Predicting stiffness and strength of birch pulp:Polylactic acid composites

This paper studies failure of birch pulp–polylactic acid composites. Stiffness and strength are calculated using the theory of short fibre composites and the results are compared to experimental data. The results differed from the experimental values by 0–6%. With less aligned fibres the short fibre theory is not feasible. The performance of the 40 wt% birch pulp – polylactic acid composite is predicted with X-ray microtomography based finite element modelling, and the results are compared with experiments. Stiffness results differed from experiments by 1–17% . By adding into the models a third material phase representing the interface between the fibres and the matrix, the stress–strain c…

Measuring intrinsic thickness of rough membranes: application to nanofibrillated cellulose films

Adequate measurement of thickness of sheet-like materials or membranes is most important for quantifying their properties such as density, barrier properties and mechanical strength. Depending on the surface roughness of the membrane, the thickness measured by standard micrometre devices (apparent thickness) may considerably overestimate the actual geometrical mean thickness (intrinsic thickness) required for such purposes. In this work, we present a method for correcting the measured apparent thickness value of thin membranes for their surface roughness, thereby obtaining an improved estimate of the intrinsic thickness. The surface roughness data required for the correction can be obtained…

Multiscale microstructural characterization of particulate-reinforced composite with non-destructive X-ray micro- and nanotomography

Abstract Methods based on X-ray tomography are developed to study the relevant statistical quantities describing the microstructural inhomogeneity of particulate reinforced composites. The developed methods are applied in estimating microstructural inhomogeneity parameters of composites containing metallic glass particles in metal matrix, extruded in varying pressure loads. This study indicates that the critical characteristics with regard to the effect of particle clustering are cluster size and shape, local volume fraction of particles in the cluster and the distance between clusters. The results demonstrate that the spatial distribution of reinforcement is very uneven and the amount of p…

Effective elastic properties of biocomposites using 3D computational homogenization and X-ray microcomputed tomography

A 3D computational homogenization method based on X-ray microcomputed tomography (μCT) was proposed and implemented to investigate how the fiber weight fraction, orthotropy and orientation distribution affect the effective elastic properties of regenerated cellulose fiber-polylactic acid (PLA) biocomposites. Three-dimensional microstructures reconstructed by means of the X-ray μCT were used as the representative volume elements (RVEs) and incorporated into the finite element solver within the computational homogenization framework. The present method used Euclidean bipartite matching technique so as to eliminate the generation of artificial periodic boundaries and use the in-situ solution d…

Curvelet-based method for orientation estimation of particles from optical images

A method based on the curvelet transform is introduced to estimate the orientation distribution from two-dimensional images of small anisotropic particles. Orientation of fibers in paper is considered as a particular application of the method. Theoretical aspects of the suitability of this method are discussed and its efficiency is demonstrated with simulated and real images of fibrous systems. Comparison is made with two traditionally used methods of orientation analysis, and the new curvelet-based method is shown to perform better than these tradi- tional methods. peerReviewed

Sensory Organ Investment Varies with Body Size and Sex in the Butterfly Pieris napi

Simple Summary Pollinating insects rely on a range of senses such as vision, olfaction, gustation, and mechanosensation to utilise, locate, and fly between floral resources. The size of different sensory organs determines their sensitivity and provides an indication of their relative importance—larger organs can enhance sensitivity by increasing the number or size of sensing structures. However, increasing the relative size of an organ would require additional energy for developing and maintaining it. This likely leads to a trade-off between the energy invested into different sensory systems within individuals. To explore how the size of the sensory organs vary with body size in insect poll…

Kuituverkostojen yksityiskohtainen analysointi korkean resoluution kolmiulotteisista kuvista

Hierarchical imaging and computational analysis of three-dimensional vascular network architecture in the entire postnatal and adult mouse brain

