modified wood. Determining adhesive bond performance for chemically modified wood is important no... more modified wood. Determining adhesive bond performance for chemically modified wood is important not only in relation to its commercial utility but also because this information helps in understanding wood bond durability. Although wood modification is usually used to improve anti-swell efficiency, the modification can alter adhesive bond performance. Generally, modification is expected to diminish adhesion by making the wood surface less polar and less porous, resulting in poorer adhesive wetting of the wood and fewer chemical bonds between the two surfaces. On the other hand, chemical modification can help the wood bonds to pass water exposure durability tests because modified wood will swell less. Given the great variety of wood adhesives, species, and modification methods, a simple theory does not explain bonding behaviour. However, our model that takes into account the mechanism for dissipating stress induced by moisture-driven dimensional change, as well as general adhesion theo...
Acetylation of wood imparts moisture durability, decay resistance, and dimensional stability to w... more Acetylation of wood imparts moisture durability, decay resistance, and dimensional stability to wood; however, making durable adhesive bonds with acetylated wood can be more difficult than with unmodified wood. The usual explanation is that the acetylated surface has fewer hydroxyl groups, resulting in a harder-to-wet surface and in fewer hydrogen bonds between wood and adhesive. This concept was evaluated using four different adhesives (resorcinol–formaldehyde, emulsion polymer isocyanate, epoxy, and melamine–formaldehyde) with unmodified wood, acetylated wood, and acetylated wood that had been planed. Strikingly, acetylation did not hinder adhesive bonds with a waterborne resorcinol–formaldehyde adhesive that bonded equally well to both unmodified and acetylated yellow poplar. An epoxy adhesive bonded better to the acetylated wood than to the unmodified wood, in contrast to an emulsion polymer isocyanate, which gave less durable bonds to acetylated than to unmodified wood. Planing...
Proteins were the main wood bonding adhesives for centuries, but they were displaced by fossil fu... more Proteins were the main wood bonding adhesives for centuries, but they were displaced by fossil fuel-based adhesives in the 20 century because synthetic adhesives offered better water resistance, ease of use, and lower cost. Recently, studies using a polyamidoamine– epichlorohydrin (PAE) curing agent have led to soybeanbased adhesives that are being used commercially for inte rior plywood, engineered wood flooring, and particleboard (1). Commercial products typically use the less expensive soy flour, while the majority of the published research has been on the soy protein isolate and purified glycinin and conglycinin proteins (2). Although soy flour contains about equal proportions of carbohydrate and protein (Fig ure 1), the common assumption is that the protein provides most of the adhesive strength. Thus, to make better prod ucts, it is important to understand protein structure and how other components in natural products are altering the performance of these adhesives. For pro...
Treated wood has generally been more difficult to bond than untreated wood for a variety of reaso... more Treated wood has generally been more difficult to bond than untreated wood for a variety of reasons. Alkaline copper quat (ACQ) and copper azole (CA-B), the most prominent substitutes for chromated copper arsenate (CCA), are difficult to bond consistently. Using a phenol-resorcinol-formaldehyde (PRF) adhesive formulated for bonding to CCA-treated wood, we examined the bonding of southern yellow pine treated with CCA, ACQ, or CA-B. In durability tests, bonds were not as durable in the ACQ- or CA-B-treated southern yellow pine as in the CCA-treated or untreated pine as measured by delamination. Using differential scanning calorimetry (DSC), we determined that the adhesive tends to react more quickly with ACQ- or CA-B-treated southern yellow pine than with untreated or CCA-treated southern yellow pine. A hydroxymethylated resorcinol primer (HMR) did not penetrate as well into ACQ- or CA-B-treated southern yellow pine as into untreated wood, suggesting that PRF penetration is not as eff...
Understanding the structure-property relationships for proteins as adhesives is complicated due t... more Understanding the structure-property relationships for proteins as adhesives is complicated due to the complex and changeable colloidal nature of most proteins. An abundant source of protein in many parts of the world is the soybean, but the inexpensive soy flour is only 50% protein with the remainder being an approximately equal split of soluble and insoluble carbohydrates. These carbohydrates have been considered the cause of the poor strength under wet conditions for bonded wood products. However, removal of the soluble and/or insoluble carbohydrates did not lead to dramatic improvement in wet bond strength, showing that the native protein is not a great adhesive. In contrast, hydrothermal treatment of the purer proteins provided much higher strength showing the importance of thermal history when considering the use of soy protein in adhesive systems.
