Porosity Profiles Research Articles

전기비저항을 활용한 지층의 간극률 산정

전기비저항 탐사는 광범위한 영역을 신뢰성 높고 경제적으로 평가 할 수 있는 장점이 있어 다양한 지층에 폭넓게 사용되고 있다. 본 논문의 목적은 수변지역에서 측정한 전기비저항 값을 통해 심도에 따른 설계상값인 간극률을 도출하고자 하였다. 전기비저항탐사는 낙동강 주변의 충적층에서 수행되었으며, 탐사측선은 135 m로 두 곳의 지역에서 활용하였다. 측정한 전기비저항을 간극률로 전환하기 위하여 Archie's law를 이용하였으며, Archie's law의 관련된 상수는 현장에서 채취한 시료를 이용하여 도출하는 것이다. 상수값을 활용하여 심도에 따른 간극률 주상도를 도시하였으며 근접위치에서 수행한 표준관입시험의 N값과 비교하여 신뢰성을 평가하였다. 비교결과 N값이 증가할수록 간극률 값이 작아지는 합리적인 관계가 나타났으며, 본 연구에서 활용한 기법을 통하여 물리탐사 기법의 다양한 활용성을 기대한다. The electrical resistivity survey has advantages of obtaining high reliable values in wide area through economical method. The objective of this study is estimation of porosity profile by using electrical resistivity. The electrical resistivity survey is performed in alluvium and the two electrode arrays are applied with 135 m profiles. The Archie's law is used to obtain the porosity through the electrical resistivity and the factors in Archie's law is estimated by using the consolidation test. The predicted porosity in a depth is compared with N-value measured by Standard Penetration Test and the trend shows reasonable. The study demonstrates that the geophysical method may be widely applied to obtain the design parameters.

Silk as a biocohesive sacrificial binder in the fabrication of hydroxyapatite load bearing scaffolds

Limitations of current clinical methods for bone repair continue to fuel the demand for a high strength, bioactive bone replacement material. Recent attempts to produce porous scaffolds for bone regeneration have been limited by the intrinsic weakness associated with high porosity materials. In this study, ceramic scaffold fabrication techniques for potential use in load-bearing bone repairs have been developed using naturally derived silk from Bombyx mori. Silk was first employed for ceramic grain consolidation during green body formation, and later as a sacrificial polymer to impart porosity during sintering. These techniques allowed preparation of hydroxyapatite (HA) scaffolds that exhibited a wide range of mechanical and porosity profiles, with some displaying unusually high compressive strength up to 152.4 ± 9.1 MPa. Results showed that the scaffolds exhibited a wide range of compressive strengths and moduli (8.7 ± 2.7 MPa to 152.4 ± 9.1 MPa and 0.3 ± 0.1 GPa to 8.6 ± 0.3 GPa) with total porosities of up to 62.9 ± 2.7% depending on the parameters used for fabrication. Moreover, HA-silk scaffolds could be molded into large, complex shapes, and further machined post-sinter to generate specific three-dimensional geometries. Scaffolds supported bone marrow-derived mesenchymal stem cell attachment and proliferation, with no signs of cytotoxicity. Therefore, silk-fabricated HA scaffolds show promise for load bearing bone repair and regeneration needs.

Structural changes in spruce wood during different steps of steam explosion pretreatment

Abstract Steam explosion (SE) is a promising hydrothermal pretreatment technology for future biorefineries. In this study, the three steps of the steam explosion process, (1) the steam treatment (2) the explosion, and (3) the impact step were separately considered and their effects on structural changes of wood were studied. The SE experiments were performed on single wood pieces in different experimental set-ups at 7 and 14 bar pressure with 5 and 10 min treatment times. Mercury porosimetry and environmental scanning electron microscopy analyses were conducted to characterise both internal and external changes in the wood. It was found that the explosion step is not responsible for the disintegration of the wood material into small pieces; instead, the disintegration occurs due to impact of softened wood chips. However, the porosity profiles of the tracheids change during the explosion step. Altogether, all three steps of the SE process contribute in a synergistic way to an increase in pore size and total intrusion volume.

Fabrication of vertical light emitting diode based on thermal deformation of nanoporous GaN and removable mechanical supporter.