The formation of new blood vessels and the establishment of vascular networks are crucial during brain development, in the adult healthy brain, as well as in various diseases of the central nervous system. Here, we describe a step-by-step protocol for our recently developed method that enables hierarchical imaging and computational analysis of vascular networks in postnatal and adult mouse brains. The different stages of the procedure include resin-based vascular corrosion casting, scanning electron microscopy, synchrotron radiation and desktop microcomputed tomography imaging, and computational network analysis. Combining these methods enables detailed visualization and quantification of t…

Contact formation in random networks of elongated objects

The effect of steric hindrance is an important aspect of granular packings as it gives rise to, e.g., limitations on the densities of ordered and disordered packings, both of which are essentially defined by the geometry of the constituents. Here we focus on random packing of rods via deposition and their distributions of contact number and segment length. Such statistical properties are relevant for mechanical properties of the structures, but the (quite large) steric effects on them have not been addressed in previous studies. We therefore develop a theory that describes the statistical properties of rod packings, while taking into account that the deposited rods cannot overlap and thus i…

Publisher Correction: X-Ray Nanotomography of Individual Pulp Fibre Bonds Reveals the Effect of Wall Thickness on Contact Area

Fibre bonds play an essential role in various properties of paper. Much research has focused on their strength, but the determination of the actual contact area also provides a challenge. Many of the research methods rely on optical tools, which are restricted by the wavelength of light that is utilised. Novel X-ray computed tomography devices utilise X-rays in studying the inner structure of materials, and surpass the optical methods in terms of resolution, allowing detection of even smaller details and variations in distance between the fibres in the bond intersection area. X-ray nanotomography was used to image 26 individual cellulose fibre bonds made of springwood and summerwood fibres …

A non-destructive X-ray microtomography approach for measuring fibre length in short-fibre composites

An improved method based on X-ray microtomography is developed for estimating fibre length distribution of short-fibre composite materials. In particular, a new method is proposed for correcting th ...

Influence of Welding Time on Tensile-Shear Strength of Linear Friction Welded Birch (Betula pendula L.) Wood

Linear friction welding of wood is a bonding process applied to wood and during which a stiff bond line is formed by the softening and rehardening of wood components to form a composite material composed mainly of wood fibres embedded in a modified lignin matrix. Unfortunately, the bonds tend to spontaneously delaminate or lose their strength when exposed to moist conditions. Some approaches were previously applied to overcome this problem, but so far a suitable solution has not been found. This paper presents results of applying post-welding thermal modification to reduce the moisture sensitivity of welded wood. The experiments included welding of birch wood, thermal modification under sup…

X-ray micro-tomography based FEM modelling of hygroexpansion in PLA composites reinforced with birch pulp fibres

This article presents a microscale modelling approach coupled with X-ray computed micro-tomography for the evaluation of material properties of polylactic acid (PLA) reinforced by birch pulp fibers under the effect of moisture. The results in terms of elastic moduli and hygroexpansion deformation were found in good agreement with the measurements taken at different levels of water uptake.

Stain-free virtual histology of Bombus terrestris compound eyes by laboratory phase-contrast nano-CT

The visual systems of pollinating insects are studied to understand the effects of a changing environment, and are to date imaged using microscopy or micro-CT. Microscopy only allows two-dimensional imaging and conventional micro-CT requires heavy-metal staining of the samples. Here we present virtual histology of compound eyes of bumblebee (Bombus terrestris) using a laboratory nano-CT system. Propagation-based phase-contrast CT allows three-dimensional imaging of samples without using any staining. Micrometre-resolution images of the microanatomy of the eyes were reconstructed, and the features identified in CT (cornea, crystalline cones, pigment, photoreceptor cells, basement membrane) w…

Swelling of cellulose fibres in composite materials: Constraint effects of the surrounding matrix

Swelling of cellulose fibres in composite materials : Constraint effects of the surrounding matrix

Curvelet-based method for orientation estimation of particles

A method based on the curvelet transform is introduced for estimating from two-dimensional images the orientation distribution of small anisotropic particles. Orientation of fibers in paper is considered as a particular application of the method. Theoretical aspects of the suitability of this method are discussed and its efficiency is demonstrated with simulated and real images of fibrous systems. Comparison is made with two traditionally used methods of orientation analysis, and the new curvelet-based method is shown to perform clearly better than these traditional methods.

