Recyclability of Linerless PSA Stamps, 1995 Pulping Conference Proceedings

Said Abubakr, David W. Bormett, John H. Klungness, Gary M. Scott, Nancy Ross-Sutherland, Timothy V. Stagg, Dart S. Moy

USDA Forest Service

Alim A. Fatah

Rajendra Kumar

United States Postal Service

Paul R. LaBrosse - 3M

Pilot-scale separation sequences were used to assess the recyclability of postage stamp material. Several different levels of pressure-sensitive adhesive (PSA) stamp material were investigated. The process involved preparing the paper stock, removing contaminants, and measuring contamination level throughout the process. Stock was prepared by shredding and high consistency pulping, which involved diluting the pulp, screening, cleaning, flotation deinking, and washing. The efficiency of contaminant removal was evaluated by dirt count of dyed handsheets. The results indicated that the linerless stamped material could be pulped to free the pulp fiber from the adhesive and ink. The release coating in the material did not cause any problems and could not be detected. Much of the ink was removed in the forward cleaner, which is typical of inks with a density greater than that of water. Conventional screening and cleaning processes were satisfactory for reducing the adhesive levels in the material. However, high levels of contamination required additional processing steps. Future work will include investigations into new technologies such as the use of enzymes and high-shear field separations.