Bio-based Adhesives Research Articles

木材用接着剤の硬化特性解析と天然系接着剤の新規開発に関する研究

木材用接着剤の硬化特性解析と天然系接着剤の新規開発に関する研究

Optimum Process Parameters for Plywood Manufacturing using Soya Meal Adhesive

In view of the environmental concern and the adverse health effects with the use of formaldehyde-based plywood adhesives, there is a renewed interest to develop bio-based adhesives alternate to the petroleum-based adhesives. Current efforts are towards the development of adhesives by using soya meal powder as a major composition. This adhesive is applied on the eucalyptus veneers which are hot pressed within the specified range of temperature and pressure for manufacturing plywood. The manufactured plywood samples are tested for the flexural strength using three-point bend test. The Taguchi approach is adopted and ANOVA analysis is performed for identifying the optimum plywood manufacturing parameters (viz. temperature and pressure) to achieve the optimum Modulus of Rupture (MOR). The flexural strength estimates using the additive law and the developed empirical relation are matching well with test results.

Effects of Particle Size on the Morphology and Water- and Thermo-Resistance of Washed Cottonseed Meal-Based Wood Adhesives.

Water washing of cottonseed meal is more cost-efficient and environmentally friendly than protein isolation by means of alkaline extraction and acidic precipitation. Thus, water-washed cottonseed meal (WCSM) is more promising as biobased wood adhesives. In this work, we examined the effects of the particle size on the morphology and adhesive performance of WCSM. Pilot-scale produced and dried WCSM was treated by three grinding methods: (1) ground by a hammer mill and passed through a 0.5-mm screen, (2) further ground by a cyclone mill and passed through a 0.5-mm screen, or (3) further ground by a ball mill and passed through a 0.18-mm screen. Micro-morphological examination revealed two types of particles. The filament-like particles were mainly fibrous materials from residual linters. Chunk-like particles were more like aggregates or accumulations of small particles, with proteins as the major component. Further grinding of the 0.5-mm Hammer product with the Cyclone and Ball mill led to more fine (smaller) particles in the WCSM products. The impact of further grinding on the dry and soaked adhesive strengths was minimal. However, the decrease of the hot and wet strengths of WCSM products by the additional grinding was significant (p ≤ 0.05). Data presented in this work is useful in developing the industrial standards of WCSM products used in wood bonding.

Vital Gluten for Particleboard Production: Effect of Wood-Particle Moisture on Board Properties

Abstract Growing environmental awareness is leading to an increased interest in the use of biobased adhesives and proteins such as vital gluten. The purpose of this study was to investigate the influence of the wood-particle moisture content, water application, and press time on the internal bond strength, thickness expansion, and thickness swelling of particleboards glued with vital gluten. Green and dried wood particles with similar moisture content were achieved through drying or water addition and were blended with vital gluten powder and pressed for 1 to 3 minutes. The results show that not only the pressing time and moisture content, but also the way of achieving the moisture content, has a strong impact on the performance of the boards. At comparable moisture content, never-dried (green) particles with high moisture content in combination with a dry adhesive application produced boards that performed better than boards made of dry particles with water addition to simulate liquid adhesive application.

Nanopaper Properties and Adhesive Performance of Microfibrillated Cellulose from Different (Ligno-)Cellulosic Raw Materials.

The self-adhesive potential of nanocellulose from aqueous cellulosic suspensions is of interest with regard to a potential replacement of synthetic adhesives. In order to evaluate the performance of microfibrillated cellulose from different (ligno-)cellulosic raw materials for this purpose, softwood and hardwood powder were fibrillated and compared to sugar beet pulp as a representative non-wood cellulose resource, and conventional microfibrillated cellulose produced from bleached pulp. An alkali pre-treatment of woody and sugar beet raw materials enhanced the degree of fibrillation achieved, same as TEMPO-mediated oxidation of microfibrillated cellulose. Nanopapers produced from fibrillated material showed highly variable density and mechanical performance, demonstrating that properties may be tuned by the choice of raw material. While nanopaper strength was highest for TEMPO-oxidated microfibrillated cellulose, fibrillated untreated sugar beet pulp showed the best adhesive performance. Different microscopic methods (AFM, SEM, light microscopy) examined the interface between wood and fibrillated material, showing particular distinctions to commercial adhesives. It is proposed that fibrillated material suspensions, which achieve bond strength up to 60% of commercial urea-formaldehyde adhesive, may provide a viable solution to bio-based adhesives in certain applications where wet-strength is not an issue.