SUMMARY Wood products are quite durable if exposure to moisture is minimized; however, most uses ... more SUMMARY Wood products are quite durable if exposure to moisture is minimized; however, most uses of wood involve considerable exposure to moisture. To preserve the wood, chemicals are used to minimize moisture pickup, to prevent insect attack, and/or to resist microbial growth. The chemicals used as preservatives can interfere with adhesive bonds to wood. Given the many potential modes of failures and of interference with bond formation by treatment chemicals, a way to systematically analyze the problem is needed. With the use of several tests, the source of the problem can be generally identified; this information allows the adhesive supplier to understand how to systematically adjust the adhesive formulation to improve bond strength. This is important because new wood-protection chemicals continue to be developed to overcome the limitations of existing treatment chemicals.
Volatile organic compounds (VOCs) are a wide–ranging group of chemicals that contain carbon plus ... more Volatile organic compounds (VOCs) are a wide–ranging group of chemicals that contain carbon plus other atoms, such as oxygen and hydrogen, and exist in the gaseous phase at ambient indoor temperature due to their vapor pressures. Most VOCs around the world are from natural sources such as plants and animals, but some VOCs are also emitted from manufactured products, including wood products.1 At high enough indoor concentrations, some VOCs may lead to human discomfort or health issues, especially for high–risk groups such as infants or elderly individuals with compromised respiratory systems.2 Most of the research has been focused on formaldehyde emissions from urea–formaldehyde adhesives used in interior wood products, although the VOCs from particleboard have been studied.3 Thus, this study was to developed background VOC emission data on commercially available engineered wood products manufactured in North America.4 Data collected from this research are strictly emission data from...
Although wood has been bonded for thousands of years, truly durable bonds for exterior conditions... more Although wood has been bonded for thousands of years, truly durable bonds for exterior conditions have existed for only about 50 years. Despite the large volume of adhesives used in this market for production of lami nated lumber and composites, factors that lead to durable bonds are still being explored. Understanding the factors that determine good versus poor bonds is not easy because of the chemical and structural complexities of wood. Het erogeneity abounds, from the macro-scale growth rings and cellular construction to the nano-scale domains of the three constituent polymers. Given the reduction in avail ability of large-diameter trees, the amount of laminated and composite wood products is increasing. Improved un derstanding of factors that lead to durable wood bonds is critical for making more cost-effective products. Use of wood products in structural applications re quired more highly cross-linked adhesives to provide the necessary creep resistance. However, this resu...
Woodworkers know that wood is porous in that adhesive flows into lumens for a mechanical interloc... more Woodworkers know that wood is porous in that adhesive flows into lumens for a mechanical interlock (1) and that wood absorbs water, allowing the use of water-borne adhesives. However, the anatomical aspects of wood that lend to its porosity are much more complicated and have a greater influence on adhesive performance than is normally realized or discussed. This porosity can have both positive and negative effects on adhesive performance. A greater appreciation of how porosity relates to adhesive performance is important in designing new and improved adhesive formulations.
Determining adhesive bond performance for chemically modified wood is important not only in relat... more Determining adhesive bond performance for chemically modified wood is important not only in relation to its commercial utility but also because this information helps in understanding wood bond durability. Although wood modification is usually used to improve anti-swell efficiency, the modification can alter adhesive bond performance. Generally, modification is expected to diminish adhesion by making the wood surface less polar and less porous, resulting in poorer adhesive wetting of the wood and fewer chemical bonds between the two surfaces. On the other hand, chemical modification can help the wood bonds to pass water exposure durability tests because modified wood will swell less. Given the great variety of wood adhesives, species, and modification methods, a simple theory does not explain bonding behaviour. However, our model that takes into account the mechanism for dissipating stress induced by moisture-driven dimensional change, as well as general adhesion theories and adhesi...
