An aqueous binding composition is provided comprised of a polyanhydride based polymer, which polyanhydride based polymer has been purified through the use of an azeotrope. The resulting binder is effective, particularly for binding glass fibers, yet substantially odor free. A fibrous material is provided that is coated with a water-resistant cured binder formed in accordance with the process of the present invention wherein adjoining fibers are bound at cross-over points. Such bound fibrous material is free of a phenol-formaldehyde resin and substantially free of odor. It has been found that by removing purities such as cumene and acetophenone from a polyanhydride binder, e.g., a styrene maleic anhydride based polymer based binder, an effective binder for glass fiber is obtained while also avoiding an odor problem.