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This study investigated a new technique for obtaining wood powders from whole logs (Pinus sylvestris L.) in a single-step operation. The performance of a prototype multi-blade shaft mill (MBSM) was evaluated using a designed series of experiments including three input parameters, i.e., the moisture content of the log, milling blade speed and log feeding speed, combined with multilinear regression (MLR) analysis. The milling performance was characterised by specific milling energy, particle size distribution and bulk density of powder. For MBSM powders (80 to 95% particles

The objective of this work was to investigate the use of hydrothermal pre-treatment and enzymatic retting to remove non-cellulosic compounds and thus improve the mechanical properties of hemp fibre/epoxy composites. Hydrothermal pre-treatment at 100 kPa and 121 °C combined with enzymatic retting produced fibres with the highest ultimate tensile strength (UTS) of 780 MPa. Compared to untreated fibres, this combined treatment exhibited a positive effect on the mechanical properties of hemp fibre/epoxy composites, resulting in high quality composites with low porosity factor (αpf) of 0.08. Traditional field retting produced composites with the poorest mechanical properties and the highest αpf of 0.16. Hydrothermal pretreatment at 100 kPa and subsequent enzymatic retting resulted in hemp fibre composites with the highest UTS of 325 MPa, and stiffness of 38 GPa with 50% fibre volume content, which was 31% and 41% higher, respectively, compared to field retted fibres.

The wide variation of mechanical properties of natural fibers limits their applications in matrix composites. The aim of this study is to evaluate the properties of hemp fibers from different stem sections (top, middle and bottom) and to assess fungal retting pretreatment of hemp from different stem sections with the white rot fungi Phlebia radiata Cel 26 and Ceriporiopsis subvermispora. For the untreated hemp fibers, no apparent difference in tensile behavior for fiber bundles from different stem sections was observed, and more than 90% tested samples demonstrated plastic flow behavior. Fiber strength and stiffness were highest for the fibers from the top and middle stem sections. These properties were related to the compositional make up and morphological properties of hemp fibers, notably the secondary fiber cell contents. In fungal retting, there was a strong dependence of depectinization selectivity on stem section, which decreased from bottom to top presumably due to the significantly higher lignin content in the bottom section than in the top section (middle section was in between). Consequently, the fungal retting caused a lower reduction in strength of fibers from the bottom section than in those from the top stem section, and essentially reversed the influence of stem section on fiber tensile strength through depectinization selectivity. At whole hemp stem level, the fungal retting with P. radiata Cel 26 exhibited better mechanical properties with an ultimate tensile strength, strain and stiffness of 736 MPa, 2.3% and 42 GPa, respectively, while fibers treated with C. subvermispora exhibited lower mechanical properties of 573 MPa, 1.9% and 40 GPa, respectively. The study thus also showed that less variable and high strength fibers may be produced using the dependence of depectinization selectivity on stem section for composite application.

The large variability in the mechanical properties of hemp fibers is an issue in relation to their use in high-grade composites. The objective of the present study was to determine the optimal growth stage for harvesting hemp fibers for use in composites and to evaluate the effect of field retting time on mechanical performance of the fibers. Reduction in bast content and thickness of the primary bast fiber layer in stems were found to be highly significant ( P

Classical field retting and controlled fungal retting of hemp using Phlebia radiata Cel 26 (a mutant with low cellulose degrading ability) were compared with pure pectinase treatment with regard to mechanical properties of the produced fibre/epoxy composites. For field retting a classification of the microbial evolution (by gene sequencing) and enzyme profiles were conducted. By phylogenetic frequency mapping, different types of fungi, many belonging to the Ascomycota phylum were found on the fibres during the first 2 weeks of field retting, and thereafter, different types of bacteria, notably Proteobacteria, also proliferated on the field retted fibres. Extracts from field retted fibres exhibited high glucanase activities, while extracts from P. radiata Cel 26 retted fibres showed high polygalacturonase and laccase activities. As a result, fungal retting gave a significantly higher glucan content in the fibres than field retting (77 vs. 67%) and caused a higher removal of pectin as indicated by lower galacturonan content of fibres (1.6%) after fibres were retted for 20 days with P. radiata Cel 26 compared to a galacturonan content of 3.6% for field retted fibres. Effective fibre stiffness increased slightly after retting with P. radiata Cel 26 from 65 to 67 GPa, while it decreased after field retting to 52 GPa. Effective fibre strength could not be determined similarly due to variations in fibre fracture strain and fibre-matrix adhesion. A maximum composite strength with 50 vol% fibres of 307 MPa was obtained using P. radiata Cel 26 compared to 248 MPa with field retting.

