Paper Physics

Intact fibers were deformed by homogenization after beating. The homogenization increased the amounts of deformations (kinks and curl) in the fibers. The fibers retained their highly swollen nature during the deformation. The influence of the fiber deformations on the strength properties of the softwood kraft pulp fiber network was significant. The fiber deformations decreased fiber segment activation in the fiber network compared to undeformed fibers. The decreased fiber segment activation resulted in decreased tensile and tensile stiffness indices but in increased tear and fracture toughness indices of the pulp sheets. The results also indicated that the zero-span fiber strength measurement was not dependent on fiber curl and kinks, but is likely dependent on the load distribution uniformity of the 3-dimensional fiber wall structure. TIIVISTELMÄ Ehjiä kuituja jauhettiin, jonka jälkeen kuituja deformoitiin homogenisoimalla. Homogenisointi kasvatti kuitujen kiharuutta ja kinkkien lukumäärää kuiduissa. Kuitujen korkea turvonneisuus säily deformoitumisesta huolimatta. Kuitujen deformoitumisen vaikutus havupuusulfaattiselluloosakuituverkoston ominaisuuksiin oli huomattava. Kuitudeformaatiot alensivat kuitusegmenttien aktivoitumista kuituverkostossa verrattuna deformoimattomiin kuituihin. Alhainen kuitusegmenttien aktivoituminen kuituverkostossa johti alhaiseen veto-ja vetojäykkyys ominaisuuksiin, mutta samalla korkeisiin repäisylujuus-ja murtositkeysominaisuuksiin. Tulokset indikoivat myöskin, että zero-span kuidun lujuus mittaus ei ole riippuvainen kuitujen kiharuudesta tai kinkkien lukumäärästä vaan todennäköisimmin kuituseinämän 3-dimensionaalisesta kuorman jakautumisesta kuituseinämä rakenteessa.

The aim of this work was to gain a better understanding of the changes occurring in softwood strength properties and fiber wall structure after mechanical treatment was applied to the chip/fiber matrix during kraft cooking. Mechanical treatment of fibers during industrial and laboratory production of pulp is common. In the pulp mill the pulp is mixed, pumped and shear forces are applied to the fiber at different temperatures and under different chemical conditions. The main objective of this research was to investigate the reasons for fiber strength loss and to examine the changes that really affect fiber strength.

In this study the effects of mechanical treatment of kraft pulp fibers, at different temperatures, on pulp and pulp strength properties were investigated. The beating demand increased while the tear index and zero-span tensile strength of treated pulps decreased as the treatment temperature was increased from 100 o C to 170 o C. The carbohydrate compositions measured as monosaccharides after acid hydrolysis of the pulps were the same. The small differences in fiber deformation of the bleached pulps could not explain the severe strength losses at 170 o C. The fracture analysis, together with the results of a fractionation study of treated pulps, indicated that single fiber strength was lost. The results also indicated that the fiber damage resulting from mechanical treatment at high temperature under alkaline cooking conditions led not to a reduction in interfiber bonding ability.

In this study fiber cell wall porosity was altered by fiber line simulation in a laboratory. The changes in the fiber cell porosity were analyzed with a water retention value (WRV) test. Pore size distributions were measured by differential scanning calorimetry (DCS), and atomic force microscopy (AFM) was used to determine the cell wall pore area from cross sections of the S2 layer of the cell wall. WRV was shown to correlate with the amount of water in the pores with a diameter of at least 200 nm. Changes in the non-freezing and total bound water did not affect the WRV. The calculated shrinkage forces generated by the capillary forces in different pore cell wall structures correlated with the sheet densities generated by fiber networks. It was observed that the swelling of the cell wall, defined as an increase in the diameter of the cell wall, was most likely not occurring or was very difficult to detect.

