Optical Brightener OB is a heat-resistant and chemically stable fluorescent brightening agent that increases whiteness and provides brighter colors. It is used to counteract the yellow color of the polymer and produce a whiter appearance. Optical brighteners create brilliance through the fluorescent process of invisible ultraviolet absorption and visible blue emission. Optical Brightener OB Pure Powder 99%min with CAS No.7128-64-5.