Isikhumba se-EPU noma ungayibiza ngezindwangu zesikhumba ze-PU ezincibilikayo noma isikhumba se-PU esingancibiliki futhi le nto iyisikhumba sokwenziwa se-PU esithuthukisiwe.Isakhiwo se-EPU sizinzile futhi sineminyaka engu-7-15 ukumelana ne-hydrolysis futhi le nto entsha ihambisana nemvelo.