Effects of particle clustering on the plastic deformation and damage initiation of particulate reinforced composite utilizing X-ray CT data and finite element modeling

In this paper, a new simulation technique which can include microstructural inhomogeneity of particulate reinforced composites is proposed to accurately study deformation pattern and damage mechanism in these composites. Three dimensional microstructures constructed from XCT images incorporated into finite element modeling codes with minimal approximation to capture the effects of cluster size, local volume fraction of particles in the cluster and the distance between clusters as relevant statistical quantities describing the microstructural inhomogeneity of particulate reinforced composites. A quantitative parameter as degree of clustering is defined to consider particle clustering effect.…

The number of contacts in random fibre networks

There is a wide range of materials that can be considered as nonwoven random networks of fibres. Such materials include glass-fibre mats, filters, various paper products and structural components of cells and tissues. The mechanical properties of these kinds of networks have been studied extensively for many decades. As many of such networks form more or less two-dimensional structures, they can, to a good approximation, be considered to consist of randomly distributed fibres or filaments connected at their crossings points. Recent development of the resolution of X-ray computed tomography have enabled imaging of the three dimensional structure of such materials with a resolution sufficient…

Online measurement of floc size, viscosity, and consistency of cellulose microfibril suspensions with optical coherence tomography

AbstractIn this study, cellulose microfibril (CMF) suspensions were imaged during pipe flow at consistencies of 0.4%, 1.0%, and 1.6% with optical coherence tomography (OCT) to obtain images of the structure and the local velocity of the suspension. The viscosities obtained by combining pressure loss measurement with the OCT velocity data showed typical shear thinning behavior and were in excellent agreement with viscosities obtained with ultrasound velocity profiling. The structural OCT images were used to calculate the radial and the axial floc sizes of the suspension. A fit of power law to the geometrical floc size–shear stress data gave the same power law index for all consistencies, sug…

Time-resolved X-ray microtomographic measurement of water transport in wood-fibre reinforced composite material

Natural fibre composites are prone to absorb moisture from the environment which may lead to dimensional changes, mold growth, degradation of mechanical properties or other adverse effects. In this work we develop a method for direct non-intrusive measurement of local moisture content inside a material sample. The method is based on X-ray microtomography, digital image correlation and image analysis. As a first application of the method we study axial transport of water in a cylindrical polylactic acid/birch pulp composite material sample with one end exposed to water. Based on the results, the method seems to give plausible estimates of water content profiles inside the cylindrical sample.…

Effects of defects on the tensile strength of short-fibre composite materials

Abstract. Heterogeneous materials tend to fail at the weakest cross-section, where the presence of microstructural heterogeneities or defects controls the tensile strength. Short-fibre composites are an example of heterogeneous materials, where unwanted fibre agglomerates are likely to initiate tensile failure. In this study, the dimensions and orientation of fibre agglomerates have been analysed from three-dimensional images obtained by X-ray microtomography. The geometry of the specific agglomerate responsible for failure initiation has been identified and correlated with the strength. At the plane of fracture, a defect in the form of a large fibre agglomerate was almost inevitably found.…

Black Bioinks from Superstructured Carbonized Lignin Particles

A renewable source of carbon black is introduced by the processing of lignin from agro-forestry residues. Lignin side streams are converted into spherical particles by direct aerosolization followed by carbonization. The obtained submicron black carbon is combined with cellulose nanofibers, which act as a binder and rheology modifier, resulting in a new type of colloidal bioink. The bioinks are tested in handwriting and direct ink writing. After consolidation, the black bioinks display total light reflectance (%R) at least three times lower than commercial black inks (reduction from 12 to 4%R). A loading of up to 20% of nanofibers positively affects the cohesion of the dried bioink (1 to 16…

Microstructural evaluation and recommendations for face masks in community use to reduce the transmission of respiratory infectious diseases

