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Thermo-hydro-mechanical (THM) processing can improve the intrinsic properties of wood, produce new materials, and give desired form and function to new applications. THM treatments change the mechanical properties of wood and may change its viscoelastic properties as well. Therefore, the objective of this study was to assess the viscoelastic properties of THM-treated wood at several humidity and load levels. To explore these changes, this study applied a THM treatment to beech (Fagus sylvatica L.) wood with steam (620 kPa) and heat (170 °C), followed by densification and increased temperature (200 °C) in a hot-press, which was then cooled while under pressure. Two initial specimen thicknesses before THM treatment were used to study the difference between density ratios. Specimens were tested in a humidity-controlled dynamic mechanical analyser (DMA) to apply creep stress with different loading levels (20% and 30% of expected modulus of rupture) and relative humidity levels (30%, 50%, and 65% RH). The creep compliance/recovery response was monitored, and dynamic moduli were measured before and after the application of creep stress. The loss modulus measured was highest for specimens tested at 65% RH and lowest in specimens tested at 30% RH, which is a direct result of the viscous response of the material. Increased damping of the specimens was also observed at higher RH, which is typical for wood products due to added moisture in the cell wall acting as a plasticizer to cell wall polymers. Like previous studies, THM treatment lowered the equilibrium moisture content (EMC) of densified wood specimens, which affected their mechanical performance. THM treatment yields higher strength and lower EMC, suggesting that this product could be suitable for structural applications where their service life is in an indoor environment. THM treatment also resulted in decreased creep compliance and recovery compliance as compared to control specimens.

The surprising lack of literature on using the very common wood adhesive polymeric methylenediphenyl diisocyanate (pMDI) with protein adhesives may be because of perceived poor improvement of protein wet strength. Reacting pMDI with the flour (soy or canola) before adding water unexpectedly improves wood bonding compared to adding the pMDI to an aqueous protein slurry. Mixing the liquid pMDI with the oilseed flour produces a free-flowing powder with up to 50% of pMDI to flour by weight. The mixture slowly reacts since the isocyanate band in the infrared spectra remains for several days but diminishes with time. Adding pMDI increases the dry and wet strength of wood bonds using Automated Bonding Evaluation System (ABES) testing and levels off at about 50%. Similarly, adding the polyamidoamine-epichlorohydrin (PAE) cross-linker to the oilseed flour increases dry and wet bond strength, but the effect levels off at about 20% of PAE. However, the combination of these two cross-linkers added to the flours results in greater dry and wet shear strength than either one alone. In addition to tests using ABES (ASTM D 7998), the increase in strengths is also observed—but with a diminished effect—in bonding plywood using the interior plywood strength test ASTM D 906.

Understanding why wood bonds fail is an excellent route toward understanding how to make them better. Certifying a bonded product usually requires achieving a specific load, percent wood failure, and an ability to withstand some form of moisture exposure without excessive delamination. While these tests protect the public from catastrophic failures, they are not very helpful in understanding why bonds fail. Understanding failure often requires going beyond what meets the naked eye, conducting additional tests, probing the wood surface, the fracture surface, adhesive properties, and the interaction of wood and adhesive during bond formation and service. This review of wood bond analysis methods reviews fundamentals of wood bonding and highlights recent developments in the analyses and understanding of wood bonds. It concludes with a series of challenges facing the wood bonding community.

To meet newer environmental standards, modified plant proteins have been studied as no‐added formaldehyde wood adhesives for interior applications. Many methods have been developed to increase the wet strength of wood products bonded with soy adhesives. These methods involve modifying the soy in separate steps prior to formulating the adhesive or adding a polymerizable co‐reactant to the soy. We show that adding periodate, permanganate, or iodate to soy flour improved the strength of soy adhesive bonds in small‐scale testing and in plywood shear, especially when tested under wet conditions. Periodate improved the bond strength of other plant materials (lupine, canola, and cottonseed) but none of these produced as high of a wet strength as the soy flour. We investigated other oxidants with plant proteins. Permanganate was quite effective and iodate was somewhat effective, whereas nitric acid, chlorate, perchlorate, and bromate were not effective in increasing wet strength. The available data are consistent with oxidation of the carbohydrate–protein mixture in plant flours to provide adhesives with increased wet strength in wood bonds. This mechanism was also supported by the improved wet strength with the addition of dialdehydes (glyoxal and glutaraldehyde). The purified soy protein also gave strength improvement with periodate. Published 2019. This article is a U.S. Government work and is in the public domain in the USA. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1017–1023

