Determination of optimal wood-dowel welding parameters for two North American hardwood species

Rotational wood-dowel welding has been shown to rapidly produce wood joints of considerable strength without any adhesive. The technique offers an opportunity to increase productivity and reduce costs in the furniture industry. The objective of the study was to define optimal wood-dowel welding parameters for two North American hardwood species frequently used for indoor appearance products: sugar maple (Acer saccharum) and yellow birch (Betula alleghaniensis). Optimized parameters for individually studied species were determined using a rotational wood-dowel welding machine designed for the technique. A comparative analysis of wood-dowel welding parameters was performed. The investigated parameters for both species were grain orientation, rotational speed, and insertion speed. Temperature profile measurements at the interface during rotational wood-dowel welding were also carried out. Optimal welding mechanical properties were determined from the dowel withdrawal strength using a standard tensile strength test. Results revealed a significant interaction between species, rotational speed, and insertion speed. Sugar maple produced wood joints with higher withdrawal strength than yellow birch. The best results for sugar maple and yellow birch were obtained with a rotational speed of 1000?rpm. A 25?mm?s^?1 insertion speed produced significantly stronger welded joints in sugar maple than at 12.5?mm?s^?1. For yellow birch, a 16.7?mm?s^?1 insertion speed provided the best results. Both species and rotational speed had a significant effect on peak temperature at the interface during welding. Peak welding temperatures with optimal parameters were 244 and 282?°C for sugar maple and yellow birch, respectively.     

Wood Welding: Chemical and Physical Changes According to the Welding Time

Wood welding using linear friction is a technique that has been developed in the past five years. The goal of this study was to analyze the microstructure development in the interphase enabling the wood-to-wood adhesion without any adhesive. Chemical and physical analyses have been carried out using infrared thermography, mechanical shear tests, transmitted light microscopy and X-ray densitometry. They have been considered as efficient to qualify the characteristics of the welded joints. The aim of this paper is to present a study using these analysis methods to observe the physical modifications of the wood in the interphase according to the welding time. The welding process of beech wood (Fagus sylvatia) with a welding time between 0 and 11 s could be divided into three different phases. The first phase describes changes in the physical and chemical characteristics of the wood. Densification and anatomical modifications occur in this phase. The second phase represents stabilization of the welded joint. The last phase of the cycle is a conditioning phase. All phases are controlled by the heat spread in the interphase and the time of heat exposure. Various parameters such as welding time, shear strength, temperature and width of the welded joint have been correlated and a hypothesis on the chemical reactions occurring in the interphase has been put forth. This study allowed discovering a window of parameters in which the quality of the welded joint is quite stable. Improving the quality of manufactured welded wood products without adhesive can now be done more easily due to this method.     

Enhancing water resistance of welded dowel wood joints by acetylated lignin

Low molecular mass acetylated organosolv lignin from wheat straw and from depolymerised low sulphur organosolv wood lignin have been shown to markedly improve both the water resistance and the mechanical performance of welded dowel wood joints. The acetylated oligomers distribution and extent of acetylation of the two lignins were determined by Matrix assisted laser desorption ionization-time-of-flight mass spectrometry. Extensive acetylation was confirmed by CP-MAS ¹³C NMR spectrometry. Force–displacement measurements on welded dowel joints to which acetylated wood lignins were added showed a ductile behaviour. This is due to the interpenetration of the elastic acetylated lignin network into the more rigid composite network of the welded interphase.     

Eco-Friendly Adhesives Based on Tannin and N,N-Bis(2-Hydroxy-Ethyl) Fatty Amides (HEFAs) from Non-Traditional Oils for Wood Bonding

Abstract

Wood adhesives were formulated using tannin and N,N-bis(2-hydroxyethyl) fatty amides (HEFAs). The natural tannin-based adhesives can be used to replace formaldehyde-based adhesive systems and thereby reduce formaldehyde and volatile organic compound (VOC) emissions from adhesives used for plywoods. Performance properties of the adhesively bonded wood joints viz., tensile strength, impact strength and chemical resistance were measured. N,N-bis(2-hydroxyethyl) fatty amides (HEFAs) from non-traditional oils were mixed with a pure tannin-based adhesive as a crosslinker, and this increased the tensile strength, impact strength and chemical resistance of wood joints. The results revealed that a high performance and eco-friendly adhesive system for wood can be successfully formulated using tannin and HEFA.     

