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.     

Alkaline peroxide mechanical pulping of wheat straw with enzyme treatment

Alkaline peroxide mechanical pulping (APMP) of wheat straw with enzyme treatment was studied. Instead of direct enzyme pretreatment on wheat straw, an alternative treatment method was used, in which coarse pulps from refiner defibrated wheat straw rather than wheat straw were pretreated with a crude enzyme containing mainly xylanase, then impregnated with alkaline H₂O₂ solution and further refined. The optimum conditions of enzyme treatment were xylanase dosage of 10–15 IU/g of oven-dried wheat straw, 90 min, 50–60°C, pulp consistency of 5–10%, and initial pH of 5.0, and those for chemical impregnation were 6% NaOH, 70–80°C, 60–90 min, and 4 to 5% H₂O₂. Enzyme treatment improved pulpability of wheat straw by the APMP process, and final pulp quality such as brightness, breaking length, and burst index of pulp. Pulp from the APMP process with enzyme treatment could be bleached to a brightness of 70.5% ISO by two-stage H₂O₂ bleaching sequence with only 4% H₂O₂, and breaking length of the bleach pulp reached 4470 m.     

Significance of fatigue for mechanical defibration

The fatigue induced by high-frequency cyclic loading on the compressibility and tensile properties of wood and wood cell walls was quantified. The non-elastic behavior of fatigued and reference samples was similar, whereas their elastic behavior differed, as expected. Next, the effects of the dynamic fatigue on the mechanical pulping process were quantified by grinding fatigued and untreated samples and by comparing the paper strength produced by the two pulps against the consumed pulping energy. Pre-introducing fatigue increased the energy efficiency of grinding and may allow designing a more energy efficient mechanical pulping process.     

Introduction of one-carbon units during anthraquinone-catalysed pulping of wood

Anthraquinone- and tetrahydroanthraquinone-catalysed pulping of $\text{Pinus}$$\text{radiata}$ has given 10-methyl-9-anthrone (2) and derivatives (3) and (4), introduction of the carbon substituent involving carbohydrate constituents of the wood.     

Itaconic acid is a mammalian metabolite induced during macrophage activation

Itaconic acid (ITA), or methylenesuccinic acid, is not generally classified as a mammalian metabolite. Using NMR-based metabolomics and (13)C-labeling, we have detected ITA in both macrophage-like VM-M3 and RAW 264.7 tumor cell lines as well as stimulated and unstimulated primary murine macrophages. Macrophage activation by addition of lipopolysaccharide and IFN-γ markedly increased ITA production and secretion. Crude cell extracts synthesize ITA via decarboxylation of cis-aconitate, indicative of a novel mammalian cis-aconitic decarboxylase activity. Our results highlight a previously unidentified biosynthetic pathway related to TCA cycle metabolism in mammalian cells and a novel metabolite that likely plays a role in macrophage-based immune response.     

Chemical transformations of lignin during the biodegradation and organosolv pulping of deciduous wood

The lignins from the liquors in the organosolv pulping of aspen wood treated with wood-destroying fungi have been investigated using quantitative¹H and¹³C NMR spectroscopy and exclusion liquid chromatography. It has been shown that the biodegradation of lignin takes place in different ways according to the complex of enzymes produced by the fungi. Phanerochaete sanguinea causes degradation through predominant cleavage at alkyl-phenyl bonds, and Trametes villosus at the C-C bonds of the aliphatic chain. In addition to degradation reactions, polymerization (condensation) reactions also take place with the appearance of new C_ar-O-C and C_ar-C bonds. It has been established that the biological pretreatment of aspen wood ensuring partial degradation of the lignin leads to its more ready extraction in the process of organosolv pulping.Wood Chemistry Division of the Irkutsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 603–610, July–August, 1995. Original article submitted May 23, 1994.     

DsbA is a redox-switchable mechanical chaperone

DsbA is a ubiquitous bacterial oxidoreductase that associates with substrates during and after translocation, yet its involvement in protein folding and translocation remains an open question. Here we demonstrate a redox-controlled chaperone activity of DsbA, on both cysteine-containing and cysteine-free substrates, using magnetic tweezers-based single molecule force spectroscopy that enables independent measurements of oxidoreductase activity and chaperone behavior. Interestingly we found that this chaperone activity is tuned by the oxidation state of DsbA; oxidized DsbA is a strong promoter of folding, but the effect is weakened by the reduction of the catalytic CXXC motif. We further localize the chaperone binding site of DsbA using a seven-residue peptide which effectively blocks the chaperone activity. We found that the DsbA assisted folding of proteins in the periplasm generates enough mechanical work to decrease the ATP consumption needed for periplasmic translocation by up to 33%.