Our future bioeconomy depends on increased utilization of renewable lignocellulosic biomass. Controlling the diffusion of chemicals, such as inorganic ions, within secondary plant cell walls is central to many biomass applications. However, insufficient understanding of intra-cell-wall diffusion within secondary plant cell walls is hindering the advancement of many lignocellulosic biomass applications. In this work, X-ray fluorescence microscopy was used to measure diffusion constants of K+, Cu2+, and Cl− diffusing through loblolly pine (Pinus taeda) cell wall layers under 70%, 75%, or 80% relative humidity (RH). Results revealed that diffusion constants increased with RH, the larger Cu2+ diffused more slowly than the K+, and the Cl− diffusion constant was the same as that for the counter cation, indicating cations and anions diffused together to maintain charge neutrality. Comparison with electrical conductivity measurements showed that conductivity is being controlled by ion mobility over these RH. The results further support that intra-cell-wall diffusion of inorganic ions is a Fickian diffusion process occurring through rubbery amorphous polysaccharides, which contradicts previous assertions that intra-cell-wall diffusion is an aqueous process occurring through water pathways. Researchers can now utilize polymer science approaches to engineer the molecular architecture of lignocellulosic biomass to optimize properties for specific end uses.

The properties of cured wood adhesives are difficult to study because of the loss of water and other components to the wood, the influence of wood on the adhesive cure, and the effect of adhesive penetration on the wood interphase; thus, normal testing of a neat adhesive film is generally not useful. Most tests of wood adhesive bond strength are slow, laborious, can be strongly influenced by the wood and do not provide information on the kinetics of cure. Test method ASTM D 7998-19, however, can be used for fast evaluation of the strength of wood bonds. The use of a smooth, uniform, and strong wood surface, like maple face-veneer, and sufficient bonding pressure reduces the adhesion and wood strength effects on bond strength. This method has three main applications. The first is to provide consistent data on bond strength development. The second is to measure the dry and wet strengths of bonded lap shear samples. The third is to better understand the adhesive heat resistance by quickly evaluating thermal sensitivity and distinguishing between thermal softening and thermal degradation.

The improved fungal decay resistance exhibited by modified wood has been attributed to inhibited diffusion of decay precursors and subsequent degradation products through the wood cell wall. However, data relating the effect of modification to diffusion through wood cell walls is lacking. Synchrotron X-ray fluorescence microscopy paired with an in situ humidity chamber was used to observe the transport of an implanted model metabolite, potassium (K+) ions, in wood cell walls as a function of relative humidity (RH) and extent of the wood modification acetylation. The RH threshold for K+ transport in wood cell walls increased with increasing levels of acetylation between 0 and 20 wt percentage gain (WPG), which clearly indicates that acetylation inhibits ion transport in the modified wood cell walls. The reduced equilibrium moisture content (EMCR or moisture based on wood polymer mass) thresholds were also calculated, but the trend of EMCR thresholds with WPG was inconclusive. Although the results provided support to the proposed mechanism that diffusion inhibition in acetylated wood caused decay resistance, the results could not confirm that diffusion inhibition was the most important mechanism. The observed inhibition of K+ transport in acetylated wood should motivate additional work to understand how chemical modifications affect cell wall diffusion and the implications for producing decay-resistant wood.