Fiber deformation is generally considered to be changes in the three-dimensional form of the fiber and fiber damage is considered to be changes in the strength properties of the fiber and fiber network. Usually, fiber deformation and fiber damage occur simultaneously and together are referred to as fiber damage. In this study fiber damage occurring in pulps made from pine and spruce round wood and sawmill chip raw materials were examined in the laboratory. Damage was carried out in the laboratory by mixing the pulp at the end of the cook (170 o C) for 15 minutes. The curl index, kink index, fiber length and strength properties were measured for unbleached pulps made from these raw materials as a function of PFI beating. The damaged spruce pulps had lower wet zero-span tensile strength than the damaged pine pulps, although the strengths of the undamaged pulps were at the same level. Furthermore, this study showed that spruce fibers were more deformed than pine fibers under the same mechanical treatment conditions. The results also showed that the tensile index of unbeaten fibers was a good indication of fiber deformation. The curl of the deformed fibers decreased during PFI-beating whereas the curl of the undeformed fibers increased. TIIVISTELMÄ MEKAANISEN KÄSITTELYN VAIKUTUS ERI RAAKA-AINEISTA VALMISTETTUJEN HAVUPUUSELLUKUITUJEN OMINAISUUKSIIN Kuitujen muodonmuutoksia pidetään yleensä kuitujen kolmidimensionaalisina muutoksina ja kuituvaurioita muutoksina kuitujen ja kuituverkoston lujuudessa. Kuitujen muodonmuutokset ja kuituvauriot ilmenevät usein yhdessä ja niihin viitattaessa puhutaan kuituvaurioista. Tutkimuksessa tarkasteltiin kuusipölli-ja kuusisahahakkeesta sekä mäntypölli-ja mäntysahahakkeesta

We develop a constitutive model of paper's in-plane biaxial tensile response accounting for the elastic-plastic hardening behavior, and its orthotropic character. The latter aspect is motivated by machine-made papers, which, in contrast to isotropic laboratory handsheets, are strongly oriented. We focus on modeling paper's response under monotonic loading, this restriction allowing us to treat the elastic-plastic response as a physically nonlinear elastic one. A strain energy function of a hyperbolic tangent form is developed so as to fit the entire range of biaxial and uniaxial experiments on a commercial grade paper. This function may then be introduced as the free energy function into a model based on thermomechanics with internal variables. #

An idealized ®ber network model is developed to study particle sieving by percolation. The model is based on a Poisson line ®eld in two dimensions, whereby the ®bers are modeled as in®nite length strips of ®nite width, while particles are modeled as circular disks. The probabilistic sieving problem is equivalent to percolation of disks through convex polygons of the Poisson line ®eld. The area-based probability of retention (equivalently, percolation) is described by an equation which depends on a single non-dimensional number that is proportional to the number of ®ber per unit area and the particle size. The physical meaning and the applicable range of this number are discussed. Finally, using a Monte Carlo simulation, the model is generalized to anisotropic Poisson line ®elds. Ó (M. Ostoja-Starzewski). 0307-904X/00/$ -see front matter Ó 2000 Elsevier Science Inc. All rights reserved. PII: S 0 3 0 7 -9 0 4 X ( 9 9 ) 0 0 0 5 5 -4

This study presents structural and mechanical properties of WO3 thin films deposited on glass substrates at different temperatures by radio frequency reactive magnetron sputtering. WO3 films deposited at temperatures up to 200°C are found as amorphous, but crystalline at 300 and 400°C. Chemical analysis reveals the overstoichiometry of the films. The diffusion of sodium ions from glass substrates occurs at higher temperatures. The adhesion critical loads of WO3 films deposited at room temperature and at 200, 300 and 400°C are found to be 670, 990, 1080 and 830 mN respectively using microscratch tests with a 25 μm probe. Scratch hardness increases with the rise of temperature. The depth of penetration and wear track width decrease with temperature, indicating an improved penetration and wear resistance at temperatures up to 300°C. Scanning electron microscopy images reveal that the coatings fail due to wedge and recovery spallation during scratch and wear tests respectively.

http://www.ingentaconnect.com/content/maney/se/2012/00000028/00000010/art00011

Structural and chemical investigations on electrodeposited nickel-phosphorous alloy coatings by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) are described. Electrodeposition of nickel-phosphorous coatings has been carried out galvanostatically in a hypophosphite bath at two different current densities, namely 20 and 80 mA cm -2. XRD has shown a broad peak indicating an amorphous structure in both cases. XPS shows the presence of Ni 2P compound. XPS also reveals the amount of phosphorous in both coatings to be around 10.20 wt.%. SIMS has shown that the coating deposited at lower current density (20 mA cm -2) has a broad coating-substrate interface, possibly due to some porosity in this coating. The presence of some oxygen contamination at the coating-substrate interface is also evidenced through SIMS in both cases. The usefulness of XPS and SIMS in the characterization of electrodeposited coatings is demonstrated.


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