Micro and nanofibrillated cellulose (MNFC) as additive in complex suspensions: influence on rheology and dewatering

The traditional forest products, such as paper, packaging and viscose products, have their well-established place, but further efforts urgently need to be made to meet growing ecological demands, increasing economic pressure and to develop new technologies for utilisation of high performance materials. Nanocellulose applied in paper making suspensions and as water retention control aids may introduce additional strength properties in traditional products, and when considered for coatings may deliver oil and gas barrier properties as well as targeted liquid interactions based on surface energy criteria and designed pore and gel network structures. The properties increase the potential for their use in a broad range of novel products. The processes, firstly by which nanocellulose is both created, as part of cellulose structures in nature, and subsequently produced determine their aqueous suspension rheology and dewatering behaviour, and thus, by using knowledge of their rheological behaviour when utilised in complex suspensions, will support the creation of new controls in water-based production processes. The use of rheology for the characterisation of nanocellulose suspensions and their applications in a range of industries as diverse as the oil and papermaking industries has been the subject of numerous studies in recent years. Although many studies have been conducted relating to papermaking furnishes and their water suspensions while including nanocellulose containing materials, these rheological investigations were conducted independently from conditions of dynamic dewatering. For the first time, this work sets out to observe and try to overcome experimental difficulties related to rheometry and dynamic dewatering of high consistency viscoelastic gel-like nanocellulose suspensions using a variety of experimental techniques and methods. Once reliable rheological measurements were designed and the methodology established, the work goes on to analyse the possible structures attained by nanocellulose containing suspensions in combination with macroscopic fibres, pigments and fibril dispersing polymers, which traditionally are used as pigment flocculant water retention aids. These analyses are used to support and challenge the basic hypotheses of the thesis in relation to the impact these structures will have on properties such as process applicability, phase separation, substrate coverage, coating and material uniformity.