Hydraulic conductivity of conifer sapwood varies greatly between and within annual rings due to varying dimensions and numbers of tracheids, lumina and bordered pits, complex relationships and non-linearities. Existing laboratory methods are too tedious and expensive for large scale studies for instance of genetics, tree improvement and silvicultural practices, and their spatial resolution is not enough for information on seasonal weather effects which may reflect vulnerability to drought. The article presents a set of integrated models estimating radial variations in hydraulic conductivity at the tracheid level, at 25 µm resolution. A rationalised model was designed for the organisation of tracheids and the water transport through lumina and bordered pits. Within this, pressure drops at flow along lumina and at passages of pits are estimated and integrated to provide local estimates of lumen and xylem conductivities with same radial resolution. The estimated lumen conductivities varied from maximum 0.030 m2/(s·MPa) in earlywood to minimum 0.001 m2/(s·MPa) in latewood. Estimated pressure drops on pit passages reduce these values with about 80 and 90 % into xylem conductivities of 0.006 and 0.0001 m2/(s·MPa) in same earlywood and latewood. Sample means of modelled trunk xylem conductivities were correlated with data from laboratory analyses, resulting in R2 > 0.50. 

Apple and RISE Research Institutes of Sweden are committed to contribute to solving the ongoing plastic pollution crisis. In a joint undertaking, we have created an innovative, low-density, resilient, cellulose foam, based on responsibly sourced wood pulp that can be sustainably produced and recycled in the paper packaging recycling stream. Its structure and mechanical properties suggest it could replace fossil-based materials, such as polymeric foams, commonly used in packaging, insulation, and light weight composites. To accelerate progress, and shorten time to market, we are now inviting partners to build on the work we have done and develop the material toward different applications.

Hygroexpansion, CP/MAS 13C-NMR, WAXS and SAXS measurements were carried out on sheets made from four different commercial pulps of varying lignin content. Non-directional laboratory sheets were made at different press levels from the pulps following different degrees of beating. The sheets were dried both freely and with restraints. Measurements were made on sheets before and after moisture cycling to determine hygroexpansion coefficients, changes in cellulose average lateral fibril dimensions and average cellulose crystallite sizes, with the aim of understanding macroscale and nanoscale changes as the result of moisture cycling. Within the sheets consistent and statistically significant structural changes were observed on both macro and nanoscale. On the macroscale, moisture cycling consistently induced irreversible shrinkage in sheets dried with restraints, but less so in the case of sheets dried freely. The hygroexpansion coefficients were typically higher for freely dried sheets compared with sheets dried with constraints. On the nanoscale, moisture cycling consistently caused an increase in the average crystallite sizes (WAXS) and the average lateral fibril dimensions (CP/MAS 13C-NMR), though the latter occurred with poor statistical significance. These changes were interpreted as an increase in the degree of order in the cellulose fibril interior/cellulose crystallite. There were no profound differences in the nanoscale changes observed for sheets dried with restraints and for sheets dried freely. Changes in the fibre wall nanostructure were of similar magnitudes when comparing results from freely dried low grammage sheets (less abundant inter-fibre joints) with freely dried sheets of higher grammage (more abundant inter-fibre joints). No obvious correlations were found between the macroscale and nanoscale measurements. The proposed explanation for this was that the nanoscale structural changes occurred similarly throughout the entirety of the fibre wall, independent of the proximity to an inter-fibre joint, and that the nanoscale structural changes were mainly the result of water penetrating into the interior of cellulose fibril aggregates. By using the same fibril model for evaluation of CP/MAS 13C-NMR and WAXS data, good-to-reasonable agreement were found for estimates of the degree of cellulose crystallinity. 