Funding Information: A.K., H.Y. and R.J. also acknowledges the funding through Academy of Finland BESIMAL (Decision No. 334197) and Aalto University, Department of Communications and Networking. This work has also received funding in part from the EPSRC UK (grant number EP/R012091/1). A.K. would also like to thank Mr. Volkan Kaplan for the fruitful discussions in the early concept generation. Publisher Copyright: © 2022 The Author(s) Background and Objective: Recommendations for the use of face masks to prevent and protect against the aerosols (≤5µm) and respiratory droplet particles (≥5µm), which can carry and transmit respiratory infections including severe acute respiratory syndrome coro…

Use of micro-tomography for validation of method to identify interfacial shear strength from tensile tests of short regenerated cellulose fibre composites

The interfacial shear strength of short regenerated cellulose fibre/polylactide composites was characterized by means of an industry-friendly adhesion test method. The interfacial shear strength was back-calculated from the experimental tensile stress-strain curves of composites by using a micro-mechanical model. The parameters characterizing the microstructure of the composites, e.g. fibre length and orientation distributions, used as input in the model were obtained by micro-tomography. The investigation was carried out on composites with untreated and surface treated fibres with various fibre weight contents (5wt%, 10wt%, and 15wt% for untreated fibres, and 15wt% for treated fibres). The…

Towards ductilization of high strength 7XXX aluminium alloys via microstructural modifications obtained by friction stir processing and heat treatments

Abstract High strength 7XXX aluminium series reach exceptional strength, higher than all other industrial aluminium alloys. However, they suffer from a lack of ductility compared to softer series. This work presents a procedure to improve the ductility of 7475 Al alloy in high strength condition, reaching a true fracture strain of 70% at full 500 MPa T6 yield strength. Using friction stir processing (FSP) and post-FSP heat treatments, 100% of industrial rolled material T6 yield stress is maintained but a 180% increase in fracture strain is measured for the processed material. This ductility improvement is studied by in-situ synchrotron X-ray tomography and is explained by the reduction of i…

A stochastic shape and orientation model for fibres with an application to carbon nanotubes

Methods are introduced for analysing the shape and orientation of planar fibres from greyscale images of fibrous systems. The sequence of image processing techniques needed for segmentation of fibres is described. The identified fibres were interpreted as deformed line segments for which two shape and two orientation parameters are estimated by the maximum likelihood method. The methods introduced are shown to perform quite well for simulated systems of deformed line segments with known properties. They were applied to TEM images of carbon nanotubes embedded in polycarbonate.

Lignin Inter-Diffusion Underlying Improved Mechanical Performance of Hot-Pressed Paper Webs

Broader use of bio-based fibres in packaging becomes possible when the mechanical properties of fibre materials exceed those of conventional paperboard. Hot-pressing provides an efficient method to improve both the wet and dry strength of lignin-containing paper webs. Here we study varied pressing conditions for webs formed with thermomechanical pulp (TMP). The results are compared against similar data for a wide range of other fibre types. In addition to standard strength and structural measurements, we characterise the induced structural changes with X-ray microtomography and scanning electron microscopy. The wet strength generally increases monotonously up to a very high pressing tempera…

Contact formation in random networks of elongated objects

The effect of steric hindrance is an important aspect of granular packings as it gives rise to, e.g., limitations on the densities of ordered and disordered packings, both of which are essentially defined by the geometry of the constituents. Here we focus on the random packing of rods via deposition and their distributions of contact number and segment length. Such statistical properties are relevant for mechanical properties of the structures, but the (quite large) steric effects on them have not been addressed in previous studies. We therefore develop a theory that describes the statistical properties of rod packings, while taking into account that the deposited rods cannot overlap and th…

Strength of cellulosic fiber/starch acetate composites with variable fiber and plasticizer content

In this experimental study, the performance of injection-molded short flax and hemp fibers in plasticized starch acetate were analyzed in terms of strength. Parameters involved in the analysis are a variable fiber and plasticizer content. The measured strength of the composites varies in the range of 12–51 MPa for flax fibers and 11–42 MPa for hemp fibers, which is significantly higher than the properties of the unreinforced starch acetate matrix. The micro-structural parameters used in modeling of composite strength were obtained from optical observations and indirect measurements. Some of these parameters were qualitatively verified by X-ray microtomography.

