Layer-like fatigue is induced during mechanical pulping

The question whether fatigue is induced during mechanical pulping was addressed experimentally. The grinding process was interrupted to image partly ground spruce samples. The grinding was performed at five different feed velocities using two different grindstones. This approach allowed creating an in situ snapshot of the developing grinding zone in the wood samples. The depth profiles of the stiffness modulus and nm-scale pores, close to and within, the grinding zone were quantified by ultrasonic pitch-catch measurements and thermoporosimetry. To perform these profiling measurements, wood material was iteratively removed layer-by-layer with a microtome from the sample surface after taking the snapshot. The grinding-induced changes in cell morphology inside the sample were imaged using microcomputed tomography, whereas the changes on the surface of the samples were imaged with optical microscopy and SEM. A layer that penetrated 0.5–1.5 mm into the sample exhibiting up to 80% decreased stiffness modulus—compared to the unaltered sample parts—was detected when the Wave-type grindstone was employed. The corresponding layer thickness was 0.3 mm with the conventional grindstone. The results match previously measured temperature profiles, and confirm the Atack-May hypothesis that grinding induces a fatigue layer. Confirming this old, widely used hypothesis is significant for the field of energy efficiency research related to mechanical pulping and may provide new opportunities for grinding research.     

ESR study of structural changes in high-density polyethylene subjected to cyclic tensile stress

Bulk-crystallized high-density polyethylene is subjected to cyclic tensile stress and then irradiated by γ-rays to “spin-label” polymer molecules. The change of crystalline texture in the fatigue process before initiation of necking is detected by the ESR method. The line-resolution parameter of the ESR spectrum, which reflects the degree of regularity of molecular arrangement, first decreases, then increases somewhat, and finally becomes almost constant during fatigue cycling. The concentration of radicals trapped in a fatigued sample is larger than that in the unfatigued one. The excess radicals disappear during heating by a process of low activation energy in the temperature region of the mechanical γ dispersion. The degree of crystallinity evaluated from x-ray diffraction and density scarcely changed during fatigue cycling. The size of the mosaic block crystals estimated from the radical trapping capacity showed a rapid decrease at the initial stage of fatigue. The x-ray paracrystalline analysis indicates a similar but not so drastic decrease. These results lead to the conclusion that the slight disordering of crystalline texture accompanying the decomposition of mosaic block crystals in the lamellae occurs at the initial stage of the fatigue process, following which crystals reform somewhat and then remain unchanged until the initiation of necking.     

Tying together the ultrastructural modifications of wood fibre induced by pulping processes with the mechanical properties of paper

The composition and ultrastructural arrangement of cell wall polymers in wood fibres have determining influence on the properties of wood derived materials. It is therefore important to improve our understanding of the relationship between fibres organisation, the modifications induced by pulping treatments, and the resulting paper sheet mechanical properties. The different treatments to which fibres are subjected during the manufacturing of pulps and papers induce morphological and micro-structural alterations due to the removal of wall constituents and of microfibrillar elements. The impact of pulping processes on fibres was investigated at the ultrastructural scale of transmission electron microscopy. Particular attention was given to the effects of beating in refiners at various intensities on the ultrastructure of fibres. The most characteristic effects consisted of delaminations, microfibril disorganisation, and even fractures, of varying importance depending on the intensity of the mechanical refining. The consequences of internal alterations and surface modifications of the fibres were examined in relation to the paper sheet mechanical properties. Correlations between the type of alteration observed in the fibres and its possible impact on a given paper mechanical property are suggested. With similar approaches, the effects of drying and recycling were studied.     

