Value-added mechanical pulps for light weight, high opacity paper

Brightness, strength, economy, and paper machine runnability are common concerns of papermakers who use virgin or recycled fiber furnishes. Fiber loading, a process that precipitates calcium carbonate partially inside the fiber lumen, is a cost-effective technology that could substantially upgrade mechanical pulp furnishes. This study demonstrates the optical and physical handsheet property advantages of fiber loading typical newsprint and thermomechanical pulp (TMP) furnishes. Inclusion of hydrogen peroxide during fiber loading prevented the expected alkaline darkening. Moreover, brief heating of the pulp after complete carbonate conversion resulted in several additional brightness points. Alternative approaches for stabilizing the brightness of fiber-loaded blends of mechanical and de-inked pulps are presented. Our comparison of strength and optical properties of handsheets made by these methods suggests that fiber loading can be used to produce paper with high opacity and low basis weight from mechanical pulp.