REMINISCENCES OF A PAPER CHEMIST: PAST TRENDS AND FUTURE DIRECTIONS

The highlights of my career are presented here, starting from my early work on colloidal hydrodynamics, followed by applications of colloidal hydrodynamics to papermaking chemistry, and finally by my recent work on cellulose chemistry. Examples will be given that emphasize the need to understand fundamental concepts in explaining complex phenomena. My mentor and predecessor, Professor Stanley Mason, once told me that, after having spent several years on the study of papermaking suspensions, he considered such systems too complex to be understood from basic scientific principles and shifted his research to model systems, such as the motion of slender bodies in well-defined flow fields. As a result of his work on model systems, he became a world expert in microrheology (nowadays usually referred to as micro-hydrodynamics) and received many awards. In my early career, I considered this a challenge and decided to concentrate on fundamental phenomena relevant to papermaking suspensions, such as particle collisions in flow, shear-induced aggregation, particle deposition on surfaces in well-defined flow fields, kinetics of polymer adsorption, and so on, in the hope that such knowledge could one day be used in explaining the complex behaviour of papermaking suspensions. In the late 80s, I considered that we had accumulated enough fundamental knowledge to attack the study of papermaking suspensions and learned that their behaviour could indeed be explained by the fundamental knowledge we (and others) had accumulated. This was very gratifying for me, having closed the loop that my predecessor had started. For about 25 years, we studied many aspects of papermaking chemistry such as fines and filler retention, polymer and polyelectrolyte adsorption on fillers and fibres, wet-web strength agents, internal and surface sizing agents, dyes and yellowing inhibitors, and flotation deinking. We showed that the location of addition points for chemical additives could be rationalized by the kinetics of particle and polymer interactions on a paper machine. With the decline in production of printing papers, my work shifted to cellulose chemistry, with the objective of making novel biorenewable materials. In this field, we have been quite successful. Cellulose chemistry has an immense potential to contribute to a sustainable forest-based bioeconomy. All this research would not have been possible without the contribution of numerous students and postdocs, to whom I am extremely grateful.