Evaluation of new organosolv dissolving pulps. Part I: Preparation, analytical characterization and viscose processability

New acidic organosolv pulping processes, such as Acetosolv, Formacell and Milox, promise to have superior potential in terms of purification selectivity and specific investment costs. Consequently, a thorough investigation of these new acidic pulping processes in comparison to state-of-the-art acidic magnesium sulfite technology was conducted. The impact of pulping and bleaching parameters on the physical and chemical characteristics was studied to compare process efficiency and selectivity for each type of pulp made from Eucalypt wood. In addition to a detailed analysis of the chemical composition and physical properties on a molecular and supramolecular level, the TCF-bleached dissolving pulps were tested for their applicability in viscose fiber production. The influence of pulp properties as determined by standard and advanced analytical methods on process performance and selected fiber properties is emphasized.     

Microstructural cumulative material degradation and fatigue-failure micromechanisms in wood-pulp fibres

This paper establishes the fundamental micro-mechanisms associated with the conversion of single wood pulp fibres into fibres suitable for the production of paper. It deals with an examination of the morphological and structural changes taking place in pulp fibres being subjected to cyclic mechanical actions that are representative of those experienced by fibres in mechanical refiners. Implementing the experimental procedure previously described (Hamad, 1994), qualitative answers are provided to such questions as what material property changes are associated with the various identifiable micro-mechanisms and how is the extent of damage accumulation related to wood species, pulping type, refining energy, and the number of cycles? A collation of the underlying themes responsible for material degradation indicates that a recognition of the regions of high-localized deformation and the manner in which cracks grow as well as the general weakening of the material due to structural damage and mechanical degradation of the fibre cell wall material, provide an insight into the way in which single fibres are rendered suitable for papermaking by mechanical refining.     

Effect of Cyclic Deformation on Magnetorheological Elastomers

Fatigue properties of magnetorheological elastomer (MRE) samples were investigated based on cis-polybutadiene rubber by using a fatigue test machine. Three MRE samples with iron particles mass fraction of 60%, 70%, and 80% were fabricated, and their properties dependence of three strain amplitudes (50%, 75%, and 100%) were measured. The absolute magnetorheological (MR) effect, storage modulus, and loss modulus of MRE samples after fatigue were evaluated by a modified dynamic mechanical analyzer. The results revealed that MR effect, storage modulus, and loss modulus of MREs containing 80% iron particles depended strongly on the strain amplitudes and the number of cycles, while storage mod-ulus and loss modulus of MREs containing 70% iron particles also depended on the strain amplitudes and the number of cycles but not as strongly as sample which contains 80% iron particles, but the properties of MREs containing 60% iron particles after cyclic deforma-tion were almost independent of the fatigued conditions. In order to investigate the fatigue mechanism of MREs, the sample was carried out with a quasi-static tensile testing and its surface morphology during testing was observed in situ by scanning electron microscopy.     

Morphological study of fatigue-induced damage in isotactic polypropylene

This article reports initial results of an investigation whose aim is to characterize fatigue damage induced in semicrystalline polymers subjected to uniaxial high cycle fatigue. Herein we report results obtained from fatiguing tensile bars of high molecular weight compression-molded alpha-phase iPP. Samples were fatigued for up to one million cycles at a frequency of 2 Hz. During fatigue, in situ measurements of dynamic mechanical response and energy densities were recorded. Postmortem morphological studies were also conducted using SEM of etched surfaces and TOM. The results show that damage formation occurs in a regularly spaced array of crazes. This damage, its evolution, and energetics are discussed as they relate to the overall fatigue life of the material. A methodology to isolate the energy consumption for the formation of a single craze is given. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2751–2760, 1998     

Defibration mechanisms of autohydrolyzed Eucalyptus wood chips

The objective of this study was to evaluate the influence of autohydrolysis on mechanical defibration of Eucalyptus wood chips. The autohydrolysis process changed notably the mechanical properties of Eucalyptus chips. The removal of mainly hemicelluloses undoubtedly decreased the overall pulp yield. Hemicellulose losses cannot be solely accounted for the changes in the wood and pulp properties, because the autohydrolysis also caused changes in lignin. When comparing the mechanical pulp fibers of the original wood chips with the fibers resulting from the autohydrolyzed wood material, it was clear that the rupture point shifted from the secondary wall to the middle lamella, confirmed by X-ray photoelectron spectroscopy measurements. This study revealed the mechanical behavior of autohydrolyzed wood chips and can provide useful information for integration of mechanical pulp mills into the biorefinery concept in the future.     