Physico-mechanical properties of plywood bonded with ecological adhesives from Acacia mollissima tannins and lignosulfonates

The objective of this research was to develop ecological adhesives for bonding plywood panels using lignosulfonates, a common waste product of the wood pulp industry, and natural tannin extracted from Moroccan bark of Acacia mollissima using different process. Natural tannin and lignin were used in wood adhesives formulation to substitute resins based on phenol and formaldehyde. To achieve this, the lignosulfonates were glyoxalated to enhance their reactivity and the used tannins obtained by three different extraction methods were compared with commercial mimosa tannin. The proportion of Acacia mollissima tannins and lignosulfonates, the pressing time, the pressing temperature, and the pressure used were studied to improve mechanical properties, and bonding quality of plywood panel. The properties of plywood panels produced with these adhesives were tested in accordance with normative tests. Thus, the tensile strength, and the shear strength were measured. The results showed that the performance of the plywood panels made using biobased tannin adhesives was influenced by physical conditions such as pressure, press temperature as well as by chemical conditions, such as the tannin-lignin ratio. It exhibited excellent mechanical properties comparable to commercially available phenol-formaldehyde plywood adhesives. This study showed that biobased adhesives formulations presented good and higher mechanical performance and no formaldehyde emission.

Preparation, Characterization and Mechanical Properties of Bio-Based Polyurethane Adhesives from Isocyanate-Functionalized Cellulose Acetate and Castor Oil for Bonding Wood.

Nowadays, different types of natural carbohydrates such as sugars, starch, cellulose and their derivatives are widely used as renewable raw materials. Vegetable oils are also considered as promising raw materials to be used in the synthesis of high quality products in different applications, including in the adhesive field. According to this, several bio-based formulations with adhesion properties were synthesized first by inducing the functionalization of cellulose acetate with 1,6-hexamethylene diisocyanate and then mixing the resulting biopolymer with a variable amount of castor oil, from 20% to 70% (wt). These bio-based adhesives were mechanically characterized by means of small-amplitude oscillatory torsion measurements, at different temperatures, and standardized tests to evaluate tension loading (ASTM-D906) and peel strength (ASTM-D903). In addition, thermal properties and stability of the synthesized bio-polyurethane formulations were also analyzed through differential scanning calorimetry and thermal gravimetric analysis. As a result, the performance of these bio-polyurethane products as wood adhesives were compared and analyzed. Bio-polyurethane formulations exhibited a simple thermo-rheological behavior below a critical temperature of around 80–100 °C depending on the castor oil/cellulose acetate weight ratio. Formulation with medium castor oil/biopolymer weight ratio (50:50 % wt) showed the most suitable mechanical properties and adhesion performance for bonding wood.

Flame-Retardant Pressure-Sensitive Adhesives Derived from Epoxidized Soybean Oil and Phosphorus-Containing Dicarboxylic Acids

In this study, novel biobased pressure-sensitive adhesives (PSAs) derived from epoxidized soybean oils and carboxylic acid-terminated polyesters were developed with flame retardance, thermal stability, and peel strength comparable to those of current PSAs. The dynamic mechanical analysis indicated that the PSAs exhibited a dynamic mechanical response consistent with related high-performance PSAs. The thermal properties of the PSAs were investigated by thermogravimetric analysis, and the results suggested that the onset decomposition temperatures in both nitrogen and air atmospheres were improved by incorporating both 9,10-dihydro-10-[2,3-di(hydroxycarbonyl)propyl]-10-phosphaphenanthrene-10-oxide (DDP) and 2-(6-oxido-6H-dibenz oxaphosphorin-6-yl)-1,4-hydroxyethoxyphenylene (DOPO-HQ-HE) as the flame-retardant monomer. Microscale combustion calorimetry, the limiting oxygen index test, UL-94, and the test method for flame resistance of PSA tapes were used to evaluate the flame retardance of the PSAs....

Bio-Based Adhesives and Evaluation for Wood Composites Application.

There has been a rapid growth in research and innovation of bio-based adhesives in the engineered wood product industry. This article reviews the recent research published over the last few decades on the synthesis of bio-adhesives derived from such renewable resources as lignin, starch, and plant proteins. The chemical structure of these biopolymers is described and discussed to highlight the active functional groups that are used in the synthesis of bio-adhesives. The potentials and drawbacks of each biomass are then discussed in detail; some methods have been suggested to modify their chemical structures and to improve their properties including water resistance and bonding strength for their ultimate application as wood adhesives. Moreover, this article includes discussion of techniques commonly used for evaluating the petroleum-based wood adhesives in terms of mechanical properties and penetration behavior, which are expected to be more widely applied to bio-based wood adhesives to better evaluate their prospect for wood composites application.

Development of sustainable bio-adhesives for engineered wood panels – A Review

Stricter legislation on formaldehyde emissions as well as growing consumer interest in sustainable raw materials and products are the main driving factors behind research on bio-based adhesives, as alternatives to amino-based ones, for wood panels.

