Patrick A. C. Gane

Potential Use of Micro- and Nanofibrillated Cellulose Composites Exemplified by Paper

Naturally abundant, biodegradable, and sustainable plant and wood fibres are composed of smaller and progressively mechanically stronger entities. These smaller structural load-bearing cellulosic fibrils, termed as micro- and nanocellulosic fibrils, can be separated by defibrillating the pulp fibres with either mechanical, chemical, enzymatic, and ultrasound sonication methods or a combination of these treatments. Engineered biopolymer, like cellulosic fibrils, and inorganic mineral composite structures have the potential to create new material properties and applications. This chapter deals with the production, characterisation, and application of cellulosic fibril-precipitated calcium carbonate structures in printing and writing paper. We enunciate a novel composite paper consisting of cellulosic fibrils and precipitated calcium carbonate as the backbone structure and reinforced with a minimal fraction of long fibres. However, recent research investigations show that cellulosic fibrils and their composites find wide application across different fields of manufacturing such as polymers and plastics, medicine, construction, and automotive industries.

Ink adhesion failure during full scale offset printing: causes and impact on print mottle

The aim of this work was to develop a solid knowledge on formulation effects controlling offset ink-paper coating adhesion and to identify key factors of the coating and printing process affecting it. Focus lay on comprehending the impact of pigment dispersant on ink-paper coating adhesion and ultimately on the print quality of offset prints.The work covers laboratory studies, a pilot coating trial designed to produce coated material with a span in surface chemistry and structure, and an industrial offset printing trial.The lab scale studies quantified ink-paper coating adhesion failure during ink setting with a developed laboratory procedure based on the Ink-Surface Interaction Tester (ISIT) and image analysis. Additional polyacrylate dispersant resulted in slower ink setting and reduced ink-paper coating adhesion, with a dependence on its state of salt neutralisation and cation exchange, mainly in the presence of moisture/liquid water.The industrial printing trial on pilot coated papers was designed to study how these laboratory findings affected full scale offset print quality. These trials confirmed the dispersant-sensitive effect on ink-paper coating adhesion, especially at high water feeds. Evaluation of prints from the printing trial resulted in two fundamentally different types of ink adhesion failure being identified. The first type being traditional ink refusal, and the second type being a novel mechanism referred to as ink-lift-off adhesion failure. Ink-lift-off adhesion failure occurs when ink is initially deposited on the paper but then lifted off in a subsequent print unit. In this work, ink adhesion failure by this ink-lift-off mechanism was observed to occur more often than failure due to ink refusal.Print quality evaluation of the industrial prints suggested that water induced mottle was caused by a combination of ink-surface adhesion failure, creating white spots on the print, together with variation in ink layer thickness due to emulsified ink.