To accelerate development of new and improved wood adhesives for engineered wood products, the optimal adhesive penetration into wood needs to be better understood for specific products and applications. Adhesive penetration includes both flow of adhesives into wood micron-scale voids and infiltration into the polymer components of the wood cell wall layers. In this work, X-ray computed tomography (XCT) and X-ray fluorescence microscopy (XFM) were used to study adhesive flow and infiltration. Model wood–adhesive bondlines were made using loblolly pine (Pinus taeda) latewood substrates and bromine-substituted phenol formaldehyde (BrPF) resins with different weight-average molecular weights (MW). The Br substitution facilitated both qualitative and quantitative observations using XCT and XFM. The BrPF resin flow into wood was visualized using XCT volume reconstructions and quantified by calculating the weighted penetration (WP). Examination of the shape of the cured BrPF–air interface in longitudinal tracheid lumina revealed that capillary action often played a role in BrPF flow. XFM mapping revealed the pathways of BrPF infiltration into the wood cell walls, and the results were used to calculate BrPF cell wall weight percent gain (WPGCW) in individual wood cell walls. Both WP and WPGCW decreased with increasing BrPF MW. Additionally, the middle lamella had higher WPGCW than its neighboring secondary cell walls, and within a given bondline the WPGCW decreased with increasing distance of the cell from the bondline. The results provide new insights that are needed in the development of improved models to understand and predict wood–adhesive bondline performance.

To simulate fuel oil spills occurring during catastrophic floods, short-term absorption of two chemicals, n-hexadecane (representative of semivolatile organic compounds in fuel oil) and water, into southern yellow pine was gravimetrically monitored as a function of time at ambient conditions. Different scenarios were run on the basis of (1) the order of contamination (n-hexadecane followed by water or vice versa) and (2) whether the wood lateral sides were covered with epoxy. The experiments were designed to evaluate fast initial sorption, allowing separate estimation of the end-grain (i.e., total longitudinal) and lateral (i.e., surface longitudinal) liquid penetration. Presaturation of wood with water did not significantly impede the subsequent penetration of n-hexadecane, whereas the presaturation of wood with n-hexadecane led to a significant decrease of the subsequent water uptake. This difference in penetration on the basis of the order of application was explained by the differences in the...

Contamination of wooden framing structures with semivolatile organic chemicals is a common occurrence from the spillage of chemicals, such as impregnation with fuel oil hydrocarbons during floods. Little information is available to understand the penetration of fuel oil hydrocarbons into wood under ambient conditions. To imitate flood and storage scenarios, the sorption of n-hexadecane (representing fuel oil hydrocarbons) and water by southern yellow pine was studied using gravimetric techniques at ambient temperature and pressure. The sorption curves obtained had three distinct regions, reflecting three different sorption phases. Lower sorption coefficients were obtained for nonpolar n-hexadecane than for water, leading to n-hexadecane maximum mass uptake values being half those of water. Lower penetration values were obtained for epoxy-coated wood compared with uncoated wood, apparently because of the inaccessibility of diffusion paths along the wood lateral surface and slower air removal from ...

Wood material surface properties play an important role in adhesive bond formation and performance. In the present study, a test method was developed to evaluate the integrity of the wood surface, and the results were used to understand bond performance. Materials used were rotary cut birch (Betula pendula Roth) veneers, produced from logs soaked at 20 or 70 °C prior to peeling and followed by drying at 160 °C. Surface quality was evaluated through surface roughness measurement, SEM imaging, lathe check depth evaluation and surface integrity testing. The results show that soaking logs at 70 °C rather than at 20 °C before peeling produced veneers with decreased surface roughness, shallower lathe checks and better integrity. All these parameters are mainly affected by the lathe check depth, which is observed on the loose side of veneer. On the tight side of veneer, the only detectable differences were the mode of cell wall failure observed under SEM, and the greater amount of very fine particles loosely bound to the surface. Higher soaking temperature also produced a surface with “hairy” structure and larger surface area, which could promote strong adhesive bond development. The surface integrity measurements were found to be very useful for evaluating the quality of veneer surfaces.

As a result of the dominance of urea formaldehyde (UF)-bonded particleboard, it seemed worthwhile to examine formaldehyde emissions years after production. A California Air Resources Board (CARB) phase II-compliant commercial particleboard produced with a UF resin adhesive was compared to a no-added formaldehyde (NAF)-particleboard produced with Soyad&trade, adhesive resin for formaldehyde emissions during exposure to elevated humidity and temperature conditions after being in a room at 21 &plusmn, 1.9 &deg, C, 50 &plusmn, 3.3% relative humidity for 3.5 years. A modified version of EN 717-3 was used to collect formaldehyde emissions under typical along with higher temperature and humidity conditions. The formaldehyde emissions from the commercial particleboard panel bonded with a UF adhesive even after the 3.5 years of exposure greatly increased only during exposure of the panels to elevated heat and humidity compared to typical testing conditions. The amounts were the same as those with the previous shorter-term study. In contrast, formaldehyde emissions from the NAF-bonded particleboard were not as susceptible (in absolute terms) to increases in temperature and relative humidity conditions.