Although wood was one of the earliest materials to be adhesively bonded, the factors that contrib... more Although wood was one of the earliest materials to be adhesively bonded, the factors that contribute to strong wood bonds are still not well understood. Wood is a very complex substrate in that it is non-uniform in most aspects. On the macro scale, it is a porous structure with different sized and shaped voids for fluid flow. The structural cells contain four different wall layers, and there is a middle lamella region between the cells. Each cell wall layer is made up of different amounts of three structural components: cellulose, mostly present as a crystalline and rigid polymer; hemicellulose, a mixture of branched carbohydrate polymers; and a matrix of lignin, a crosslinked aromatic polymer. Wood is easy to bond, probably because of its porosity and polar surface. However, few adhesives make a bond that can withstand exterior conditions. With wood, generally the most severe condition involves either stress under wet conditions or cycles of water soaking followed by rapid drying. ...
The accelerated test methods that distinguish between acceptable and unacceptable wood adhesives ... more The accelerated test methods that distinguish between acceptable and unacceptable wood adhesives generally involve subjecting the bonded assembly to abnormally rapid and extreme moisture exposure or cycling. In the United States and Canada, these tests for moisture durability have been established, but selection of the appropriate test methods for the different service classes (extent of water exposure) is still being discussed in some cases. For establishing these standards, a better understanding of the information provided by these tests about the bondline durability is important. Most studies involve different adhesives with the same wood species and evaluate bond efficacy using strength and percentage of wood failure. We studied different wood species, especially in durability testing, to provide crucial insight into the factors that contribute to a durable bond and demonstrate the utility of the percentage of wood failure. The bonding and bond durability of white oak, sugar ma...
As a result of the dominance of urea formaldehyde (UF)-bonded particleboard, it seemed worthwhile... more 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™ adhesive resin for formaldehyde emissions during exposure to elevated humidity and temperature conditions after being in a room at 21 ± 1.9 °C, 50 ± 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 shorte...
Thermo-hydro-mechanical (THM) processing can improve the intrinsic properties of wood, produce ne... more 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%...
Journal of Polymer Science Part A: Polymer Chemistry
To meet newer environmental standards, modified plant proteins have been studied as no‐added form... more 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
modified wood. Determining adhesive bond performance for chemically modified wood is important no... more modified wood. Determining adhesive bond performance for chemically modified wood is important not only in relation to its commercial utility but also because this information helps in understanding wood bond durability. Although wood modification is usually used to improve anti-swell efficiency, the modification can alter adhesive bond performance. Generally, modification is expected to diminish adhesion by making the wood surface less polar and less porous, resulting in poorer adhesive wetting of the wood and fewer chemical bonds between the two surfaces. On the other hand, chemical modification can help the wood bonds to pass water exposure durability tests because modified wood will swell less. Given the great variety of wood adhesives, species, and modification methods, a simple theory does not explain bonding behaviour. However, our model that takes into account the mechanism for dissipating stress induced by moisture-driven dimensional change, as well as general adhesion theo...
Acetylation of wood imparts moisture durability, decay resistance, and dimensional stability to w... more Acetylation of wood imparts moisture durability, decay resistance, and dimensional stability to wood; however, making durable adhesive bonds with acetylated wood can be more difficult than with unmodified wood. The usual explanation is that the acetylated surface has fewer hydroxyl groups, resulting in a harder-to-wet surface and in fewer hydrogen bonds between wood and adhesive. This concept was evaluated using four different adhesives (resorcinol–formaldehyde, emulsion polymer isocyanate, epoxy, and melamine–formaldehyde) with unmodified wood, acetylated wood, and acetylated wood that had been planed. Strikingly, acetylation did not hinder adhesive bonds with a waterborne resorcinol–formaldehyde adhesive that bonded equally well to both unmodified and acetylated yellow poplar. An epoxy adhesive bonded better to the acetylated wood than to the unmodified wood, in contrast to an emulsion polymer isocyanate, which gave less durable bonds to acetylated than to unmodified wood. Planing...
