Acetylation board

Imamura etal. (1986) exposed particleboard made from acetylated wood to the termite species Coptotermes formosanus and Reticulitermes speratus. A forced feeding test according to the JWPA standard 11-1981, where the untreated or acetylated wood was the only food source, and a choice feeding test (where wood specimens were randomly placed on a termite breeding colony for 30 days) were used. With C. formosanus, there was limited attack of the fully acetylated boards, with about 50 % termite mortality after 3 weeks in forced feeding tests, whereas with R. sparatus there was virtually no attack and 100% mortality. 

Figure 5 (2J) shows changes in thickness of aspen flakeboards made from control and acetylated flakes using a phenolic adhesive at different relative humidities. After four cycles of 30 to 90 percent RH, control boards swelled 30 percent in thickness, while acetylated boards at 17 9 WPG swelled about 5 percent. 

In similar bending-creep tests, both control and acetylated pine particleboards made using melamine-urea-formaldehyde adhesive failed because T. palustris attacked the adhesive in the glueline ( ). Mycelium invaded the inner part of all boards, colonizing in both wood and glueline in control boards but only in the glueline in acetylated boards. 

Acetylated pine flakeboards have also been shown to be resistant to attack in a marine environment ). Control flakeboards were destroyed in 6 months to 1 year, mainly because of attack by Limnoria tripunctata, while acetylated boards showed no attack after 2 years. 

It is of interest that veneer-faced low-density particleboards made from acetylated veneers and acetylated core particles showed excellent dimensional stability in both liquid water and humidity tests and were resistant to attack by fungi in an 8-week soil block test [57]. Furthermore, during the 150-day bending-creep test, the totally acetylated boards showed no strength or weight loss during exposure to T. palustris. 

There have been several studies on the changes in mechanical properties of fiberboards made from chemically modified wood fiber. Hardboards made from control and acetylated hemlock fiber using 7% phenyl-formaldehyde adhesive were tested. In static bending, MOR was reduced by 23% and MOE reduced by 16% in acetylated boards as compared to control boards [38]. Tensile strength parallel to the surface was reduced by 5% but there was no... 

Fiberboards made from control and acetylated aspen fiber were made using 8% phenol-formaldehyde resin and tested in static bending. MOR increased by 15% and MOE increased by 40% in acetylated fiberboards compared to controls [39]. The acetylated boards were reported to have a more uniform density and a more consolidated surface as compared to controls. 

Property enhancement by acetylation has been frequently reported over the years in other reconstituted wood products such as flakeboards, particleboards, and fiberboards [8,9,11,12,59-64]. Table 16 shows the laboratory decay test of low-density acetylated particleboards made from perishable albizzia wood. They were resistant to attack by Tyromyces palustris (brown rot), Coriolus versicolor (white rot), and Chaetomium globosum (soft rot) above 12% WPG. These acetylated boards with 20% WPG also exhibited an improved resistance to attack by the destructive Formosan termite, Coptotermes formosanus, in the laboratory. However, their performance was unsatisfactory in the wet tropics with a higher hazard of termite attack. High resistance to fungal and bacterial attack in acetylated southern pine and aspen flakeboards was evidenced in laboratory and fungus cellar tests [12]. 

In a study of acetylation of loblolly pine oriented strand board (OSB) flakes, it was found that reactivity of the wood increased in proportion to the juvenile wood content, when moving from the base to the top of the tree (Hon and Bangi, 1996). However, no difference in reactivity was found in moving from the core to the outer shell (i.e. radially). Rowell and Plackett (1988) found no difference in the reactivity of the heartwood and... 

Research on resin-bonded boards has used wood chips, or fibres, that are acetylated prior to composite manufacture. In almost all cases, acetylation has been achieved by using uncatalysed acetic anhydride. Significant improvements in dimensional stability proportional to the WPG of the wood particles have been reported when acetylated wood is used, and there is also a reduction in irreversible swelling (e.g. Bekere etal., 1978 Arora etal., 1981 Rowell etal., 1986a-e, 1989, 1990, 1991,1995 Yoshida etal., 1986 Youngquist etal., 1986a,b, 1988 Larsson and Tillman, 1989 Subiyanto etal., 1989 Vick etal., 1991 Clemons etal., 1992 Kajita and Imamura, 1993 Sasaki and Kawai,... 

Youngquist etal. (1988) found improvements in both resin distribution and IB values when suitable emulsifiers were used in conjunction with waterborne resins, but considered it unlikely that the improvement in performance could be justified on cost grounds. It was postulated that acetylated wood interfered with the polymerization of the resin, so that it was not fully cured. It has also been suggested that acetic acid, which may be released during board pressing, could accelerate resin curing of resol type resins. In a study to determine whether this was so, acetylation of wood was found to slightly reduce... 

The generally poorer mechanical properties exhibited by acetylated lignocellulosic material in composites bonded using aqueous resin systems was considered by Korai etal. (2001). Fibres of yellow cedar (Chamaecyparis nootkatensis) were acetylated to a WPG of 24.8 % and then ozonated to different extents to increase the hydrophilicity of the fibre surface. Boards were fabricated from the fibres using an aqueous MF resin. Ozonation improved IBS of boards fabricated from acetylated fibres, proportional to level of ozone charge, and resulted in IBS values comparable to those of nonacetylated controls at higher levels of ozonation. However, although ozonation also improved MOR, the values obtained for acetylated fibres were always less than those obtained with unmodified fibres. 

