Fiberboards Made from Acetylated Bagasse Fiber

Bagasse fiber was acetylated with acetic anhydride alone to various levels of acetyl weight gain. Acetylation causes the bagasse fiber to become more hydrophobic, as evidenced by a lowering of the equilibrium moisture content as the level of acetylation increased. Acetylated bagasse fiber and fiberboards made from acetylated fiber at acetyl weight gains of about 17% had an equilibrium moisture content of about one-third that of controls at all relative humidities tested. Fiberboards made from acetylated fiber swelled at a much slower rate and to a lesser extent as compared to control fiberboards. Internal bond strength was higher in acetylated fiberboards, while moduli of rupture and elasticity were slightly lower in acetylated boards than in control boards

Determination of Dimensional Stabilization of Wood Using the Water-Soak Method

Erroneous results can be obtained by the water-soak method in determination of dimensional stability that Chemically treated wood. Leaching of bulking chemicals results in a loss of dimensional Stability that can be determined only after an initial soaking cycle. After a first soaking cycle, values for percet dimensional stabilization are more realistic for those treatments where the bulking chemical has reacted with cell-wall components. Where the bulking chemical is not bound to cell-wall components, leaching during the first soaking cycle removes most of the chemical, so that in the second soaking cycle, values for percent of dimensional stability are very low. It is important that the test method used be tailored to fit the end use of the product. For products stabilized only against changes in humidity, a second soaking cycle should not be used to determine dimensional stability. Treatments that only fill cell lumens and do not bulk the cell wall result in a low degree of dimensional stability

Effects of Moisture on the Chemical Modification of Wood With Epoxides and Isocyanates

The effects of moisture on the reaction of epoxides and isocyanates with wood were investigated. Ponderosa pine at 0%, 5%, and 10% equilibrium moisture contents was reacted separately with either propylene oxide or butylene oxide catalyzed with triethylamine, or with butyl isocyanate catalyzed with dimethylformamide. Five successive treatments were performed while recycling the treatment solutions on specimens with 5% and 10% equilibrium moisture contents. Grinding and extracting the treated wood showed significant losses of nonbonded chemical at these original moisture levels. When antishrink efficiency was determined on propylene oxide treated wood using the double water-soak method, a high resistance to dimensional changes was observed on the first water-soak cycle. Most of this dimensional stability was lost based on the second water-soak cycle, showing that nonbonded polymer had been extracted. Somewhat higher antishrink efficiency values were obtained for butylene oxide and butyl isocyanate treatments. Gas chromatographic determination of products from the propylene and butylene oxide/triethylamine treating solutions showed little water buildup. Total accountable volatile products decreased with successive treatments on specimens originally containing 5% and 10% moisture, indicating the formation of nonvolatile polyglycols in the wood cell wall. Determination of butyl isocyanate solutions following each treatment showed that one quarter or less of the active isocyanate was lost due to reaction with the water in the wood

Reaction of Isocyanates with Southern Pine Wood to Improve Dimensional Stability and Decay Resistance

Ethyl, n-propyl, and n-butyl isocyanates reacted with wood without catalyst to yield modified southern pine that was 30 to 50% more dimensionally stable than unmodified specimens and that had improved decay resistance. Phenyl and p-tolyl isocyanates and 1,6-diisocyanatohexane, isophorone diisocyanate, and tolylene-2,4-diisocyanate formed nonbonded polymers in wood voids and did not increase dimensional stability. In the presence of 35% dimethylformamide, however, n-butyl and phenyl isocyanates, 1,6-diisocyanatohexane and tolylene-2,4-diisocyanate reacted with wood, resulting in increased dimensional stability. The best dimensional stability and decay resistance of all specimens tested were shown by those modified with n-butyl isocyanate in the presence of 35% dimethylformamide. The dimensional stability was 70% better than that of unmodified specimens and the weight lost in the decay test was 2%, indicating a high resistance to decay

Stabilization of Acoustical Properties of Wooden Musical Instruments By Acetylation

Because variable humidity affects the acoustic properties of wood, manufacturers of wood instruments must minimize dimensional changes caused by the absorption of water. Acetylation reduces the moisture content of the cell wall, thereby increasing the stability of the acoustic and dimensional properties of wood under conditions of changing humidity. The acetylation of wood slightly reduces sound velocity (by about 5%) and also reduces sound absorption when compared to unreacted wood. Hence, acetylation does not change the acoustic converting efficiency

