Preparation of wood adhesives based on tannins and glycerol esters ( triacetate ) (original) (raw)
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Properties of Pine Bark Tannin-based Adhesive Produced with Various Hardeners
BioResources, 2018
Tannin-based adhesives are alternative bio-based products that can be used in the wood panel industry instead of synthetic adhesives that contain formaldehyde. For the production of these adhesives, formaldehyde is utilized generally as a hardener as in its synthetic counterparts. In this study, adhesive formulations were prepared using eight different hardeners and tannin powder from Turkish red pine (Pinus brutia) barks. While the shortest gel time values in the adhesive formulations were identified in the samples prepared with formaldehyde and paraformaldehyde, the longest gel time was obtained in the formulation prepared with tris(hydroxymethyl)nitromethane. As a result of the dry bonding tests, the values closest to the commercial UF adhesive were found in descending order as paraformaldehyde, formaldehyde, hexamine glyoxal, and poly[(phenyl isocyanate)-co-formaldehyde] (pMDI). According to the wet bonding strength test results, the adhesive samples in which furfural, tris(hydroxymethyl)nitromethane, and benzaldehyde were used as hardeners did not achieve wet bonding strength. As a result of thermogravimetric analysis (TGA), commercial UF adhesive samples had dramatically lower thermal stability than all of the formulations prepared with tannin. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectral analysis revealed that new chemical bonds were established between the tannin and hardeners.
Glycerol as a renewable resource for wood adhesives
Mariusz Mamiński , Paweł Parzuchowski 2 , Piotr Borysiuk 1 and Piotr Boruszewski 1 Warsaw University of Life Sciences – SGGW, 159 Nowoursynowska St. 02-776 Warsaw, Poland Warsaw University of Technology, 3 Noakowskiego St., 00-664 Warsaw, Poland Abstract. An approach allowing for conversion of renewable resource glycerol to polyglycerols useful in polyurethane technology and cross-linking with isocyanates was presented. It was shown that hyperbranched polyglycerols could be substitutes for petroleum-based polyols and raw materials for polyurethane wood adhesives. The shear strengths of the resultant adhesive joints made on solid wood exceeded that of the substrate.
Holz als Roh- und Werkstoff, 1996
The alkaline extraction of tannins from Pinus pinaster bark was studied as regards the influence of solid/liquid ratio, extraction time and NaOH concentration on the yield and Stiasny number of the extracts precipitated at pH 2. The extract with the highest Stiasny number(97) was copolymerized with a previously prepared resol to afford a resin with a 1 : I phenol/tannins ratio. Plywood boards of Eucalyptus globulus bonded with this resin at board humidities of 10 or 16%, temperatures of 130 or 185 ~ and press times of 5 or 8 rain all passed the WBP knife test (with one exception for the longer press time). We conclude that this resin is superior to commercial phenol-formaldehyde resins as regards its tolerance to moisture in plies and adhesive, its press time requirement, and its ability to bond veneers of woods known for their high levels of adhesive-repellent substances. Tanninkleber zum Verleimen sehr feuchter Furnierbh)'tter: EinfluB der Tanninextraktion und der PreBbedingungen Die Alkaliextraktion von Tanninen aus Pinus pinaster wurde untersucht im Hinblick auf den Einflufl des Flottenverh~iltnisses, der Extraktionszeit und der NaOH-Konzentration anf die Ausbeute und die Stiasnyzahl der Extrakte nach Ausflillen bei pH 2. Der Extrakt mit der h/Schsten Stiasnyzahl (97) wurde mit Resol copolymerisiert, so daft sich ein Phenol-Tannin-Verh~ltnis yon 1:1 ergab. Alle Sperrh61zer, die aus Eukalytus-globulus-Furnieren mit Feuchten yon 10 oder 16% mit diesem Harz verleimt waren (Prefltemperaturen 130 oder 185 ~ Preflzeiten 5 oder 8 Minuten), bestanden entsprechende Qualit~itstests. Eine Ausnahme bildeten Sperrh6lzer, die bei l~ingerer Preflzeit hergestellt waren). Dieses Tanninharz erscheint uns kommerzieilen PF-Harzen fiberlegen in Hinsicht auf seine Feuchtetoleranz in Furnier und Harz, die Preflzeit und das BindevermiSgen auch ftir H61zer, die als schwerverleimbar gelten.
Characterization of Tunisian Aleppo pine tannins for a potential use in wood adhesive formulation
Industrial Crops and Products, 2014
The phenolic composition of Tunisian Aleppo pine barks was studied. Colorimetric assays, Fourier transformed infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) were used to examine Aleppo pine tannins. Analyzes showed that Aleppo pine barks are rich in condensed tannins, especially in procyanidin and prodelphinidin tannins. The reactivity to formaldehyde test (Stiasny number) showed the possible use of Aleppo pine tannins in wood adhesive formulation. Thermomechanical analysis (TMA) and strength analysis of Aleppo pine tannin/hexamin based resin showed important bonding properties.
