Shive Content Research Articles

A multicriteria approach to quantify contaminant shives in industrial batches of flax fibres

Residual shives have a major impact on the quality and performance of flax textile and composite preforms. Quantifying the content of shives in batches of scutched flax fibres is a time-consuming and operator-dependent process. Although the shive content can be estimated from the chemical composition, our aim here is to explore a series of effective, reliable and complementary approaches to quantifying shives. Various methods are presented: microscopic observations, analytical biochemistry (monosaccharides, lignins), indirect methods (infrared spectroscopy) and dynamic morphological analysis (QICPIC). A reference standard was first analysed and then compared with batches of flax tow fibre of unknown shive content from current industrial production. This approach shows that calibration curves can be established by applying each selected method to batches with known fibre and shive content. In addition, a database was generated to determine the shive content of industrial batches using partial least squares (PLS) regression. Finally, a detailed study of shives in industrial batches is presented, comparing the different analytical methods.

СТАНДАРТИЗАЦІЯ ЛЛЯНОЇ СИРОВИНИ: ПОРІВНЯЛЬНИЙ АНАЛІЗ ДОСВІДУ США ТА УКРАЇНИ

The main problem in the primary processing of bast fiber raw materials is Ukraine's significant lag in the field of standardization compared to the USA, which negatively affects production efficiency, product quality, and competitiveness in the global market. The article aims to provide a comprehensive comparative analysis of flax raw material quality assessment systems in Ukraine and the USA, identify the key reasons for Ukraine's lag, and develop practical solutions to address these issues. The research found that while Ukraine still relies on outdated standards for flax fiber quality evaluation, which are primarily based on organoleptic methods and do not take into account modern requirements, the USA is actively developing and implementing innovative standards that regulate a wide range of quality indicators, such as fiber fineness, strength, color, shive content, and other important parameters. The main reasons for Ukraine's lag in the field of flax standardization include persistent economic difficulties, obsolete infrastructure and equipment, insufficient funding for scientific research, and weak integration with international standardization organizations. The authors propose a set of solutions to overcome these challenges, which involve increasing state support for the flax industry, intensifying research efforts aimed at developing new methods for assessing the quality of flax raw materials, harmonizing national standards with international ones, deepening international cooperation, and fostering the development of industry associations and clusters. The article emphasizes the necessity of introducing modern instrumental methods for assessing the quality of flax raw materials, such as spectrophotometry for color measurement, computer vision systems for analyzing fiber structure, and automated methods for determining fineness and shive content. The importance of developing standards for new and innovative flax products to expand the range, improve the competitiveness of domestic products, and enter promising markets is underlined.

Oil flax straw processing and utilization

Flax (Linum usitatissimum) is widely used as a source of linen oil and fiber. As a rule, the flax varieties are suitable for either seeds and oil or stem fibers production. The “fiber” varieties bring low seed, while the “oil” ones have poor fibers. The straw of the oil flax is not suitable for the textile industry and has to be burned or degraded naturally in the field. However, it contains a low DP cellulose, which can be used at least for varnish production. The main challenge in the industrial application of the oil flax cellulose is separating the cellulose fibers and shive enriched in lignin. On the other hand, the relatively low cost of the final products restricts the set of tools allowing such separation. Here, we describe a machine designed for oil flax straw scutching having an efficiency of 500 kg/h at the power of 6.5 kW and producing fiber with the residual shive content of 15 % (tow yield $\sim 25$ %). We also suppose several ways to further convert the obtained tow into microcrystalline or fluff-like cellulose (WRV $\sim 9$ ). The suggested process runs below the water boiling point and atmospheric pressure and could be held in the plastic reactors.

