Fiber Bond Research Articles

The role of fibre bonds in permanent curl of paper and how it is affected by crosslinking

Irreversible deformation of paper is a challenge for both printer operation and product quality, particularly in inkjet printing with water-based inks. Here we are investigating permanent paper curl, which is the residual curl of paper after drying of the ink (i.e., it is not the immediate paper curl due to wetting). The key aim of this work was to test the hypothesis that permanent paper curl is created by partial opening and rearrangement of the fibre–fibre bonds in the wetted paper layer. In order to test this hypothesis, we produced paper with crosslinked fibre–fibre bonds that do not open in the presence of water. Polyamideamine epichlorohydrin (PAE) and 1,2,3,4-butanetetracarboxylic acid were used as crosslinking agents and properties of the treated paper samples were analysed. Both agents led to significantly improved wet strength of the papers, furthermore we indeed found that the permanent curl of crosslinked papers was strongly reduced. Other curl related mechanisms like differences in fibre swelling, paper hydroexpansion and liquid penetration were not able to explain the reduction in curl. The finding that the creation of fibre–fibre bonds unaffected by water prevents permanent curl of paper after wetting and redrying leads to the conclusion that the mechanism for creating permanent paper curl after wetting is related to the partial opening and rearrangement of fibre–fibre bonds in the wetted paper. Possible pathways to apply these findings to paper production are discussed, for example switchable or temporary wet strength agents.

Effectiveness evaluation of different steel fibers on the shear strength of reinforced SFRC slender beams without web rebars

Current studies have mainly focused on the effect of specific steel fibers on the shear performance of steel fiber-reinforced concrete (SFRC) slender beams. However, there has been a lack of in-depth research evaluating the effectiveness of different steel fibers through a statistically comparative analysis of experimental data from various researchers. Existing design methods do not fully account for the impact of all types of steel fibers on the shear capacity of SFRC slender beams, providing very limited guidance on selecting appropriate steel fibers. This highlights the need for research to verify the strengthening effectiveness of different steel fibers. This paper establishes databases comprising 232 shear-failed reinforced SFRC beams with four other types of steel fibers straight wire, deformed wire, deformed cut-sheet and ingot mill, based on a comprehensive review of published literature. These databases complement an existing database of 280 reinforced SFRC beams using hook-end wire steel fibers as shear reinforcement. The databases are used to evaluate the validity of several well-known existing formulas for predicting the shear capacity of beams and to determine the fiber bond factor values that reflect the diverse strengthening effects of different steel fibers. Utilizing a simi-empirical synergetic prediction model for the shear strength of reinforced SFRC slender beams with hook-end wire steel fibers, the shear resistances of test beams in databases with the other four types of steel fiber are analyzed. The primary contributors to shear capacity are identified as the uncracked shear-compression SFRC and the dowel action of longitudinal tensile steel bars. The contribution of steel fibers is linked to the shear resistance of uncracked shear-compression SFRC. From a practical design perspective, a conservative prediction formula is verified, aligning with the lower boundary of the tested shear strength obtained from the database of beams. Finally, suitable steel fibers for s enhancing the shear strength of reinforced SFRC beams without web rebars are suggested based on their effectiveness.

Foaming and cross-linking of cellulose fibers using phytic acid

Bio-based compounds have become the focus in the development of next-generation materials. The polyphosphated structure and availability of phytic acid has sparked an interest to understand its properties and apply it to making fire-retardant fabrics. However, its degradative effect on natural fibers sets limitations to its potential uses. In this study, we unveiled a new dimension to explore with phytic acid: cellulose fiber foams. Phytic acid enabled synergistic foaming with carboxymethyl cellulose albeit causing issues in long-term wet foam stability. Adding cellulose fibers to this mixture and drying at 160 °C produced solid foams with increased compressive strength and stiffness; comparable to foams cross-linked with the commonly used citric acid. The reduced contact area in low-density fiber networks allowed the cross-linking between phytic acid and the fiber network to mitigate structural weakening due to fiber degradation. Imaging also revealed the formation of a film encompassing fiber bonds; attributed to the strong interaction between phytic acid and carboxymethyl cellulose. Furthermore, phytic acid imparted self-extinguishing fire-retardant properties to the cellulose fiber foams measured using thermogravimetric analysis and cone calorimetry. This work showcases a simple new application for phytic acid without the use of catalysts or solvents. It serves to encourage further development of green practices to continuously challenge the industrial landscape.