Protein translocation is facilitated by DsbA chaperone in a redox-dependent manner.     

Pressure induced mechanical properties of boron based pnictides

The elastic and thermodynamical properties of the III–V semiconductors as BY (Y = N, P, As) are calculated in zincblende and NaCl phases by formulating an effective interionic interaction potential. This potential consists of the long-range Coulomb, the Hafemeister and Flygare type short-range overlap repulsion extended up to the second neighbour ions and the van der Waals (vdW) interaction. The variations of elastic constants with pressure follow a systematic trend identical to that observed in other compounds of ZnS type structure family and the Born relative stability criteria is valid in boron monopnictides. From the elastic constants the Poisson's ratio ν, the ratio R_S/B of S (Voigt averaged shear modulus) over B (bulk modulus), elastic wave velocity, average wave velocity and thermodynamical property Debye temperature are calculated. By analyzing the Poisson's ratio ν and the ratio R_S/B we conclude that at low pressures the boron monopnictides are brittle in nature in ZnS phase and ductile nature at high pressures in both ZnS and NaCl phases. To our knowledge this is the first quantitative theoretical prediction of the pressure dependence of ductile (brittle) nature of BY compounds.     

Dissolution of ionisable groups and lignocellulosic components during low-temperature kraft pulping of pinus radiata

A wide range of kraft pulps from radiata pine produced by low-temperature kraft pulping in flow-through reactors was assessed for carboxyl and hexenuronic acid (HexA) contents using the conductometric titrations and UV spectrophotometer, respectively. The Kappa number of pulps varied from 20.8 to 84.7 when using a cooking liquor of 1 M effective alkali as Na₂O, 25% sulfidity, and cooking time of 100–250 min. The experimental results showed that the carboxyl groups (including HexA) and HexA groups dissolved and their residual values in the pulp samples correlate linearly with Kappa number and pulp yield. The dissolving rate of all carboxyl groups is much faster than the loss of HexA. The HexA/lignin ratio decreased non-linearly with Kappa number.     

Abnormality in using cyclic fatigue for ranking static fatigue induced slow crack growth behavior of polyethylene pipe grade resins

Slow crack growth behavior in polyethylene pipe grade resins were studied using both static fatigue (stress-rupture) and cyclic fatigue tests. This was done to better understand the applicability of cyclic fatigue in the prediction of slow crack growth ranking determined from the static fatigue test. In all polyethylene pipe grade resins tested at 80 °C, reduced crack growth failure times were exhibited when the cyclic fatigue test was employed. However, when applied to rank the resins through their slow crack failure times, the cyclic fatigue results did not always confirm those obtained from the static fatigue test. That is, in some cases, a resin with higher slow crack resistance ranking (longer failure times) than another resin in static fatigue exhibited lower ranking (shorter failure times) in the cyclic fatigue test. This abnormality of reversal in ranking is not a general observation but does occur. Based on the data obtained so far, when resins with smaller differences between static fatigue and cyclic fatigue slow crack growth failure times are compared with those resins having larger differences, the chances of correctly predicting the ranking obtained from static fatigue using cyclic fatigue tend to decrease. Hence, it is suggested that one needs to practice caution when using cyclic fatigue to predict the static fatigue ranking of resins for slow cracking resistance. Some insight into the cause of such abnormality is discussed with reference to creep-fatigue interactions.     