The impact of sulphonation and hot-pressing on low-energy high-temperature chemi-thermomechanical pulp

Abstract Hot-pressing high-yield pulp-based paper, at a temperature well above the softening temperature of lignin, increases paper density and strength. Here, it is investigated whether improved paper strength can be achieved and whether lower pressing temperatures can be used in combination with the increased sulphonation of high-temperature chemi-thermomechanical pulp (HTCTMP). Moist paper sheets from low-energy Norway spruce HTCTMP were hot pressed at temperatures up to 270 °C. Sulphite charges of 25–120 kg/bdt were used during impregnation, preheating, and refining at 180 °C with an electric energy demand of 370–500 kW h/bdt to a shive content of 1%. The pulps were mixed with 20% bleached unrefined kraft pulp to ensure that the sheet formation would not be hampered by the pulp coarseness. A tensile index of 70 kN m/kg was reached with the highest sulphite dosage at a pressing temperature of only 150 °C, versus 60 kN m/kg for the corresponding market CTMP. To obtain high wet strength, the highest temperature was required, while the sulphite charge was found to be of minor importance. This study has shown that it is possible to obtain strong and wet-stable paper products from HTCTMP, with a yield of 94–96% and a low energy demand at reduced pressing temperature.

Introduction to the Novel Plate for Manufacturing Thermomechanical Pulp

Refiner plates for manufacturing thermomechanical pulp (TMP) exhibit heavy and blunt-bar edges because they are manufactured via casting. Thus, replacing a cast plate that has exhausted its service life is time-consuming and a large amount of energy is required to reach the target freeness. To overcome the limitations of conventional cast plates for manufacturing TMP and chemi-TMP (CTMP), new dissimilar metal-joining technology was applied to lighten the TMP plate. A lightweight aluminum alloy was used as the base of the plate, and stainless steel alloy exhibiting excellent wear resistance was used as the bars. The lightweight plate, which was manufactured by inserting the bars into the base plate, can reduce the weight of the plate by up to a quarter compared with the cast plate. The refining performance of the lightweight plate was also similar or better than those of the cast plate. Particularly, the target freeness can be reached faster because the bar edge of the lightweight plate of a vertical bar shape was sharper than those of cast bars with a draft angle. This lightweight TMP plate obtained better results than the cast plates regarding the raw material throughput, shives content, and strength property development. However, the brightness of TMP and CTMP in the lightweight plate were slightly lower compared with those in the cast plate.

Development of fibre properties in mill scale high- and low consistency refining of thermomechanical pulp (Part 1)

Abstract The aim of this study was to evaluate changes in fibre properties with high (HC)- and low consistency (LC) refining of TMP and determine how these contribute to tensile index. Two process configurations, one with only HC refining and another with HC refining followed by LC refining were evaluated in three TMP mainline processes in two mills using Norway spruce. An increase in tensile index for a given applied specific energy was similar for all LC refiners in the three lines, despite differences in the fibre property profiles of the feed pulps. Compared with only HC refined pulps at a given tensile index, HC+LC refined pulps had greater fibre wall thickness, similar fibre length, strain at break and freeness, but lower light scattering coefficient, fibre curl and external fibrillation. The degree of internal fibrillation, determined by Simons’ stain measurements, was similar for both configurations at a given tensile index. The results indicate that the increase in tensile index in LC refining is largely influenced by a decrease in fibre curl and in HC refining by peeling of the fibre walls. Compared at a given tensile index, the shive content (Somerville mass fraction) was similar for both HC+LC and HC refining.

Effect of flax shives content and size on the hygrothermal and mechanical properties of flax concrete

This paper presents an experimental investigation of the hygrothermal and mechanical properties of green concrete containing different content and size of flax shives. This allows it to respond to different applications in the building domain. Results of microscopic observations by using scanning electron microscopy show that the flax shives have a very complex and porous microstructure. The latter allowed for good hydric and thermal behaviour with a high moisture buffer capacity of which the minimum and maximum were 2.03 and 2.82, respectively. This allows it to be classified as an excellent moisture regulator. Flax concrete with a mass composition of 14.5% of flax shives in bulk, 35% of binder (tradical PF70) and a water-to-binder ratio of 1.45 gave a bio-based material with an average compressive strength of 0.8 MPa; it is, therefore, used as an insulation and filling material in buildings.