Kraft pulping of Eucalyptus nitens wood chips biotreated by Ceriporiopsis subvermispora

Eucalyptus nitens and E. globulus are wood species used in kraft pulping in Chile and Australia. Although E. nitens adapts very well to cold regions it requires more severe cooking conditions to produce bleachable kraft pulps. An attempt was made to find out whether a pre‐treatment with Ceriporiopsis subvermispora would improve its performance during kraft pulping and the pulp properties. The biotreatment of the chips carried out for a period of 15 days resulted in 13.3% lignin loss and a limited glucan degradation (2%). The pulping of biotreated samples required lower active alkali charge to reach the target kappa number compared to the control untreated sample and exhibited better pulping selectivity. The pulp yield increased by 3% and 1.5% for the pulps of 22 and 16 kappa numbers, respectively. The biotreated pulp's strength properties were improved and were similar to those of E. globulus reference pulp. Copyright © 2006 Society of Chemical Industry     

Screening of Ophiostoma Species for Removal of Eucalyptus Extractives

Abstract

Ophiostoma species have been demonstrated to metabolize wood extractives and be useful to the pulp and paper industry. In order to have new isolates for the Asian market, Eucalyptus camaldulensis logs were harvested from forest sites in central Taiwan and 28 strains of the Ophiostoma genus were isolated from them. These strains were subsequently inoculated onto Eucalyptus wood chips to evaluate their effects on weight losses of wood and the amounts of acetone extractives degraded. At the same time, Gas Chromatography-Mass Spectroscopy (GC-MS) analysis was conducted and by using calibration curves and a database of GC-MS mass spectra, changes in lipophilic compounds were analyzed. Fatty acids, hydrocarbons, sterol compounds, sterol esters, and triglycerides were significantly reduced after two weeks’ inoculation by the fungal strains. The results show that six of the strains were capable of reducing the lipophilic fractions by more than 60% in a two-week treatment. DNA of the most effective strains were analyzed and found to be a variant of Ophiostoma querci.     

CHARACTERIZATION BY INFRARED SPECTROMETRY OF LIGNINS OF THREE EUCALYPTUS SPECIES

Lignin is, after cellulose, the main component of most vegetable fibers. The term lignin is very widely used and it is considered as a mixture of ramified natural polymers, of great structural complexity, with prevalence of aromatic structures, particularly phenolics where any defined repeated unit does not exist [1].

Eucalyptus is the common name of a gender of trees of the Mirtáceas family. The species Eucalyptus pellet F. Muell, Eucalyptus citriodora Hook and Eucalyptus saligna Smith are very diffused in Pinar del Río county.

In the Center of Studies of the Forest Biomass of the Pinar del Río University man works in the chemical characterization of these species, for their best use.

In this work, lignin IR spectra from the wood of these three eucalyptuses species, obtained by means of treatment with H₂SO₄ and from three heights of the tree trunk, are studied and compared.     

Influence of Welding Parameters and Wood Properties on the Water Absorption in Scots Pine Joints Induced by Linear Welding

Wood welding is an environmentally-friendly and very quick technique to yield wood joints in just a few minutes and without using any adhesives. The only limitation of welded wood is that the joint is suitable only for interior use. Exterior use, or use in an environment with varying humidity requires water resistance of the welded joints. An investigation was performed to determine the effects of welding parameters and wood properties on water absorption in the weldline and how to reduce it through controlling the production parameters. The influences of welding pressure, welding time, and heartwood/sapwood on water absorption in the weldline of Scots pine (Pinus sylvestris) joints were investigated. Specimens composed of two pieces of heartwood or sapwood, each of dimensions 200 mm × 20 mm × 20 mm, were welded together to form specimens of dimensions 200 mm × 20 mm × 40 mm. The specimens were allowed to stand in 5-mm-deep tap water and then they were taken out of the water one at a time and scanned in 10-min intervals until the first crack appeared in the weldline. An X-ray Computerized Tomography scanner was employed to monitor water movement and density change in weldlines during water absorption–desorption. All three evaluated parameters showed significant effect on water absorption. Samples of heartwood welded by 1.3 MPa welding pressure and 1.5 s welding time showed the lowest water absorption.     