Sodium periodate has been shown to cleave glucose by specific oxidation to yield a number of non-volatile aldehydes which can react with the phenolic compounds in tannin extract and lead to tannin cross-linking and hardening. This approach to prepare a tannin resin useable for wood adhesives can be used by either treating with periodate a mixture of tannin and glucose, or to treat glucose beforehand with periodate to cleave it and generate the aldehydes, and only afterwards to mix it with the tannin. The results obtained with these two methods are identical, but the latter method avoids oxidation of tannin. The aldehydes were generated either by direct cleavage of glucose C–C bonds carrying vicinal oriented hydroxyls, or by recombination of the aldehydes so formed by aldol condensation or by water elimination between two aldehyde groups. MALDI ToF analysis indicated that all the three types of aldehydes appeared to react with the polyphenols in the tannin. Thermomechanical analysis (TMA) and plywood bonded with the tannin + glucose + periodate mixes gave good bonding results, with dry, 24 h cold water soaking and 3 h at 63 °C shear strength values improving concomitantly to the proportion of periodate used for the oxidation step.

Although formaldehyde emissions from interior wood products have been extensively studied emissions of other volatile organic compounds VOCs have received less attention and engineered products are seldom study Thus thirteen commercially ndash bonded engineered wood products structural plywood oriented strandboard structural composite lumber I ndash joists and glued ndash laminated timber from North America were evaluated for VOCs using methods developed for interior bonded wood products The dominate volatiles for the different products were greatly dependent on wood species and bonding process used preventing a universal conclusion In fact the volatiles from the adhesives seem to play a minor role For example the volatiles of Douglas fir plywood and southern pine plywood and oriented strandboard are all quite different from each other These data provide a basis for any future studies on bonded structural engineered wood products

Understanding and controlling molecular-scale interactions between adhesives and wood polymers are critical to accelerate the development of improved adhesives for advanced wood-based materials. The submicrometer resolution of synchrotron-based X-ray fluorescence microscopy (XFM) was found capable of mapping and quantifying infiltration of Br-labeled phenol-formaldehyde (BrPF) into wood cell walls. Cell wall infiltration of five BrPF adhesives with different average molecular weights (MWs) was mapped. Nanoindentation on the same cell walls was performed to assess the effects of BrPF infiltration on cell wall hygromechanical properties. For the same amount of weight uptake, lower MW BrPF adhesives were found to be more effective at decreasing moisture-induced mechanical softening. This greater effectiveness of lower MW phenolic adhesives likely resulted from their ability to more intimately associate with water sorption sites in the wood polymers. Evidence also suggests that a BrPF interpenetrating polymer network (IPN) formed within the wood polymers, which might also decrease moisture sorption by mechanically restraining wood polymers during swelling.

Although proteins are naturally good adhesives, often the most economical source has a significant carbohydrate component. Our prior studies have shown that commercial soy protein isolates (CSPI) give very good dry and wet bond strength for wood bonding, but the strengths are much lower for soy flour, especially under wet conditions. One large difference between these soy products is the percentages of carbohydrates, which generally provide poor bond strength under wet conditions. A variety of commercial isolates, concentrates, and flours were examined for their adhesive properties using a small-scale bond test that emphasizes cohesive bond strength. In studying how much the carbohydrates weaken the bond strength, we learned that the carbohydrate interference is only part of the difference between commercial soy flour and purified soy proteins (isolate and concentrate). An even larger factor is the denaturation of the isolate in the CSPI. Thus, it is important to realize that the CSPI performance...