Low consistency refining combined with screen fractionation: Reduction of mechanical pulping process complexity

Process intensification is a process development methodology aimed at a considerable reduction in the energy consumption and process complexity. The approach has been applied to mechanical pulping process design. A process denoted as HC-LC-S consisting of single stage high consistency (HC) refining, followed by low consistency (LC) refining and screening was evaluated in mill trials at the Holmen Paper Braviken Mill in Sweden. After LC refining, the pulp was screened, and the reject fraction was fed back to LC refining. Two HC primary refiner types were evaluated, namely single disc (SD) and double disc (DD). Double disc chip refining was more suitable than SD refining for the HC-LC-S process because of the higher light scattering and lower shives content of the final pulp. The tensile index and shives content of the pulp produced with the DD-LC-S process was similar to that of the reference process, consisting of single stage DD refining and HC reject refining, but the fibre length and light scattering were somewhat lower. The specific refining energy was approximately 200 kWh/adt lower for the DD-LC-S process compared with the reference. Additionally, the auxiliary specific energy was 100 kWh/adt lower for the HC-LC-S processes, since a number of equipment units were omitted.

Increasing pulp yield in kraft cooking of softwoods by high initial effective alkali concentration (HIEAC) during impregnation leading to decreasing secondary peeling of cellulose

AbstractPulp yield can be improved by a more homogeneous delignification of the chips, achieved by improved impregnation prior to the cooking stage. Complete and efficient impregnation is obtained by increasing the diffusion rate by means of an impregnation liquor with a high initial effective alkali concentration (HIEAC). In the present study, the effect of HIEAC in the impregnation was evaluated and compared to a reference impregnation procedure and a prolonged impregnation. After the various impregnation scenarios, the alkali concentration was always adjusted to the same level in the beginning of the cooking stage. Impregnation with a HIEAC resulted in yield improvements by 1–1.5% units, due to a higher cellulose yield and possibly also to higher yield of glucomannan. The HIEAC with an even alkali distribution within the chips prior to the cooking stage resulted in a more uniform delignification carbohydrate degradation. Yield increase obtained by uniform delignification is due to both decreased shives content as well as less secondary peeling.

Preparation of Eucalyptus pulp by mild condition of low-temperature, atmospheric pressure, and short-reaction-time with high-boiling-point solvent and pulp properties

Chemical pulp was prepared by the low-temperature, atmospheric pressure, and short reaction time pulping of Eucalyptus wood chips using a high-boiling-point solvent. The pulping conditions and pulp properties were evaluated. After the digestion of the Eucalyptus chips, pulp containing 6% residual lignin was obtained in 59.6% yield. It exhibited a low shive content and a sufficiently pulped appearance. With subsequent digestion at 110 °C for 60 min, the shive content further decreased, and fiber bundles disintegrated by simple mechanical stirring. The fiber length and width of the pulp were 500–577 and 20.1–27.9 μm, respectively, and the fiber roughness was 8.8–16.8 mg/100 m. The degree of crystallization of the pulp proportionally increased with cooking temperature. The brightness of the pulp with ~ 6% residual lignin content was greater than 52% ISO, and the zero-span tensile strength and viscosity gradually increased with pulping time.

Separation of Fiber and Shivesfrom Decorticated Flax

Decorticated flax contains a significant amount of shive, which limits applications of flax fiber. Separation of shive from flax fiber is essential to improve the resulting product‘s quality. The intention of this study was to use the pneumatic method for separation of flax fiber from shive. Differences between the terminal velocities of flax fiber and shive particles were investigated to assess the viability of the pneumatic method to separate these particles. Individual fiber and shive particle properties were measured and characterized vis-a -vis their width, length, mass, and terminal velocities. A generic fiber sorter was used for the sorting tests with two types of decorticated flax fibers as treatments: Grades 1 and 2 having initial fiber purity (i.e., content) of 51% and 15%, respectively. The results of the pneumatic tests showed that the length of fiber particles did not influence the terminal velocities of fiber. For shive content, an increase in mass and width showed an increasing trend in terminal velocity. The ranges of terminal velocities for shive and fiber particles were 1.22 to 4.10 m s-1 and 0.41 to 1.14 m s-1, respectively, which were significantly different. The results of the sorting tests showed that the sorting method resulted in the fiber purity of approximately 80% for Grade 1 and 66% for Grade 2, which was a significant improvement when compared to their initial purities. This study demonstrated the potential of pneumatic and sorting methods for improving fiber quality.