A method for measuring wetting and swelling of bentonite using X-ray imaging

A non-invasive method based on X-ray imaging for measuring deformation and water transport in wetting and swelling bentonite samples is introduced. Sequential X-ray images taken of the samples were used to calculate the attenuation coefficient and deformation. These results, together with careful calibration, allowed finding the dry density and water content distributions and their temporal evolution in the wetting and swelling samples. A specific correction technique, based on regularly taking reference X-ray images of aluminum plates of varying thickness, was developed and used to take into account X-ray beam instabilities and thus to improve the accuracy of density analysis. Large deform…

Orthogonal switching of AMS axes during type-2 fold interference : Insights from integrated X-ray computed tomography, AMS and 3D petrography

We applied X-ray computed microtomography (μ-CT) in combination with anisotropy of magnetic susceptibility (AMS) analysis to study metamorphic rock fabrics in an oriented drill core sample of pyrite-pyrrhotite-quartz-mica schist. The sample is extracted from the Paleoproterozoic Martimo metasedimentary belt of northern Finland. The μ-CT resolves the spatial distribution, shape and orientation of 25,920 pyrrhotite and 153 pyrite grains localized in mm-thick metapelitic laminae. Together with microstructural analysis, the μ-CT allows us to interpret the prolate symmetry of the AMS ellipsoid and its relationship to the deformation history. AMS of the sample is controlled by pyrrhotite porphyro…

Characterization of three-dimensional microstructure of composite materials by X-ray tomography

Analysis methods for X-ray microtomographic images of short fibre composite materials were developed. The methods enable estimation of microstructural properties of the material, e.g., aspect ratio and orientation of fibres. Being based on X-ray microtomography and image analysis, the methods are nondestructive and do not require user intervention. In particular, a method for determination of the aspect ratio of fibres was first developed. The method contains an assumption about similarity of the shape of the fibres. The assumption was relaxed in an improved method that can estimate cross-sectional properties of fibres, too, e.g., cross-sectional area. Additionally, the effect of finite ima…

Curvelet-based method for orientation estimation of particles from optical images

A method based on the curvelet transform is introduced to estimate the orientation distribution from two-dimensional images of small anisotropic particles. Orientation of fibers in paper is considered as a particular application of the method. Theoretical aspects of the suitability of this method are discussed and its efficiency is demonstrated with simulated and real images of fibrous systems. Comparison is made with two traditionally used methods of orientation analysis, and the new curvelet-based method is shown to perform better than these tradi- tional methods. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of th…

Mechanical properties of natural fiber composites produced using dynamic sheet former

Composites formed from wood fibers and man-made cellulosic fibers in PLA (polylactic acid) matrix, manufactured using sheet forming technique and hot pressing, are studied. The composites have very low density (due to high porosity) and rather good elastic modulus and tensile strength. As expected, these properties for the four types of wood fiber composites studied here improve with increasing weight fraction of fibers, even if porosity is also increasing. On the contrary, for man-made cellulosic fiber composites with circular fiber cross-section, the increasing fiber weight fraction (accompanied by increasing void content) has detrimental effect on stiffness and strength. The differences …

Non-destructive automatic determination of aspect ratio and cross-sectional properties of fibres

A novel method for computerised estimation of the aspect ratio distribution and various cross-sectional geometrical properties of fibres in short-fibre reinforced composites is proposed. The method, based on X-ray micro-computed tomography, is non-destructive and does not require user intervention. Based on results on specially fabricated model material, the accuracy and precision of the method seems adequate. The method is applied in analysing a manufacturing process of wood fibre reinforced thermoplastic composite. The results indicate a significant decrease of the aspect ratio of fibres during the processing steps. Finally, the feasibility of the method is assessed by estimating paramete…

