Adhesive distribution related to mechanical performance of high density wood fibre board

In a full-scale mill experiment two groups of high density wood fibre boards were produced. While one group was bonded with a standard melamine reinforced urea-formaldehyde adhesive, a second group was bonded with a modified adhesive yielding systematically improved board properties at identical amounts of adhesive applied. By means of a novel fluorescence-microscopic method using the dye Acriflavine to colour the cured adhesive after board production, adhesive distribution within the industrial produced boards was evaluated and quantified. Very clear differences in the size distribution of the two adhesives were found, leading to the conclusion that a relationship exists between adhesive distribution and mechanical board performance.     

Development and characterization of a wood adhesive using bagasse lignin

Bagasse is spent fiber left after extraction of sugar. It is mainly used as a fuel to concentrate sugarcane juice. In the present work, the possibility of preparing wood adhesives from bagasse has been explored. The parameters for the preparation of a lignin phenol formaldehyde (LPF) adhesive, (lignin concentration, formaldehyde to phenol molar ratio, catalyst concentration, reaction time and reaction temperature) have been optimized. It was found that up to 50% of phenol can be substituted by bagasse lignin to give LPF wood adhesive having better bonding strength in comparison to a control phenol formaldehyde (CPF) wood adhesive. Prepared resins were characterized using IR, DSC and TGA. IR spectra of LPF resin showed structural similarity with CPF resin. Thermal stability of LPF resin was found to be lower as compared to CPF resin. DSC studies reveal a lower curing temperature for LPF adhesive in comparison to CPF adhesive. A shelf-life study reveals that LPF exhibits consistent behavior as compared to CPF in respect to adhesive strength.     

Preparation,characterization and properties of an organic siloxane-modified cassava starch-based wood adhesive

A new method of preparing a cassava starch-based wood adhesive with high performance using hydrogen peroxide, acrylamide, butyl acrylate (BA), and an organic siloxane as an oxidant, a hard co-monomer, a soft co-monomer, and crosslinking agent, respectively, is proposed. The effects of various parameters on the shear strength, the water resistance, and the viscosity of the adhesive were investigated. The results showed that the shear adhesive strength in dry state and wet state of cassava starch-based adhesive could reach 6.11 MPa and 3.05 MPa, respectively. The organic siloxane, when added, could reduce the content of the hydroxyl on the starch molecule, and promote the crosslinking of the starch molecules, improving the bonding strength and water resistance.     

Durability of PBI adhesive bonded joints under various environmental conditions

Structural adhesives are finding increasing use in many applications. However, their utilization at elevated temperature has always been a challenge due to their low thermal and mechanical properties. However, in recent years, the development of high performance polymers have overcome the problem of using adhesive bonding at high temperature to some extent. Polybenizimidazole (PBI) is one such recently emerged high performance polymer with excellent thermal and mechanical properties. It has a tensile strength of 160 MPa and a glass transition temperature (T_g) of 425 °C. Due to its excellent thermal and mechanical properties, it has the potential to be used as an adhesive under various environmental conditions. In the present work, efforts are devoted to explore the potential of using PBI at high temperature and in hot-wet environmental conditions. M21 and DT120 epoxy based carbon fiber composite bonded joints were prepared and tested. Both M21/carbon composite and DT120/carbon composite have exhibited a reduction in joint strength of about 16% and 25% respectively after 1000 h of conditioning in a hot-wet environment. However, a reduction in lap shear strength of 52% and 56% is observed when composite bonded joints were tested at 80 °C.     

Covalent bonding of wood through chemical activation

The reaction of softwood thermomechanically pulped fibres with succinic anhydride (SA) and its subsequent reaction with hexamethylene diamine (HMDA) were examined, the latter employing the coupling agents dicyclohexylcarbodiimide, or diisopropylcarbodiimide. FTIR and ¹³C NMR studies showed amide linkages were produced between SA modified fibres and the diamine. Wood veneers were covalently bonded using this technology. It was found that during hot pressing bonding occurs between SA treated veneers and HMDA without the need for a coupling agent.     

