Use of additives to enhance the properties of cottonseed protein as wood adhesives

Soy protein is currently being used commercially as a “green” wood adhesive. Previous work in this laboratory has shown that cottonseed protein isolate, tested on maple wood veneer, produced higher adhesive strength and hot water resistance relative to soy protein. In the present study, cottonseed protein and soy protein isolates were tested on different wood types, and cottonseed protein again showed better performance relative to soy protein. Furthermore, the effects of several protein modifiers were evaluated, including amino acids, fatty acids, and other organic molecules with cationic or anionic charges. Aspartic acid, glutamic acid, acetic acid, butyric acid, and adipic acid gave improved performance when included with cottonseed protein isolate whereas no significant effect was observed on soy protein isolate. Both dry adhesive strength and hot water resistance were tested. The enhanced performance observed with these additives provides an additional incentive for the use of cottonseed protein in this application.     

Soy-oil-based waterborne polyurethane improved wet strength of soy protein adhesives on wood

Soy-oil-based waterborne polyurethane (WPU) is used to improve wet strength in shear test of wood bonded with an adhesive of soy protein isolate (SPI) by dispersing WPU into SPI slurry. WPU׳s effects on the physiochemical properties of WPU-SPI adhesives are characterized through Fourier transform infrared spectrum, transmission electron microscopy, thermal analysis, contact angle, and mechanical strength. Wet strength of the WPU-SPI adhesives increases by 65% compared to SPI control. Moreover, the microstructure of WPU has effects on the interactions between WPU and SPI. In this study, smaller and more uniform distributed WPU0002 is easier to interact and form stronger crosslinking network with protein than WPU0500. The stronger interaction between WPU0002 and protein results in increased viscosity and bond strength. The WPU-SPI blended adhesives show significantly improved wet strength, demonstrating their potential as wood adhesives.     

乙烯基乳液-异氰酸酯木材胶粘剂的研究

介绍了一种乙烯基乳液－异氰酸酯木材胶粘剂,探讨了配方中主要成分对胶粘剂性能的影响。该胶具有良好的胶接性、耐水性。     

Shear strength and water resistance of modified soy protein adhesives

Soy protein polymers recently have been considered as alternatives to petroleum polymers to ease environmental pollution. The use of soy proteins as adhesives for plywood has been limited because of their low water resistance. The objective of this research was to test the water resistance of adhesives containing modified soy proteins in walnut, maple, poplar, and pine plywood applications. Gluing strength and water resistance of wood were tested by using two ASTM standard methods. Glues with modified soy proteins had stronger bond strength than those containing unmodified soy proteins. Plywood made with glue containing urea-modified proteins had higher water resistance than those bonded with glues containing alkali-modified and heat-treated proteins. After three 48-h cycles of water-soaking, followed by 48 h of air-drying, no delamination was observed for either walnut or pine specimens glued with the urea-modified soy protein adhesives. Gluing strength for wood species with smooth and oriented surface structure was lower than for those with rough, randomly oriented, surface structures. Wood species with greater expansion of dimensions during water-soaking had a higher delamination rate than those showing less expansion.     

Characterization of canola oil based polyurethane wood adhesives

A novel bio-based poly (ether ester) polyol containing both primary and secondary functional groups was synthesized from canola oil using a low cost and efficient procedure. In this work, use of the new canola oil derived polyol for the production of polyurethane (PU) adhesives was demonstrated. The canola oil based PU adhesives had similar or better adhesive properties in terms of lap shear strength than three commercial PU adhesives. The effect of NCO/OH ratio and temperature on adhesive characteristics on wood bonding was also evaluated by lap shear tests. It was found that the use of an elevated curing temperature (i.e. 100 °C), as well as optimized NCO/OH molar ratio (higher than 1.5/1.0), improved the wood adhesive properties. The overall chemical resistance of bio-based PU adhesives to cold water, acid and alkali was comparable to that of commercial PU adhesives whilst its resistance to hot water was superior.     

