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.

Influence of fibrillar cellulose on pigment coating formulation rheology

Coating suspension rheology influences the coating performance at high speeds. The quality of the coated and printed papers is also affected by the rheology of the suspension. For good coating results, it is crucial to optimize the water retaining properties of coating colours. The observation that fibrillar cellulose (MFC) could be used in paper coating formulations as a co-binder, since it is biodegradable and has good shear thinning properties, raises a question about the process ability of coating colours which have cobinder substituted with fibrillar cellulose. In this study, fibrillar cellulose is used to substitute the standard, synthetic co-binder material, carboxymethyl cellulose thus affecting both dewatering and rheological properties of coating colours. Reactivity of the MFC fibers in coating colour formulation is strongly dependent on the fineness of the fibrillar material as well as on its consistency, pre-treatment and refining route. In the present study the consolidation of coating colour layers has been studied using rheology as the main tool. This method combines the use of standard viscoelastic and static dewatering tools, Åbo Academy Gravimetric Dewatering Device and Brookfield viscometer, with the use of MRC300 Rheometer accompanied with an Immobilization cell. The rheological behaviour of all coating colours that have fibrillar cellulose as co-binders was found to be similar. Lower water retention and faster immobilization of filter cake were accompanied with higher shear thinning behaviour. This conclusion was strengthened by the recovery measurements, which showed that the fibrillar material containing coatings have a prolonged recovery time after high shear. A linear correlation between gravimetric (static) water retention and immobilization time, on the one hand and elasticity and prolonged recovery time on the other was found for fibrillar cellulose containing coating colours, regardless of the type of fibrillar material or pigment blend

Novel device for determining the effect of jetting shear on the stability of inkjet ink

Inkjet printing is a rapidly expanding technology for non-contact digital printing. The focus for the technology has changed from office printing of text and image documents increasingly toward wider applications, including large-scale printing of on demand books and packaging or ultra-small-scale functional printing of microscopic volumes of precious/rare materials formulated for use in precisely printed digitally defined patterning arrays, such as printed diagnostics, flexible electronics, anti-counterfeiting, etc. For efficiency, as well as resource management and conservation, predicting the stable runnability of an inkjet ink remains largely a key unknown. Today the only way to know often means simply trialling it, which at best takes time, and at worst incurs costs rectifying possible equipment damage. We propose a mechanically driven displacement device providing constant high-shear flow rate through an extended capillary. This differs from a standard capillary viscometer, which is commonly pressure driven only and lacks the ability to mimic consistent volume flow inkjetting. The novel method is used to study the aqueous colloidal stability of polymer solution, latex polymer suspensions and complete pigment-containing inks, including a reference pigment only comprising suspension. The results reveal the tendency to build agglomerates, determined by dynamic light scattering particle size distribution, optical and electron microscopy. Liquid phase parameters, including surface tension, and suspension intrinsic viscosity are also studied. Repeated application of high shear is seen to act as a milling process for pigment and agglomerate building tendency for latex binder. Consequences for ink jettability are discussed

Acid dissociation of surface bound water on cellulose nanofibrils in aqueous micro nanofibrillated cellulose (MNFC) gel revealed by adsorption of calcium carbonate nanoparticles under the application of ultralow shear

At ultralow shear rate (similar to 0.01 s(-1)), acting below the yield stress of the aqueous gel, adsorption of calcium carbonate nanoparticles (<~100 nm) onto cellulose nanofibrils is induced without pigment–pigment preflocculation. Dispersant-free and polyacrylate treated dispersed carbonate particles are compared. Initially, it is seen that the polyacrylate dispersed material does not adsorb, whereas the dispersant-free carbonate adsorbs readily under the controlled ultralow shear conditions. However, repeated cycles of ultralow shear with intermittent periods in the rest state eventually induce the effect as initially seen with the dispersant-free calcium carbonate. The fibril suspension in the bulk is slightly acidic. The addition of buffer to a controlled pH in the case of the dispersant treated particles maintained a similar delay in the onset of adsorption, but adsorption occurred eventually after repeated cycles. During this cycling process, in parallel, the pH gradually drops under repeated cycles of ultralow shear, opposite to expectation, given the buffering capacity of calcium carbonate. The conductivity, in turn, progressively increases slightly at first and then significantly. The action of surface bound water on the nanofibril is considered key to the action of adsorption, and the condition of ultralow shear suggests that the residence time of the particle in contact with the nanofibril, acting under controlled strain against diffusion in the gel, is critical. It is proposed that under these specific conditions the calcium carbonate nanoparticles act as a probe of the nanofibril surface chemistry. The hydrogen bonded water, known to reside at the nanofibril surface, is thus considered the agent in the carbonate-surface interaction, effectively expressing an acid dissociation, and the calcium carbonate nanoparticles act as the probe to reveal it. An important phenomenon associated with this acid dissociation behaviour is that the adsorbed calcium carbonate particles subsequently act to flocculate the otherwise stable cellulose material, leading to release of water held in the aqueous gel matrix structure. This latter effect has major implications for the industrial ease of use of micro and nanofibrillar cellulose at increased solids content. This novel mechanism is also proposed for use to enhance the dewatering capability in general of complex cellulose-containing gel-like water-holding suspensions.Peer reviewe