Although it is well known that wood can absorb liquids, the full impact of this phenomenon on resulting adhesive cure and performance is not well understood. In a related soy adhesive study, aspects of this phenomenon were not fully anticipated and resulted in a significant impact on adhesive bond quality. In essence, the wood being bonded acted like chromatography media, filtering relatively smaller molecules from the surrounding adhesive matrix and altering the local composition of the adhesive material. Through the use of soy adhesives containing glycerin, the infiltration of glycerin analogs into wood cell walls has been determined and related with the impact on bondline and wood properties. The impacts of infiltration and chromatographic separation on the cured adhesive are also discussed.

Adhesives have played and will continue to play an important role in the efficient utilization of wood resources. Early Egyptians used adhesives to attach rare veneers to wood furniture. Today, adhesives play a vital role in allowing almost all types and sizes of wood to be converted to functional products. For centuries, wood was bonded using biobased adhesives. In the 20th century, synthetic adhesives gradually took over because they were typically more effective and cost less. Refinement of these adhesives led to a great expansion in the bonded wood products industry by growing existing markets and allowing development of new bonded products. The 20th century also saw an increased understanding of wood adhesive chemistry and product performance knowledge. These trends continue in the 21st century along with the potential for more biobased adhesives. The increased use of engineered wood products will continue along with more utilization of other wood and plant resources, such as bamboo, for the production of bonded products.

Most adhesive studies employing wood veneer as the substrate assume that it is a relatively uniform material if wood species and veneer thickness are constant. In the present study, veneers from rotary cut birch (Betula pendula Roth) were produced from logs harvested in spring, autumn and winter, and soaked at 20°C and 70°C prior to peeling. Firstly, veneers produced from logs felled in autumn were dried at 103°C for 24 h and subsequently half of these veneers were heat-treated at 180°C for 3 h. In addition, veneers produced from logs felled in all three seasons were dried at 160°C for 3.5 min to simulate industrial drying. The wettability of veneers was evaluated goniometrically, and bonding strength was evaluated with an automated bonding evaluation system (ABES). The results show that soaking birch logs at 70°C rather than at 20°C before peeling, or harvesting trees in the spring rather than in the autumn or winter, gives rise to veneers with enhanced wettability and higher bond strengths with a phenol-formaldehyde adhesive. Changes in the preparation and history of a veneer surface may have a profound effect on the development of adhesive bonds.

To understand the influence of formaldehyde/urea ( F / U ) mole ratio on the properties of urea–formaldehyde (UF) resins, this study investigated hardness of cured UF resins with different F / U mole ratios using a nanoindentation method. The traditional Brinell hardness ( H B ) method was also used for comparison. The H B of cured UF resin films with different F / U mole ratios was determined after exposing the films to different post-curing temperatures. The nanoindentation method was employed for these films to measure Meyer hardness ( H M ) and reduced modulus ( E r ) which have been used to calculate the elastic modulus ( E s ) of cured UF resins. As the F / U mole ratio decreased, the H B decreased continuously, indicating a less rigid network structure in low F / U mole ratio UF resins. The higher the post-curing temperature, the greater the value of H B . The H M value also showed a similar trend as a function of F / U mole ratio. However, the E r and E s did not show a consistent trend as exhibited by H M and H B . Both H M and E r showed much greater variation in the coefficient of variation (COV) at lower F / U mole ratios 1.0 and 1.2, indicating a more heterogeneous composition of these resins. Linear relationships between H M and E r indicate that heterogeneity of the surface composition of samples contributes greatly to variations in the measured values. This variability is discussed in terms of crystal structures present in the cured UF resins of low F / U mole ratios.

Soy flour adhesives using polyamidoamine-epichlorohydrin (PAE) resin as the curing agent are being used commercially to make bonded wood products. The original studies on the soy-PAE adhesives used...

We studied the high temperature performance of soy meal processed to different protein concentrations (flour, concentrate, and isolate), as well as formulated soy-based adhesives, and commercial nonsoy adhesives for comparison. No thermal transitions were seen in phenol-resorcinol-formaldehyde (PRF) or soy-phenol-formaldehyde (SoyPF) or in as-received soy flour adhesive during differential scanning calorimetry scans heating at 10 °C/min between 35 and 235 °C. Heat flow rates decreased in the order soy flour (as received) > SoyPF > PRF > emulsion polymer isocyanate (EPI). In thermogravimetric analysis (TGA) scans from 110 to 300 °C at 2 °C/min, total weight loss decreased in the order soy flour (as-received)>SoyPF > PRF > casein > maple > EPI. For bio-based materials, the total weight loss (TGA) decreased in the order soy flour (as-received) > concentrate, casein > isolate. Dynamic mechanical analysis from 35 to 235 °C at 5 °C/min of two veneers bonded by cured adhesive showed 30–40% decline in storage mod...