Extractive Profiles in the Production of Sulfite Dissolving Pulp from Eucalyptus Globulus WOOD

The profile of major families of extractives soluble in acetone and dichloromethane during the production of acid sulfite dissolving pulp from Eucalyptus globulus wood was assessed. Nearly 85% of total extractives were removed from wood during pulping and nearly 11% in the course of E-O-P pulp bleaching and secondary pulp screening. Unlike extractives of polyphenolic origin that were almost completely removed after the alkaline extraction stage (E), fatty acids were the main retained component in fully bleached pulp followed by sterols and fatty alcohols. Throughout the bleaching steps, the profiles of extractives were not necessarily decreasing and depended on their reactions with bleaching reagents and the presence of auxiliary chemicals (e.g. antifoams). In this context, the content of fatty acids and fatty alcohols was mostly vulnerable. It has been suggested that Fock reactivity of dissolving pulps is unaffected by extractives at concentrations up to 0.3%.     

Some Aspects of Bond Formation and Failure in Adhesive Wood Joints

An investigation has been made of the effect of varying glue-spread on the bond strength of holly (Ilex aquifolium) using three adhesives and three different wood sections. The glue-spreads are lower than those normally used, and it has been found with edge-grain joints that 100% cohesive wood failure can occur with a glue-spread as low as 2.7mg/cm². Scanning electron microscopy shows that interlocking between adhesive and adherend does not occur. Factors leading to delamination and joint failure are discussed.

Lignin, without further addition, has been shown to be a useful wood adhesive. It has also been shown that it is possible to make end-grain joints without the use of an adhesive; the lignin present in the wood specimens is considered to be responsible for such joints.     

Influence of Weldling Parameters on Weldline Density and Its Relation to Crack Formation in Welded Scots Pine Joints

Exterior use of welded wood laminates without further treatment is not recommended. Frictional welded joints have poor resistance to moisture variation, especially to drying. Therefore, application of welded woods is limited to interior use without exposure to highly variable air humidity. Influences of some welding and wood parameters such as welding pressure, welding time and heartwood/sapwood on weldline density of Scots pine (Pinus sylvestris) joints were investigated. Interdependence between density and water resistance of weldline (in terms of crack time) was also studied by comparing the results of this investigation with those of the earlier studies. Specimens composed of two wood pieces, each measuring 20 mm × 20 mm × 200 mm, were welded together to form a specimen measuring 40 mm × 20 mm × 200 mm by a vibration movement of one wood surface against another at a frequency of 150 Hz. An X-ray Computerized Tomography scanner was used to measure weldline density. Weldlines of sapwood produced by 1.3 MPa welding pressure and 1.5 s welding time showed the highest density. No correlation between weldline density and crack time was evident.     

Physico‐Mechanical Properties and the TVOC Emission Factor of Gypsum Particleboards Manufactured with Pinus Massoniana and Eucalyptus Sp.

The effect of wood species on the TVOC emission factor and the physico‐mechanical properties of GPBs is investigated. Of the two wood species, the water absorption was higher for the GPBs made using Eucalyptus sp. than for those using Pinus massoniana. The Eucalyptus sp. GPBs pressed at room temperature, 40 and 60 °C all demonstrated higher moisture absorption than commercial GPBs. The TVOC emission factor decreased with increasing press temperature, especially for Eucalyptus sp. but remained under ‘excellent’ grade as defined by the KACA. From these results, GPB with higher content of wood particles should be considered for the replacement of wood‐based panels such as particleboard and medium density fiberboard (MDF).

     

Ultrasonic welding of all-polypropylene composites

In this study, the mechanical properties of ultrasonic welded lap joints of all-polypropylene composite (APPC) were investigated and compared to the interlaminar properties of the composite sheet itself. The process control parameter was welding time: welded samples were prepared with an ultrasonic welding machine in the 0.1–1.0 second time range. In most cases, the shear strength of the welded samples exceeded that of the unwelded APPC. Although it was found that during the ultrasonic welding process, the reinforcing tapes partially melted in the welding zone (WZ), the seam remained strong enough because the heat released and the pressure applied during the welding process further improved the consolidation of the APPC layers. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48799.     