Peridynamics-based model of composite lamina with progressive variations in mechanical properties

An analytical model of the fiber-reinforced composite lamina is constructed based on bond-based peridynamics (PD), which utilizes variable matrix bonds and fiber bonds to evaluate the static properties of matrix and fiber materials, respectively. The bond stiffness of the matrix is determined by trigonometric functions, and fibers are represented by constants. The proposed PD model describes the continuous variations in the static properties of composites as a function of fiber angle. Both the conventional analytical method and the PD method are used to solve the failure-free elastic deformation issue. The two methods estimate maximum errors in the displacement of material points in the x and y directions of 0.01 % and 4.86 %, respectively, indicating good consistency. The failure propagation of the preexisting crack layer under the axial tensile load is simulated and the obtained failure modes are in good agreement with experimental results. The proposed composite lamina model simulates the influence of fiber direction on overall behavior through various matrix bond stiffness. Breaking through the limitation of constant matrix bond stiffness in conventional models, is conducive to promoting the further development of bond-based composite PD models.

A multiaxial multiscale compressive thermo-mechanical damage model for Fiber Reinforced Cementitious Composites (FRCC)

In the current study, a multiaxial multiscale compressive stress-strain model for Fiber Reinforced Cementitious Composites (FRCC) was innovatively developed. The proposed model was on the basis of the theory of thermodynamics, multiscale theory and internal variable theory. The free energy function and dissipation function were established to characterize the elastic and plastic deformation of FRCC, respectively. The multiscale behaviors of FRCC in meso-scale and macro-scale was taken into account. In meso-scale, the energy dissipation functions of fiber in tension and bond-slip deformation in the interface transition zone (ITZ) were established. The resistance to cracking of cementitious matrix through the fiber bond stress were taken into account. In macro-scale, the thermo-mechanical coupling contributions of plastic damage, thermal damage, yield surface and hardening evolution were creatively considered in the potential function within thermodynamics framework. The influence of types and volume fractions of fibers on the reinforcement mechanism was discussed. When the temperature is higher than the melting point of fiber, the fiber influence coefficients was employed. The sensitivity of yield surface was discussed. The numerical predictions of this developed model were carried out for validation. The nonlinear stress-strain responses of concrete were accurately captured at temperatures ranges from 20 °C to 800 °C compared with the experimental data, which indicates the accuracy and applicability of the proposed model.

Liquid penetration in hydrophobised cellulose based sheets

Controlling the liquid transport within cellulose-based materials is crucial for numerous applications, including printing, bio-assays, packaging, and cleaning. To control liquid transport and quality, post-processes such as calendering, a way of compressing and smoothen the paper using hard pressure rollers, and hydrophobisation, are commonly employed. To understand how these processes influence liquid uptake, this study uses an Ultra-Fast Imaging (UFI) NMR method to analyse moisture profiles during liquid uptake in various cellulose-based paper sheets with diverse levels of hydrophobisation and calendering. It is demonstrated that calendering decreases penetration speed and increases swelling. The reduction in penetration speed could be linked to a decrease in permeability upon calendering, as measured by the Gurley air permeance. Additionally, it is observed that hydrophobisation delayed and slowed down liquid uptake in the paper samples, and, in extreme cases, completely altered the liquid uptake phenomena. With substantial hydrophobisation, liquid penetration no longer proceeded with a well-defined liquid front but exhibited huge levels of fingering. Furthermore, is was observed that within highly hydrophobised paper, fibres were first prewetted, initiating a first swelling, before the pores between fibres could be filled. Subsequently, water could enter the pores between, allowing fibre bonds to be broken, leading to a second swelling of the paper sheet. The improved understanding will contribute to better control of the flow within cellulose-based materials, benefiting applications such as printing, packaging and microfluidics.