Switchable ionic liquids enable efficient nanofibrillation of wood pulp

Use of switchable ionic liquid (SIL) pulp offers an efficient and greener technology to produce nanofibers via ultrafine grinding. In this study, we demonstrate that SIL pulp opens up a mechanically efficient route to the nanofibrillation of wood pulp, thus providing both a low cost and chemically benign route to the production of cellulose nanofibers. The degree of fibrillation during the process was evaluated by viscosity and optical microscopy of SIL treated, bleached SIL treated and a reference pulp. Furthermore, films were prepared from the fibrillated material for characterization and tensile testing. It was observed that substantially improved mechanical properties were attained as a result of the grinding process, thus signifying nanofibrillation. Both SIL treated and bleached SIL treated pulps were fibrillated into nanofibers with fiber diameters below 15 nm thus forming networks of hydrophilic nature with an intact crystalline structure. Notably, it was found that the SIL pulp could be fibrillated more efficiently than traditional pulp since nanofibers could be produced with more than 30% less energy when compared to the reference pulp. Additionally, bleaching reduced the energy demand by further 16%. The study demonstrated that this switchable ionic liquid treatment has considerable potential in the commercial production of nanofibers due to the increased efficiency in fibrillation.     

Pulp depitching in the bisulfite pulping step

OS-20 nonionic surfactant produced in Russia was used as a depitching additive in bisulfite pulping. OS-20 ensures efficient depitching of bisulfite pulp produced from various kinds of wood (spruce, aspen, birch wood or their blends). The strongest decrease in the total and “harmful” pitch content in pulping in the presence of the surfactant was reached for spruce and aspen wood and for the blend of spruce and birch wood.     

On the prevalence of side reactions during ionosolv pulping of Norway spruce with 1-butyl-3-methylimidazolium acesulfamate

We report on the low efficiency of 1-butyl-3-methylimidazolium acesulfamate ([BMIM]Ace) at delignifying Norway spruce. A systematic kinetic and structural study of [BMIM]Ace pulping of spruce wood at 120 °C allowed shedding light on the structure of the reaction products and the nature of the reaction. In particular, wood residues and extracts were thoroughly characterized with a wide range of analytical techniques including ¹H NMR, ¹³C NMR, ³¹P NMR, XRD, TGA, MS, FT-IR, conductivity, and elemental analysis. This extensive structural study evidenced prominent degradation of the acesulfamate anion into sulfate salts in lieu of the expected delignification. This unexpected behavior in view of previous reports of [BMIM]Ace pulping potency of wood is explained by extensive derivatization of minute lignin extracts with the sulfate salts, which can lead to an overestimation of delignification yields.     

The pyrolysis process of wood biomass samples under isothermal experimental conditions—energy density considerations: application of the distributed apparent activation energy model with a mixture of distribution functions

This work deals with the isothermal pyrolysis of Pine and Beech wood samples and kinetic studies, using the thermo-analytical technique, at five different operating temperatures. Pyrolysis processes were investigated by using the distributed apparent activation energy model, which involves the complex mixture of different continuous distribution functions. It was found that decomposition processes of wood pseudo-components take place in different conversion areas during entire pyrolyses, whereby these areas, as well as the changes in apparent activation energy (E _a) values, are not the same for softwood and hardwood samples. Bulk density (Bden) and energy density (ED) considerations have shown that both biomass samples suffer from low Bden and ED values. It was concluded that pyrolysis can be used as a means of decreasing transportation costs of wood biomass materials, thus increasing energy density. The “pseudo” kinetic compensation effect was identified, which arises from kinetic model variation and wood species variation. In the current extensive study, it was concluded that primary pyrolysis refers to decomposition reactions of any of three major constituents of the considered wood samples. Also, it was established that primary reactions may proceed in parallel with simultaneous decomposition of lignin, hemicelluloses and cellulose in the different regions of wood samples, depending on the operating temperature. It was established that endothermic effects dominate, which are characterized with devolatilization and formation of volatile products. It has been suggested that the endothermic behavior that arises from pyrolyses of considered samples may indicate the endothermic depolymerization sequence of cellulose structures.     

