30. Furan-Based Adhesives

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(from 0.5 to 4% with respect to OD wood). The amount of the binder was kept constant in all experiments (7% with respect to OD wood). The internal bond strength of the materials obtained was found to increase with increasing amounts of hydrogen peroxide, whereas the thickness swelling followed the inverse trend. The use of both 2 alone and its mixture with ammonium lignosulfonate showed very good bonding capability. Bishop pine gave the highest internal bonding and white fir yielded the lowest thickness swelling and water absorption when the mixture of ammonium lignosulfonate with 2 was used as a binder. The least efficient adhesive was found to be the formaldehyde–lignosulfonate system. The differences between wood species were attributed to their different contents of extractives. In another study, Philippou et al. [28] studied the effect of the composition of the bonding materials on the properties of Douglas fir particleboards. Thus, the proportion between 2 and ammonium lignosulfonate was varied as follows: 10/0, 9/1, 8/2, 7/3, 6/4, 5/5, 2.5/7.5, and 0/10. In this work, the wood was also activated by hydrogen peroxide (2% w/w with respect to OD wood) and the catalysts used were ferric chloride and maleic acid. Ammonium lignosulfonate without 2 failed to develop resistance to boiling water whereas 2 without ammonium lignosulfonate gave good mechanical and water resistance properties. However, the use of a mixture containing six parts of lignosulfonate and four parts of 2 yielded boards with the highest internal bond strength and water resistance values. Increasing the amount of resin with respect to wood was found to produce an increase in the elasticity and rupture moduli and a decrease in water absorption and thickness swelling. The boards prepared exhibited strength and resistance to cold and boiling water comparable to those made using classical phenol–formaldehyde resins. In a third investigation, Philippou et al. [29] studied the effect of the processing parameters on the mechanical properties of particleboards made from Douglas fir wood treated with ammonium lignosulfonate and 2 as a binder in the presence of maleic acid as a catalyst. They showed that increasing the pressing temperature from 121 to 177 C or the pressing time from 4 to 8 min, progressively enhanced the internal bond strength and the water resistance of the treated boards. The water resistance was found to be further improved by the addition of a small amount of wax (0.5% w/w with respect to OD wood) in the binder mixture. Leitheiser et al. [30] prepared water dilutable furan resins as binders for particleboard and showed that the resulting composites could be used for exterior applications. These resins were readily water dilutable and had low viscosities, which made their application with conventional equipment an easy process. Kelley et al. [31] prepared wood panels from Acer saccharum var. Marsh. with various binders. They first activated the surface of the wood by nitric acid and bonded the particles with tannin, 2, and a mixture of the two, with and without maleic acid. In all cases, the particleboards obtained exhibited shear strengths as high as that obtained from a control system made with a conventional phenol–formaldehyde binder. However, the acidic treatment of wood appeared to have only a slight effect on the mechanical properties of the panels bonded with the tannin–2– maleic acid system. Subramanian et al. [32] subjected Douglas fir wood flakes to a nitric acid treatment followed by a grafting reaction with 2(1-aziridinyl)ethyl methacrylate and 2. They showed that the amount of carboxylic acid groups at the wood surface had increased substantially, thus enhancing its reactivity towards both reagents. Philippou and Zavarin [33] studied the interactions between lignocellulosic materials, 2, and maleic acid in the presence or absence of hydrogen peroxide. They used white fir wood flour, microcrystalline cellulose, milled-wood lignin, and ammonium lignosulfonate and followed their interactions with the binder by differential scanning calorimetry (DSC) and concluded that a graft copolymerization between hydrogen peroxide activated wood, 2, and ammonium lignosulfonate had occurred. Balaba and Subramanian [34] studied the Copyright © 2003 by Taylor & Francis Group, LLC
polymerization of 2 catalyzed by the surface acidity resulting from treating wood with nitric acid. They followed the polymerization by intrinsic viscosity measurements and showed that there were two reaction regimes. The first was found to obey zero order kinetics, with an activation energy of 53.4 kJ/mol, whereas the second could not be exploited because of polymer precipitation following the formation of network structures. In 1985, experiments on an industrial scale were carried out jointly at Quaker Oats Chemicals and Collins Pine Company particleboard plants [35]. In these trials 1 was used as an extender in a polymeric methylene diphenyl isocyanate (MDI) binder (1:MDI ¼ 1:3 w/w). The main conclusions which could be reached from these trials were that savings in binder levels, pressing time, and temperature and drying requirements could be obtained compared with the corresponding performances of standard phenol– formaldehyde and urea–formaldehyde systems. Nguyen and Zavarin [36] studied graft polymerization of 2 on cellulosic materials. They showed that 2 in an aqueous medium at pH 2.0 and 90 C did not copolymerize with the cellulose surface in the presence of H2O2/Fe 2þ . However, under the same conditions, poly2 was efficiently grafted onto cellulosic fibers and the amount of homopolymer of 2 was negligible. In these conditions, the amount of grafted poly2 reached 68% w/w with respect to OD fibers. They also showed that working at higher temperature and with more concentrated media yielded higher grafting efficiency. Sellers [37] prepared plywoods from southern pine (major structural species) and yellow poplar (most representative decorative species) using polymeric methyl diphenyl diisocyanate adhesive in the presence of 1 as a reactive diluent in order to reduce the adhesive costs. These formaldehyde-free plywood composites did not suffer delamination after accelerated-aging tests and, although the interfacial failure did not satisfy the requirements for structural plywood, they approached or exceeded requirements for decorative applications. Schultz [38] prepared an exterior plywood resin based on 2 and paraformaldehyde. Three-ply assemblies from yellow pine were bonded at different processing conditions and showed that the curing time necessary for these systems was longer than that which was generally required for conventional gluing systems. The use of veneers with a high moisture content (9.5 instead of 5.1%) had very negative effects on the strength properties of the plywood prepared. Pizzi [39] also prepared particleboard urea–furfural–formaldehyde binders. He concluded that a partial substitution of formaldehyde with 1 led to an enhanced CH2O emission and explained this unexpected feature in terms of two competitive reactions. In fact, he showed that in the resins which contained both formaldehyde and 1, the higher stability to hydrolysis of the 1–urea bonds induced the release of formaldehyde from the final product. New adhesives from furfural-based diamines and diisocyanates were prepared by Holfinger and coworkers [40,41]. They produced flakeboards alternatively bonded with phenol–formaldehyde, MDI, and 5,5 0 -ethylidene difurfuryl diisocyanate (14) adhesives and showed that the strength properties of flakeboards prepared with 14 were slightly lower than those based on MDI and higher than those prepared with phenol–formaldehyde resins. Thus, the internal bond strength values of flakeboards bonded with MDI and 14 at 3% resin content, were 1.33 and 0.97 MPa, respectively [41], which are much higher than the value required by American standard ANSI/A208.1 (0.41 MPa). Copyright © 2003 by Taylor & Francis Group, LLC
Page 1 and 2: 30 Furan-Based Adhesives Mohamed Na
Page 3 and 4: a few furanic monomers and resins a
Page 5 and 6: laboratory [2,7,8]. The success of
Page 7 and 8: V. FURAN RESINS AS FOUNDRY BINDERS
Page 9: The interest in this type of proces
Page 13 and 14: Recently, Schneider et al. [47] fab
Page 15 and 16: epoxy resin based on bisphenol A an
Page 17 and 18: Macro-diisocyanates based on the re
Page 19 and 20: 24. A. Pizzi, D. du T. Rossouw, and

30. Furan-Based Adhesives

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