Nanocelluloses are seen as the basis of high-performance materials from renewable sources, enabling a bio-based sustainable future. Unsurprisingly, research has initially been focused on the design of new material concepts and less on new and adapted fabrication processes that would allow large-scale industrial production and widespread societal impact. In fact, even the processing routes for making nanocelluloses and the understanding on how the mechanical action fibrillates plant raw materials, albeit chemically or enzymatically pre-treated, are only rudimentary and have not evolved significantly during the past three decades. To address the challenge of designing cellulose comminution processes for a reliable and predictable production of nanocelluloses, we engineered a study setup, referred to as Hyper Inertia Microfluidizer, to observe and quantify phenomena at high speeds and acceleration into microchannels, which is the underlying flow in homogenization. We study two different channel geometries, one with acceleration into a straight channel and one with acceleration into a 90° bend, which resembles the commercial equipment for microfluidization. With the purpose of intensification of the nanocellulose production process, we focused on an efficient first pass fragmentation. Fibers are strained by the extensional flow upon acceleration into the microchannels, leading to buckling deformation and, at a higher velocity, fragmentation. The treatment induces sites of structural damage along and at the end of the fiber, which become a source for nanocellulose. Irrespectively on the treatment channel, these nanocelluloses are fibril-agglomerates, which are further reduced to smaller sizes. In a theoretical analysis, we identify fibril delamination as failure mode from bending by turbulent fluctuations in the flow as a comminution mechanism at the nanocellulose scale. Thus, we argue that intensification of the fibrillation can be achieved by an initial efficient fragmentation of the cellulose in smaller fragments, leading to a larger number of damaged sites for the nanocellulose production. Refinement of these nanocelluloses to fibrils is then achieved by an increase in critical bending events, i.e., decreasing the turbulent length scale and increasing the residence time of fibrils in the turbulent flow. © 2022 The Authors.

Abstract: Moisture absorption in the cell wall structure of wood is well known to induce considerable swelling of the wood exerting high expansion forces. This swelling is mainly induced by the sorptive action of the hydroxyl groups of the carbohydrate wood polymers; cellulose and hemicelluloses. On the ultrastructural level, there are, however, still questions with regard to the detailed deformations induced by this moisture absorption. Here, FTIR spectroscopy and synchrotron-radiation-based X-ray diffraction were used on paper samples to study the deformation of the cellulose crystals as a consequence of moisture absorption and desorption. Both techniques revealed that the moisture absorption resulted in a transverse contraction of the cellulose crystals accompanied by a somewhat smaller elongation in the cellulose chain direction. The deformations were found to be a direct response to the increased moisture content and were also found to be reversible during moisture desorption. It is hypothesised that these deformations are a consequence of the swelling forces created by the combined longitudinal and lateral expansions of the non-crystalline cellulose molecules and the glucomannan hemicellulose aligned along the cellulose crystals. These forces will impose a lateral contraction of the cellulose crystals, as well as a longitudinal extension of it. Graphic abstract: [Figure not available: see fulltext.]. © 2021, The Author(s).

Large deformations under in-plane compression of paperboard appear in forming processes like hydroforming, pressforming and deep drawing, but the mechanisms of deformation have not been studied on a micromechanical level. A constrained in-plane compression test is presented. This test allows for in-plane compression, buckling, wrinkling and compaction. The constrained compression test is realized using a DEBEN CT-500 in-situ tester for laboratory microtomography and synchrotron microtomography. Experiments with five different materials spanning from laboratory handsheets to commercially available multi-layered paperboards are performed. Image processing is used to observe the local out-of-plane fiber orientation and compaction. A phenomenological investigation of the deformation behavior of these materials is presented. Delamination is found to be the primary mechanisms of failure in the multi-layered boards. Furthermore, a porous network structure, created by using long and minimally refined softwood fibers, is found to facilitate the formation of uniform wrinkles and compaction.