Four different methods (vapour-phase acetylation using acetic anhydride, acetylation using ketene gas, liquid phase acetylation using acetic anhydride/xylene, or neat acetic anhydride) were used to acetylate pine wood chips to a variety of WPGs for the production of MUF-bonded particleboards (Nilsson etal., 1988). Composite boards were exposed to unsterile soil in fungal cellar tests. Boards made from ketene acetylated chips were not found to be resistant to decay at the maximum WPG level achieved (17 %) with a liquid acetic anhydride modification, no decay was recorded at a WPG level of c. 18 % after 12 months exposure, whereas with a vapour-phase treatment at the same WPG, evidence for decay was found. 

The production of MDF from allylated wood fibres has also been reported (Ogawa and Ohkoshi, 1997). The IBS of the 4 mm thick boards was superior to control boards (unmodified fibres bonded with PF resin), provided that the temperature of the allylation reaction and board density was sufficiently high. The MOR was markedly inferior to that of control boards in all cases (c. 10 MPa for allylated compared with c. 60 MPa for controls, at a board density of 800 kg m ). Blending of the allylated fibres with acetylated fibres caused a decrease in IBS, but did not affect MOR. It is perhaps significant that no free-radical initiator was used during hot-pressing in either study, which may account for the lack of reactivity of the allylated surfaces. 

Chow, P., Harp, T., Meimban, R., Youngquist, J.A. and Rowell, R.M. (1994). Biodegradation of acetylated southern pine and aspen composition board. International Research Group on Wood Preservation, Doc. No. IRGAVP 94 0020. 

Fuwape, J.A. and Oyagade, A.O. (1999). Strength and dimensional stability of acetylated Gmelina and Sitka spruce particle board. Journal of the Timber Development Association of India, 45(1/2), 5-10. 

Gomez-Bueso, J., Westin, M., TorgUsson, R., Olesen, P.O. and Simonson, R. (1999a). Composites made from acetylated UgnoceUulosic fibers of different origin. Part I. Properties of dry-formed fiber boards. Holz als Roh- und Werkstoff, 57(6), 433-438. 

Imamura, Y., Nishimoto, K. and Rowell, R.M. (1987). Internal bond strength of acetylated flake-board exposed to decay hazards. Mokuzai Gakkaishi, 33(12), 986-991. 

Nilsson, T., Rowell, R.M., Simonson, R. and Tillman, A.-M. (1988). Fungal resistance of pine particle boards made from various types of acetylated chips. Holzforschung, 42(2), 123-126. 

Rowell, R.M., Youngquist, J.A. and Imamura, Y. (1988). Shength tests on acetylated aspen flake boards exposed to a brown-rot fungus. Wood and Fiber Science, 20(2), 266-271. 

We are in the process of producing fiberboards from various types of acetylated lignocellulosic fibers. Most of our research has been on pine or aspen particleboards or flakeboards, so the data presented here on dimensional stability and biological resistance come mainly from these types of boards. 

The rate of swelling in liquid water of an aspen flakeboard made from acetylated flakes and phenolic resin ( ) is shown in Figure 3 During the first 60 min, control boards swelled 55 percent in thickness, while the board made from flakes acetylated to 17 9 WPG swelled less than 2 percent. During 5 days of water soaking, the control boards swelled more than 66 percent, while the 17.9 WPG board swelled about 6 percent. 

Control boards made from bamboo particles using a phenolic adhesive swelled about 10 percent after 1 h, I5 percent after 6 h, and 20 percent after 5 days. Particleboards made from acetylated bamboo particles swelled about 2 percent after 1 h and only 3 percent after 5 days (35) ... 

Thickness changes in a six-cycle water-soaking/ovendrying test for an acetylated aspen flakeboard are shown in Figure 4 ( ). Control boards swelled more than 70 percent in thickness during the six cycles, compared with less than I5 percent for a board made from acetylated flakes. Acetylation greatly reduced both irreversible and reversible swelling. 

In a similar five-cycle water-soaking/ovendrying test on bamboo particleboards, control boards swelled more than 30 percent, while boards made from acetylated particles swelled about 10 percent. 

Particleboards and flakeboards made from acetylated flakes have been tested for resistance to several different t5 pes of organisms. In a 4-week termite test using Reticulitermes flavipes (subterranean termites), boards acetylated at 16 to 17 WPG were very resistant to attack, but not completely so (, 36,37) This may be attributed to the severity of the test. However, since termites can live on acetic acid and decompose cellulose to mainly acetic acid, perhaps it is not surprising that acetylated wood is not completely resistant to termite attack. 

Deflection-time curves for flakeboards are shown in Figure 6. The curves show an initial increase of deflection for both control and acetylated flakeboards, then a stable zone, and finally, for control boards, a steep slope to failure. The study showed that less than mm of deflection was caused by creep due to moisture alone ( U). 

Table IV shows that acetylation greatly reduced weight loss and errosion rate due to loss of surface fiber from aspen flakeboards. The rate of errosion for boards made from acetylated flakes is half that of control boards. In outdoor tests, flakeboards made from acetylated pine flakes were still light yellow in color when control boards had turned dark orange to light gray.

Methyl eugenol 013,4-dimethoxy-l-allylbenzene [95-15-2] was fust characterized in 1915 as a powerful attractant for the male oriental fruit fly, Dams dorsalis, and attracts at least 60 other closely related Dams spp. Raspberry ketone [5471-51-2] or l-(4-/>-hydroxyphenyl)-2-butanone [5471-51-2] (174) is an equally powerful attractant for the melon fly, Dams mmrbitae, and the Queensland fmit fly, D. tryoni, and at least 180 other closely related Dams spp. The acetyl ester (cue-lure) (175) is more volatile and is a synthetic parakairomone especially effective for monitoring infestations by these species. Methyl eugenol and cue-lure [3572-06-3] have been used successfully in "male annihilation" of the oriental fmit fly and the melon fly by applying them to fiber board blocks or pieces of twine together with malathion or naled insecticides and distributing them over infested areas at doses of 15 g of attractant and 1 g of the insecticide per ha. 

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