A GaN vertical light emitting diode (LED) based on the novel lift-off method was demonstrated by high temperature regrowth over nanoporous (NP) GaN template formed by electrochemical (EC) etching. A two-step EC etching process was employed on a SiO2 patterned GaN surface to fabricate a nanoporous template with a controlled porosity profile, which enabled better structural stability than a single NP GaN. During the regrowth of LED structures, the high porosity GaN layer produced large coalesced voids due to the thermal deformation of nanopores. LED layers were then separated from the sapphire substrate and transferred to a Mo substrate by the removal of the SiO2 mechanical supporters that held the LED structure to suppress cracks and damage during the process. The vertical LEDs fabricated using this technique showed improved optical power emission as well as low series resistance.

Flow uniformizing distribution panel design based on a non-uniform porosity distribution

The conditions required for a flow resistance element to uniformize a non-uniform flow in a two-dimensional channel were derived in terms of a non-uniform porosity profile. The validity of this approach was confirmed through a numerical analysis over a wide range of parameter conditions. The proposed equation for the non-uniform porosity distribution gave satisfactory results for a wide variety of velocity profiles at the channel inlet. For sufficiently thick orifices, the equation was valid over a wide range of average porosities, from 0.3 to 0.6. For thin orifices, satisfactory uniformity was obtained only for a mean effective porosity over a narrow range of 0.42–0.48. Two different methods of generating variable porosity, using a constant hole size plus variable blocking plates or using a constant blocking plate size plus variable holes, did not show any appreciable difference in results.

Physical mechanisms involved in slug transport and pipe blockage during horizontal pneumatic conveying

Moving slugs of plastic pellets were investigated in-situ during low velocity pneumatic conveying in horizontal pipelines. Slug characteristics including the profile of pressure, pressure gradient, particle velocity, porosity, radial and wall shear stresses, aspect and behaviour were combined to obtain a complete picture of moving slugs. The objective was to gain unique knowledge on the physical mechanisms involved in slug formation, transport, and decay and the occurrence of pipe blockage. Slugs in both stable and unstable states were analysed. A strong correlation between particle velocity and wall stresses was found, which suggests that the stresses responsible for the high pressure loss characterising slug flow may result mostly from the transfer of particle impulses to the pipe wall. Most slugs were found to be denser at the rear where particle velocity was the highest, thus leading to slug shortening over time. This phenomenon was successfully modelled using both Newton's 2nd law and the ideal gas law and prediction of particle velocity showed good agreement with experimental values. In contrast, other slugs were found to extend due to the particles at the front moving faster than the particles at the rear. Pipe blockage was found to result from insufficient permeation of the slug by the conveying gas, indicating that sufficient material permeability is a condition for slug flow to occur.

Identifying Limiting Mechanisms in the Li/O2 Battery through Models and Experiments

Li/O2 batteries are of contemporary interest because of their high theoretical gravimetric energy density of ~11 kWh/kg. However, several factors limit the cell’s discharge depth and rechargeability. Commonly cited factors include transport of oxygen to the cathode surface, pore clogging, and charge transport, but current literature lacks consensus on which of these are most significant. To gain insight on the relative importance of these mechanisms, we investigated the cell’s limiting behavior using a combination of theory and experiment.A nanoscale stochastic model was developed to simulate the growth of a single Li2O2 nucleation site during discharge. Growth progressed according to a kinetic Monte Carlo routine in which the probability of an incremental growth step is weighted according to the local Li+ and O2 concentrations. The predicted Li2O2 morphologies are consistent with SEM observations: Li2O2 deposits appear spherical in shape when the cell is discharged at low current density (~0.1 mA/cm2), but conform to the cathode surface when discharged at high current density (~1.0 mA/cm2). From this analysis, it is possible to determine that the change in morphology is due to the surface concentration of Li+ rather than the O2 concentration. Since Li2O2 is a bulk insulator, only the cathode surface experiences an increased Li+ concentration.Building on these observations, a continuum model was also developed to examine the limiting factors on a more macroscopic scale. This model included Li+ and O2 mass transport, electrolyte potential, Butler-Volmer kinetics, and changes in porosity and surface area from Li2O2 deposition. The time-dependent concentration and porosity profiles were computed using a finite difference method. Neither the oxygen concentration nor the cathode porosity of the model cell decreased an appreciable amount during discharge. Additionally, the model cell discharged indefinitely when the electrical resistivity of the Li2O2 layer was neglected. These results suggest that Li2O2 resistivity, rather than oxygen transport or pore clogging, is the primary limiting mechanism in the Li/O2 battery and likely plays a significant role in rechargeability and cell lifetime.Cell cycling experiments suggest that Li2O2 resistivity limits charging capabilities as well. For cells that were allowed to fully discharge to 2.35 V (an underpotential of 0.6 V), the capacity of the cell faded quickly within the first 10 cycles. However, if the discharge step was stopped prior to the drop in cell voltage, the capacity could be retained over an extended number of cycles. This finding is consistent with the growing number of reports in the field, which shows that extend cycle life of Li/O2 batteries can be achieved by enforcing strict limits on the depth of discharge. We contend that this feature is a natural consequence of the voltage drop due to ohmic resistance through the Li2O2 layer. At full discharge, the resistance becomes significant during the subsequent charge stage, preventing the Li2O2 furthest from the cathode surface from oxidizing. At partial discharge, however, the Li2O2 layer is below this critical thickness, allowing for a more complete recharge.Our observations point to direct approaches for enhancing lifetime and cycling stability of Li/O2 batteries, without the tradeoffs inherent in interrupted discharge experiments. The talk will also show that electrode and electrolyte designs that build rationally on these ideas lead to Li/O2 cell configurations that approach the potential of this battery platform. Through ex-situ and in-situ physical and electrochemical characterization, we also analyze the cathode surface and discuss how physical features of the battery cathode evolve during discharge and charge of the cell.Figure 1: Comparison of simulated Li2O2 morphologies and SEM images of discharged cathodes at current densities of 0.05 mA/cm2 (top) and 0.2 mA/cm2 (bottom).