Rods glued in engineered hardwood products part I: Experimental results under quasi-static loading

Glued-in Rods (GiR) represent an adhesively bonded structural connection widely used in timber engineering. Up to now, common practice largely focused on softwood. Most structural adhesives have been, accordingly, specifically formulated to perform on softwood, in particular spruce. The increased use of hardwood, and corresponding engineered wood products (EWP), calls for deeper insights regarding GiR for the connection thereof. This paper, the first of a two part series, presents an overview over extensive research carried with 9 adhesives, 3 EWP, and 4 types of rods. Investigations started at component level, by fully characterising all adhesives, EWP, and rods. They were then extended to characterise the behaviour of interfaces, providing by this a methodology for selecting adhesives. Investigations at full scale followed, involving 5 different adhesives, 3 EWP, and 4 rod types. A total of 180 individual samples were tested. The results allowed to draw conclusions about the relationship between performance of GiR connections, and mechanical properties of their components. This relationship, however, has been found to be relatively weak. The companion paper will present a design methodology based on the material properties determined herein, and explain the ambiguous relationship between performance of the GiR and the mechanical properties of the adhesive, wood, and rods     

Evaluation of a structural epoxy adhesive for timber-glass bonds under shear loading and different environmental conditions

This article presents a study of timber-glass adhesive joints. It examines the shear specimen and shear tools preparation process and the evaluation of the results backed up with an overview of existing similar studies. The chosen adhesive was a cold-curing two-component structural bonding epoxy resin (Mapei Adesilex PG1). The shear tests were performed under different temperatures and the timber samples had different moisture contents. A simple shear test tool was designed and was clamped into a universal testing machine for the shear test. The force and crosshead displacement values from the universal testing machine were used for evaluating the results. The environmental conditions of 20 °C and 5% timber moisture content resulted in the highest average shear strength obtained from the shear tests of the analysed joints (9.89 MPa), whereas the environmental conditions of 50 °C and 20% timber moisture content resulted in the lowest average shear strength (3.42 MPa). It was found that the joint strength is dependent on the environmental temperature and timber moisture content. Moreover, the shear specimen load-displacement behaviour at the environmental temperature of 50 °C was linear and nonlinear – depending on the timber moisture content. The most frequent failure type was timber failure. Additionally, a nonlinear contact finite element analysis was performed to demonstrate the additional shear specimen rotation due to the clearance between the shear specimen and shear tools. This impact was evaluated regarding the stress distribution in the bond line. The evaluated epoxy resin adhesive was proved to be suitable for timber-glass bonds.     

Bio-adhesives from soy protein concentrate and montmorillonite: Rheological and thermal behaviour

The incorporation of different amounts of montmorillonite (MMT) to soy protein concentrate (SPC) was used to improve the performance of the bio-nano-adhesive obtained. X-Ray diffraction, rheology, thermogravimetric analysis and scanning electronic microscopy were carried out to characterize the adhesives, and dry and wet strength was used to determine the adhesion strength. In the rheological measurement, the incorporation of up to 3 wt% of MMT did not modify the consistency index values of the SPC, while an increase in the flow consistency index for higher concentrations can be observed due to a strong interaction between MMT and the protein. Besides, the flow point values increase four times with respect to the value obtained for SPC alone. The decomposition temperature of SPC increases with the addition of MMT, which provides a tortuous pathway that obstructs the diffusion of volatile products out of the bio-nano-adhesive. Further addition beyond 5 wt% led to the formation of agglomerates, as verified by SEM. Moreover, the roughness of the fractured surface of the matrix can explain the decrease of the net adhesion of the nano-particles to the SPC suspensions.     