Proteins were the main wood bonding adhesives for centuries, but they were displaced by fossil fu... more Proteins were the main wood bonding adhesives for centuries, but they were displaced by fossil fuel-based adhesives in the 20 century because synthetic adhesives offered better water resistance, ease of use, and lower cost. Recently, studies using a polyamidoamine– epichlorohydrin (PAE) curing agent have led to soybeanbased adhesives that are being used commercially for inte rior plywood, engineered wood flooring, and particleboard (1). Commercial products typically use the less expensive soy flour, while the majority of the published research has been on the soy protein isolate and purified glycinin and conglycinin proteins (2). Although soy flour contains about equal proportions of carbohydrate and protein (Fig ure 1), the common assumption is that the protein provides most of the adhesive strength. Thus, to make better prod ucts, it is important to understand protein structure and how other components in natural products are altering the performance of these adhesives. For pro...
Treated wood has generally been more difficult to bond than untreated wood for a variety of reaso... more Treated wood has generally been more difficult to bond than untreated wood for a variety of reasons. Alkaline copper quat (ACQ) and copper azole (CA-B), the most prominent substitutes for chromated copper arsenate (CCA), are difficult to bond consistently. Using a phenol-resorcinol-formaldehyde (PRF) adhesive formulated for bonding to CCA-treated wood, we examined the bonding of southern yellow pine treated with CCA, ACQ, or CA-B. In durability tests, bonds were not as durable in the ACQ- or CA-B-treated southern yellow pine as in the CCA-treated or untreated pine as measured by delamination. Using differential scanning calorimetry (DSC), we determined that the adhesive tends to react more quickly with ACQ- or CA-B-treated southern yellow pine than with untreated or CCA-treated southern yellow pine. A hydroxymethylated resorcinol primer (HMR) did not penetrate as well into ACQ- or CA-B-treated southern yellow pine as into untreated wood, suggesting that PRF penetration is not as eff...
Understanding the structure-property relationships for proteins as adhesives is complicated due t... more Understanding the structure-property relationships for proteins as adhesives is complicated due to the complex and changeable colloidal nature of most proteins. An abundant source of protein in many parts of the world is the soybean, but the inexpensive soy flour is only 50% protein with the remainder being an approximately equal split of soluble and insoluble carbohydrates. These carbohydrates have been considered the cause of the poor strength under wet conditions for bonded wood products. However, removal of the soluble and/or insoluble carbohydrates did not lead to dramatic improvement in wet bond strength, showing that the native protein is not a great adhesive. In contrast, hydrothermal treatment of the purer proteins provided much higher strength showing the importance of thermal history when considering the use of soy protein in adhesive systems.
SUMMARY Wood products are quite durable if exposure to moisture is minimized; however, most uses ... more SUMMARY Wood products are quite durable if exposure to moisture is minimized; however, most uses of wood involve considerable exposure to moisture. To preserve the wood, chemicals are used to minimize moisture pickup, to prevent insect attack, and/or to resist microbial growth. The chemicals used as preservatives can interfere with adhesive bonds to wood. Given the many potential modes of failures and of interference with bond formation by treatment chemicals, a way to systematically analyze the problem is needed. With the use of several tests, the source of the problem can be generally identified; this information allows the adhesive supplier to understand how to systematically adjust the adhesive formulation to improve bond strength. This is important because new wood-protection chemicals continue to be developed to overcome the limitations of existing treatment chemicals.
Volatile organic compounds (VOCs) are a wide–ranging group of chemicals that contain carbon plus ... more Volatile organic compounds (VOCs) are a wide–ranging group of chemicals that contain carbon plus other atoms, such as oxygen and hydrogen, and exist in the gaseous phase at ambient indoor temperature due to their vapor pressures. Most VOCs around the world are from natural sources such as plants and animals, but some VOCs are also emitted from manufactured products, including wood products.1 At high enough indoor concentrations, some VOCs may lead to human discomfort or health issues, especially for high–risk groups such as infants or elderly individuals with compromised respiratory systems.2 Most of the research has been focused on formaldehyde emissions from urea–formaldehyde adhesives used in interior wood products, although the VOCs from particleboard have been studied.3 Thus, this study was to developed background VOC emission data on commercially available engineered wood products manufactured in North America.4 Data collected from this research are strictly emission data from...