Soy flour adhesives using a polyamidoamine-epichlorohydrin (PAE) polymeric coreactant are used increasingly as wood adhesives for interior products. Although these adhesives give good performance, higher bond strength under wet conditions is desirable. Wet strength is important for accelerated tests involving the internal forces generated by the swelling of wood and plasticization of the adhesive with increasing humidity. Soy proteins are globular due to their hydrophobicity; thus, it was expected that adding modifiers to open the protein structure should improve protein–protein and protein–wood interactions to help withstand both internal and external forces applied to the bond. Because modifiers have been shown to improve the performance of soy protein isolate adhesives, use of these modifiers has been examined as a way to improve soy flour adhesives. Protein-disrupting chaotropic agents (urea, guanidine hydrochloride, and dicyandiamide), surfactants (sodium dodecyl sulfate or cetyltrimethylamm...

During the rotary peeling of veneer for plywood or the laminated veneer lumber manufacture, checks are formed in the veneer that are as deep as 70–80% of the veneer thickness. The results of this study show that, during adhesive bond testing, deep lathe checks in birch (Betula pendula Roth.) veneer significantly reduce the shear strength and the percent wood failure of phenol-formaldehyde (PF) – bonded plywood. The results also show that specimens tested with the checks pulled open or closed can fail by different mechanisms. Dried rotary peeled birch veneers were sanded to create uniform surfaces with lathe check depths varying from 30% to 90% of veneer thickness. Then, 7-ply plywood was manufactured with a commercial PF resin. After the preparation of the test specimens, the check depth of each specimen was measured microscopically. Subsequently, bond quality was measured according to EN 314. The results show that veneer checking alone can bring EN 314 specimens to the brink of failure even with an excellent adhesive. These findings stress the importance of measuring the depth of lathe checks and considering the orientations of checks during the testing to get a better understanding of bond quality in veneer-based products.

It is well documented that temperature and humidity can influence formaldehyde emissions from composite panels that are produced using urea-formaldehyde (UF)–type adhesives. This work inve...

Heating logs prior to peeling positively affects the surface properties of veneer as well as the wood-adhesive bond strength. However, the mechanism behind this increase in strength is not fully understood. The aim of the present study was to separate the influence of soaking temperature and peeling temperature on the physical surface properties and bonding quality. Rotary-cut birch (Betula pendula Roth) logs were soaked at 70 °C, and half of them were subsequently cooled to 20 °C prior to peeling. Surface roughness measurements, scanning electron microscopy (SEM), surface integrity testing, color measurements, and wood-adhesive bond testing were conducted with an automated bonding evaluation system. The results showed that logs soaked at 70 °C and peeled at 20 °C had roughness, color, integrity, bond strength, and wetting properties more similar to logs soaked and peeled at 70 °C than those soaked and peeled at 20 °C. In every test conducted, the effect of soaking temperature was greater than the effect of peeling temperature. High-temperature soaking not only caused softening of the material during the peeling process, but it also caused irreversible changes in the wood material, which affected the veneer surface characteristics and bond strength development.

This work is to examine ways to chemically modify soy proteins flours and analyze the results and determine the adhesive performance. Reaction with acetic anhydride converts amine and hydroxyl groups to amides and esters, respectively that are less polar and can make the adhesive more water resistant.The succinic anhydride reacts with these same groups but the products have terminal carboxylic acid groups that can react with the polyamidoamine-epichlorohydrin (PAE) resin that is used to cross-link the soy adhesives for improving bond strength. The attenuated total reflectance infrared spectroscopy (ATR-IR) is used to examine changes in the soy flour in going from unmodified to acetylated and succinylated state.

