Flakeboard

Geimer, R.L., Mahoney, R.J., Loehnertz, S.P, Meyer, R.W., Influence of process induced damage on the strength of flakes and flakeboards. Research Paper FPL 463, USDA Forest Products Lab., Madison, Wl, 1985. 

Rowell etal. (1987b) produced PF-bonded flakeboard from acetylated southern pine (21.6 % WPG) or aspen (17.6 % WPG) flakes. This was not completely resistant to attack by termites Reticulitermes flavipes) in a 4-week test. It was thought that acetylation was less effective in preventing termite attack than other chemical modifications because cellulose decomposition in the intestines of termites leads to acetic acid formation in any case. 

Hadi etal. (1995) examined the resistance of PF-bonded flakeboards of acetylated rubberwood to attack by dry wood (Cryptotermes cynocephalus) and subterranean... 

Hadi, Y.S. (1992). Acetylated flakeboard properties In Pacific Rim Bio-Based Composites Symposium Chemical Modification of Lignocellulosics, Plackett, D.V. and Dunningham, E.A. (Eds.). FRI Bulletin, 176, pp. 9-15. 

Houts, J.H. van, Winistorfer, P.M. and Wang, S.Q. (2003). Improving dimensional stability by acetylation of discrete layers within flakeboard. Forest Products Journal, 53(1), 82-88. 

Okino, E.Y.A., Santata, M.A.E., Souza, M.R. de and Sousa, M.E. de (2001). Dimensional stability and mechanical properties of acetylated Hevea brasiliensis flakeboards. Journal of Tropical Forest Products, 7(1), 96-102. 

Rowell, R.M. and Plackett, D.V. (1988). Dimensional stability of flakeboards made from acetylated Pinus rculiata heartwood or sapwood flakes. New Zealand Journal of Forestry Science, 18(1), 124-131. 

Rowell, R.M., Tillman A.-M. and Simonson, R. (1986c). A simplified procedure for the acetylation of hardwood and softwood flakes for flakeboard production. Journal of Wood Chemistry and Technology, 6(3), 427 48. 

Rowell, R.M., Tilhnan, A.-M. and Zhengtian, L. (1986e). Dimensional stabilization of flakeboard by chemical modification. Wood Science and Technology, 20(1), 83-95. 

Rowell, R.M., Esenther, G.R., Nicholas, D.D. and Nilsson, T. (1987b). Biological resistance of southern pine and aspen flakeboards made from acetylated flakes. Journal of Wood Chemistry and Technology, 7(3), 427-440. 

Vick, C.B., Krzysik, A. and Wood, J.E. (1991). Acetylated isocyanate-bonded flakeboards after accelerated aging. Dimensional stabihty and mechanical properties. Holz als Roh- und Werkstoff, 49(6), 221-228. 

Youngquist, J.A., Krzysik, A. and Rowell, R.M. (1986a). Dimensional stability of acetylated aspen flakeboard. Wood and Fiber Science, 18(1), 90-98. 

Reactive organic chemicals can be bonded to cell wall hydroxyl groups on cellulose, hemicelluloses, and lignin. Much of our research has involved simple epoxides (1 3) and isocyanates (4), but most of our recent effort has focused on acetylation. Acetylation studies have been done using fiberboards (5f6), hardboards (7 11) particleboards (12-20), and flakeboards (21-23), using vapor phase acetylation (8,2 257, liquid phase acetylation (, ), or reaction with ketene (28). 

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. 

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. 

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. 

Figure 3—Rate of swelling in liquid water of aspen flakeboard made from acetylated flakes. O = control + = 7 3 WPG ...

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. 

Using this bending-creep test on aspen flakeboards, control boards made with phenol-formaldehyde adhesive failed in an average of 71 days with T. palustris and 212 days with T. versicolor (4l). 

Flakeboards bonded with 5 percent phenol-formaldehyde adhesive. 

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). 

Mycelium fully covered the surfaces of isocyanate-bonded control flakeboards within 1 week, but mycelial development was significantly slower in phenol-formaldehyde-bonded control flakeboards. Both isocyanate- and phenol-formaldehyde-bonded acetylated flakeboards showed surface mycelium colonization during the test time, but the fungus did not attack the acetylated flakes, so little strength was lost. 

After a l6-week exposure to T. palustris, the internal bond strength of control aspen flakeboards made with phenol-formaldehyde... 

Figure 6--Deflection-time curves of phenol-formaldehyde- (PF-) and isocyanate- (IS-) bonded flakeboards in bending-creep tests under progressive fungal attack by T. palustris (upper) and T. versicolor (lower). = PF control = PF acetylated = IS control O = IS acetylated.

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. 

Other properties of lignocellulosic composites can be improved by changing the basic chemistry of the furnish (fQ). Acetylation has been shown to improve ultraviolet resistance of flakeboards. 

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.

Table IV. Weight Loss and Rate of Erosion for Acetylated Aspen Flakeboard After Accelerated Weathering...

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