Accuracy of hygro-expansive curl predictions for paper sheets based on homogenised 2D and 3D network representations

Paper, a porous-fibrous network, is made up of hydrophilic fibres, which are notably susceptible to deformations due to variations in moisture content. The response of paper sheets to full or partial wetting, based on the water-induced fibre swelling, has mostly been predicted in the past using highly idealised two-dimensional network geometries. The purpose of the present paper is to establish how precisely the two-stage process of determining effective hygro-expansivity under uniform wetting by a two-dimensional model followed by bending analysis using a continuum model predicts the curl of a fully three-dimensional network. In the present multi-scale modelling work, the moisture-induced homogenised sheet scale curl, derived from hygro-elastic deformations using non-uniform moisture profiles, is analysed based on an idealised non-woven three-dimensional fibrous network finite element model. First, the effective paper sheet swelling properties, derived computationally for the uniform wetting condition, are compared with analytically homogenised hygro-elastic properties. Whereas the analytically predicted elastic modulus has an inaccuracy of only ∼5%, the hygro-expansivity coefficient is over-predicted by roughly a third for a network with straight fibres. The difference is smaller if waviness of the fibres and wrap-around in the fibre bonds are taken into account. Fibre alignment turns out to have little influence. Subsequently, paper sheet curl predictions made by the analytical model are compared with that computed from the three-dimensional network model. The inaccuracy of the fully analytical model, based on the two-dimensional network description, relative to the fully detailed three-dimensional computational model with straight fibres is on the order of 40%–50%. The fidelity of the simple model is primarily constrained by the inaccuracy of the effective hygro-expansion coefficient. If the expansivity extracted from the three-dimensional simulations under uniform wetting is inserted, the inaccuracy drops to less than 10%. The continuum bending description hence performs adequately, provided it is based on a reliable estimation of the uniform expansion behaviour of the material.

Glueless formaldehyde-free biocomposites with high strength based on the three-dimensional structure of wood fibres

The efficient utilization of small-diameter shrub resources holds significant potential in averting forest resource waste and mitigating carbon emissions. Herein, glueless biocomposites were prepared using waste small-diameter Buxus megistophylla via alkali pre-treatment and thermal molding. Instead of simple hot-pressing, the biocomposites were prepared using thermal molding, which allows the release of edge stresses in a high-pressure environment. After alkali pretreatment, the flexural and tensile strength of the biocomposites increased by 66.08% and 74.12%. Alkali pre-treatment forms reactive alkali-cellulose, facilitating fiber bonding. Structural disruption leads to fiber swelling, increasing surface area and hydrogen bonding, especially on cellulose. This process disrupts and reconstitutes crystalline regions, enhancing crystallinity. Lignin liberated from the lignin-hemicellulose polymer transitions to a molten state, serving as an adhesive to fortify fiber bonds, creating a 3D lattice structure and hydrophobic surface (Water contact angle 85°). Furthermore, these biocomposites, being adhesive-free and non-emitters of harmful gases like formaldehyde, hold promise as sustainable materials for architectural decoration and furniture applications.

Relationship between chemical and mechanical degradation of aged paper: fibre versus fibre–fibre bonds

Relationship between chemical and mechanical degradation of aged paper: fibre versus fibre–fibre bonds

Natural down fiber-reinforced and polypyrrole-modified silk fibroin composite aerogel for efficient solar steam generation toward seawater desalination and wastewater treatment