Shear Refinement of Formaldehyde-Free Corn Starch and Mimosa Tannin (Acacia mearnsii) Wood Adhesives
Journal of Adhesion Science and Technology, 2011
The aim of this work was to reduce the viscosity of formaldehyde-free corn starch-mimosa tannin wood adhesives, without adversely affecting the mechanical properties of the product. The reduction of viscosity was achieved using shear refinement. The study focused on the physical phenomena before cross-linking of the wood adhesive. The physical (rheological characterization) and mechanical (bond strength) properties of formaldehyde-free corn starch and mimosa tannin wood adhesives were measured. The results showed that the shear refinement (290 rpm and 5 min, optimal conditions) reduced the viscosity of the corn starch-mimosa tannin wood adhesives (from 100 000 to 458 Pa s) with the advantage of being stable over time. Mechanical tests showed that the shear refinement did not influence the mechanical properties of corn starch-mimosa tannin wood adhesives.
Tannin-modified soybean protein concentrate for wood adhesive
Journal of Applied Research in Technology & Engineering
Soybean protein concentrate (SPC) modified with condensed mimosa tannin (CT) were employed as eco-friendly and formaldehyde-free adhesives for glued-wood joints. Eucalyptus grandis wood boards free of knots and cracks were used as substrate. Thermogravimetric analysis (TGA) showed that tannin provided higher thermal stability to the adhesive, which allowed expanding the temperature range for hot pressing. Apparent viscosity and dynamic angle contact were measured to evaluate the influence of tannin content on rheological behaviour and the wettability process. A classic shear-thinning behaviour was observed for all adhesives. Apparent viscosity and equilibrium contact angle reached a maximum value for low CT content. This effect was attributed to the existence of associative interactions between CT and SPC. Bonding quality parameters (wood failure percentage and shear strength) of the glued-wood joints were measured according to EN 302-1:2004 standard. 1 % CT w/w on SPC adhesive show...
Recent developments in eco-efficient bio-based adhesives for wood bonding: opportunities and issues
Recent developments and trends in the field of eco-efficient bio-based adhesives are reviewed. Eco-efficient means efficient with regard to both ecological and economical aspects. The recent developments in tannin adhesives without the use of any aldehyde-yielding compounds under the conditions of use, or even without the use of any hardeners, are described. Lignin adhesives are discussed next. Developments in protein adhesives, particularly the recent development in soy protein adhesives, are then addressed. Several new trends in carbohydrate adhesives, namely as modifiers of existing adhesives, by forming degradation compounds such as furanic compounds which can then be used as adhesives building blocks, and directly as wood adhesives, even in the form of liquified wood, are addressed. Unsaturated oil adhesives based on epoxidized unsaturated vegetable oils are also described, as well as an example of cashew nut shell oil modified by a new and inexpensive method of ozonolysis to yield an adhesive by self-condensation of the material. The review addresses last the new process of solid wood welding by mechanical friction without the use of any adhesive, in which the wood interfacial region itself is used as the binder.
Characterization of a formaldehyde-free cornstarch-tannin wood adhesive for interior plywood
European Journal of Wood and Wood Products, 2010
This study investigated the physical properties (rheological and thermogravimetric analysis) of cornstarch-tannin adhesives and the mechanical properties (dry tensile strength and 3-point bending strength) of plywood made using cornstarch-tannin adhesives. This adhesive was evaluated for its utility in interior plywood manufacture. The optimum cure temperature and cure time of cornstarch-tannin adhesives were 170 °C and 4 min, respectively. Plywood bonded with formaldehyde-free cornstarch-tannin adhesive exhibited excellent mechanical properties comparable to commercially available phenol-formaldehyde plywood adhesives. It was found that cornstarch-tannin panels which do not contain formaldehyde and with an emission equal to that of heated but unbound wood can be obtained by the use of hexamethylenetetramine (hexamine) as hardener.
SN Applied Sciences, 2020
Polyvinyl acetate emulsion (PVAc) is an essential class of adhesives for woodworking applications. However, it suffers from low water resistance. In the present research, wattle tannin was incorporated in synthesised PVAc emulsion at ratios ranging from 0 to 6 wt.% in PVAc emulsion. The study was carried out in two parts. The first part focuses on understanding the effect of the presence of tannin in PVAc emulsion on its adhesive performance. The second part deals with the study of the variation in adhesive properties of tannin PVAc emulsion adhesive by introducing isocyanate crosslinker in the system. DMA was employed to understand the glass transition and rheology behaviour. FTIR was used to assess the reaction of tannin with isocyanate crosslinker. Contact angle measurement was measured using goniometry to understand the surface wettability achieved by incorporating tannin in the PVAc emulsion system. Detail study on adhesive strength was carried out by bonding wood substrates followed by measuring bonding strength in wet conditions as per BS EN 204 and heat resistance as per DIN EN 14257 (WATT 91). The presence of tannin in the system enhances water and heat resistance property which gets further improved in the presence of isocyanate crosslinkers. The observed effect is due to better wetting of substrate by adhesive, hydrogen bonding between tannin and components in adhesive, and dense crosslinking formed by the reaction of isocyanate crosslinker.