GP-21 # has excellent acid and alkali resistance, with better alkali resistance than GP-10 #. Suitable for: all room temperature strong alkaline media and strong alkaline media below 100 ℃ and with a pH value of 13 or below. And it has excellent acid resistance and can be applied to any concentration of strong acid media such as hydrochloric acid, sulfuric acid, sulfurous acid, hydrobromic acid, hydroiodic acid, chloroacetic acid, nitric acid, nitrous acid, etc. below 140 ℃ (except for phosphoric acid and hypophosphite, the selection of conditions containing phosphoric acid and hypophosphite depends on the specific reaction concentration and reaction temperature)