Processing of dense nanostructured HAP ceramics by sintering and hot pressing

A nanosized HAP powder was sintered and hot pressed, in order to obtain dense HAP ceramics. In a first series of experiments, the powder was isostatically pressed into uniform green compacts and sintered at temperatures ranging from 1000 °C to 1200 °C in air atmosphere for different times. In a second series, the isostatically pressed green compacts were hot pressed in argon atmosphere at 900 °C, 950 °C and 1000 °C. The SEM micrograph of the sample sintered at 1200 °C for 2 h showed a uniform 3 μm mean grain size dense microstructure. In the case of hot pressed HAP compacts, full dense, translucent nanostructures were obtained having mean grain size below 100 nm and improved mechanical properties. With the grain size decreasing from 3 μm to 50 nm, the fracture toughness of pure HAP ceramics increased from 0.28 MPa m^1/2 to 1.52 MPa m^1/2.     

Carbon-ceramic composites from coal tar pitch and clays: application as electrocatalyst support

Carbon-ceramic composites have been prepared and characterised by different techniques (electron microscopy, X-ray microanalysis, X-ray diffraction and cyclic voltammetry). The effect on the conductivity of the thermal treatment temperature of the composites and the structure of the starting ceramic has been analysed. The results demonstrate that the layered structure of the clay determines their conductivity. The composites prepared are conductors and the conductivity goes through a maximum with increasing thermal treatment. Platinum has been successfully deposited on the carbon-ceramic composite by chemical and electrochemical methods. A better distribution of platinum and smaller particle sizes are obtained by the electrochemical method. The direct electrooxidation of methanol in acid medium has been studied on platinum-modified carbon-ceramic electrodes.     

Rods glued in engineered hardwood products part II: Numerical modelling and capacity prediction

The second part of this series of two papers presents the modelling and strength prediction of Glued-in Rods (GiR) experimentally investigated in Part I. Unlike what has been documented in previous publications, significant effort was put into extensive modelling of all components (adhesive, wood, and rods), in particular regarding stress components other than shear. Based upon the material modelling, stresses inside the GiR were estimated through Finite-Element Analysis (FEA), which indicated that transverse tensile strength are at least as significant as shear stresses in their magnitude. Both results mitigate previous research findings that focused on shear-dominated failure mechanisms and neglected transverse tensile strength. Combining the material characterisation with FEA, and reformulating strength in probabilistic terms, then allowed to perform predictions of joint capacities for all 60 experimentally investigated GiR-configurations. The comparison between predicted and experimental values showed a good agreement wit relative difference amounting to –3% for beech GLT, –2% for oak GLT, and +1%, respectively. Unlike Fracture Mechanics and Cohesive Zone Modelling, necessary parameters were solely obtained independently from the GiR itself, and no single parameter had to be back-fitted on the experimental results of the GiR. Results clearly showed that transverse tensile strength of the wood is at least as important as shear strength for joint capacity of GiR, and that longitudinal strength plays a minor role.     

The nanocomposites of carbon nanotube with Sb and SnSb0.5 as Li-ion battery anodes

Nanocomposites of carbon nanotubes (CNTs) with Sb and SnSb_0.5 particles were prepared by chemical reduction of SnCl₂ and SbCl₃ precursors in the presence of CNTs. SEM and TEM imaging showed that the Sb and SnSb_0.5 particles are uniformly deposited on the CNT exterior and in the CNT web. These CNT-metal composites are active anode materials for lithium ion batteries, showing improved cyclability compared to unsupported Sb and Sn-Sb particles and higher reversible specific capacities than CNTs. The reversible capacities were as high as 462 mAh/g for CNT-36 wt.% Sb and 518 mAh/g for CNT-56 wt.% SnSb_0.5. After 30 cycles, the capacity was 62.1% of the initial capacity for the former and 67.2% of the initial capacity for the later. In comparison Sb and SnSb_0.5 could only retain 17.7 and 23.5%, respectively of their initial capacities in the same number of cycles. The improvement in cyclability may be attributed to the nanoscale dimension of the metal particles and CNTs’ role as a buffer in relieving the mechanical stress induced by specific volume changes in electrochemical lithium insertion and extraction reactions.     