Grinding process for the production of nanofibrillated cellulose based on unbleached and bleached bamboo organosolv pulp

Nanofibrillated cellulose (NFC) is a type of nanomaterial based on renewable resources and produced by mechanical disintegration without chemicals. NFC is a potential reinforcing material with a high surface area and high aspect ratio, both of which increase reinforcement on the nanoscale. The raw materials used were unbleached and bleached bamboo organosolv pulp. Organosolv pulping is a cleaner process than other industrial methods (i.e. Kraft process), as it uses organic solvents during cooking and provides easy solvent recovery at the end of the process. The NFC was produced by treating unbleached and bleached bamboo organosolv pulps for 5, 10, 15 and 20 nanofibrillation cycles using the grinding method. Chemical, physical and mechanical tests were performed to determine the optimal condition for nanofibrillation. The delamination of the S2 layer of the fibers during nanofibrillation contributed to the partial removal of amorphous components (mainly lignin), which have low polarity and improved the adhesion of the fibers, particularly the unbleached cellulose. The transverse modulus of elasticity of the unbleached NFC was highest after 10 nanofibrillation cycles. Further treatment cycles decreased the modulus due to the mechanical degradation of the fibers. The unbleached NFC produced by 10 cycles have a greater transverse modulus of elasticity, the crystallite size showed increase with the nanofibrillation, and after 5 nanofibrillation cycles, no differences are observed in the morphology of the fibers.     

Effect of mechanical grinding on the reaction pathway and kinetics of the thermal decomposition of hydromagnesite

Effect of mechanical grinding of hydromagnesite on the reaction pathway and kinetic behaviors of the thermal decomposition process was investigated by means of thermoanalytical techniques, together with crystallographic and morphological measurements. A crystalline hydromagnesite, the as-received sample, was decomposed in two distinguished mass loss steps of overlapped dehydration-dehydroxylation and dehydroxylation-decarbonation via an amorphous intermediate of carbonate compound. Thermal decomposition of an amorphous hydromagnesite, obtained by mechanical grinding of the as-received sample, was characterized by three well-separated decomposition processes of dehydration, dehydroxylation and decarbonation. The kinetic behaviors of the respective decomposition steps were estimated separately using a mathematical deconvolution of the partially overlapped reaction steps. From the formal kinetic analyses of the respective reaction processes, it was revealed that the dehydration and dehydroxylation processes indicate the decelerate rate behaviors controlled by diffusion, while the rate behavior of nucleation limited type is predominant for the decarbonation process.     

以制浆造纸产业为平台的生物炼制新模式

本文通过分析木质生物质炼制与制浆造纸工业之间的关系,提出以制浆造纸产业为平台的生物炼制模式。在蒸煮制浆前,增加对原料预抽提处理,提取半纤维素等成分用于生产乙醇燃料和（或）其他化工化学品,抽提残渣则采用传统化学法、高得率法或有机溶剂法制浆,实现植物纤维原料多组分分离综合利用。该模式给制浆造纸产业提供一条可持续发展的新思路。     

