The production of high-bulk mechanical pulp sheets by fractionation and the addition of microfibrillated lignocellulose

There has been a growing interest in broadening the application of mechanical pulp, particularly in the development of high-bulk sheets with a wide range of physical and optical properties. This study explores incorporating microfibrillated lignocellulose (MFLC) into fractionated and unfractionated bleached chemi-thermomechanical pulp (BCTMP) of spruce-pine-fir (SPF) to develop high-bulk, strengthened composite. MFLC was generated from BCTMP-aspen through low-consistency (LC) refining, and BCTMP-SPF fibers were fractionated using a Bauer-McNett fiber classifier. The properties of the resulting composite sheets were compared with those sheets prepared from SPF-LC refined pulp at different specific refining energies. The resulting handsheets and Dynamic Sheet Former sheets were analyzed for freeness, fiber length, fine percentage, curl index, bulk, tensile index, tensile energy absorption, stretch percentage and tear index. Additionally, the morphology of the sheets was assessed using scanning electron microscopy. The findings showed that adding MFLC to BCTMP-SPF whole pulp and long fiber fractions presents a promising energy saving and green approach to increase sheets stretch, tensile and tear strength while preserving sheet bulk, potentially extending their application for packaging.