Low dosage sulfite pretreatment at different refining temperatures in mill scale TMP production

This thesis focuses on the electric energy efficiency of single stage double disc refining for production of printing grade mechanical pulp from Norway spruce wood chips. The thesis is based on the hypothesis, that more energy efficiency refining can be attained by balanced increases of wood softening and refining intensity. Five mill scale trials were performed where wood softening and refining intensity was varied by applying or changing the following process parameters and variables:Chip pretreatment/impregnation with waterLow dosages of sodium sulfite (Na2SO3) added to impregnationTemperature and retention time in the atmospheric preheater binRefining temperature (housing pressure)Feeding segment design combined with increased production rateBy combining suitable increases in wood softening and refining intensity, it was possible to reduce the specific electric energy consumption in refining by 15% (~290 kWh per bone dry ton (bdt)) while preserving important pulp properties within ±5%, compared to the standard double disc refining process. This was done by combining chip impregnation, using an addition of 0.36% (on bone dry basis) sodium sulfite, with a new feeding segment design which enabled 25% higher production rate.When using the new feeding segment design at an increased production rate at unchanged wood softening, it led to reduced fiber length and increased sheet light scattering coefficient at certain tensile index, compared with the standard segment design at normal production rate. This is consistent with the effects normally seen when the refining intensity is increasing. The specific electric energy consumption was 8% lower at a tensile index of 43.5 Nm/g (on Rapid Kothen laboratory sheets) compared to refining at lower intensity using the standard segment design at normal production rate.Mechanical chip pretreatment with subsequent water impregnation showed a reduction in specific electric energy consumption of 6% (~120 kWh/bdt). When chip impregnation was applied in a later trial with a milder chip compression, it led to increased wood softening seen as better preserved fiber length and reduced light scattering coefficient. This resulted in a reduction in tensile index at certain specific electric energy consumption when applied with the standard refining condition but to an increase in tensile index when applied with refining at higher intensity using the feeding segment design at higher production rate.An addition of 1.2% sodium sulfite during impregnation led to a sulfonate content of pulps of ~0.28% (as Na2SO3 equivalents, including post sulfonation) and an average increase in tensile index of about 8.3 Nm/g, when compared to unsulfonated pulps at certain specific electric energy consumption. The increase in tensile index correlated with increased delamination and internal fibrillation of fibers (measured by Simon’s staining), which indicate that the increase in tensile index for sulfonated pulps was a result of improved fiber flexibility and collapsibility. The reduction in disc gap at certain specific electric energy consumption in refining due to an increased wood softening after sulfonation may explain the increase in delamination and internal fibrillation for sulfonated pulps. The smaller disc gap probably led to a more intense refining, i.e. loading at higher deformation rates due to a higher degree of deformation in bar crossings.Different temperatures (80 vs. 97°C) and retention times (6 vs. 9 min.) in the atmospheric preheater bin were studied. This showed that the lower temperature and shorter retention time was beneficial for the tensile strength and light scattering of pulp when applying low dosage sodium sulfite pretreatment. This was most likely a result of too high degree of wood softening prior to defibration in the breaker bar zone when combining low dosage sodium sulfite pretreatment with the higher preheating bin temperature at longer retention time.Different refining temperatures (4.6 and 6.4 bar(g) refiner housing pressure) were evaluated both without and with low additions (0.6% and 1.2%) of sodium sulfite. Raising the refining temperature increased tensile index by 3.2 Nm/g and the addition of 1.2% sodium sulfite by 8.6 Nm/g. The combined increase (~12 Nm/g) was similar to the effect of increasing the specific electric energy consumption by 380 kWh/bdt, when comparing pulps at equal tensile index. However, the pulps produced with increased refining temperature and sodium sulfite addition had lower light scattering coefficient at certain tensile index. The combination of increased refining temperature and addition of 0.6% sodium sulfite was interesting and resulted in pulp with higher tensile index, light scattering coefficient and brightness together with lower shives content at certain specific electric energy consumption, compared with pulp produced at the lower refining temperature without addition of sodium sulfite.Finally, an implementation of the technology presented here is discussed in relation to the Braviken mill (Holmen Paper AB, Norrkoping, Sweden) concerning reduction in electric energy consumption and steam recovery. The technology has potential to reduce the electrical energy use by ~100 GWh/year at the Braviken paper mill, where this study was performed.