Influences of process and formulation parameters on powder flow properties and immunogenicity of spray dried polymer particles entrapping recombinant pneumococcal surface protein A

Particle size, antigen load and its release characteristic are the three the main attributes of polymer particles based vaccine delivery systems. The present studies focus on the formulation of spray dried polylactide microparticles entrapping pneumococcal surface protein A (PspA). Influence of process variables during polymer particle formation were optimized by using half-factorial design. Feed rate and atomization pressure during spray drying were found to be the most important parameters for achieving uniform size particles. Spray drying of preformed particles from different stages of solvent evaporation method resulted in formation of particle having different porosity and protein release profile. Presence of polyvinyl alcohol in the external aqueous phase not only contributed towards regulating the size of particles but also influenced the burst release of protein from particles. Polymer particles entrapping PspA elicited robust IgG responses both in mice and in rats. Antigen load in microparticles correlated with the antibody titer indicating the maintenance of protein integrity during particle formation using spray drying. Both, process engineering and formulation parameters during spray drying influenced the particles in terms of size, load and antigen release characteristics.

Use of Steel Slag as Coarse Aggregate for the Production of Pervious Concrete

Pervious concrete is a type of concrete with significantly increased water permeability, ensuring increased rates of drainage of rainfall. The high porosity is achieved by removing a large percentage of fine aggregates from the mix. The present paper is an approach for the addition of steel slag as a substitute for coarse aggregates in pervious concrete. More specifically, three types of aggregates have been used: steel slag, construction and demolition wastes and conventional limestone aggregates. The produced pervious concretes are compared for their properties, such as water permeability, compressive strength and abrasion behaviour. Also this paper contains the study of the porosity analysis of these pervious concrete mix designs by using porosity profiles produced from X-ray CT Scanning. According to the results of this paper, it is observed that the incorporation of industry by-products or of Construction and Demolition (C&D) wastes leads to better abrasion behaviour, and to the increase, in some cases, of the compressive strength and of the water permeability.

Investigation of the effects of several porosity variation profiles on performance and pollutants emission of the porous media burners

SummaryThis paper presents results of numerical investigation on the effect of using variable porosity porous media burner on its performance and pollutant emission. A two‐dimensional axisymmetric model for premixed methane/air combustion in porous media has been developed. This code solves the continuity, Navier Stokes, solid and gas energies, and chemical species transport equations using the finite volume method. The pressure and velocity have been coupled with the SIMPLE algorithm. In this paper, the results of applying two different profiles of porosity instead of constant porosity for two zones of burner have been presented. The results showed that by applying porosity variation along the burner, the peak temperature can be decreased about 4.5%, and subsequently, the amount of exhaust pollutants such as NOx can also be decreased while increase in pressure losses along the burner is negligible. In addition, the effects of excess air ratio, volumetric heat transfer coefficient, inlet velocity, chemical kinetics, conductivity coefficient, and wall temperature on the porous media burners with variation of porosity are investigated. Copyright © 2014 John Wiley & Sons, Ltd.

