealed with a poly, or paint. I have poly-sealed particleboard shelving, etc. in kitchen cabinets with good success, but I don't see it holding up to foot traffic. What is underneath the particleboard? Is it sturdy, any bounce in the floor? Is the floor level? From my experience with remodeling 70's, and 80's built houses, 4' x 8', 5/8" - 3/4" particleboard was used as underlayment installed over a plywood subloor. If it was me, I would look at installing a floating laminate floor, or possibly hardwood - better overall than trying to refinish particleboard.