Adhesion properties of soy protein with fiber cardboard

Adhesion properties of soy protein isolate (SPI) on fiber cardboard and effects of press conditions, pre-pressing drying time, and protein concentrations on gluing strength were investigated. Shear strength increased as press time, press pressure, and/or press temperature increased. The effect of temperature on shear strength became more significant at high press pressure. The shear strength of the SPI adhesive on fiber cardboard decreased by 12–25% after water soaking. Shear strength increased as pre-pressing drying time increased and reached its maximal value at about 10 min. An SPI/water ratio of 12∶100 (w/w) gave the highest gluing strength. The specimens showed complete cohesive failure (fiber cardboard failure) except for soaked specimens pressed at low press temperature, low pressure, and short press time. Specimens pressed at 25°C and 2 MPa for 5 min with pre-pressing drying time of 10 min and an SPI/water ratio of 12∶100 (w/w) had T-peel strength and tensile bonding strength of 1.15 N/mm and 0.62 MPa, respectively, without water soaking, and 1.11 N/mm and 0.24 MPa, respectively, with water soaking.     

Mussel adhesive protein as an environmentally-friendly harmless wood furniture adhesive

Recent adhesive technologies have focused on the development of high-quality and eco-friendly adhesives. Thus, there is a gradual shift from the currently used chemical-based adhesives toward harmless adhesives with improved quality and performance. Here, we evaluated the potential use of bacteria-produced recombinant mussel adhesive protein (MAP) as a harmless wood furniture adhesive. We formulated a MAP wood adhesive as an inclusion body type for economical preparation, and we confirmed its harmlessness through the non-detection of volatile organic compounds and heavy metals. The formulated MAP showed sufficiently strong bulk adhesive strength for the dried gluing of wood adherends. We also found that the formulated MAP wood adhesive exhibits robust adhesion in various environmental conditions, including open assembly times, incubation times, temperatures, and humidity levels. In summary, the developed recombinant MAP could be successfully used as a promising environmentally-friendly, harmless wood furniture adhesive.     

Comparison of Canola and Soy Flour with Added Isocyanate as Wood Adhesives

Canola is widely grown in the northern latitudes for its vegetable oil, generating large quantities of residual, low value canola flour used as animal feed. The common wood adhesive poly(diphenylmethylene diisocyanate) (pMDI) should react with the wide variety of functional groups in proteins. Therefore, it would seem that canola flour with added pMDI could be an effective adhesive. Two main questions are addressed in this study: How do the wood adhesive properties of canola flour compare to the better-studied soy flour? How well do proteins, which contain an abundance of functional groups, cure with the very reactive pMDI? These questions were addressed using the small-scale adhesive strength test ASTM D-7998, with various adhesive formulations and bonding conditions for canola flour plus pMDI compared to soy adhesives. The more challenging wet cohesive bond strength was emphasized because the dry strengths were usually very good. Generally, soy adhesives were better than canola ones, as was the polyamidoamine-epichlorohydrin cross-linker compared to pMDI, but these generalizations can be altered by the conditions selected. Three-ply plywood tests supported the small-scale test results.     

大豆基胶粘剂的研究进展

介绍了大豆蛋白的结构与组成,综述了近年来国内外大豆基胶粘剂的发展概况和改性进展,提出了研发中存在的问题以及发展大豆基胶粘剂的意义。     

改性大豆蛋白胶粘剂的研究进展

天然高分子大豆蛋白有着一些卓越的功能特性，可以用作胶粘剂。而改性大豆蛋白胶粘剂功能特性更优越。近几十年，作为环境友好绿色化工产品，改性大豆蛋白胶粘剂的研究与应用开发均取得了很大的进展，综述了大豆蛋白改性技术、改性大豆蛋白胶粘剂的特性及其应用。     

大豆基胶粘剂的性能表征

介绍了大豆蛋白质的结构、组成和大豆基胶粘剂的改性原理;着重介绍了大豆基胶粘剂的力学性能、耐水性能、热学性能、防腐性能、结构特征及表面形貌的实验研究与表征方法;提出了大豆基胶粘剂性能表征中存在的问题及发展方向。     

大豆蛋白胶粘剂的化学改性研究进展

由于石油危机和环境污染,传统的甲醛胶粘剂受到了严峻挑战,用天然可再生物质制取环保、绿色胶粘剂已成为趋势。文章就大豆蛋白胶粘剂性能、化学改性方法及其在环保型胶粘剂的应用前景进行全面描述。     

Evaluation of wood bonding performance of water-washed cottonseed meal-based adhesives with high solid contents and low press temperatures