Wood bonding by mechanically‐induced in situ welding of polymeric structural wood constituents

Mechanically induced wood fusion welding, without any adhesive, is shown here to yield rapidly bonding wood joints satisfying the relevant requirements for structural application. The mechanism of mechanically induced vibrational wood fusion welding is shown to be due mostly to the melting and flowing of amorphous cells–interconnecting polymer material in the structure of wood, mainly lignin, but also some hemicelluloses. This causes a partial detachment, the “ungluing,” of long wood cells and wood fibers and the formation of an entanglement network drowned in a matrix of melted material which then solidifies, thus forming a wood cell/fiber entanglement network composite with a molten lignin polymer matrix. During the welding period some of the detached wood fibers which are no longer being held by the interconnecting material are pushed out of the joint as excess fiber. Crosslinking chemical reactions of lignin and carbohydrate‐derived furfural also occur. Their presence has been identified by CP‐MAS ¹³C‐NMR. These reactions, however, are relatively minor contributors during the very short welding period. Their contribution increases after welding has finished, which explains why relatively longer holding times under pressure after the end of welding contribute strongly to obtaining a good bond. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 243–251, 2004     

Impact of effective alkali and sulfide profiling on Eucalyptus globulus kraft pulping. Selectivity of the impregnation phase and its effect on final pulping results

BACKGROUND: Eucalyptus globulus is an important wood source for paper production and, in the last few years, great efforts have been made to assess its chemical specificities and improve the kraft pulping efficiency. Despite the existence of several works concerning mostly the kinetics of E. globulus kraft pulping there is a lack of systematic studies on the initial phase of pulping as well as on the impact of effective alkali (EA) charge profiling on the kraft pulping performance of this species. The aim of the present work is to assess the effect of initial effective alkali and sulfide charges on the lignin and carbohydrates removal on the impregnation phase and to investigate the effect of EA splitting charge on the whole E. globulus pulping process efficiency. RESULTS: When the EA charge at impregnation phase increases, the amount of dissolved wood increases until it reaches a constant value of about 20%. Maximum polysaccharide removal at impregnation phase was about 10% of total wood weight. Glucose removal during impregnation was attributed to the degradation and/or dissolution of E. globulus glucans. For EA charges at impregnation phase higher than ～15%, xylan retention on wood was roughly constant. Despite the differences found at impregnation phase on the amount of dissolved wood and lignin removal, it was demonstrated that these differences are almost completely attenuated until the end of the kraft pulping process. CONCLUSION: In the case of E. globulus, for a constant effective alkali charge, alkali profiling does not affect the whole kraft pulping performance. Copyright © 2007 Society of Chemical Industry     

Mechanical Properties of Weldbonded Joints of Advanced High Strength Steels

In lightweight car body shell mass production, due to requirements on vehicle weight reduction and carbon dioxide emissions, joining of advanced high strength steels (AHSS) with different joining procedures and especially hybrid bonding techniques is becoming more and more important. One of these hybrid bonding techniques is the combination of resistance spot welding and adhesive bonding called weldbonding. One of the important advantages of weldbonded joints in comparison to resistance spot welded joints are the enhanced mechanical properties. To guarantee sufficiently high quality conditions regarding the strength of the weldbonded joints, the influences of the applied adhesive systems and of different base metal combinations are studied. This is carried out for both non-corrosive and corrosive environments and for the choice of different joining parameters settings. In particular, the mechanical behaviour of the weldbonded joints is investigated under quasi-static, impact and fatigue loads. Furthermore, the energy absorption of the weldbonded joints for both non-corrosive and corrosive environments is studied. It is shown that the weldbonded joints possess higher mechanical strengths in all load cases (quasi-static, impact and fatigue). Corrosive attack affects weldbonded joints, and the quasi-static strength is reduced. Resistance spot welded joints are not affected by the corrosive attack, but even after several weeks of corrosive attack, the quasi-static strength of weldbonded joints remains higher than that of resistance spot welded joints.     