Dimensionally Stabilized, Very Low Density Fiberboard

In this study, fiberboards with a specific gravity ranging from 0.2 to 0.5 were made using acetylated, steam-treated, and untreated fiber. In all boards, dimensional stability increased as specific gravity decreased from 0.5 to 0.2. Fiberboards made from acetylated fiber were more dimensionally stable than boards made from steam-treated fiber at all specific gravity levels tested. Steam-treated fiberboards resulted in a 15% weight loss of hemicelluloses and some loss of lignin and extractives. Boards with a specific gravity of 0.2 had a low modulus value, which was probably due to poor adhesion between fibers

Strength Tests on Acetylated Aspen Flakeboards Exposed to a Brown-Rot Fungus

Aspen flakeboards made from control flakes and acetylated flakes at 18% acetyl weight gain using phenol-formaldehyde or isocyanate adhesives were subjected to a bending creep test under progressive brown-rot fungal attack with Tyromyces palustris. Deflection of the boards was measured as a function of time until failure. Isocyanate-bonded control flakeboards failed in an average of 26 days, while isocyanate-bonded acetylated boards showed little deflection after 100 days in test. Average weight loss of isocyanate-bonded control boards at failure averaged 6.2%, while the acetylated boards showed about 1.0% weight loss at the end of 100 days. Phenol-formaldehyde-bonded control flakeboards failed in an average of 76 days, while acetylated boards showed little deflection after 100 days in test. Average weight loss of phenol-formaldehyde-bonded control boards at failure averaged 8.6%, while the acetylated boards showed no weight loss after 100 days

Dimensional Stability of Acetylated Aspen Flakeboard

This study was conducted to determine if thickness swelling of flakeboards, which is much greater than that of plywood or solid wood, can be improved by chemical modification of the constituent wood flakes prior to board manufacture. The chemical treatment involved acetylation of oven-dry aspen ring flakes with a 50/50 mixture of acetic anhydride and xylene. Thickness swell of treated and control samples was measured by either immersion in water for periods of up to 10 days or exposure to 90% relative humidity for periods of up to 20 days. Treated samples exhibited one-sixth to one-seventh the thickness swelling of controls for the water-soak test. Similar trends were observed for humidity exposure

Stability of Acetylated Wood To Environmental Changes

Acetylated wood is more dimensionally stable and resistant to biological attack than unacetylated wood. In this study, the stability of acetylated wood was tested under various pH, temperature, and moisture conditions. Ground acetylated southern yellow pine and aspen flakes were treated with buffer ranging from 2 to 8 pH, exposed at 24 C, 50 C, or 75 C for different periods, and tested for acetyl content. At 24 C, acetylated wood was more stable at pH 6 than pH 2, 4, or 8. At 50 C and 75 C, acetylated wood was more stable at pH 4 than at the other pH values. The half-life of acetylated wood continuously in contact with a buffered liquid at pH 6 and 24 C was approximately 30 years. For acetylated wood used under normal circumstances, the half-life would be expected to be much longer. Acetylated southern yellow pine and aspen flakes were also (1) kept at 90% relative humidity at 27 C for 6 years or (2) cycled (42-day cycle) between 90 and 30% relative humidity for 5 years. The loss of acetyl was less than 2% in both the constant and cyclic relative humidity tests. The stability of acetylated wood suggests that such wood can be used for products exposed to changes in humidity

Effect of Humidity on Vibrational Properties of Chemically Modified Wood

Changes in vibrational properties of wood can be used to determine changes in the wood cell wall resulting from chemical modification. The dynamic Young's modulus to specific gravity ratio (E'/γ) and internal friction (tan δ) for chemically modified wood compared to those for untreated wood showed major differences in cell-wall modification and lumen filling modification. Increasing the moisture content of the cell wall also has a major effect on the vibrational properties of chemically modified wood. In general, treatments that resulted in lowering the moisture content of the cell wall also lowered internal friction within the cell wall. Vapor phase reactions with formaldehyde had the greatest effect in stabilizing the cell wall against changes in dynamic mechanical properties with increasing moisture content