Characterization of spatial porosity and mineral distribution of crystalline rock using X-ray micro computed tomography, C-14-PMMA autoradiography and scanning electron microscopy

The spatial porosity and mineral distribution of geological materials strongly affects transport processes in them. X-ray micro computed tomography (X-mu CT) has proven to be a powerful tool for characterizing the spatial mineral distribution of geological samples in 3-D. However, limitations in resolution prevent an accurate characterization of pore space especially for tight crystalline rock samples and 2-D methods such as C-14-polymethylmethacrylate (C-14-PMMA) autoradiography and scanning electron microscopy (SEM) are needed. The spatial porosity and mineral distributions of tight crystalline rock samples from Aspo, Sweden, and Olkiluoto, Finland, were studied here. The X-mu CT were use…

Micrometer-resolution reconstruction and analysis of whole mouse brain vasculature by synchrotron-based phase-contrast tomographic microscopy

AbstractNervous tissue metabolism is mainly supported by the dense thread of blood vessels which mainly provides fast supplies of oxygen and glucose. Recently, the supplying role of the brain vascular system has been examined in major neurological conditions such as the Alzheimer’s and Parkinson’s diseases. However, to date, fast and reliable methods for the fine level microstructural extraction of whole brain vascular systems are still unavailable. We present a methodological framework suitable for reconstruction of the whole mouse brain cerebral microvasculature by X-ray tomography with the unprecedented pixel size of 0.65 μm. Our measurements suggest that the resolving power of the techn…

X-ray micro-computed tomography investigation of fibre length degradation during the processing steps of short-fibre composites

The mechanical properties of composites in the fibre direction are mainly attributed to the fibre slenderness, or aspect ratio. A trade-off between performance and processability is usually required, and dependent on the intended application. If the fibre length could be retained or not severely degraded during various processing steps towards the injection-moulded component, a stiffer and stronger composite product could be obtained. The processing steps for injection moulded wood-fibre composites here include: Pulping, commingling, extrusion, pelletizing, and injection moulding. To tune the processing parameters systematically for retained fibre length, it would be useful to investigate t…

Three-Dimensional Microstructural Properties of Nanofibrillated Cellulose Films

Abstract: Nanofibrillated cellulose (NFC) films have potential as oxygen barriers for, e.g., food packaging applications, but their use is limited by their hygroscopic characteristics. The three-dimensional microstructure of NFC films made of Pinus radiata (Radiata Pine) kraft pulp fibres has been assessed in this study, considering the structural development as a function of relative humidity (RH). The surface roughness, micro-porosity, thickness and their correlations were analyzed using X-ray microtomography (X–μCT) and computerized image analysis. The results are compared to those from scanning electron microscopy and laser profilometry. Based on a series of films having varying amounts…

Laboratory phase‐contrast nanotomography of unstained Bombus terrestris compound eyes

Imaging the visual systems of bumblebees and other pollinating insects may increase understanding of their dependence on specific habitats and how they will be affected by climate change. Current high-resolution imaging methods are either limited to two dimensions (light- and electron microscopy) or have limited access (synchrotron radiation x-ray tomography). For x-ray imaging, heavy metal stains are often used to increase contrast. Here, we present micron-resolution imaging of compound eyes of buff-tailed bumblebees (Bombus terrestris) using a table-top x-ray nanotomography (nano-CT) system. By propagation-based phase-contrast imaging, the use of stains was avoided and the microanatomy co…

Structural characterisation of wood pulp fibres and their nanofibrillated materials for biodegradable composite applications

Introduction: The utilization of wood pulp fibres in composite materials has gained major interest during the last years. One of the major motivations has been the potential of wood pulp fibres and their nanofibrillated derivatives for increasing the mechanical properties of some materials. However, in order to exploit the full potential of wood pulp fibres and cellulose nanofibrils as reinforcement in hydrophilic and hydrophobic matrices, several characteristics of fibres and their interactions with a given matrix need to be understood. With the increasing capabilities of novel microscopy techniques and computerized image analysis, structural analysis is moving forward from visual and subj…