A pilot scale study has been made of the concept of adding fibre-based strength agents (fines enriched (FE)-pulp or highly refined (HR)-pulp) in a board middle ply containing chemithermomechanical bleached pulp (CTMP) in order to increase bending stiffness of the board while maintaining Z-strength. It has been demonstrated that the bending stiffness of a sheet consisting of a top ply and a CTMP based middle ply could be improved by increasing the CTMP fraction and preventing Z-strength loss via addition of a fibre based strength agent. Compared with the reference pulp, both Z-strength and bulk increased for three of the compositions, namely 65% CTMP with 5% strength agent of either FE or HR type and 85% CTMP with 10% HR-pulp. FE-pulp was found to be more efficient than HR-pulp concerning bending stiffness improvement. While the highly-refined fibres of the strength agents had a negative effect on the drainage resistance and press dryness, an increased share of CTMP increased the press dryness linearly. FE-pulp and HR-pulp had the same impact on press dryness. Press solids could be improved by approximately 2% without significantly reducing the bulk by increasing press loads.

 For the first time in the Bioeconomy research program at RISE, corrugatedboard has an own research area. Research is building around the main driving forcesin the corrugated board value chain like e-commerce, improved box performance anddigital printing. The main weakness of corrugated board, its moisture sensitivity, isalso addressed.These main driving forces and weaknesses of corrugated board are mirrored in thethemes of this large research program area:Fibre sorption and deformation mechanismsFundamental knowledge on the mechanisms behind moisture sorption and deformation on fibre level is developed to increase moisture and creep resistance throughmodification of paper materials. State of the art methods for characterization ofthe fibre ultra- and nano-structure such as Fourier transform infra-red spectroscopy(FTIR), small angle X-ray scattering (SAXS), and wide angle X-ray scattering (WAXS)give new insights on mechanisms and clarify effects of moisture as well as chemicalmodifications.Papermaking for improved base sheetsConcepts that are explored are fibre-based strength additives produced with novelrefining techniques, and modified ZD-profiles in the sheet for better mechanical properties.Box mechanicsMechanical performance of structures such as corrugated board boxes can be predicted through physically based mathematical modelling by taking the behaviour ofthe constituent materials as well as the geometry into account. Appropriate materialmodels for the corrugated board are identified and finite element models for simulation of corrugated board packaging performance are developed.Tool for inkjet printability on corrugatedThere is a genuine need for improved inkjet printability on corrugated materials thanksto rapid development in e-commerce as well as digitalization along the corrugatedvalue chain. Effective measurement methods and knowledge around ink-substrateinteractions are developed to enable board producers and converters to have effective product development and predictable printability on not only liners but also oncorrugated materials.

Research has been carried out into the possibility of producing a paper with textile-like characteristics on a paper machine. The furnish used consisted of a mixture of 25% bleached softwood kraft pulp refined to 30 SR, 25% dissolving pulp and 50% synthetic fibres. The latter fraction consisted of 15% sort-cut (4mm) polylactic acid (PLA) fibres and 35% viscose fibres cut to 5-8mm. A commercial surfactant was used as foaming aid and sheets were formed on a pilot machine from a bubbly dispersion (foam forming). A production method was developed in which the synthetic fibres were only injected intermittently into the pulp flow. Sheets containing 35% of 8mm long viscose fibres, 25% kraft pulp, 25% dissolving pulp and 15% of 4mm long PLA fibres were successfully produced. Sheets had good formation with furnish air fractions as low as 25%. The sheets made from the mixture of kraft pulp and synthetic fibres had softness comparable with facial wipes and other tissue products while also having significantly higher tensile strength. Proactive adjustment of the surfactant addition enabled the surface tension and the forming process to be stably maintained during the sudden changes in the fibre feed flows.

This is the final report for the Innventia/RISE Bioeconomy research programme area “Source-Efficient Paper and Board Making”, which was executed 2015-2017.The overall aim of the Source Efficient Paper and Board Making was to improve the resource efficiency in paper and board production. This was achieved by combining paper chemistry, paper physics and process technology. A particular goal was to reduce raw material consumption through the use of stronger materials or creation of bulk, which are needed to maintain bending stiffness and mechanical properties if the grammage is reduced. The work in the project has been carried out in laboratory scale and in pilot scale using the FEX pilot paper machine and the dynamic flow loop.