A MAIN ROUTE FOR THE EFFICIENT UTILIZATION OF WOOD RESOURCES IS TO RE- DUCE WOOD TO SMALL PIECES AND THEN BOND THEM TOGETHER (FRIHARTAND HUNT 2010). ALTHOUGH HUMANKIND HAS BEEN BONDING WOOD SINCE EARLY EGYPTIAN CIVILIZATIONS, THE QUALITY AND QUANTITY OF BONDED WOOD PRODUCTS HAS INCREASED DRAMATICALLY OVER THE PAST 100 YEARS WITH THE DEVELOPMENT OF NEW ADHESIVES AND WOOD PRODUCTS.

Whenever a nanoindent is placed near an edge, such as the free edge of the specimen or heterophase interface intersecting the surface, the elastic discontinuity associated with the edge produces artifacts in the load–depth data. Unless properly handled in the data analysis, the artifacts can produce spurious results that obscure any real trends in properties as functions of position. Previously, we showed that the artifacts can be understood in terms of a structural compliance, Cs, which is independent of the size of the indent. In the present work, the utility of the SYS (Stone, Yoder, Sproul) correlation is demonstrated in its ability to remove the artifacts caused by Cs. We investigate properties: (i) near the surface of an extruded polymethyl methacrylate rod tested in cross section, (ii) of compound corner middle lamellae of loblolly pine (Pinus taeda) surrounded by relatively stiff wood cell walls, (iii) of wood cell walls embedded in a polypropylene matrix with some poorly bonded wood–matrix interfaces, (iv) of AlB2 particles embedded in an aluminum matrix, and (v) of silicon-on-insulator thin film on substrate near the free edge of the specimen.

There is a need to develop models that evaluate the interaction of wood adhesives at the macroscopic level to explain observations on the durability of bonded wood laminate products with changing moisture conditions. This paper emphasizes a model that relates durability to strain on the bondline caused by wood swelling. The effect of this strain is discussed in relation to two groups of adhesives with different chemistry, structure–property and adhesive–wood interaction relationship models. The in situ polymerized adhesive group involves highly cross-linked polymers with a rigid backbone that need to limit the swelling of the wood surface to provide a durable bond. The pre-polymerized adhesive group includes polymers with backbone flexibility and limited cross-linking so that they can thus distribute the swelling strain within the adhesive. These models emphasize the importance of the adhesive–wood interactions and end-use application for establishing the performance criteria.

A recently described plant cell wall dissolution system has been modified to use perdeuterated solvents to allow direct in-NMR-tube dissolution and high-resolution solution-state NMR of the whole cell wall without derivatization. Finely ground cell wall material dissolves in a solvent system containing dimethylsulfoxide-d(6) and 1-methylimidazole-d(6) in a ratio of 4:1 (v/v), keeping wood component structures mainly intact in their near-native state. Two-dimensional NMR experiments, using gradient-HSQC (heteronuclear single quantum coherence) 1-bond (13)C--(1)H correlation spectroscopy, on nonderivatized cell wall material from a representative gymnosperm pinus taeda (loblolly pine), an angiosperm Populus tremuloides (quaking aspen), and a herbaceous plant Hibiscus cannabinus (kenaf) demonstrate the efficacy of the system. We describe a method to synthesize 1-methylimidazole-d(6) with a high degree of perdeuteration, thus allowing cell wall dissolution and NMR characterization of nonderivatized plant cell wall structures.

The standard Oliver–Pharr nanoindentation analysis tacitly assumes that the specimen is structurally rigid and that it is both semi-infinite and homogeneous. Many specimens violate these assumptions. We show that when the specimen flexes or possesses heterogeneities, such as free edges or interfaces between regions of different properties, artifacts arise in the standard analysis that affect the measurement of hardness and modulus. The origin of these artifacts is a structural compliance (Cs), which adds to the machine compliance (Cm), but unlike the latter, Cs can vary as a function of position within the specimen. We have developed an experimental approach to isolate and remove Cs. The utility of the method is demonstrated using specimens including (i) a silicon beam, which flexes because it is supported only at the ends, (ii) sites near the free edge of a fused silica calibration standard, (iii) the tracheid walls in unembedded loblolly pine (Pinus taeda), and (iv) the polypropylene matrix in a polypropylene–wood composite.