The bending and tension strength of furniture joints bonded with polyvinyl acetate nanocomposites

Furniture is the general name given for the portable equipment used in various human activities such as seating, working and relaxing. They can be a product of design and is considered a form of decorative art. They can widely be manufactured with different adhesives. Biodegradable and biobased adhesives which have no toxic compounds and non-dangerous elements have been selected since the furniture is generally benefited in interior locations. Meanwhile, polyvinyl acetate (PVAc) is a thermoplastic polymer which is widely used in the furniture industry. In this study, tension and bending strength of the furniture joints bonded with polyvinyl acetate adhesives filled with nano-TiO2 and nano-SiO2 were investigated. Three materials; oak (Quercus robur) wood, beech (Fagus orientalis) wood and plywood made with beech veneers were selected, and the joints were prepared by mortise and tenon joints. The results showed that the maximum value for the tension strength and bending strength were obtained to beech wood and oak wood in 2% addition of nano-SiO2 fillers. The minimum values for the tension and bending strength nano-SiO2 were found to plywood and 4% loading.

Bio-Renewable Sources for Synthesis of Eco-Friendly Polyurethane Adhesives—Review

Bio-renewable sources used during manufacturing of polyurethane (PU) adhesives have been used extensively from last few decades and replaced petrochemical based PU adhesive due to their lower environmental impact, easy availability, low cost and biodegradability. Bio-renewable sources, such as vegetable oils (like palm oil, castor oil, jatropha oil, soybean oil), lactic acid, potato starch and other bio-renewable sources, constitute a rich source for the synthesis of polyols which are being considered for the production of “eco-friendly” PU adhesives. Various bio-renewable sources for synthesis of bio-based PU adhesives and their potential applications are discussed in this review. This paper will focus on the progress of research in bio-based materials for adhesive application.

Characterization Of Plywoods Produced By Various Bio-Adhesives

The increasing environmental concern and adverse health effects with the use of formaldehyde-based plywood adhesives has led to an interest in developing adhesives based on renewable resources. The main objective of this study was to explore and develop environmental friendly bio-based adhesives suitable for manufacturing plywood. Three different adhesives were prepared, one using soya meal powder and the other two using tamarind kernel powder as the major constituents. In the soya meal adhesive (SMA), water, pine oil and fresh hydrated lime were used for the preparation of the adhesive. Different methods were adopted in preparing the two tamarind adhesives, Tamarind Adhesive 1 (TA1) in which water, formalin and glucose were used and Tamarind Adhesive 2 (TA2) in which hot water and boric acid were used. These three adhesives were characterized in detail using Field Emission Scanning Electron Microscopy (FESEM) and X-Ray Diffraction (XRD). The FESEM images reveal the presence of dispersed particles in all the adhesives but the matrix of these adhesives varies. SMA shows a continuous matrix structure while the TA1 reveal agglomerated matrix structure and TA2 show more of continuous matrix with few agglomerated portions. The XRD analysis reveals the amorphous nature of all the three bio-adhesives. The XRD pattern of TA1 is similar to that of urea formaldehyde with a peak at around 20°, an indication of the presence of formalin, while the absence of such a peak in the other two adhesives is a clear indication of absence of dangerous formaldehyde. It can be concluded that the presence of dispersed particles in a continuous matrix and the absence of formaldehyde in SMA makes it superior in its properties. In spite of the presence of dispersed particles, the agglomerated matrix structure in TA1 might show inferior properties but the presence of formalin makes it similar in nature to that of urea formaldehyde. The combination of agglomeration and more of continuous matrix structure with dispersed particles and absence of formaldehyde in TA2 might make it similar in properties with SMA.

Analysis and Testing of Bisphenol A-Free Bio-Based Tannin Epoxy-Acrylic Adhesives.

A tannin-based epoxy acrylate resin was prepared from glycidyl ether tannin (GET) and acrylic acid. The influence of the reaction condition for producing tannin epoxy acrylate was studied by FT-MIR, 13C-NMR, MALDI-TOF spectroscopy and shear strength. The best reaction conditions for producing tannin epoxy acrylate resin without bisphenol A was by reaction between GET and acrylic acid in the presence of a catalyst and hydroquinone at 95 °C for 12 h. FT-MIR, 13C-NMR and MALDI-TOF analysis have confirmed that the resin has been prepared under these conditions. The joints bonded with this resin were tested for block shear strength. The results obtained indicated that the best strength performance was obtained by the bioepoxy-acrylate adhesive resin prepared at 95 °C for a 12-h reaction.

