Filter bags made of PP needle felt (polypropylene) have specific properties. Thanks to high resistance to acids and alkalis, polypropylenes are suitable for use in chemically aggressive working environments. Their disadvantage is a relatively low working temperature of 80-100°C, which considerably limits their applicability.
In the field of dry filtration polypropylene is sometimes used in galvanizing, in the production of fertilizers, or in specific applications where the filtered medium contains strong acids or strong alkalis.
We find polypropylene with water repellent finish (based on a silicone bath) or oil and water repellent finish (based on a chemical resin bath). Both finishes protect the material from moisture and facilitate the cleaning of the filter bags from the accumulated dust.
Polypropylene without a water and oil repellent finish is commonly used in liquid filtration.