Water-washed cottonseed meal (WCSM) has been shown as a promising bio-based wood adhesive. In this work, we tested the bonding strength of WCSM slurries with high solid contents and low press temperatures per industrial input for non-structural applications as European Standard Class D1 wood adhesives. Increasing the WCSM content from 11 to 20% and 30% did not substantially change the adhesive strength but increased the viscosity of WCSM slurries dramatically. The shear strength at break of the maple wood pairs bonded at 40 and 60 °C was lower than that of maple pairs bonded at 100 °C. However, the shear strength of the pairs bonded at lower temperatures (40 and 60 °C) could be improved by extending the press time from 20 to 120 min. Addition of citric acid (CA) improved the viscosity of the WCSM adhesive at 20% solid content, but lowered the adhesive strength. The addition of denaturing reagent sodium dodecyl sulfate (SDS) showed reverse impacts on the adhesive strength and viscosity, compared to CA addition. Based on these observations, eight adhesive slurries were formulated with 20 and 30% of WCSM, 3% of CA or SDS, or 9.6% or 19.1% of denaturing reagent guanidine hydrochloride (GdmCl), and their bonding strengths were tested. These formulations could be used as the basis for developing low temperature WCSM-based wood adhesives to meet the criteria of both operational flowability and shear strength of the domestic furniture and small utensils niche markets for forest products.     

Wood adhesive properties of cottonseed protein with denaturant additives

Most commercial wood adhesive use either formaldehyde-based resins or polyurethanes, both of which include potentially toxic chemicals in their formulations. As a result, proteins are being considered as greener and more sustainable wood adhesives. While most of the protein adhesive studies focus on soy proteins, there is also interest in exploring alternatives. In this work, testing of the adhesive performance of cottonseed protein isolate was undertaken in the presence of protein denaturants, i.e. guanidine hydrochloride (GuHCl), sodium dodecyl sulfonate (SDS), urea, and alkali. For comparison, soy protein isolate was also included in the study. At optimal dosage levels, the dry adhesive strength of cottonseed protein isolate could be enhanced by 38, 25, or 47% with SDS, GuHCl, or urea, respectively. The dry adhesive strength and hot water resistance of cottonseed protein isolate was generally superior to that of soy protein isolate, with or without the denaturants. Thus, the combination of cottonseed protein with an optimal concentration of a denaturant may be a potentially promising polymeric system for use as wood adhesives.     

豆基蛋白质胶粘剂改性及应用研究

为了降低豆基蛋白质胶粘剂的黏度、提高胶合板的耐沸水胶接强度和满足工业化的生产要求,对传统豆基蛋白质胶粘剂进行改性,并通过胶粘剂的黏度、pH值、凝胶时间、耐沸水胶接强度以及热分析结果等确定了改性剂的合理用量。然后以热压温度、热压时间、热压压力和涂胶量作为试验因素,以胶接强度作为考核指标,采用正交试验法优选出制备胶合板用改性豆基蛋白质胶粘剂的较佳工艺条件。结果表明:改性剂的合理用量(质量分数)是40%;胶合板的较佳热压工艺参数是热压温度140℃,热压时间5 min,热压压力1.2 MPa,双面涂胶量310 g/m2;在此较佳热压工艺条件下制备的胶合板,其耐沸水胶接强度较理想(为1.12 MPa),并且满足Ⅰ类胶合板的标准要求。     

Adhesive properties of water-washed cottonseed meal on four types of wood

The interest in natural product-based wood adhesives has been steadily increasing due to the environmental and sustainable concerns of petroleum-based adhesives. In this work, we reported our research on the utilization of water-washed cottonseed meal (WCM) as wood adhesives. The adhesive strength and water resistance of WCM adhesive preparations on poplar, Douglas fir, walnut, and white oak wood veneers were tested with press temperatures of 80, 100, and 130 °C. Our data indicated that raising the hot press temperature from 80 to 100–130 °C greatly increased the bonding strength and water resistance of the WCM adhesives. The general trend of the adhesive strength of WCM on the four wood species was Douglas fir > poplar ≈ white oak > walnut. The rough surface of Douglas fir with tipping features could enhance the mechanical interlocking between the wood fibers and adhesive slurry, contributing to the high adhesive strength. The dimensional swelling of the bonded wood pairs due to water soaking was in the order: thickness > width (i.e. perpendicular to the wood grain) > length (i.e. parallel to the wood grain). The greatest dimensional changes were observed in Douglas fir specimens. However, the highest decrease in adhesive strength by water soaking was with poplar wood specimens. These observations suggested that the wood dimensional changes were not dominant factors on water weakening the bonding strength of these wood pairs.     

