CTMP in Fine Papers: Impact of CTMP on Permanence of Alkaline Papers, 1991 Papermakers Conference Proceedings

Fine papers have traditionally been produced using fully bleached chemical pulps. With advancements in pulping and papermaking technology, papers utilizing high-brightness high-yield pulps can now be produced that blur the conventional distinction between "freesheet" and "groundwood" grades. Economic advantages can be obtained by replacing hardwood kraft by bleached chemithermomechanical pulp (CTMP) and higher levels of calcium carbonate filler. To determine the runnability, printability and end-use performance of such papers, a number of production runs using up to 50% CTMP in the furnish have been made on commercial papermachines. Since these papers were alkaline and buffered by calcium carbonate, they represented a good test case to evaluate the impact of lignin-containing pulps on permanence properties in an acid-free environment.

The commercially-produced papers have been evaluated in accelerated aging tests at both 100 degrees C/low humidity and 90 degrees C/50% relative humidity. Permanence has been compared versus freesheet controls by monitoring pH, optical properties, tear resistance and fold endurance. Differences between the CaCO3 -filled CTMP papers and freesheet papers in the degree of yellowing during these tests were surprisingly small. AU unaged papers had good fold endurance and papers containing as much as 30% CTMP met the initial tear properties proposed for permanent papers in ANSI Z39.48. Loss of properties during aging showed the expected dependence on pH, but little or no impact of the CTMP content. It is concluded that high quality lignin-containing pulps can be used as furnish components for papers that will maintain physical properties during long term storage.