Topographical and Microstructural Property Evolution of Air Plasma-Sprayed Zirconia Thermal Barrier Coatings

The effects of process parameters on thermal barrier coating (TBC) formation and microstructural properties have been studied. Further understanding of the evolution of properties such as porosity and hardness is an important aspect in the design of efficient TBCs. Plasma-sprayed yttria-stabilized zirconia was coated onto mild steel substrates. The torch was held perpendicular to the substrate to form cone-shaped deposits. Standoff distance (SOD) (80, 90, and 120 mm) and time (15, 30, and 60 s) were altered to investigate the microstructural property relationships of the coatings. Shape characteristics of the coatings were measured via a coordinate measuring machine, and surface roughness measurements were acquired using a 3D optical profiler. The deposition efficiency and coating roughness were affected by SOD and the evolving contour of the underlying surface. Hardness and porosity profiles were mapped to display the effect of process parameters. Dynamic parameters such as particle trajectory, evolving impact angle and dwell time affected changes in porosity, hardness, and density for each coating profile.

Characterization of deep saline aquifers in the Bécancour area, St. Lawrence Lowlands, Québec, Canada: implications for CO2 geological storage

The present paper provides a case study of the assessment of the potential for CO2 storage in the deep saline aquifers of the Becancour region in southern Quebec. This assessment was based on a hydrogeological and petrophysical characterization using existing and newly acquired core and well log data from hydrocarbon exploration wells. Analyses of data obtained from different sources provide a good understanding of the reservoir hydrogeology and petrophysics. Profiles of formation pressure, temperature, density, viscosity, porosity, permeability, and net pay were established for Lower Paleozoic sedimentary aquifers. Lateral hydraulic continuity is dominant at the regional scale, whereas vertical discontinuities are apparent for most physical and chemical properties. The Covey Hill sandstone appears as the most suitable saline aquifer for CO2 injection/storage. This unit is found at a depth of more than 1 km and has the following properties: fluid pressures exceed 14 MPa, temperature is above 35 °C, salinity is about 108,500 mg/l, matrix permeability is in the order of 3 × 10−16 m2 (0.3 mDarcy) with expected higher values of formation-scale permeability due to the presence of natural fractures, mean porosity is 6 %, net pay reaches 282 m, available pore volume per surface area is 17 m3/m2, rock compressibility is 2 × 10−9 Pa−1 and capillary displacement pressure of brine by CO2 is about 0.4 MPa. While the containment for CO2 storage in the Becancour saline aquifers can be ensured by appropriate reservoir characteristics, the injectivity of CO2 and the storage capacity could be limiting factors due to the overall low permeability of aquifers. This characterization offers a solid basis for the subsequent development of a numerical hydrogeological model, which will be used for CO2 injection capacity estimation, CO2 injection scenarios and risk assessment.

Periodic porous silicon thin films with interconnected channels as durable anode materials for lithium ion batteries

A novel porous Si (PSi) films with interconnected channels and periodic nanostructures are fabricated by a facile electrochemical etching method. The films thus obtained feature highly porous structures with nano-branches connecting pores, possessing periodically varying porosity profiles along the film thickness direction. These periodic porous Si films are found to be promising anode materials for rechargeable lithium ion batteries with a high reversible specific capacity over 2500 mAh g−1 and capacity retention over 83% after 60 cycles, which compares favorably with the conventional Si-based electrodes, including the commercially available Si nanoparticles, sputtered Si thin films, and the normal porous Si films with homogenous porosities. The improved cycling stability achieved on the periodic porous Si film is ascribed to its special nanoporous morphology featuring high surface area, interconnecting nano-branches, and structural periodicity, which helps efficiently accommodate the volume expansion and contraction along both the vertical and the planner directions during lithiation and delithiation.

Fabrication and characteristics of chitosan sponge as a tissue engineering scaffold.