The desire to make more biobased and lower-cost bonded wood products has led to an interest in replacing some phenol and formaldehyde in wood adhesives with soybean flour. Improved knowledge of the soy protein properties is needed to relate resin chemistry to resin performance before and after wood bonding. To expose the soy protein’s functional groups, it needs to be disrupted, with minimal hydrolysis, to maximize its incorporation into the final polymerized adhesive lattice. The best conditions for alkali soy protein disruption were to maintain the temperature below 100 °C and react the soy flour with sodium hydroxide at pH 9–12 for about 1 hour. A gel permeation chromatography procedure was optimized to determine conditions for selectively breaking down the high molecular weight soy protein fragments that contribute to high adhesive viscosity. This method and extraction data were used to evaluate the reaction of the disrupted soy flour protein with formaldehyde and phenol to provide a stable adhesive. The results were used to develop more economical adhesives that are ideally suited for the face section of oriented strandboard.

Water-resistant bonds are important in many wood products and have been hard to obtain with many bio-based adhesives. Using a three-step process, water-soluble soy flour has been converted into adhesives that cure into an insoluble material for water-durable adhesives. The process consists of denaturation of soy flour, followed by modification with formaldehyde and then conversion via co-polymerization with a suitable cross-linking agent into an insoluble material. Both formaldehyde and phenol-formaldehyde are used as cross-linking agents. The extent of conversion into the cross-linked copolymer was assessed with a 24-h water extraction procedure and via elemental analysis. Soy-based resins with 44–86% conversion of soluble soy flour have been successfully prepared with up to complete conversion of the protein component. These resins were also used to prepare strandboards of comparable performance to a control commercial phenol-formaldehyde resin. A direct relationship between the percentage of soy flour ...

Fermentation residues (consisting of incompletely fermented fiber, adherent bacterial cells, and a glycocalyx material that enhanced bacterial adherence) were obtained by growing the anaerobic cellulolytic bacteria Ruminococcus albus 7 or Clostridium thermocellum ATCC 27405 on a fibrous fraction derived from lucerne (Medicago sativa L.). The dried residue was able to serve as an effective co-adhesive for phenol-formaldehyde (PF) bonding of aspen veneer sheets to one another. Testing of the resulting plywood panels revealed that the adhesive, formulated to contain 30% of its total dry weight as fermentation residue, displayed shear strength and wood failure values under both wet and dry conditions that were comparable with those of industry standards for PF that contained much smaller amounts of fillers or extenders. By contrast, PF adhesives prepared with 30% of dry weight as either unfermented lucerne fiber or conventional fillers or extenders rather than as fermentation residues, displayed poor performance, particularly under wet conditions.

Hot-melt polyamides are an important market for the dimer acid made from the tall oil fatty acids liberated during the Kraft pulping process. These polyamides bond well to many substrates, but not to polyvinyl chloride (PVC), commonly called vinyl. Dimer-based polyamides made from secondary amines such as piperazine bond well to vinyl. No model for this unique adhesion has been proposed even though many commercial adhesives and other patents have utilized this feature of dimer-based polyamides. This paper examines the validity of models based on mechanical interlock, rheological properties, solubility parameters, and acid–base interactions. Available data are consistent with the acid–base model, which depends on the availability of tertiary amides made from secondary amine to bond to the vinyl hydrogen in contrast to the strong internal polyamide hydrogen bonding of secondary amides made from primary amines. Poly(ester-amides) with a similar proton acceptor ability also bond to vinyl.

The embedding of electrical/electronic connections and components is becoming more critical as these are being used in more hostile environments. These environments include automotive uses and industrial plants. Embedding of electrical or electronic connections in automobiles is important, as more functions are computer controlled. A wide range of processes and materials are used for making these embedded connectors, but durability of the assembly is critical to long-term performance. A good embedding material needs to have very specific properties to protect the connection under a variety of conditions. The typical polymers used in these applications have been epoxies, silicones, and urethanes. Each polymer has advantages and disadvantages that determine its suitability to a specific application. There are also newer materials, such as thermoplastic and thermoset dimer-based polyamides. These newer materials can overcome some of the processing or performance limitations of the typical polymers now being used.