A method and apparatus is disclosed in which a plurality of envelopes (38) are arranged and aligned in face-to-face relationship to form at least one batch (28) of envelopes (38). The batches (28) of envelopes (38) are conveyed around the endless conveying loop (250) oriented in a substantially vertical plane and defining upper and lower horizontal conveying paths. The edges (46,48,50,52) of the envelopes (38) are sprayed with a liquid envelope material degrading agent that functions more effectively when heated. The envelope edges (46,48,50,52) are contacted with planar heating members (72;92) and the envelopes (38) are bent inwardly so that the edges (46,48,50,52) are laterally displaced out of the planes defined by the major portions of the associated envelopes (38) to promote more effective contact of the envelope edges (46,48,50,52) with the heating members (72:92) whereby the envelope material is degraded along the edges (46,48,50,52).