Use of organosolv lignin in phenol-formaldehyde resins for particleboard production: II. Particleboard production and properties

The objective of this work was to demonstrate the utility of lignin-based resins designed for application as an adhesive in the production of particleboard. Bond qualities of lignin-phenol-formaldehyde resins, phenolated-lignin-formaldehyde resins and commercial phenol-formaldehyde (PF-com) resin were assessed by using an automatic bonding evaluation system, prior to production of particleboards. In order to evaluate the quality of lignin-based resins, particleboards were produced and physical and mechanical properties were investigated. These physical properties included internal bond, modules of rupture and modulus of elasticity. Thickness swell and water absorption properties of particleboards bonded with lignin-based resins were also determined. The lignin-based resins have been reported previously in Part I of this study. The results showed that particleboards bonded with phenolated-lignin formaldehyde resins (up to 30% lignin content) exhibited similar physical and mechanical properties when compared to particleboards bonded with PF-com. The work has indicated that phenolated-lignin formaldehyde resins (up to 30% substitution level) can be used successfully as a wood adhesive for constructing particleboard. The performance of these panels is comparable to those of boards made using PF-com resin.     

Preparation,structure, and property of wood flour incorporated polypropylene composites prepared by a solid‐state mechanochemical method

In this article, a solid‐state mechanochemical method based on a pan‐mill equipment was used to prepare 60 wt % loading of wood flour (WF) incorporated polypropylene (PP) wood–plastic composite (WPC) with good comprehensive performance. The particle size distribution, crystallization, microstructure, and properties of the prepared WPC were accordingly investigated. The results show that under co‐effects of the strong shear force field of pan milling and the compatibilization of PP grafted maleic anhydride (PP‐g‐MAH), the mixture of PP and WF is effectively pulverized and homogeneously mixed. Meanwhile, the WF particles are adequately activated by exposure of their characteristic functional groups, which is beneficial to the interfacial mechanochemical reaction. PP‐g‐MAH and PP prove to be in situ grafted onto WF particles surface during pan milling, thus resulting in the substantial enhancement in both the dispersion of the added WF fillers in PP matrix and the interfacial bonding. The mechanochemical effects of pan milling could also remarkably promote the heterogeneous nucleation effect of WF particles on PP crystallization and influence the dynamic mechanical behavior of composite. Compared with the unmilled and uncompatibilized composite, the milled and compatibilized WPC material possesses greatly enhanced mechanical performance and shows good application prospects. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43108.     

Preparation, electrical and elastic properties of new anisotropic expanded graphite-based composites

New composite materials with application to catalyst supports or adsorbents are presented. They are made of compressed expanded graphite of various densities first impregnated by polyfurfuryl alcohol and next pyrolyzed and activated. The resultant materials are monoliths comprising a graphite backbone coated by a thin layer of active carbon. The electrical conductivity and the dynamic elastic moduli are measured on each kind of material, namely before and after carbonization, and finally after activation. The results are shown to be consistent with a percolation phenomenon: the conductivity and the rigidity thresholds are derived, and several theoretical considerations and comparisons with pure expanded graphite are made. The discussion leads to a better understanding of the structure of the materials before and after impregnation, namely the graphite backbone and the graphite-polymer or carbon composites. Besides, their conductive and elastic properties are shown to be very good. Hence, the materials are expected to have fair thermal conductivities, to be electrically regenerable (application as adsorbents) and to have an interesting life time (application as catalyst supports).     

Fabrication of tubular SiCf/SiC using different preform architectures by electrophoretic deposition and hot pressing

This paper reports the processing feasibility of electrophoretic deposition combined with hot pressing in the fabrication of dense tubular SiC_f/SiC composites using a cylindrical mold. A simulation of pressure distribution using ANSYS software was performed by varying the angular inclinations in a cylindrical mold with an ‘out → in’ configuration so as to ensure a maximum and uniform conversion of vertical hot press force to the lateral side of a centrally-located preform through graphite powder. The simulation revealed an inhomogeneous pressure distribution along the height of the preform, which could be minimized by mold optimization to achieve a more uniform tube density. To verify this, two different preform architectures such as 0/90° woven 2-D fabric rolled in a jelly state and filament winding with two plies having an inter-ply angle of 55° were hot-pressed using a mold fabricated based on the simulation after infiltrating the matrix phase by electrophoretic deposition. The density of the tube could be increased with more uniform microstructures. Although the tube using a filament winding preform exhibited a lower flexural strength (105 MPa) and relative density (90%) than those with the preform rolled in a jelly state (221 MPa, 95%), the results revealed a high degree of fiber pull-out due to the PyC coating on the SiC fiber.     