Although wood has been bonded for thousands of years, truly durable bonds for exterior conditions... more Although wood has been bonded for thousands of years, truly durable bonds for exterior conditions have existed for only about 50 years. Despite the large volume of adhesives used in this market for production of lami nated lumber and composites, factors that lead to durable bonds are still being explored. Understanding the factors that determine good versus poor bonds is not easy because of the chemical and structural complexities of wood. Het erogeneity abounds, from the macro-scale growth rings and cellular construction to the nano-scale domains of the three constituent polymers. Given the reduction in avail ability of large-diameter trees, the amount of laminated and composite wood products is increasing. Improved un derstanding of factors that lead to durable wood bonds is critical for making more cost-effective products. Use of wood products in structural applications re quired more highly cross-linked adhesives to provide the necessary creep resistance. However, this resu...
Woodworkers know that wood is porous in that adhesive flows into lumens for a mechanical interloc... more Woodworkers know that wood is porous in that adhesive flows into lumens for a mechanical interlock (1) and that wood absorbs water, allowing the use of water-borne adhesives. However, the anatomical aspects of wood that lend to its porosity are much more complicated and have a greater influence on adhesive performance than is normally realized or discussed. This porosity can have both positive and negative effects on adhesive performance. A greater appreciation of how porosity relates to adhesive performance is important in designing new and improved adhesive formulations.
Determining adhesive bond performance for chemically modified wood is important not only in relat... more Determining adhesive bond performance for chemically modified wood is important not only in relation to its commercial utility but also because this information helps in understanding wood bond durability. Although wood modification is usually used to improve anti-swell efficiency, the modification can alter adhesive bond performance. Generally, modification is expected to diminish adhesion by making the wood surface less polar and less porous, resulting in poorer adhesive wetting of the wood and fewer chemical bonds between the two surfaces. On the other hand, chemical modification can help the wood bonds to pass water exposure durability tests because modified wood will swell less. Given the great variety of wood adhesives, species, and modification methods, a simple theory does not explain bonding behaviour. However, our model that takes into account the mechanism for dissipating stress induced by moisture-driven dimensional change, as well as general adhesion theories and adhesi...
Although wood was one of the earliest materials to be adhesively bonded, the factors that contrib... more Although wood was one of the earliest materials to be adhesively bonded, the factors that contribute to strong wood bonds are still not well understood. Wood is a very complex substrate in that it is non-uniform in most aspects. On the macro scale, it is a porous structure with different sized and shaped voids for fluid flow. The structural cells contain four different wall layers, and there is a middle lamella region between the cells. Each cell wall layer is made up of different amounts of three structural components: cellulose, mostly present as a crystalline and rigid polymer; hemicellulose, a mixture of branched carbohydrate polymers; and a matrix of lignin, a crosslinked aromatic polymer. Wood is easy to bond, probably because of its porosity and polar surface. However, few adhesives make a bond that can withstand exterior conditions. With wood, generally the most severe condition involves either stress under wet conditions or cycles of water soaking followed by rapid drying. ...
The accelerated test methods that distinguish between acceptable and unacceptable wood adhesives ... more The accelerated test methods that distinguish between acceptable and unacceptable wood adhesives generally involve subjecting the bonded assembly to abnormally rapid and extreme moisture exposure or cycling. In the United States and Canada, these tests for moisture durability have been established, but selection of the appropriate test methods for the different service classes (extent of water exposure) is still being discussed in some cases. For establishing these standards, a better understanding of the information provided by these tests about the bondline durability is important. Most studies involve different adhesives with the same wood species and evaluate bond efficacy using strength and percentage of wood failure. We studied different wood species, especially in durability testing, to provide crucial insight into the factors that contribute to a durable bond and demonstrate the utility of the percentage of wood failure. The bonding and bond durability of white oak, sugar ma...
As a result of the dominance of urea formaldehyde (UF)-bonded particleboard, it seemed worthwhile... more 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™ adhesive resin for formaldehyde emissions during exposure to elevated humidity and temperature conditions after being in a room at 21 ± 1.9 °C, 50 ± 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 shorte...
Thermo-hydro-mechanical (THM) processing can improve the intrinsic properties of wood, produce ne... more 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%...
Journal of Polymer Science Part A: Polymer Chemistry
To meet newer environmental standards, modified plant proteins have been studied as no‐added form... more 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
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