Extending Near Infrared Reflectance(NIR) Pulp Yield Calibrations to NewSites and Species

Abstract

Recently, we demonstrated that the accuracy of pulp yield predictions for wood samples from a site (Gog) new to their calibration (Tasmania‐wide Eucalyptus nitens) was greatly improved by adding five Gog samples to the calibration set. In this study we investigated the addition of Gog samples to the Tasmania‐wide E. nitens set, with the aim of further improving predictive accuracy. It was demonstrated that the addition of a single Gog sample to the Tasmania‐wide calibration set was sufficient to greatly reduce predictive errors and that the inclusion of at least 3 Gog samples in the Tasmania‐wide set was sufficient to give relatively stable predictive errors. The addition of different sets of 5 Gog samples to the Tasmania‐wide calibration, however, caused predictive errors to vary between sets. The standard deviation of pulp yield for the prediction set (20 Gog samples) was important, with sets having the largest standard deviations giving the best predictive statistics. Finally, the Tasmania‐wide E. nitens calibration was enhanced using samples from a different species (Eucalyptus globulus) and applied successfully to other E. globulus samples.     

Analysis of the Mechanical Behavior of Wood and Welded Wood under Tensile–Shear Loads Using a Modified Arcan Device

Abstract

The aim of this work was to analyze the possibility of using a modified Arcan device to characterize the mechanical behavior, under tensile–shear loads, of wood and of wood assemblies obtained using friction welding without any adhesive. This process is interesting as only friction energy is used to assemble the two pieces of wood; thus, the process is characterized by low environmental impact and by easier recycling at the end of the product’s life. For this assembly technique to become widespread in industry, it is necessary to develop numerical tools in order to predict the behavior of such assemblies under complex loads. Thus, it is also necessary to obtain a large data base of experimental results under various tensile–shear loads, in order to analyze the multi-axial mechanical behavior of such welded assemblies. However, few experimental devices have been proposed in the literature, and furthermore, very few papers in the literature analyze the complex mechanical behavior of wood. This paper describes the use of a modified Arcan test to analyze the behavior of wooden blocks and their welded assemblies. The stress state in the middle of the specimens used was not homogenous and, thus, finite element simulations were required to determine the stress distributions. These simulations were possible as the load transmitted by the tensile loading machine was known. Some experimental results are presented in the case of beech wood in a transversal direction.     

Collapse of Eucalyptus nitens Wood After Drying Depending on the Radial Location Within the Stem

Collapse is almost certain to occur in the industrial drying of Eucalyptus nitens and, as such this prevents the lumber manufacturing industry in Chile from producing commercial solid wood products from this species. This problem is still unsolved, and different studies to reduce collapse are currently underway. In this exploratory study, shrinkage and collapse after drying of Eucalyptus nitens was measured for boards cut from different radial locations within the stem (core, transition, and outer wood from pith to bark) and having different annual ring orientations (flat-sawn and quarter-sawn). Though exploratory, the results appear to confirm that pieces that were cut from the center of the trees were less susceptible to collapse than pieces cut from the transition zone between the center and the periphery. On average, collapse in transition wood was approximately 50% higher than the collapse observed in wood cut from the central zone of the trees.     

Influence of wood extractives on two-component polyurethane adhesive for structural hardwood bonding

ABSTRACT

When bonding wood for structural applications, the wood–adhesive bond is influenced by a variety of factors. Besides the physical and mechanical properties of wood species, their chemical composition, e.g. wood extractives, can play a role in bonding wooden surfaces. A two-component polyurethane system (2C PUR) was chosen to better adapt to the current adhesion problem. The influence of extractives on crosslinking was determined by Attenuated Total Reflection-Fourier Transform Infrared Spectrometer (ATR-FTIR) and on the rheological behavior in terms of gel point and storage modulus. Therefore, 2C PUR was mixed with 10% of eight common wood extractives separately. Furthermore, the mechanical properties of beech wood (Fagus sylvatica L.) bonded with extractive enriched adhesive were tested by means of tensile shear strength tests and evaluation of wood failure. These results of ATR-FTIR clearly show that the majority of crosslinking was terminated after 12 hr. Acetic acid and linoleic acid expedited the isocyanate conversion during the first 2.5 hr. The curing in terms of gel point and storage modulus of 2C PUR was accelerated by starch, gallic acid, linoleic acid, and acetic acid. Heptanal, pentanal, 3-carene, and limonene decelerated the curing. All extractives lowered the storage modulus determined after 12 hr. The bonding of beech wood with extractive–adhesive blends showed a slight decrease of the mechanical properties, with the exception of a marginal increase in the case of linoleic acid and pentanal.

In summary, it can be said that 2C PUR is sensitive to the influence of wood extractives and can therefore be partly held responsible for adhesion problems occurring when extractives in surface-wide and higher contents are available.