Cells, growth factors, and scaffolds are the three main factors required to create a tissue-engineered construct. After the appearance of bovine spongiform encephalopathy (BSE), considerable attention has therefore been focused on nonbovine materials. In this study, we examined the properties of a chitosan porous scaffold. A porous chitosan sponge was prepared by the controlled freezing and lyophilization of different concentrations of chitosan solutions. The materials were examined by scanning electron microscopy, and the porosity, tensile strength, and basic fibroblast growth factor (bFGF) release profiles from chitosan sponge were examined in vitro. The morphology of the chitosan scaffolds presented a typical microporous structure, with the pore size ranging from 50 to 200 μm. The porosity of chitosan scaffolds with different concentrations was approximately 75–85%. A decreasing tendency for porosity was observed as the concentration of the chitosan increased. The relationship between the tensile properties and chitosan concentration indicated that the ultimate tensile strength for the sponge increased with a higher concentration. The in vitro bFGF release study showed that the higher the concentration of chitosan solution became, the longer the releasing time of the bFGF from the chitosan sponge was.

Methods for in-situ porosity determination of moving porous columns and application to horizontal slug flow pneumatic conveying

Two methods were developed to investigate the porosity of moving slugs in situ during horizontal slug flow pneumatic conveying. The first method consists in applying a permeability model in combination with measurements of pressure loss and fluid velocity along the slugs. A review of existing models describing the resistance of porous structures to fluid flow revealed that the semi-empirical model of Ergun is particularly suitable to investigate the porosity profile along moving slugs. The second method consists in a direct determination method involving a slug-catcher able to catch a moving slug in a fraction of a second and simultaneously separate it into three horizontal layers. Those two methods were applied to analyse the porosity of naturally occurring slugs during pneumatic transport of polypropylene pellets. It was found that in contrast to common belief, slugs are slightly fluidised structures that do not display any porosity gradient over the pipe cross-section height. The slug porosity appeared independent of the gas conveying velocity, all slugs displaying an average porosity around 0.41, which is slightly higher than the bulk porosity of 0.38. Most of the slugs displayed a rear that is denser than the front. However, some slugs had a front that is denser than the rear while other slugs displayed a relatively constant porosity over the entire length. Those unique results refuting the commonly used hypothesis that slugs are compact structures give a new incentive to the area of slug flow pneumatic conveying. While bulk solids mechanics can no longer be applied to explain the stresses induced by moving slugs, the validity of other theories that imply that slugs are fluidised structures should be investigated.

Influence of the porosity profile and sets of Ergun constants on the main hydrodynamic parameters in the trickle-bed reactors

The Eulerian multiphase code has been applied for the comparative simulation of the experimental results obtained for varying flow rates of both fluid phases and for systems of various physicochemical properties used in the laboratory trickle-bed reactor (TBR). Therefore six different radial porosity profiles and three sets of the Ergun constants used in the relations defining the interphase momentum exchange have been implemented into the CFD code. The mean relative error of the pressure drop and of the averaged holdup as well as the standard deviation determined with respect to the experiments have been used as the criterion for the validation of the theoretical model. These values explicitly confirmed the necessity of applying the radial porosity profile in the beds of low values of the D/dp ratio i.e. for laboratory equipment in order to obtain accurate values of the pressure drop and the averaged holdup. They also enabled to select the optimum radial porosity correlation and the optimum Ergun constants in the relations of interphase momentum exchange which in consequence could be recommended for the modeling of the hydrodynamics in the laboratory TBR by means of the CFD code.

Diffusive anisotropy in low-permeability Ordovician sedimentary rocks from the Michigan Basin in southwest Ontario