Pulp property development Part II: Process nonlinearities and their influence on pulp property development

It is shown in this paper that knowledge of the spatially measured temperatures inside the refining zone in TMP refiners is essential in describing non-linear dynamics of high consistency refining. By expanding the pulp and handsheet properties using piece-wise linear functions into the time domain, an auto-regressive model can be applied to verify that the tempera-ture and the consistency profiles, in combination with the motor load and production rate, are key input candidates when modeling changes in different pulp properties. The model accuracy is analyzed using process information captured at different time and operating conditions. It is also shown that it is more complex to estimate and validate the tensile index than the mean fiber length and Somerville shives content, especially close to refiner operating limits where a shift in the process gain may occur. This type of switched dynamics in tensile index estimation at a specific consistency is related to non-linear behaviors where the fiber pad distribution most likely undergoes a local collapse.

The effect of different variables on in-plane radial permeability of natural fiber mats

There has been a vast growth in manufacturing of fiber reinforced plastics by means of liquid composite molding such as resin transfer molding and vacuum-assisted resin transfer molding processes. In these processes, compression of the porous media and pressure of the injected resin result in in-mold forces that need to be determined. Limited information exists regarding the processing parameters and extent of reinforcing potential natural fibers have in polymer matrices. Current study investigates the effect of different variables such as fiber volume fraction, shive content, fiber size, wax content, and resin viscosity on permeability of five different natural fiber mats. Flax fiber with low-, medium-, and high-shive content as well as hemp and kenaf fiber mats was selected for this study and an original experimental device was setup to measure the permeability of the mentioned fiber mats based on different variables. It was found that increasing fiber volume fraction will result in reduction of permeability of all mats. The presence of shive and larger fiber size increased the permeability. Higher wax content lowered the permeability. These competing factors could be used by manufacturers to produce a mat which had optimum permeability while still maintaining acceptable strength.

Pulp property development Part I: Interlacing undersampled pulp properties and TMP process data using piece-wise linear functions

Thermo-Mechanical Pulp (TMP) refiners served in this work as an example of how to combine oversampled and undersampled variables on a common timeframe for further analysis. To get more information from the refining process, temperature measurement arrays in the refining zones were studied alongside process measurements such as motor load, production rates, plate gaps, dilution waters, pulp properties and manually measured blow-line consistency. The undersampled data set consisted of 63 laboratory samples obtained at a Swedish TMP mill, which were tested for tensile index, mean fiber length and Somerville shives content. The pulp samples were obtained at five different periods during three months to cover a large dynamic operating window. The data set was expanded using a piece-wise linear approach. The measurements inside the refining zone were shown to be important variables when interlacing the undersampled pulp properties with the oversampled process data set, consisting of 350 000 samples. Use of an extended entropy model provided a palette of information about the process conditions inside the refining zone. Particularly, the residence time and the consistency in the refining zones were essential for the pulp property development, as a link between the refining segment pattern used and the current state of refiner operation.

Low dosage sulfite pretreatment in a modern TMP-line

The effects of low dosage sulfite pretreatment combined with modern high consistency double disc refining were evaluated for production of thermomechanical pulp in a mill scale trial using Norway spruce wood at the Braviken paper mill (Holmen Paper AB, Sweden). Spruce wood chips were mechanically pretreated in an Impressafiner before impregnation with different dosages (0-1.2%) of sodium sulfite (Na2SO3) at pH 9. Approximately 23% of the added sulfite was converted to sulfonate groups in pulp, resulting in a sulfonate content of 0-0.28% (as Na2SO3). The low dosage sulfite addition increased tensile index, elongation, density, brightness and decreased shive content, light scattering and light absorption coefficients when compared at equal specific energy consumption (SEC). The increase in tensile index was proportional to dosage of sulfite. Further analyses showed that low dosage sulfite addition did not affect the distribution of the Bauer-McNett fractions nor the fibre length for pulps refined with equal SEC. However, the low dosage sulfite addition increased fibre delamination/internal fibrillation (D/IF). With the addition of 1.2% Na2SO3, it was possible to produce pulp with a tensile index of 47 Nm/g using ~320 kWh/bdt (~15%) lower refining energy, compared with pulps produced without sulfite addition.