EPDM/PP热塑性弹性体在循环应力下的老化行为研究

本文研究了动态硫化EPDM/PP热塑性弹性体的动态疲劳老化行为,考察了其力学性能的变化,并分析了产生力学性能下降的原因。实验结果表明,随着疲劳时间的延长、疲劳振幅的增大,材料的断裂强度降低,并认为疲劳过程中完全硫化的EPDM橡胶粒子和热塑性塑料PP界面处的分子链断裂、滑移导致了断裂强度的降低;紫外光的加入,加速了材料在疲劳过程的分子链断裂、滑移速率,使材料的断裂强度有更大程度的降低;在机械疲劳老化单独作用下,材料体系几乎没有发生氧化反应,而紫外光的加入,促使了机械疲劳老化过程中氧化反应的发生。     

Co-firing of biomass with coals

The combustion of coal and coal/fir (Abies bornmulleriana) wood blends at the proper ratio (20, 40, 50 wt%) was investigated with thermogravimetric analysis (TG). The influence of biomass blends on thermal and kinetic behavior of coal was studied under non-isothermal conditions. The activation energy of the samples was evaluated with the Ozawa–Flynn–Wall model which compares the combustion of these biowastes with coal under non-isothermal conditions. Our research found that blending influences activation energy of coal; moreover, activation energy related to 50 wt% blend was more similar to pure wood combustion than to coal combustion. Therefore, the activation energy profile shifted from 80.6 to 169.3 kJ/mol. The average reaction order of the samples ranged from 0.13 to 0.35.     

Microsphere valorization of forestry derived hydrolysates

A value-adding approach to the material utilization of non-cellulosic polysaccharides (NCPs) released from the lignocellulosic feedstock was realized via the formulation of renewable microspheres from wood hydrolysates using a purposely elaborated all edible water-in-oil emulsion technique. Four compositionally different hemicellulose rich wood hydrolysates were recovered from process waters in pulping and other hydrothermal treatments of hardwood and softwood. Multivariate screening designs were employed allowing for the identification and quantitation of significant process parameters and interaction effects governing the conversion of hydrolysates into small, smooth and well-defined microspheres with narrow size dispersity.     

Some electrical properties of wood pulp

The variation with temperature and frequency of the dielectric constant ε′ and the dielectric loss ε″ for sheet wood pulp and ground wood pulp were measured. Also, the effect of the relative humidity on the dielectric behavior was measured for the ground sample at 25°C. For the dry ground wood pulp, the dielectric constant is larger than that for the dry sheet sample. This may be a result of the increase in the surface area, of the decrease in the size of crystals and/or of the decrease in the degree of crystallinity on grinding of the sheet sample. The variation of ε″ with frequency passes through a maximum. From the shift of this maximum with temperature, it is found that the apparent activation energy ΔH for this relaxation is equal to 7.06 kcal/mole and it is attributed to the polarization of the OH groups in the cellulose molecule. From the relation between the dielectric constant and the specific resistivity R_s, the dissociation energy U₀ for the ground wood pulp was calculated. U₀ for this sample below and above 52% RH is 0.315 and 5.13 × 10^?12 erg, respectively. Also, the dissociation energy of Egyptian Ashmouny cotton was calculated. The variation of the electrical conductivity σ with humidity for different types of cellulosic materials is represented graphically.     

Effect of anthraquinone on brightness value and crystalline structure of pulp during soda processes

The dependence of crystalline structure and optical properties of pulp on anthraquinone (AQ) added to the soda process at different cooking times was determined in this study. Wheat (Triticum aestevum L.) straw was used as the raw material for pulp. Soda and soda-AQ processes were selected for pulping at 80 min and 120 min. The soda-AQ process improved the yield and viscosity of pulp delignification ratio for pulping in comparison with the soda process. Crystallinity of pulp samples decreased by adding anthraquinone to the soda process because of stabilized less ordered cellulose and amorphous hemicelluloses in pulp. It was determined that crystallinity of pulp samples decreased with longer cooking time, from 80 min to 120 min, in both soda and soda-AQ processes. Monoclinic structure was dominant in pulp samples; however, the triclinic structure ratio increased in both soda and soda-AQ processes compared to raw material. It was found that brightness and lightness values in pulp samples decreased when using anthraquinone depending on the changes of the crystalline structure.