30. Furan-Based Adhesives

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quantities of added 2 and the optimal ratios were found to lie between 2:1 and 1:2. Hexamethylenetetramine was added to phenol–formaldehyde resins which were formulated with a molar ratio of 1:3. The bending strengths of composites prepared using urea–2 adhesives were substantially higher than those made using phenol–formaldehyde binder. More recently, Raknes [53] studied the natural aging of 14 different commercial adhesives used in plywood manufacturing. He glued spruce (Picea abies) pieces and subjected them to 30 years of natural aging ! He concluded that the shear strength and the water resistance of samples bonded with ‘‘furfurylated’’ urea–formaldehyde resins (Cascorit 1250 and Dynorit L166, manufactured by Casco Wood <strong>Adhesives</strong>, Sweden) were still satisfactory. Kim et al. [54] explored the possibility of using 2 as a cobinder in conventional urea– formaldehyde adhesives. They successfully prepared water-insoluble poly2 as oil-in-water emulsions and added them to urea–formaldehyde in different proportions. The ensuing mixtures were used to produce particleboards from a mixture of southern pine and hardwoods (75/25). The resin content of these panels was 8% w/w based on OD wood particles and the catalyst used was ammonium sulfate at a level of 0.3% w/w with respect to the dry resins. The optimal quantity of added 2 was found to be in the range of 20–30% with respect to conventional urea–formaldehyde resins. These formulations gave panels with increased strength and low formaldehyde emission. Russian investigators [55–58] used 5 as a binder for fir (Abies) plywoods and showed that the properties of these materials met the Russian standard requirements if pressing time of about 10 min, pressing temperature of 160 C, and a platen pressure of 1.8 MPa were used. Thus, the shear strength of the plywoods reached almost 1.5 MPa, and their water uptake did not exceed 39%. The use of clay as a filler (up to 40% w/w with respect to the binder) decreased substantially the final properties of the materials [57]. Mezhov et al. [59] also studied the furfural emission from plywoods prepared using 5 as a binder (produced in situ by reaction of 1 with acetone) and showed that it was much lower than that allowed, i.e., 3–5 mg/100 g of plywood instead of 10 mg/100 g. VII. FURAN RESINS AS CEMENT ADHESIVES <strong>Furan</strong> resins have also been extensively used in formulating mortars, grouts, and ‘‘setting beds’’ for brick lining destined to be exposed to highly corrosive environments, such as concentrated acids or highly alkaline cleaning solutions [3,16,60–62]. Two techniques are used in order to realize assemblies, namely tilesetter’s and bricklayer’s methods. The first method is based on the use of quarry tiles or pavers with smooth surfaces. The second method consists in using acid-resistant brick linings. Depending on the end use, three types of bricks are used for the installation of this type of assembly, namely: (i) Red shale bricks which have the highest resistance to chemical attack. They are relatively fragile towards thermal and mechanical shocks. Typically, standard brick dimensions are 20.3 cm by 9.5 cm. (ii) Fire clay bricks which are less resistant to chemical attack, but much more stable against thermal and physical shocks. Their standard dimensions are 22.8 cm by 11.4 cm. (iii) Carbon bricks which are used to withstand hydrofluoric acid, fluoride salts, and hot, strong alkaline media. They are also very resistant to thermal shocks. In 1990, 2 was also used in order to prepare low temperature ( 10 C) hardening epoxy resin mortar adhesive [63]. For this, 2 was added as a reactive diluent to classical Copyright © 2003 by Taylor & Francis Group, LLC
epoxy resin based on bisphenol A and the adhesive thus obtained was found to have good mechanical properties. These compositions are presently being produced by the Chinese Yanan Chemical plant. More recently, 2 was used in polymer compositions in building and structural repairs and showed properties similar to those obtained with epoxy resins [64]. VIII. FURAN RESINS/GLASS FIBER COMPOSITES Corrosion-resistant glass fiber reinforced composites were also produced on the basis of furfuryl alcohol thermosetting resins [3,16,60]. Thus, many furan-based glass fiber reinforced materials have been available for many years, particularly for the storage of chlorinated aromatic and aliphatic hydrocarbon solvents. Amongst the commercial units available one finds: (i) very large scrubbing towers packed with Raschig rings. These containers are resistant to hot (up to about 120 C) HCl and organic chlorides; (ii) large brink mist eliminators typically working close to 85 C; (iii) acid wash surge tanks used to store waste liquids with a pH of about 2 at temperatures of 55–60 C; and (iv) dryer exhaust water driven coolers for incoming hot (230 C) acidic HCl and aromatic vapors. These few examples do not cover all the equipment constructed on the basis of furan resin reinforced by fiberglass but they show clearly the usefulness of these materials in different industrial areas. Other applications include the use of 2 as a matrix for fiberglass in the production of wrappings of pipes carrying corrosive liquids and vapors [12]. Thus, steel pipes previously coated with bitumen or coal tar pitch can be wrapped with a bonded glass fiber mat based on this type of resin. In this context, 2 is mixed with water in the presence of an emulsifying agent and an acid catalyst and the ensuing emulsion impregnates the mat. Then, the resulting composite is heated in order to remove the water and induce the acid-catalyzed polycondensation of the matrix. Amongst the composites used one can cite furfuryl alcohol resins reinforced with carbon filled woven glass fiber (commercialized under the name of Permanite, manufactured by the IKO Group, Canada). The main mechanical properties of such composites are: tensile, shear, flexural, and compressive strengths of 15, 20, 39, and 41 MPa, respectively. Their average density, thermal conductivity, and coefficient of thermal expansion are 1.57 kg/dm 3 , 3.44 W/(m 2 K) and 1.8 10 5 / C. Permanite-based pipes are hard, tough, and rigid with exceptional resistance to thermal shocks. They can be used up to 140 C and should be protected against high tensional, torsional, and shear loads. The combination of furanic derivatives with formaldehyde is also used in order to produce pipes. Haveg 61, manufactured by High Performance Alloys, Inc., Tipton, IN, can be cited as an example of these resins which are usually filled with acid-digested asbestos [16]. These composites are resistant to thermal shocks and have been used continuously at high temperatures (150 C). They have very low electrical and thermal conductivities. The main mechanical properties of these composites are: ultimate tensile, shear, and compressive strengths, at 26 C, of 28, 109, and 72 MPa, respectively. Their coefficient of thermal expansion is 3.2 10 5 / C. The working and hardening times of these resinous cements depend strongly on the working temperature [12]. Thus, for example, for carbon filled 2-based resin cement, the following critical values are found: at 16, 21, and 27 C the working and hardening times are 90, 60, and 30 min and 48, 20, and 12 h, respectively [12]. Copyright © 2003 by Taylor & Francis Group, LLC
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Page 3 and 4: a few furanic monomers and resins a
Page 5 and 6: laboratory [2,7,8]. The success of
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30. Furan-Based Adhesives

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