Diffusive anisotropy was investigated using samples from Upper Ordovician shale and argillaceous limestone from the Michigan Basin of southwest Ontario, Canada. Effective diffusion coefficients (De) were determined for iodide (I(-)) and tritiated water (HTO) tracers on paired cm-scale subsamples oriented normal (NB) and parallel to bedding (PB) prepared from preserved drill cores within one year from the date of drilling. For samples with porosity >3%, an X-ray radiography method was used with I(-) tracer for determination of De and porosity accessible to I(-) ions. A through-diffusion method with I(-) and HTO tracers was used for most siltstone and limestone samples with low-porosity (<3%). The De values range from 7.0×10(-13) to 7.7×10(-12) m(2)·s(-1) for shale, 2.1×10(-13) to 1.3×10(-12) m(2)·s(-1) for limestone, and 5.3×10(-14) to 5.6×10(-13) m(2)·s(-1) for siltstone and limestone interbeds within the Georgian Bay Formation shale. The sample-scale anisotropy ratios (De-PB:De-NB) for De values obtained using the I(-) tracer are 0.9 to 4.9, and the anisotropy ratios for the HTO tracer are in the range of 1.1 to 7.0. The influence of porosity distribution on diffusive anisotropy has been investigated using one-dimensional spatially-resolved profiles of I(-)-accessible porosity (shale only) and the use of AgNO3 for fixation of I(-) tracer in the pores, allowing for SEM visualization of I(-)-accessible pore networks. The porosity profiles at the sample scale display greatest variability in the direction normal to bedding which likely reflects sedimentary depositional processes. The SEM imaging suggests that diffusion pathways are preferentially oriented parallel to bedding in the shale and that diffusion occurs dominantly within the argillaceous component of the limestone. However, the fine clay-filled intergranular voids in the dolomitic domains of the limestone are also accessible for diffusive transport.

Numerical Generation of a Fixed Bed Structure

Abstract A numerical algorithm is presented for the filling process of a cylindrical column with equilateral cylinders. The process is based on simplified mechanics - the elements are added one by one until the mechanical equilibrium is reached. The final structure is examined with respect to the global and local porosity distribution. Oscillating radial porosity profile is obtained in accordance with experimental data.

Study of Lysozyme-Loaded Poly-L-Lactide (PLLA) Porous Microparticles in a Compressed CO₂ Antisolvent Process.

Lysozyme (LSZ)-loaded poly-L-lactide (PLLA) porous microparticles (PMs) were successfully prepared by a compressed CO2 antisolvent process in combination with a water-in-oil emulsion process using LSZ as a drug model and ammonium bicarbonate as a porogen. The effects of different drug loads (5.0%, 7.5% and 10.0%) on the surface morphology, particle size, porosity, tapped density and drug release profile of the harvested PMs were investigated. The results show that an increase in the amount of LSZ added led to an increase in drug load (DL) but a decrease in encapsulation efficiency. The resulting LSZ-loaded PLLA PMs (LSZ-PLLA PMs) exhibited a porous and uneven morphology, with a density less than 0.1 g·cm−3, a geometric mean diameter of 16.9–18.8 μm, an aerodynamic diameter less than 2.8 μm, a fine particle fraction (FPF) of 59.2%–66.8%, and a porosity of 78.2%–86.3%. According to the results of differential scanning calorimetry, the addition of LSZ improved the thermal stability of PLLA. The Fourier transform infrared spectroscopy analysis and circular dichroism spectroscopy measurement reveal that no significant changes occurred in the molecular structures of LSZ during the fabrication process, which was further confirmed by the evaluation of enzyme activity of LSZ. It is demonstrated that the emulsion-combined precipitation with compressed antisolvent (PCA) process could be a promising technology to develop biomacromolecular drug-loaded inhalable carrier for pulmonary drug delivery.

Papers as Functional Green Materials

Paper is constituted of natural fibers and represents a perfect example of structural multifunctional materials. Indeed, its fibrous structure is engineered to fit the different end use properties: both optical and mechanical properties are usually required. These requirements may lead to contradictory needs in terms of structure. The influence of the structure on the physical properties is classically tackled based on standard methods such as the estimation of the porosity. However, this macroscopic property is not sufficient in terms of optimization of the fibrous network. For example, fluid transport has to be controlled either in the bulk of the material or only at its surface in the case of health or printing applications. Consequently, the characterization at the macro-level of the structure has to be complemented with an experimental measurement at the fiber level. The X-ray synchrotron micro-tomography, an imaging technique, is based on X-ray transmission. It allows the structure to be analyzed in 3D. It was carried in a large instrument (ESRF, France). The characterization of samples containing different recycled fibers was carried out. In particular, the influence of the number of cycles of drying-pulping is studied. Both qualitative and quantitative characterizations are obtained. The use of recycled fibers may also be included in the elaboration of materials, taking into account the modification of the fibers in terms of morphology and mechanical properties, essentially flexibility. Mechanical properties (tensile and deformation) constitute the main examples of the analysis showing the effect of the recycling of natural fibers: the decrease in mechanical resistance of the fibrous network is explained in terms of the increase of the global porosity, essentially in the bulk of the materials. The profile of porosity in the thickness direction is found to be essential to understand the evolution of physical properties.