Expanding the property space of cellulosic materials with multifunctional polymers

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Niko Aarne Name of the doctoral dissertation Expanding the property space of cellulosic materials with multifunctional polymers Publisher School of Chemical Technology Unit Department of Forest Products Technology Series Aalto University publication series DOCTORAL DISSERTATIONS 125/2013 Field of research Forest Products Chemistry Manuscript submitted 16 April 2013 Date of the defence 6 September 2013 Permission to publish granted (date) 18 June 2013 Language English Monograph Article dissertation (summary + original articles) Abstract This work represents a fundamental effort to improve the knowledge how multifunctional polyelectrolytes affect the physical properties of fibers and the paper made from these fibers. Throughout this work, the anionic charge of the fibers were modified with a well-known method: irreversible adsorption of carboxymethyl cellulose (CMC) onto the fibers. This modification amplified the sometimes weak effect that the naturally occurring anionic charge in fibers has on the physical properties of paper. First, increasing the anionic charge of the fibers increased the strength properties of the paper and also water retention. In contrast, drying and then rewetting the fibers decreased the strength and water retention of the fibers. However, treating the anionically modified fibers with cationic polyelectrolyte could break this correlation and the water retention could be lowered without adverse effect on the strength properties. Second, a model for cellulosic fibers was developed. The model divides fibre structure to two distinct regions: (i) surface fibrils (ii) cell wall. This model helps to understand how the polyelectrolytes function when dewatering or strength increasing is needed. Third, multifunctional polymers (ionenes and diblock copolymers) could be used to widen the property space of fibers: (i) to increase the wet strength of the paper or (ii) hydrophobize paper. Ionenes do not have amine reactivity due to their quaternary amine structure like commonly used wet strength agents. Therefore, the results can be used to design more effective wet strength agents. In addition, treatment with diblock copolymer micelles allows hydrophobization of fibers with adjustable layer of hydrophobic material. This could prove valuable as the layer of hydrophobic material can be tuned effortlessly by selecting the starting block copolymer for the desired effect.This work represents a fundamental effort to improve the knowledge how multifunctional polyelectrolytes affect the physical properties of fibers and the paper made from these fibers. Throughout this work, the anionic charge of the fibers were modified with a well-known method: irreversible adsorption of carboxymethyl cellulose (CMC) onto the fibers. This modification amplified the sometimes weak effect that the naturally occurring anionic charge in fibers has on the physical properties of paper. First, increasing the anionic charge of the fibers increased the strength properties of the paper and also water retention. In contrast, drying and then rewetting the fibers decreased the strength and water retention of the fibers. However, treating the anionically modified fibers with cationic polyelectrolyte could break this correlation and the water retention could be lowered without adverse effect on the strength properties. Second, a model for cellulosic fibers was developed. The model divides fibre structure to two distinct regions: (i) surface fibrils (ii) cell wall. This model helps to understand how the polyelectrolytes function when dewatering or strength increasing is needed. Third, multifunctional polymers (ionenes and diblock copolymers) could be used to widen the property space of fibers: (i) to increase the wet strength of the paper or (ii) hydrophobize paper. Ionenes do not have amine reactivity due to their quaternary amine structure like commonly used wet strength agents. Therefore, the results can be used to design more effective wet strength agents. In addition, treatment with diblock copolymer micelles allows hydrophobization of fibers with adjustable layer of hydrophobic material. This could prove valuable as the layer of hydrophobic material can be tuned effortlessly by selecting the starting block copolymer for the desired effect.