Jean-Francis Bloch

Synchrotron radiation microtomography applied to investigation of paper

Some elements of the study of fibrous structure are presented in this paper. X-ray synchrotron microtomography is used to provide information about the three-dimensional structure. In this context a segmentation method is proposed to separate the different components of the porous material considered (paper).

Microstructural effects on the flow law of power-law fluids through fibrous media

In this work, the flow of power-law fluids through anisotropic fibrous media is revisited, upscaling the fluid flow at the pore scale with the homogenization method of multiple scale expansions for periodic structures. This upscaling technique permits a quantitative study of the seepage law by performing numerical simulation with simple two-dimensional periodic arrays of circular solid inclusions. The significant role of the solid fraction, the fluid rheology and the porous media anisotropy on the resulting macroscopic flow law is underlined from the simulation.

Gloss optical elementary representative surface.

Roughness measurements are of main importance in characterizing the optical properties of papers and prints. However, there is a lack of knowledge concerning the surface size and the spacing of the measures to be optically representative of the surface structure. Paper is a multiscale medium, and the roughness parameters extracted from the three-dimensional (3D) surface mapping depend on both the size and the step of discretization. Ray tracing, based on optical geometry, could be a tool to model the light reflection on a paper surface. Ray-tracer software was therefore developed. A new optical device was used to measure paper surface topographies at various scales. Ray tracing simulations were then performed on the 3D mapping and compared to the scattering indicatrix obtained with a classical goniometer. Hence it was possible to identify a magnification for various types of paper grades that is optically representative of the specular gloss.

Tool for the evaluation of cigarette paper marking quality

Papermaking process consists in a succession of unit operations that are successively the forming section, the press section and finally the drying section. Forming and pressing are on the scope of this paper as they may influence the aspect of the studied material: paper. The main objective is to characterize paper and more specifically its visual quality, mainly due to marking which consists in successive white and dark strips. A proposed method is described in order to analyze the quality of this visual aspect of paper, which is a very important factor for the consumer. This paper is therefore devoted to the presentation of an industrial tool to Digital Image Processing that allows the evaluation of cigarette paper marking quality. This problem is delicate as different technical and physical parameters have some influence on the paper appearance. For example the whiteness or the opacity of paper influences the evaluation of the quality of the marking. Furthermore, an expert of paper cigarette who observes the paper lying on a black support carries out the classical test of quality evaluation. Thus the reflection of light is mainly observed instead of the look- through aspect. Usually, this determination is made by the experienced eye of the expert who may distinguish between 5 to 6 classes of paper quality. Moreover, sensibility and subjectivity play an important role in this grading establishment. The aim of the presented tool is to obtain an object classification of the paper marking quality. Image analysis is used in order to mimic the expert experience. In a first step, the image acquisition is done using a standard scanner. Then developed software analyzes the obtained image numerically. The sensibility of the image analysis is high, and the results are repeatable. The classification of different cigarette papers using this method provided the same results as the human expert, pointing out the validity of the developed method. Some experimental results are presented in order to illustrate the industrial interest for this method. We present in a first part the new method to obtain an evaluation of the quality of a material property (paper aspect) from image analysis. Then example of measurements obtained on different paper samples, using a classical scanner, illustrate the proposed methodology. Finally, some comparison between the classifications obtained from the proposed method and the human expertise are presented to underline the interest of the proposed objective method.

Modeling of surface roughness: application to physical properties of paper

Papermaking process consists in a succession of unit operations having for main objective the expression of water out of the wet paper pad. The three main stages are successively, the forming section, the press section and finally the drying section. Furthermore, another operation (calendering) may be used to improve the surface smoothness. Forming, pressing and drying are not on the scope of this paper, but the influence of formation and calendering on surface roughness is analyzed. The main objective is to characterize the materials and specially its superficial structure. The proposed model is described in order to analyze this topographical aspect. Some experimental results are presented in order to illustrate the interest of this method to better understand physical properties. This work is therefore dedicated to the description of the proposed model: the studied surface is measured at a microscopic scale using for example, a classical stylus profilometry method. Then the obtained surface is transformed using a conformal mapping that retains the surface orientations. Due to the anisotropy of the fiber distribution in the plane of the sheet, the resulting surface is often not isotropic. Hence, the micro facets that identify the interfaces between pores and solid (fibers in the studied case) at the micro level are transformed into a macroscopic equivalent structure. Furthermore, an ellipsoid may be fit to the experimental data in order to obtain a simple model. The ellipticities are proved to be linked for paper to both fiber orientation (through other optical methods) and roughness. These parameters (ellipticities) are shown to be very significant for different end-use properties. Indeed, they shown to be correlated to printing or optical properties, such as gloss for example. We present in a first part the method to obtain a macroscopic description from physical microscopic measurements. Then measurements carried on different paper samples, using a classical profilometry methods, illustrate the proposed methodology. Some comparisons with conventional roughness indexes are presented. Finally, some applications, and more precisely end use properties, are shown to underline the interest of the proposed method. These geometrical characteristics may be deduced from experimental results whatever the microscopic size is.