Poor mechanical properties and low photothermal efficiency of silk fibroin (SF)-based aerogels are current challenges that need to be addressed. Herein, SF composite aerogel was developed to enhance the mechanical properties through physical interpenetration of natural down fiber (Df) and hydrogen bonds formed among SF, Df, and polypyrrole (PPy) and to improve the evaporation performance via in-situ polymerization of PPy. The resultant Df/PPy@SF aerogel showed significant improvement of compressive stress (194.29 kPa), which was 6.96 times than that of SF aerogel (27.91 kPa), and also good compression resiliency. Furthermore, due to uniform distribution of PPy and high porosity of 95.27 %, Df/PPy@SF aerogel possessed high light absorbance of 99.87 % and low thermal conductivity (0.043 W·m−1·K−1). Thus, the Df/PPy@SF aerogel evaporator demonstrated high evaporation rates of 2.12 kg·m−2·h−1 for 3.5 wt% saline water, 2.04–2.15 kg·m−2·h−1 for various dye water, and 2.10 kg·m−2·h−1 for actual dye wastewater. Moreover, the developed aerogel exhibited evaporation stability and outstanding salt-resistance when treating seawater due to continuous water supply by superhydrophilic porous aerogel. Therefore, these findings demonstrate the excellent performance of Df/PPy@SF aerogel and will inspire further research on developing natural fiber-reinforced aerogels for use in the fields of solar water evaporation, energy, and other related applications.

Fibre reinforced ultra‐high performance concrete – Rheology, fibre bond strength and flexural strength

AbstractUltra‐high performance concrete (UHPC) is characterised by a high compressive strength, high durability, and a dense microstructure. The latter causes UHPC to fail in a brittle and sometimes explosive manner. For this reason, UHPC is reinforced with microfibre reinforcement. On the one hand, these lead to increased tensile and bending loads being able to be absorbed, but above all to ductile post‐fracture behaviour. The fibres used are mostly steel fibres.An essential aspect of the fibre reinforcement is the bond strength between UHPC and metallic fibre. The bond is divided into chemical‐adhesive bond, form bond and friction bond. Depending on the shape, material and surface condition of the fibre, the individual types of bond have different effects on the concrete. To quantify these effects, fibre pull‐out tests are often carried out. These provide information about the bond strength between the fibre and the concrete. However, results of various studies show that the bond strength does not automatically correlate with the actual influence on the resulting tensile and flexural strengths of concrete components.

A conjugated bond-based peridynamic model for laminated composite materials

The bond-based peridynamic (BB-PD) theory is inadequate in describing the four independent engineering material constants of composite lamina, which results in fixed values its Poisson's ratios and shear moduli. This study presents a novel lamina conjugated BB-PD model encompasses not only the fiber bond and matrix bond, but also the transverse bond and conjugated bond pair. By defining these four basic PD bonds, the improved conjugated BB-PD model can overcome the restriction of material properties. The determination of the four basic PD micro-modulus parameters is achieved through the utilization of the equivalent relationship of strain energy density. In addition, the lamina conjugated BB-PD model is extended to deal with composite laminates with different stacking sequences. The present study validates the accuracy and applicability of the conjugated BB-PD model for composite materials by conducting simulations of the elastic deformation and progressive damage behavior of unidirectional laminae and laminates. Moreover, the proposed model provides an elucidation of the damage modes and failure mechanisms of laminated composite materials subjected to uniaxial loading.

Pullout behavior of recycled macro fibers in the cementitious matrix: Analytical model and experimental validation

A novel mechanical recycling method has been recently developed in the authors’ group for processing waste glass fiber-reinforced polymer (GFRP) composites into macro fibers, which are then incorporated into concrete to produce green fiber-reinforced concrete (FRC). The present study has been conducted for facilitating the characterization of the tensile properties of macro fiber reinforced concrete (MFRC). A trilinear bond-slip model based on the shear-lag theory has first been refined by introducing a slip coefficient to consider different slip behaviors at the final pullout stages. Such a refined trilinear bond-slip model is suitable for describing the bond-slip behavior of the recycled macro fibers embedded in the cementitious matrix. The bond parameters are obtained through an inverse analysis, in which an improved particle swarm optimization algorithm (PSO) is used. The predicted force-end slip curves are compared with the pullout test results, and a good agreement is observed counterparts with the integral absolute error (IAE) ranging from 3.05% to 5.52%, demonstrating the feasibility of the proposed analytical model. A parametric study is finally conducted to examine the sensitivity of different parameters including the fiber geometries and bond properties on the pullout behavior of the macro fibers.

