Paper fiber orientation

Han, Y. H., T. Enomae, A. Isogai, H. Yamamoto, S. Hasegawa, J. J. Song, and S. W. Jang (2006), Traditional papermaking techniques revealed by fiber orientation in historical papers, Stud. Conservation 51, 267-276. 

Place the gel holder in the transfer cell with the sandwich oriented as follows ANODE/fiber pad, filter paper, nitrocellulose, gel, filter paper, fiber pad/CATHODE. 

Numerous studies have been made of the mechanical properties of fibrous composites these include recently published papers on impact properties by Izod (1,2, 3,4) and Charpy (5,6) and drop weight (7) tests. We reported the Charpy impact fracture behavior of various glass-polyester composites regarding the effects of temperature (8,9,10), specimen size (8), and fiber orientation (10). This paper describes the effects of the tough-brittle transition in the impact behavior of glass-polyester composites which occurs with a variation of temperature and specimen size. 

As mentioned earlier, suspensions of particulate rods or fibers are almost always non-Brownian. Such fiber suspensions are important precursors to composite materials that use fiber inclusions as mechanical reinforcement agents or as modifiers of thermal, electrical, or dielectrical properties. A common example is that of glass-fiber-reinforced composites, in which the matrix is a thermoplastic or a thermosetting polymer (Darlington et al. 1977). Fiber suspensions are also important in the pulp and paper industry. These materials are often molded, cast, or coated in the liquid suspension state, and the flow properties of the suspension are therefore relevant to the final composite properties. Especially important is the distribution of fiber orientations, which controls transport properties in the composite. There have been many experimental and theoretical studies of the flow properties of fibrous suspensions, which have been reviewed by Ganani and Powell (1985) and by Zimsak et al. (1994). 

This paper describes some recently completed work on the electrical conductivity of paper. A reliable method of measuring bulk conductivity of paper, where the contact resistance is reduced to negligible values, has been developed. A study of the effect of some papermaking variables, such as the type of pulp, the degree of refining and the fiber orientation, on the bulk conductivity of paper is reported. Finally, an investigation has been made into the current transient phenomena exhibited by paper upon the application of an electric field. These transient currents were interpreted as the transport of ionic species within a water associated fibrous network making up the paper. 

Centrifugal Former. The use of a centrifugal former allows for the preparation of a sheet of paper that posseses a fiber orientation similar to the orientation present in commercial papers. With this apparatus, the fiber suspension is sprayed onto a fast rotating screen. The dynamic motion of the screen mimics the moving wire of the Fourdrinier machine and induces fiber orientation. In addition, by independently varying the flow of the fiber suspension and the speed of rotation of the screen, different degrees of fiber orientation can be obtained. 

The orientation of cellulosic fibers has some effect on the conductivity of the paper. The conductivity in the XY plane of the sheet (surface conductivity parallel to most of the fibers) may be quite different from the conductivity along the Z direction (bulk conductivity perpendicular to the fibers). Comparison of surface and bulk conductivity for a given paper sheet can thus yield information which reflects the anisostropy in the structural morphology due to fiber orientation. Bulk conductivity measurements are also important since many paper sheets used in reprographic processes are composed of a conductive base sheet coated with a dielectric material 16. One important specification for these types of papers is the value of the bulk conductivity of the base paper. 

A paper based on carbon fiber can be made using a conventional paper making plant, where chopped fiber is dispersed in a liquid carrier (normally water) containing wetting and binding agents. The dispersed fiber is removed from the slurry by vacuum deposition onto a perforated screen, washed and the carbon paper removed from the screen and dried. If a water flume is used to spread the fibers, then it is possible to give a product with more than 80% fiber orientation. Paper is used for specialist applications like loudspeaker cones. 

The stochastic reconstmction method, presented by Schulz et a/. for generating the non-woven carbon paper GDL in the PEFC is briefly described here. The reconstruction techruque creates 3D realization of carbon paper GDL based on structural inputs, namely fiber diameter, fiber orientation and porosity, which can be obtained from the fabrication specifications or from the sample SEM (scarming... 

Zamel et al. presented a study on the estimation of effective thermal conductivity of carbon paper GDL stmctures based on the aforementioned DNS formalism (Eq. 9.12). The 3D carbon paper GDL microstractures were reconstracted using the stochastic method by Schulz et al. They investigated the influence of fiber orientation, anisotropy, compression and binder fraction. Figure 9.27 shows the representative effective thermal conductivity prediction along with experimental data available in the literatirre." " ... 

Today paper making is a continuous highly sophisticated process with high demands on precision and reliability of all components. For instance the sbce opening of headboxes should have an accuracy of about 1/100 mm (or 10 pm) over a width of 10 m in order to obtain the required CD basis weight uniformity and uniform main fiber orientation in CD. Predsion in calender roll grinding should be about 3 pm, which is equivalent to 5 % deviation when comparing it for instance with a paper thickness of 60 pm. 

A major advantage of the dilution principle is that CD profiles of main fiber orientation can be rectified (Fig. 5.36 ). As mentioned before local slice bar adjustment causes cross flow in the nozzle chamber and in the exiting jet. Even a small angle of the jet velocity vector against the machine direction results in a large main fiber orientation angle. The main fiber orientation angle describes the direction of the plurality of the fibers in the paper and can be measured by laser or by ultrasonic devices. It has an impact on other important paper properties. 

The uneven jet velocity also has negative side effects on other paper properties Hfce the fiber orientation profile. 

In a follow up paper, Mlekusch [92] makes quantitative measurements by image analysis to determine the fiber orientations. In an edited book on the microstructural characterization of fiber reinforced composites [93], polishing was used to determine yam shape and for quantitative image analysis of the composite microstructure using methods found in the earlier editions of this text and by Hemsley [94]. 

Actual fabrication begins with the toy-Mp—laying of the prepreg tape onto a tooled surface. Normally a munber of plies are laid up (after removal from the carrier backing paper) to provide the desired thickness. The lay-up arrangement may be imidirectional, but more often the fiber orientation is alternated to produce a cross-ply or angle-ply laminate (Section 16.14). Final ciuing is accomphshed by the simultaneous apphcation of heat and pressme. 

The need for high deformation speeds leads to the use of shorter tensile specimens than usual. The specimen used for the results presented in this paper is presented on the right side of fig. 3. For short-fiber reinforced materials the tensile specimens are not directly injection-molded. Instead they are milled out of plates that are filled by a film gate with an almost parallel melt front. So stiffness and strength data along and transverse to the predominant fiber orientation can be measured. 

In this paper we present a constitutive relation for predicting the rheology of short glass fibers suspended in a polymeric matrix. The performance of the model is assessed through its ability to predict the steady-state and transient shear rheology as well as qualitatively predict the fiber orientation distribution of a short glass fiber (0.5 mm, L/D < 30) filled polypropylene. In this approach the total extra stress is equal to the sum of the contributions from the fibers (a special form of the Doi theory), the polymer and the rod-polymer interaction (multi-mode viscoelastic constitutive relation). 

Because the fibers generally are anisotropic, they tend to be deposited on the wire in layers under shear. There is Htde tendency for fibers to be oriented in an out-of-plane direction, except for small undulations where one fiber crosses or passes beneath another. The layered stmcture results in the different properties measured in the thickness direction as compared to those measured in the in-plane direction. The orthotropic behavior of paper is observed in most paper properties and especially in the electrical and mechanical properties. 

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