Identifying the Challenges of Implementing a European Bioeconomy based on Forest Resources

HUOM: Lehti: https://www.mas.bg.ac.rs/istrazivanje/fme/start Näyttää kaikki olevan avoinna. Sherpassa vanha tieto? FAM liitetty siltä varalta, että lehti ei ole OA.Greenhouse gas emission reduction is strongly advocated within the European Union (EU). Biomass has emerged as a renewable energy source and as manufacturing raw material with ecological credentials to mitigate carbon imbalance. The EU has defined the bioeconomy encompassing these material sources as a basis for technological and economic development. Biocenology, describing the study of natural communities, however, additionally demands inclusion of a circular economy, in which it needs to be assumed that endless renewable products are kept in continuous circulation of use and reuse. Thus, there arises the question whether the bioeconomy route alone, promoted by the EU, is sustainable. Using research literature, based on the Delphi method, and EU documents, we discuss the importance of sustainable management of bioresources. Short term solutions may remain necessary to ensure economic stability but, without embracing the circular economy, only limited mitigation of greenhouse gas emissions can be expected.Peer reviewe

Stochastic transient liquid-solid phase separation reveals multi-level dispersion states of particles in suspension

Wall slip or, more usually, liquid-solid phase separation at the boundary wall when measuring the rheological properties of particulate suspensions is normally considered an undesirable source of error.However, exclusion of a structure consisting of multiple particulates at a planar boundary can, in turn, reveal the nature of that structure and the way it interacts with other elements in the dispersion. Using a system of surface-treated ground calcite particles, designed to control lyophilicity, dispersed, respectively, in two comparative liquids, hexadecane (dispersive surface tension component only) and linseed oil (both dispersive and polar surface tension components), the relative wettability of the particulate surface can be studied. The static state is viscoelastic, with the elastic component reflecting the network of interacting forces acting to structure the particles together and/or to trap liquid within the long-range particle-particle matrix. As strain is applied under plate-plate geometry, selected aggregate structures become size-excluded at the wall, leading to a loss of shear coupling with the bulk polydisperse suspension. At high strain, given optimal solids content, this results in a stochastic transition between two discrete stress data sets, i.e. that with full shear coupling and that with only partial coupling. Stress recovery is subsequently monitored as strain is step-wise reduced, and the progress toward loss of the stochastic transient phenomenon, together with its parallel change in magnitude, is used to describe the re-formation of primary agglomerates. Cessation of the phase separation indicates re-build of the close-to-static structure. Under certain conditions it is observed that the cessation may be accompanied by a secondary relaxation of state, indicating the build of a secondary but weaker structure, likened to the well-known dual-level flocculation in aqueous colloidal suspension. Rheo-optical observations using small angle light scattering illumination (SALS) are used to confirma structure model switching from static (uncoupled with shear) to rotating (fully coupled to the boundary-defined shear) and finally uniformly sheared.Peer reviewe

The Role of Bioeconomy in the Future Energy Scenario: A State-of-the-Art Review

Funding Information: Acknowledgments: The survey is partially supported by MESTD grants from the SAF€RA project RESMOD and contract 451-03-68/2020-14/200105 (subproject TR 35017). Publisher Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland.The bioeconomy aims at decreasing reliance on fossil fuels, preventing or reducing climate change, eliminating insecurity, and efficiently using resources; however, fierce controversy exists on conceivable pathways to accomplish these objectives. The transport sector alone, which encompasses all other industrial sectors, has grown with regard to its energy demand by 50% over the past 30 years. The aim of this paper is to promote a dialogue as to whether an economy based on biomass can be more sustainable than today’s existing economies, considering that the economy needs to expand and be boosted, while creating a cascading and recycling system. This semi-systematic review paper discusses four research questions based on findings from the last 20 years: (i) What are the crucial issues in the ongoing debate on the development of a sustainable bioeconomy concept? (ii) Where are the major conflicting points and focuses? (iii) How does the bioeconomy follow current urbanization and land-abandonment trends? (iv) How will the crisis linked to the COVID-19 pandemic change these previous scenarios? As it is not easy to currently predict which pathway will be the most effective, whether it be the one taken as of now or a specific novel pathway, this article recommends following a strategy that is diverse regarding its approaches to shaping the bioeconomy and further funding of renewable energy sources, along with the involvement of urban planning. In addition, conclusions are validated through a questionnaire completed by 51 experts in the field.Peer reviewe