Enhanced tensile performance of ultra-high-performance alkali-activated concrete using surface roughened steel fibers

To improve the mechanical performance of ultra-high-performance alkali-activated concrete (UHP-AAC), the surface of steel fiber was modified using an electrolyte solution containing ethylenediaminetetraacetic acid (EDTA). The longer the steel fiber was exposed to the EDTA-electrolyte solution, the more the longitudinal peeling of the steel fiber surface was induced and the surface roughness increased. By exposing the specimens to the solution for up to 6 h, the highest fiber bond strength (11.96 MPa) and a maximum tensile strength of UHP-AAC (14.7 MPa) were obtained. The mechanical properties of UHP-AAC were also investigated using conventional long straight and twisted steel fibers. The increase in bond strength due to the triangular cross-sectional shape and untwisting torque of the twisted fiber had an overall positive effect on the mechanical properties of UHP-AAC. However, the best tensile performance of UHP-AAC, in terms of tensile strength and energy absorption capacity, was obtained when the straight steel fibers surface-refined by the EDTA-electrolyte solution for 6 h were adopted. Based on the Pearson correlation coefficient, the Weibull distribution was applied as a crack width prediction model. The results showed that the median microcrack widths formed in UHP-AAC were marginally influenced by the surface treatment using EDTA-electrolyte solution. However, the longer straight and twisted steel fibers produced wider microcracks than their counterparts. The greatly increased tensile strain capacity of UHP-AAC by using the surface-refined steel fibers was thus caused by the formation of more microcracks rather than the increase in the microcrack width.

Synthesis of vertically aligned and interconnected BN fiber skeleton for significantly improving thermal conductivity of PVDF

Seeking efficient thermal management materials for electronic components is urgent and important. BN has high thermal conductivity and good insulating properties, making it an ideal polymer filler for improving thermal conductivity. Currently, because of the weak interaction between BN and its high melting point, it is extremely difficult to construct a BN three-dimensional skeleton by direct sintering to achieve efficient heat transfer channels. In this work, vertically aligned BN three-dimensional skeletons with fiber walls were synthesized in one step by combining the in-situ conversion of precursor fibers and directional freeze-drying technology. The precursor fibers were expelled by the directionally grown ice crystals, forming vertically aligned fiber walls. Importantly, molten B2O3 produced during air calcination made the fibers bond to each other, thus obtaining the vertically aligned and interconnected BN fiber skeleton. Benefiting from the short-path fast heat transfer and low interfacial thermal resistance of the fiber walls, the obtained vertically aligned BN skeleton exhibited obvious structural advantages, resulting in composites with a unidirectional thermal conductivity of 1.372 W/(m·K) with the filling content of 25.7 wt% and high enhancement efficiency per unit volume of 32.6 %. This approach is expected to open a new avenue for developing highly thermally conductive composites with great potential.

Modifikasi Serat Kenaf (Hibiscus cannabinus L.) Menggunakan Anhidrida Propionat

Kenaf is a local crop that has great potential as a polymer composite reinforcement. However, the main weakness in strengthening composites using kenaf fiber is its hydrophilic or water-absorbing properties. To improve composite properties, surface modification of kenaf fiber is needed to enhance the structure and chemical properties of kenaf fiber. This study aims to explore the potential of chemical modification of kenaf fiber for use in composites. Chemical modification treatment of kenaf fibers was intended to improve the hydrophobicity that the compatibility between the fiber and matrix bonds are enhanced. In this study, chemical modification of kenaf fiber was performed using propionic anhydride. The modification process was done through a three-variation of retention time; 100, 200, 300 minutes at 100 °C. This research also compared the kenaf fiber properties with and without the modification process, including the analysis of the weight percent gain and surface morphological structure. The results showed that the optimal weight gain and morphological structure was at a retention time of 200 minutes.