Achieving Refining Energy Savings and Pulp Properties for Poplar Chemithermomechanical Pulp Improvement through Optimized Autohydrolysis Pretreatment

Pretreatment of biomass is expected to improve the pulp properties and facilitate the main components in the raw materials to be better used. In this work, the refining energy consumption and properties of the poplar chemithermomechanical pulp (CTMP) from different autohydrolysis pretreatment intensities of wood chips were investigated, and the pulp bleaching ability was also studied. The results showed that the CTMP with autohydrolysis pretreatment at a severity factor of 3.47 could have a 26% energy reduction in pressurized refining, a 60% energy saving in PFI refining, and 44% and 46% increases in tensile and tear indices, respectively. Autohydrolysis pretreatment prior to pulping could result in CTMP with a higher water retention value, higher fines content, better strength properties, lower shives content, and lower bulk and ISO brightness after PFI refining. The brightness of CTMP can be improved by alkaline peroxide bleaching.

Properties of wood chips for thermomechanical pulp (TMP) production as a function of spout angle

Abstract Spruce wood chips were produced under well-controlled conditions in a laboratory wood chipper at spout angles of 30°, 40°, and 50° at a cutting rate of 20 m s-1 and with a nominal chip length of 25 mm. The chips were then refined under thermomechanical pulp (TMP) conditions in a pilot refiner plant. The pulp properties such as freeness, average fiber length, and shives content were determined and evaluated as a function of specific energy consumption. For a first stage refining and for a freeness value of 350 ml, a decrease in specific electrical energy consumption could be achieved by performing the wood chipping at a spout angle of 50° as compared to 30° which is the spout angle commonly used. A patent application regarding this method has been filed and is pending. It is realized that a freeness value is not directly indicative of any quality measure, such as, for example tensile index and light scattering coefficient but the obtained results can be interpreted to be promising. Further studies are needed regarding the impact of the modified chipping process.

Characterization of polypropylene composites reinforced with flax fibers treated by mechanical and alkali methods

AbstractFlax is a type of natural fiber widely used as reinforcing materials for polymer composites. The commercially available flax fibers in Canada consist of a significant amount of shive and other impurities, which could act as stress concentration regions to negatively affect the mechanical property of composites. In this study, the shive was manually removed from the commercial flax fibers by screening and combing to obtain different shive contents from 0 to 30 wt%. By contrast, the obtained flax fibers were further treated with alkaline solution. The fibers obtained from mechanical and alkali treatment were compared on their thermal and mechanical properties. As expected, it was found that the thermal stability and mechanical properties of the flax reinforced polypropylene composites increased significantly with the removal of the shive content. However, the alkali treatment on flax fiber did not further improve the composites properties. The possible reason was that the proper mechanical treatment (screening and combing) prior to alkaline treatment effectively loosened the fiber bundles for better single fiber separation in matrix and significantly removed the impurities, thus the effect of alkaline treatment did not become obvious.

Laboratory and mill scale evaluation of biopulping of Eucalyptus grandis Hill ex Maiden with Phanerochaete chrysosporium RP-78 under non-aseptic conditions

Abstract Biopulping of Eucalyptus grandis wood chips with Phanerochaete chrysosporium RP-78 was evaluated under non-aseptic conditions in laboratory and mill wood-yard. The ability of P. chrysosporium to compete with indigenous fungi present in fresh wood chips was notorious under controlled laboratory experiments. A subsequent step involved an industrial test performed with 10-ton of fresh wood chips inoculated and maintained at 37±3°C for 39 days in a biopulping pilot plant. Biotreated wood chips were pulped in a chemithermomechanical pulping mill. Net energy consumption during refining was 745 kWh ton-1 and 610 kWh ton-1 of processed pulp for control and biotreated wood chips, respectively. Accordingly, 18.5% net energy saving could be achieved. Biopulps contained lower shive content and had improved strength properties compared to control pulps. Tensile index improved from 25±1 N m g-1 to 33.6±0.5 N m g-1 and delamination strength from 217±19 kPa to 295±30 kPa.