High-yield pulping of wood chips using low-consistency (LC) refining in combination with primary-stage high-consistency (HC) refining has previously been shown to produce paper with quality parameters (tensile strength and light-scattering coefficient) commonly targeted for newsprint with significantly less refining energy input than using only HC refining. However, questions remain on the differences in the refining action between the two refiner types and for high-yield pulping, the refiner energy demand is a crucial process parameter. Therefore, fines- and fiber-fraction development in HC and LC refining has been studied in detail using Bauer-McNett fractionation, and the respective tensile strengths of the different fractions have been compared. Quantitative and qualitative (morphological) characteristics of the isolated fine fractions have also been analyzed in detail using a newly developed automated fluorescence microscopy method and scanning electron microscopy. The results suggest the difference in LC/HC pulp properties (strength and optical) is partly derived from deviating fiber and fines morphologies and mass balances. The quality of the fines generated during HC and LC refining also differs. LC-refined pulps contain thinner fibrillar fines (thread-like) and HC-refined pulps broader fibrils such as lamellae-type fines. Flake-like fines from the outer fiber wall decreased in relative amount with energy input.

Primary refined softwood was subjected to high-consistency (HC) or low-consistency (LC) secondary refining, and the nature of the development of the internal and external fiber microstructure and ultrastructure has been compared. The primary refining of mixed softwood as a raw material was performed in pilot scale by the advanced thermomechanical pulp process. The study was aiming at the comparative characterization of LC and HC pulps at the fiber level when produced with similar and well-characterized handsheet properties. The formerly described Simons’ staining method was applied. A significant degree of fiber wall delamination/internal fibrillation (D/IF) was observed during both LC and HC refining. Both the energy input and the refining consistency had a significant impact on elevating the degree of fiber wall D/IF. The statistical evaluation of internal fiber development indicated that the fiber populations in LC- and HC-refined pulps had a similar degree of fiber wall D/IF despite having a large difference in refining energy input (420 kW h odt-1), confirming that D/IF was promoted more energy-efficiently in LC than in HC refining. The characteristic of the external fiber development from HC and LC refining was very different. Secondary LC refining promoted fiber surfaces with ribbons of thin hairlike threads arising from the inner secondary S2 layer that occasionally developed along the whole fiber length. Broad sheet- and lamellae-type external fibrillation from the S2 was typical for HC refining, and these characteristics were rarely observed in the LC pulps. The mechanisms for LC and HC fiber development are proposed. The cell wall characteristics (internal and external) of the pulp fibers appear to govern most of the physical and optical properties in handsheets.

The electrical energy consumption in thermomechanical pulping (TMP) is very high, in the range of 2 – 3 MWh/adt depending on process solution and on the product quality specifications for the paper product. Both pulpwood and energy prices have increased rapidly for some time. Due to this, the main focus of the research and development is on ways to reduce the electrical energy consumption in wood chip refining. As a step towards a more energy and cost ‐ effective refining process, Holmen Paper AB has invested in a new mechanical pulping process at its Braviken mill. In this case the primary refining stage consists of high consistency (HC) double disc refiners ‐ RGP68DD (machines with two counter rotating discs). Earlier studies on the refining conditions, such as intensity and temperature, have indicated that it should be possible to improve the energy efficiency in double disc refining while maintaining the functional pulp properties such as tensile index. The main goal of this project was to improve the energy efficiency in double disc chip refining with 150 kWh/adt to corresponding pulp properties as measured on pulp samples after refiner. In order to further improve the basic understanding of what happens to the wood fibre material when changing the process conditions, the morphological and ultrastructural changes of fibres were also studied. This part of the research work was performed in cooperation with the research program; Collaborative Research on the Ultrastructure of Wood Fibres (CRUW). This licentiate project is a part of a large development project where different techniques to improve the energy efficiency has been evaluated by means of mill scale trials at the Holmen Paper Braviken Mill. The high consistency double disc chip refining part of the project was financed by The Swedish Knowledge Foundation, Metso Paper and Holmen Paper, in cooperation with FSCN (Fiber Science & Communication Network) at Mid Sweden University. The trials were made on one of the TMP lines at the Holmen Paper Braviken mill with Norway spruce as raw material. The influence of increased specific refining energy on pulp properties were studied at different refining temperatures, refining intensity, pulp consistency and production rate. Results from these trials were later validated by means of long term trials. Intensity models and simulations for intensity changes by new segment design were made by Juha‐ Pekka Huhtanen from Tampere University of Technology, Finland. The results show that the specific energy consumption to same tensile index can be improved by means of increasing the refining pressure/temperature. The energy efficiency was improved by 80 ‐150 kWh/adt depending on load and the inlet‐ and housing pressure. The largest relative specific energy efficiency improvement was reached at low specific energy consumption levels. Similar fibre surface ultrastructure characteristics are gained by pulps with high pressure/temperature and low specific energy consumption compared to low pressure/temperature and high specific energy consumption pulps. High pressure/temperature and high specific energy consumption resulted in significantly increase in the delamination/internal fibrillation of pulp fibres. The surface ultrastructure of these fibres exhibited exposed S2 layer with long ribbontype fibrillation compared to pulps produced with lower temperature and lower specific energy consumption. When the refiner was operated at high pressure, the tensile index was preserved over the whole plate life. The specific light scattering coefficient increased with increasing pressure/temperature. A reason for this could be increased intensity caused by decreased plate gap. Increased intensity by means of refiner segment design changes resulted in large specific light scattering coefficient increase at similar tensile index, lower shives content, lower average fibre length and lower CSF at same specific energy consumption. The fresh steam consumption was reduced by the increased refiner ressure/temperature.