Investigating the effect of the type of endodontics sealer on the strength of the post fiber bond to the tooth root canal in a laboratory environment

Investigating the effect of the type of endodontics sealer on the strength of the post fiber bond to the tooth root canal in a laboratory environment

Flexural properties of ultra-high performance fiber reinforced concrete based on three-dimensional random distribution of steel fibers

The distribution of fibers and the fiber bridging affect the flexural strength and energy dissipation of ultra-high-performance fiber reinforced concrete (UHFRC) members. In this study, an analytical model to predict the flexural behavior of UHPFRC was developed based on the three-dimensional random distribution of fibers. The probability distribution model of the fiber orientation was developed as a sine function, which agreed to the measured probability data from the randomly distributed fiber specimens. The number of fibers at the fracture surface was determined addressing the effect of fiber orientation. Based on the proposed model, the method to predict the load–deflection curve of UHPFRC beam was suggested addressing the fiber bridging stress at fracture surface and tension softening effect. For verification, the four points flexural tests were conducted for six UHPFRC beam specimens. The test results showed that the peak flexural strength and energy dissipation can be predicted by the proposed model. Further, the proposed model was applicable to predict the strength and deformation capacity of existing test specimens. Based on the proposed model, the aspect ratio of fibers to prevent the brittle failure due to fiber rupture was suggested addressing the fiber tensile strength and bond strength.

Bulk characterization of highly structured tissue paper based on 2D and 3D evaluation methods

The structure of the fibre network in tissue paper can be complex and difficult to analyze, due to the presence of superimposed structures such as creping and patterns that occur, for example, in through-air-dried (TAD) tissue. Properties like high absorbency, a pleasant handfeel, and strength-related characteristics are closely related to the fibre network structure. Therefore, in addition to standard tissue testing methods, techniques that provide insights into the intrinsic properties of the tissue fibre network are essential for a deeper understanding and potential for further optimization. In this study, we utilized 2D cross-sectional images and 3D X-ray microtomography (mu-CT) to evaluate and quantify the intrinsic properties of highly structured TAD tissue. We compared the results obtained from these two methods, focusing on intrinsic thickness, porosity, and the fibre volume to fibre surface area (Fv/Fs) ratio. The open structure of the fibre network, fabric patterns, creping, and protruding fibres make it challenging to define bulk boundaries. Therefore, we examined the effect of different bulk expansion diameters on intrinsic properties. This procedure allows to quantify the effects of under- and overestimation of bulk boundaries, and to determine which regions within the fibre network are affected by bulk expansion. In terms of intrinsic thickness, both 2D and 3D evaluations show similar trends, which facilitates direct comparison of 2D and 3D data. Porosity, on the other hand, does not show any correlation between 2D and 3D-based data. Together with the Fv/Fs parameter, this leads to the conclusion that the depiction of 2D data does not represent the whole fibrous material but predominantly fibres perpendicular or close to perpendicular to the cut plane, whereas 3D data represents all fibres, fibre bonds and network connectivity. This work aims at presenting modern approaches and novel procedures to quantify intrinsic properties of open fibre structures such as tissue, but could also be applied to fibrous networks in general. The introduced methods could provide the basis for future research on the interrelations between intrinsic properties and key tissue properties such as absorbency and handfeel.

Out-of-plane uniaxial loading of paperboard: experimental procedure and evaluation

Abstract Development of three-dimensional continuum models for paperboard is an active field and the need for reliable measurements to calibrate and validate such models is evident. An experimental device and protocol for cyclic out-of-plane loading is developed. This loading sequence is present during converting operations of paperboard. The experimental tests reveals that the commonly observed soft initial non-linear response during out-of-plane compression is a structural effect that stems from the surface roughness rather than being an inherent material behavior. A gluing procedure, used to perform cyclic out-of-plane loading, is mitigating the effect of the surface roughness. Several novel cyclic loading experiments are performed, alternating between compression and tension which indicates that fiber bonds are not recovered in compression after they have been broken through delamination. Measurements also show that the transition in compression and tension is continuous, hence the use of a switch function present in a number of constitutive continuum models for paperboard is deemed questionable.