Dr. Brigitte Dix

We are deeply saddened by the loss of our colleague Dr. Brigitte Dix who died suddenly and unexpectedly on November 27, 2015, at the age of 64. Dr. Dix was born in Rinteln near Hanover, Germany, in 1951. She studied biology from 1970 to 1975 at the Technical University (TU) of Braunschweig. After graduation, she was a doctoral candidate at the German Research Centre for Biotechnology (GBF) in the Department of Biotechnology and obtained her doctorate in 1978 at the Institute for Biochemistry and Biotechnology of the TU Braunschweig. In 1979, Dr. Brigitte Dix joined the Fraunhofer Institute for Wood Research, Wilhelm-Klauditz-Institut WKI, as a research assistant. Between 1979 and 2003, she worked as a research scientist in the Department of Chemical Technology and Environmental Research (now: Department of Material Analysis and Indoor Chemistry). From 2003 onwards, Dr. Dix worked in the Department of Technology for Wood-based Materials. Dr. Brigitte Dix conducted research which focused on the processing, evaluation and use of wood-based materials and products such as particleboard, fiberboard and plywood. The core part of her research was the development and evaluation of adhesives, in particular those based on renewable resources, for wood-based materials. Her work on, for example, tannin-based resins from bark extracts, has gained significant impact and remains a relevant topic in view of recent efforts in the development of bio-based adhesives for the wood-based panels industry. Her publications on processing and properties of fiberboards based on (chemo-)thermo-mechanical pulp achieved great recognition in the academic community as well as in industry. A large amount of Dr. Dix’ work was published in close cooperation with Prof. Edmone Roffael at University of Gottingen and in earlier years with Prof. Rainer Marutzky, former director of Fraunhofer WKI. More recently, Dr. Dix has shifted her research focus towards efforts to reduce emissions from wood-based materials and products as well as towards the development of compression-molded 3D-parts based on combinations of natural fibers and thermoplastics as well as thermosets. In total, Dr. Brigitte Dix contributed to around 400 publications and 50 patents. Most of her scientific papers have been published in the European Journal of Wood and Wood Products (formerly, Holz als Rohund Werkstoff). Dr. Dix was also a frequent and competent reviewer for this journal. During her 36 years at the WKI, Dr. Dix played a key role in shaping the institute. She was also a member of the WKI works council from 1993 onwards. Despite her & Tunga Salthammer tunga.salthammer@wki.fraunhofer.de

Unique adhesive properties of pressure sensitive adhesives from plant oils

We report novel insights into the adhesive performance of bio-based pressure sensitive adhesives (PSAs). Three different homopolymers based on renewable fatty acid methyl esters were characterized in terms of their mechanical and adhesive properties. The polymers display the typical dependence of adhesive properties on molecular weight and degree of crosslinking, as quantified by shear modulus, tack and peel measurements. The absolute values of characteristic adhesion parameters are in the range of commercially available petrochemical PSAs. Curing of applied PSA films at elevated temperature results in a pronounced maximum in tack and peel strength at a critical curing time, which corresponds to a change from cohesive to adhesive failure. Thus, demand-oriented tailoring of adhesive properties can be achieved via an appropriate choice of curing time. Moreover, these bio-based adhesives offer improved adhesion on hydrophobic substrates and high water-resistance without any whitening, thus rendering them an attractive alternative to conventional petroleum-based products. These peculiar features are attributed to the high hydrophobicity of the used monomers.

Introduction to Special Issue: Wood Adhesives: Past, Present, and Future

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.

Development of Wood-Based Materials Bonded with Citric Acid*

Abstract The development of biobased adhesives without harmful chemical agents is very important for the future. In this study, citric acid was used as a wood adhesive. Citric acid (2-hydroxy-1,2,3-propanetricarboxylic acid) is a very safe substance, and it is commercially produced by the fermentation of glucose or glucose- and sucrose-containing materials. This article shows the bonding properties of citric acid in wood-based moldings and particleboards. In wood-based molding, wood and bark powders were used as elements. Citric acid powder was mixed with wood or bark powders, and the mixture was hot pressed at 200°C for 10 minutes. The wood-based moldings had good mechanical properties and excellent water resistance. When wood powder was used as an element, the specific modulus of rupture and modulus of elasticity values were 38.1 kN·m/kg and 4.9 MN·m/kg, respectively. In the case of particleboard, sucrose was used in addition to citric acid; both were dissolved in a water solution and used as an adhesive. Particleboard was manufactured at 200°C for 10 minutes. The board had good mechanical properties and water resistance. When bonded with a 25/75 ratio of citric acid and sucrose, the mechanical properties of the board were comparable to the 18 type JIS A 5908 standard. We conclude that citric acid could be used as a bioadhesive for wood.

Synthesis and characterization of acrylic polyols and polymers from soybean oils for pressure-sensitive adhesives

Soybean oil based acrylic polyol with modulated acrylate and hydroxyl functionalities was polymerized under UV radiation for biobased pressure-sensitive adhesives (PSA).

Copolymers from epoxidized soybean oil and lactic acid oligomers for pressure-sensitive adhesives

Corn based lactic acid oligomers and soybean based epoxidized oil were copolymerized under UV irradiation for biobased pressure-sensitive adhesives (PSA).