Chemical Modification of Wood with Perfluoralkyl Ethanol and 4,4'-Diphenylmethane Diisocyanate

Abstract

IntroductionChemical modifications of wood have been extensively studied during the last years. Such modifications confer to wood new properties like dimensional stability, fire and decay resistance (Rowell 1984). Of all the methods investigated, reactions using isocyanates have received a lot of attention because of their high reactivity towards the hydroxyl groups of the cell-wall polymers (Chen et al. Furthermore, fluorocarbons possess substantial hydrophobic character which reflects the low values of their cohesive energy density and surface energy. Fluorocarbon polymers have been widely studied in recent years for their unique hydrophobic and lipophobic properties (Rao and Baker 1994).This study aimed at determining if treatment of wood with mixtures of perfluoroalkyl ethanol and 4,4′-diphenylmethane diisocyanate (MDI) could enhance properties of modified wood and especially its resistance to swelling by water. Indeed, MDI can be used as a link for grafting perfluoroalkyl ethanol derivatives on wood because it can react with their hydroxyl groups to form urethane bonds (Fig. 1). Such a methodology has already been used (Ellis and Rowell 1989; Ellis 1993) using isophorone diisocyanate and an oligomer phosphonate to increase wood fire resistance. Materials and MethodsSpruce (Picea abies) wood meal was passed through a 115 mesh sieve, washed in a Soxhlet extractor with a toluene/ethanol (2 : 1, v/v) mixture (16 hours), with acetone (8 hours) and dried at 70°C for 2 days.Weighed (m 0 ) and ovendried beech blocks (Fagus sylvatica) (15 × 20 × 50 mm, radial × tangential × longitudinal) were used for dimensional stability and contact angle measurements.Perfluorohexyl ethanol [CF 3 (CF 2 ) 5 CH 2 CH 2 OH; M = 364 g/mol] and a mixture of perfluoroalkyl ethanol [Rf-CH 2 CH 2 OH; Rf: 51 % of C 6 F 13 , 39 % of C 8 F 17 , 6% of C 10 F 21 and 4 % of C 12 F 2 5 ; M = 426 g/mol] were obtained from Elf-Atochem. 4,4′-Diphenylmethane diisocyanate (MDI) was purchased from Aldrich. All chemicals were used as received without further purification. Reaction solvents were appropriately dried and purified before use. Dichloromethane was distilled over calcium hydride and stored over 4 Å molecular sieves. Acetone was dried over calcium chloride, distilled over potassium permanganate and stored over 4 Å molecular sieves.Infrared spectra of wood and modified woods were recorded on a Mattson Genesis FTIR using potassium bromide disks.Microanalyses were performed by the Service Central d'Analyse (CNRS) at Vernaison, France. Chemical modification of woodGeneral methods of preparing spruce meals and beech blocks modified with perfluoroalkyl ethanol -MDI mixtures are described in this section. Reaction of spruce wood meals with perfluorohexyl ethanol -MDI mixturesWood meals were reacted with perfluorohexyl ethanol -MDI mixtures in 4/1, 2/1 and 1/1 mass ratios of perfluorohexyl ethanol -MDI mixtures to dried wood.Wood meal (500 mg) was mixed with MDI (3.25, 1.62 or 0.81 mM; 0.81, 0.40 or 0.20 g respectively for 4/1, 2/1 and 1/1 mass ratios) ...

Tartaric acid catalyzed furfurylation of beech wood

“…Anti-swelling efficiency (ASE) was used to evaluate the dimensional stability of treated wood. The method, initially described by Rowell and Ellis (1978), was performed according to a procedure reported by Engonga et al (1999Engonga et al ( , 2000. Three replicates of treated and untreated beech wood dried for 48 h at 103 ± 1°C, cut into samples of 30 9 20 9 10 mm 3 , were measured according to their radial, longitudinal, and tangential directions to obtain the dry volume.…”

Polyurethane‐solid wood composites prepared with various catalysts. I. Mechanical properties and dimensional stabilities

“…Phenol–formaldehyde resin,3, 4 urea–formaldehyde resin,5 melamine–formaldehyde resin,6 and polyethylene glycol7 are commonly applied. Recently, some isocyanate resins have been impregnated into wood, and these have improved the dimensional stability, decay preservation, and fire resistance of the wood 8–11. However, some reports have indicated that isocyanate monomers could not improve the mechanical properties and dimensional stability simultaneously, and even decreased the mechanical properties 12…”

Wettability of waterborne coatings on chemically and thermally modified pine wood

“…[2][3][4] It is known that modification of wood can change its hydrophilic character. [5][6][7] The modified wettability of wood, however, can change its behavior with coating or gluing processes. 8 Based on this fact, low contact angles can be essentially important for sufficient paint adhesion.…”