Fiber development of mechanical pulps is normally assessed by a combination of conventional numerical analyses of fiber features using FiberMaster, PulpEye, and Kajaani instruments. When observed, changes in fiber morphology are normally subjective with use of light- and electron microscopy observations of representative fibers. Thus, visualization and quantification of changes in the fiber cell wall, like delaminaton/internal fibrillation (D/IF) induced during processing, would offer a great advantage. Here, we developed a method using Simons’ stain (SS) that allows quantification of pulp fiber development in terms of fiber wall D/IF during different process conditions, as well as statistical analysis of whole pulp fiber populations of different thermomechanical pulp (TMP) types for the degree of D/IF developed in pulp fibers. The attributes of SS for producing different colored reactions (blue, green, orange, etc.) in pulp fibers through cell wall modification during processing were used in correlation with light microscopy. The method readily measured the degree of cell wall D/IF of pulp fibers from different double-disc refined TMPs produced using varying levels of specific energy and refining pressures. The SS method revealed the presence of five sub-fiber populations in a whole pulp of a given TMP type representing different categories of fibers that possessed varying degrees of cell wall D/IF as a result of process conditions/treatments. Results of statistical analysis indicated that, while D/IF was significantly induced by both the applied refining pressure and specific energy, the effect of energy had the greatest influence. Based on statistical analysis for Bauer McNett fractions of 10, 30, and 50 mesh, we suggest that fraction 30 is the most suitable fiber fraction for the analysis of TMPs using fiber characterization procedures, as this fraction possesses the most treated fibers. The method provided useful information regarding pulp fiber development at the cell wall level that has the potential to explain pulp and paper properties developed in furnishes. The present SS method represents a valuable tool for assessing fiber development at the cell wall level in mechanical pulping.

A study was performed on stone groundwood (SGW) pulps produced on a pilot scale. The behaviour of selected juvenile and mature Norway spruce wood samples was investigated. As revealed by standard tests, sheets formed from juvenile wood showed improved light scattering properties, improved tear and tensile strength, and higher sheet density compared to those formed from mature wood. Scanning electron microscopy indicated that the differences are likely related to the manner of fibre processing and development at the ultrastructural level. Mature wood fibres showed greater fibre end breakage, a smaller long-fibre fraction, enhanced S1 fibrillation and frequently open fibres. In contrast, juvenile fibres had a 14% higher long-fibre fraction and showed typical S2 fibrillation. Fibre development of juvenile wood showed fibrillation features similar to those previously reported for thermomechanical pulp fibres. In both cases, the structural hierarchy of the wood fibre cell wall and the microfibril angle of S2 and S1 layers govern cell-wall splitting and fibrillation progression. The superior quality of the fibre furnish prepared from juvenile fibres compared to mature fibres with SGW pulping may offer an alternative process for more effective utilisation of raw materials such as top logs rich in juvenile wood.

Refining during mechanical pulping causes delamination and internal fibrillation (D/IF) of the fibre wall and changes the surface ultrastructure. Fundamental knowledge about these phenomena at the fibre cell wall level helps our understanding of the development of pulp and paper properties, which in turn facilitates the optimization of processes, helping to save energy and improve the characteristics of final products. In the present study, pulps were produced by double-disc (DD) refined thermomechanical processes (DD-TMP) and have been characterized at the fibre cell wall micro/ultrastructural level based on Fernando and Daniel’s method (2010) of Simons’ staining and scanning electron microscopy (SEM). The pulps studied were never-dried Norway spruce DD-TMP from a full-scale mill trial running under different process conditions; a) varying refining intensity, achieved by using a high-intensity turbine segment (HTS) and a standard (Ref) segment from Metso, and b) varying specific energy consumption (SEC). Improved energy efficiency was obtained with HTS segments, giving adequate or better pulp properties with respect to elongation, light scattering, Canadian Standard Freeness (CSF) at a similar tensile index level and lower energy consumption. Energy efficiency was gained through an elevated degree of D/IF and S2 fibrillation with low energy input. Both the SEC and segment designs had a significant impact on elevating the degree of D/IF. Statistical evaluation of fibre development with respect to D/IF gave evidence for improved energy efficiency in HTS refining. Ultrastructural studies on fibre surfaces showed that HTS refining produced better external fibrillation and leads to exposing the secondary S2 wall as fibre outer layer with different ribbon-type S2 fibrillation. Information obtained at the fibre wall level concerning D/IF and surface ultrastructure contribute to the fundamental knowledge about the pulp and handsheet properties and the energy efficiency of TMP processing.