Scaling properties in the molecular structure of three-dimensional, nanosized phenylene-based dendrimers as studied by atomistic molecular dynamics simulations

Three-dimensional polyphenylene dendrimers (PDs) can be prepared in ways that enable control of their shape. Their structures may be used as scaffolds with a wide variety of functionality, enabling them to be used as functional nanoparticles with a large range of possible applications, ranging from light emitting devices to biological sensors or drug delivery tools. As PDs have been synthesized only recently, their structural and chemico-physical characterization is still in its infancy. Accordingly, in this paper the shape and internal organization of three PD families based on three different cores were probed by accurate, atomistic molecular dynamics simulations (MD). Particular care was taken to ensure complete structural equilibration by implementing an MD simulated annealing protocol prior to evaluation of the molecular structure and dynamics. All dendrimer families were found to be characterized by molecular dimensions in the nano-range, and by a shape-persistent, non-spherical structure, of molecular fractal dimension around 2.5-2.6, and of surface fractal dimension practically constant and almost equal to 2 with increasing generations in all cases. The MD analysis revealed also that, for this type of dendrimers, the starburst limited generation is presumably located in correspondence of the third generation.     

Microstructure and properties of (SiC, TiB2)/B4C composites by reaction hot pressing

(SiC, TiB₂)/B₄C composites were fabricated by reactive hot-pressing B₄C, Si₃N₄, -SiC and TiC powders, with (Al₂O₃ + Y₂O₃) as sintering additives. According to the thermodynamics principles, the possible reaction equations and the reaction products for the system were determined. By means of XRD, SEM of surface thermally etched and TEM the phase composition was determined. It was shown that the phase composition of sintered body was B₄C, -SiC, BN and TiB₂, and the matrix was B₄C and -SiC. The typical values of hardness, bending strength, fracture toughness and the relative density of the composites can reach HRA 88.6, 554 MPa, 5.6 MPa m^1/2 and 95.6%, respectively. Furthermore, the microstructures of the composites were analyzed by TEM, SEM and energy spectrum methods. The results show the presence of laminated structure and a clubbed frame dispersion phase and bunchy dispersion phase among the matrix. Some intragranular structures were also found in the B₄C grains. Microstructural analysis indicates that the new formed phase, uniform and fine grains, and the layered and clubbed structure play an important role in improving the properties of the composites. Fractography and crack propagation suggest that crack deflection and crack bridging are the possible toughening mechanisms.     

Competitive adsorption of Pb, Cu and Cd ions from aqueous solutions by multiwalled carbon nanotubes

The individual and competitive adsorption capacities of Pb²⁺, Cu²⁺ and Cd²⁺ by nitric acid treated multiwalled carbon nanotubes (CNTs) were studied. The maximum sorption capacities calculated by applying the Langmuir equation to single ion adsorption isotherms were 97.08 mg/g for Pb²⁺, 24.49 mg/g for Cu²⁺ and 10.86 mg/g for Cd²⁺ at an equilibrium concentration of 10 mg/l. The competitive adsorption studies showed that the affinity order of three metal ions adsorbed by CNTs is Pb²⁺>Cu²⁺>Cd²⁺. The Langmuir adsorption model can represent experimental data of Pb²⁺ and Cu²⁺ well, but does not provide a good fit for Cd²⁺ adsorption data. The effects of solution pH, ionic strength and CNT dosage on the competitive adsorption of Pb²⁺, Cu²⁺ and Cd²⁺ ions were investigated. The comparison of CNTs with other adsorbents suggests that CNTs have great potential applications in environmental protection regardless of their higher cost at present.