Synthesis and properties of polyurethane wood adhesives derived from crude glycerol-based polyols

Crude glycerol, a waste stream of the biodiesel production process, is low-cost renewable feedstock for the production of chemicals and polymers. In this study, polyurethane (PU) adhesives were synthesized from crude glycerol-based polyols (CG-based polyols) for wood bonding applications. Effects of different variables, including hydroxyl values of CG-based polyols, chain extenders, and the molar ratio of NCO/OH on the properties of PU adhesives were investigated. The chemical structures of PU adhesives were characterized, and their thermal, mechanical, and chemical resistance properties were evaluated. The experimental results indicated that an increase of the NCO/OH molar ratio (1.3) substantially improved bonding strength by up to 38 MPa. Higher thermal stability and stronger chemical resistance to hot and cold water and to alkali and acid solutions were observed comparing to vegetable oil-based adhesives. However, the effect of the hydroxyl value of polyols on bonding strength was not significant. Additionally, bond strength of crude glycerol-based PU adhesives was comparable to that of some commercial PU wood adhesives. All these properties demonstrated the potential of CG for PU wood adhesive applications, particularly for fast-curing uses.     

改性棉籽蛋白对天然橡胶复合材料性能的影响

将间苯二酚-甲醛改性棉籽蛋白等量代替炭黑填充天然橡胶(NR),利用红外光谱对棉籽蛋白和改性棉籽蛋白进行对比分析,研究了棉籽蛋白用量对橡胶复合材料静态力学性能、热空气老化性能及生热和剪切动态性能的影响。结果表明,棉籽蛋白中的氨基被取代;改性蛋白质低于9份时NR的综合力学强度增加,回弹性提高,抗老化性能提高;改性蛋白质使橡胶复合材料的生热性能降低,储能模量升高,损耗因子降低。     

Evaluation of adhesion properties of blends of cottonseed protein and anionic water-soluble polymers

There is increasing interest in agro-based, biodegradable and eco-friendly wood adhesives as partial replacements for petroleum-based adhesives. In this work, we studied the adhesion of cottonseed protein isolate (CPI) blended with several anionic water-soluble polymers. Anionic vinyl polymers studied included poly(acrylate), poly(acrylate-co-acrylamide), poly(vinyl sulfate), poly(vinyl sulfonate), and poly(vinyl phosphonate). Anionic polysaccharides studied included three types of carrageenan, carboxymethyl cellulose (CMC), low-methoxy pectin, alginate, and chondroitin sulfate. In general, the adhesive strength of CPI increased with the addition of anionic polymer up to a certain level and then decreased with further polymer addition. Different anionic polymers showed different enhancements. The best result for vinyl polymers was observed for the CPI/poly(vinyl sulfate) blend, which exhibited a 30% improved dry strength over CPI alone. The best results for the polysaccharides were obtained for the CPI/CMC and CPI/pectin blends, with improvements in dry adhesive strength over the CPI control of 66% and 50%, respectively. The CPI/CMC and CPI/pectin blends also showed improved hot water resistance. These findings suggest that the CPI/anionic polymer blends might be useful components in biobased wood adhesive formulations.     

An All‐Natural Adhesive for Bonding Wood

A novel adhesive that is solely based on natural materials of defatted soy flour (SF) and magnesium oxide (MgO) has been investigated for preparation of five‐ply plywood panels. The resulting plywood panels met the industrial water‐resistant requirement for interior plywood. In this study, mechanisms by which an aqueous mixture of SF and MgO served as a strong and water‐resistant adhesive for bonding wood were investigated. SF was first fractionated into soy protein isolates (SPI), a water‐soluble fraction, and insoluble carbohydrates (ICs) that were mixed with MgO, respectively, for preparation of maple laminates. The water resistance of the resulting maple laminates was evaluated by a three‐cycle water‐soaking‐and‐drying (WSAD) test and a two‐cycle boiling‐water test (BWT). The mixture of MgO and the soluble fraction was not able to bond maple veneers together. The shear strengths of the resulting maple laminates before and after WSAD and BWT all had the following order: MgO–SPI > MgO–SF > SF only > MgO–IC. The water solubility of SF in the heat‐cured SF–MgO mixture was much lower than that of the heat‐cured SF. We believe that the low water solubility of SF–MgO and close interactions between MgO and soy proteins instead of soy carbohydrates were responsible for the superior strengths and high water resistance of the soy‐MgO adhesive.