Cellulose nanosheets induced by mechanical impacts under hydrophobic environment

The nanoscale structural changes of crystalline cellulose by mechanical milling was studied by high-resolution microscopy (AFM, SEM, TEM). We examined influence of environment [dry, water, silicone oil (PDMS)] on cellulose milling, finding their characteristic effects on microscopic morphology of the products. Dry milling of cellulose gave aggregated globular particles with fast decrystallization. Milling with water or PDMS caused partial dispersion of nanofibers. Milling with PDMS formed micro-platelets <1 µm thick with slight decrystallization. Remarkably, nanoscale particles isolated from PDMS-milled cellulose by sonication in ethanol contained cellulose nanosheets, typically 0.1–10 µm wide and 4.2 nm thick, apparently formed by monolayer association of elementary fibrils. TEM and electron diffraction revealed crystalline nature of nanosheets, with specific orientation of (110) plane or (200) plane perpendicular to the sheet plane. A possible mechanism of the nanosheets formation is proposed, in which the elementary fibrils are aligned parallel by mechanical impacts.     

Studies of craze fibril deformation during fatigue in polystyrene

Small-angle scattering of synchrotron x-ray radiation has been used to study the effects of fatigue on craze fibril microstructure. The results obtained during unloading and reloading during a single cycle have been compared with those predicted by a model of sinusoidally bent fibrils. In addition the total displacement of the craze boundaries was found from the change in the invariant on unloading. The mean fibril diameter D was measured at the maximum tensile strain in each cycle. Over 250 cycles, D increased by at least a factor of 2 from an initial value of 6.5 nm, with most of this change happening in the first few cycles. The increase in D must occur by fibril coalescence, a mechanism that requires that the material in craze fibrils have considerable molecular mobility, even at room temperature, 70°C below the glass transition temperature.     

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.     

Fourier-transform infrared studies of polypropylene during mechanical deformation

Quantitative Fourier-transform infrared (FTIR) measurements of frequency shifts Δν and absorbance profile asymmetry are reported for various polypropylene samples as a function of uniaxial stress σ. Generally, it was found that the frequency shift coefficient α_χ, defined by Δν = α_χσ, depended on stress rate \documentclass{article}\pagestyle{empty}\begin{document}$\dot \sigma$\end{document}, draw ratio, λ, molecular orientation f, tensile modulus E, and annealing conditions. With annealing, α_χ decreased with increasing shrinkage in the case of highly oriented isotactic PP. The α_χ values for the “helix bands” were less affected than those for the “liquid bands.” With increasing \documentclass{article}\pagestyle{empty}\begin{document}$\dot \sigma$\end{document}, generally α_χ increased to an apparent asymptotic limit. With increasing λ, f, or E, α_χ also increased from α_χ ? 0 for λ = 1 (spherulitic) to maximum values for highly oriented isotactic PP. The observed variations in α_χ can be interpreted in terms of the changes in the peak position and shape of the nonuniform molecular stress distribution. Analogous behavior with x-ray diffraction peaks obtained for polymers under stress is discussed.     

Dynamic transition in tRNA is solvent induced

Dynamics of tRNA was studied using neutron scattering spectroscopy. Despite vast differences in the architecture and backbone structure of proteins and RNA, hydrated tRNA undergoes the dynamic transition at the same temperature as hydrated lysozyme. The similarity of the dynamic transition in RNA and proteins supports the idea that it is solvent induced. Because tRNA essentially has no methyl groups, the results also suggest that methyl groups are not the main contributor of the dynamic transition in biological macromolecules. However, they may explain strong differences in the dynamics of tRNA and lysozyme observed at low temperatures.     

Annealing induced microstructure and mechanical property changes of impact resistant polypropylene copolymer

The effects of annealing on microstructure and mechanical properties of an impact resistant polypropylene copolymer(IPC) were investigated. Different annealing temperatures ranging from 80 °C to 160 °C were selected. The phase reorganization of IPC during annealing process was studied through morphological characterization technologies, including scanning electron microscopy(SEM) and transmission electron microscopy(TEM). The crystalline structure changes in the IPC sample, including the i PP matrix and PE component, were investigated using wide angle X-ray diffraction(WAXD) and differential scanning calorimetry(DSC). Dynamic mechanical analysis(DMA) was used to analyze the relaxation extent of IPC before and after annealing. The results showed that annealing induced phase reorganization in IPC and the degree of phase reorganization depended on annealing temperature. The annealed IPC samples exhibited largely increased crystallinity compared with the unannealed one. Intensified damping peak with increased molecular chain mobility was achieved for the annealed IPC samples. At an appropriate annealing temperature(140 °C), largely enhanced impact strength was achieved for the annealed IPC sample. The toughening mechanisms were analyzed based on the phase reorganization and relaxation behavior.