Printer Friendly

Protection of wood using oxy-aluminum compounds.

Abstract

The dimensional stability of wood and its resistance to decay and fire can be improved by depositing inorganic materials in the wood matrix and forming wood-inorganic composites. In this paper, four novel wood-inorganic (aluminum) composites were developed. The composites are referred to according to the oxy-aluminum compound deposited in the wood: sodium aluminate, aluminum hydroxide, magnesium aluminate, and aluminum borate. The aim of the research was to assess whether the dimensional stability and resistance of the oxy-aluminum composites to microbial attack and fire was comparable to that of wood treated with a hydrophobic chromated copper arsenate preservative (CCA-wax). Fourier transform infrared spectroscopy of the oxy-aluminum composites suggested some modification of the wood matrix, especially for the sodium aluminate or aluminum hydroxide treatments. Magnesium aluminate-treated samples had the highest weight gain (28.1%) and anti-swelling efficiency (105.4%). The sodium aluminate, aluminum hydroxide, and aluminum borate treatments had lower anti-swelling efficiencies of 70.8, 68.9, and 55.0 percent, respectively. The anti-swelling efficiency of the magnesium aluminate-treated wood decreased significantly to 58.6 percent after a severe leaching procedure. The anti-swelling efficiencies of the other treatments, however, particularly the aluminum borate treatment, were less affected by leaching, and the dimensional stability of the composites after leaching exceeded that of unleached CCA-wax-treated wood. The weight losses of the wood-inorganic composites after 30 weeks of exposure in soil varied from 2.4 percent (aluminum hydroxide) to 4.9 percent (magnesium aluminate) compared to 36.6 percent for untreated controls. None of the treatments, however, were as effective as CCA-wax at preventing decay. Thermogravimetric analysis and differential thermal analysis indicated that the oxy-aluminum composites had enhanced resistance to thermal degradation, in contrast to CCA-treated wood which showed no such resistance. Further research on a larger scale is needed to optimize and further evaluate the oxy-aluminum composites including their mechanical properties and effects on fixings.

**********

There is a strong need to develop wood protection systems that are both effective and of low toxicity (Preston 2000). Numerous studies have demonstrated that chemical modification can increase the dimensional stability, as well as the decay and fire resistance of wood (Rowell 1983), but commercial wood protection systems that rely on chemical modification of wood have been slow to evolve in North America due in part to their high cost and the sophisticated plants required to modify the wood (Preston 2000). Accordingly, there is a need to develop simpler and less costly methods of modifying wood to improve its dimensional stability and resistance to decay and fire. One possible route to achieving this is to treat the wood sequentially with two different solutions of inorganic compounds that react together to generate insoluble compounds within the cell walls (Saka 1998). In principle such treatments could be performed using simple technology as past studies have used double diffusion treatments to treat wood successfully (Markstrom et al. 1970, Mayer et al. 1995).

Aluminum is one of the most abundant elements in the soil, making up approximately 7.1 percent of the solid matter in an average soil sample and it has low mammalian toxicity (Sposito 1989). Only a few studies, however, have tested aluminum-based compounds in wood protection systems. Furuno and coworkers combined aluminum sulfate with sodium silicate to deposit aluminum silicate in wood (Furuno et al. 1991, Furuno 1992, Furuno and Imamura 1998). The resulting wood-inorganic composite showed high weight gain and had enhanced decay and fire resistance (Furuno et al. 1991), but it was highly hygroscopic and the aluminum leached easily from the wood (Furuno and Imamura 1998).

The aluminum-containing compound, aluminum potassium sulfate, hereafter referred to as alum, can form insoluble oxy-aluminum compounds when combined with some bases and salts (Kimura 1991). In this work, four wood protection systems were developed based on the dual vacuum-impregnation of wood with combinations of alum and other low-cost chemicals, namely sodium hydroxide, ammonia, magnesium chloride, and sodium tetraborate. The aim of the research was to assess whether dimensional stability and resistance of the treated wood to microbial attack and fire was comparable to that of wood treated with a hydrophobic chromated copper arsenate preservative (CCA-wax).

Materials and methods

Development of treatments and infrared spectroscopy

Initial research during the development of treatments used thin (85 [micro]m) radiata pine (Pinus radiata D. Don) wood veneers cut from defect-free sapwood blocks, as described previously by Evans (1988). Veneers were conditioned at 20[degrees] [+ or -] 1[degrees]C and 65 [+ or -] 5 percent relative humidity (RH) for five days and treated at room temperature (20[degrees]C) (Table 1):

* Sodium aluminate: Veneers were soaked for 20 hours in 3 percent NaOH and then soaked for 22 hours in 4 percent alum. Then they were briefly (10 s) dipped in acetic acid (diluted 1:1 with distilled water).

* Aluminum hydroxide: Veneers were soaked for 20 hours in alum, briefly rinsed with distilled water, and then soaked for 1 hour in concentrated ammonia.

* Magnesium aluminate: Veneers were soaked in sodium aluminate (4% alum + 3% NaOH) for 22 hours and then soaked in 2 percent Mg[Cl.sub.2] for 22 hours.

* Aluminum borate: Veneers were soaked in 1.4 percent sodium borate for 22 hours, briefly rinsed with distilled water, then soaked in 4 percent alum for another 22 hours, and then rinsed briefly with distilled water.

* Chromium trioxide: Veneers were soaked in 3.2 percent [Cr.sub.2][O.sub.3] for 20 hours and then rinsed several times with distilled water.

All treatments were followed by air-drying of the veneers.

Infrared spectra of treated veneers and the untreated control were obtained using a Perkin Elmer 1800 spectrometer coupled to a PE 7500 professional computer and an MTEC model 200 photoacoustic cell. To ensure that water uptake did not interfere with the spectra, samples were dried overnight in a vacuum desiccator over silica gel. Fourier transform infrared (FTIR) photoacoustic spectra consist of 32 scan averages taken at 8 [cm.sup.-1] resolution. The gas in the photoacoustic sample chamber was either nitrogen or helium and was selected for optimal signal generation.

Treatment of wood blocks

Wood blocks measuring 60 by 20 by 10 mm (longitudinal [L] by radial JR)] by tangential [T]) or 35 by 10 by 7.0 mm (L by R by T) were cut from defect free air-dried Scots pine (Pinus sylvestris L.) sapwood and used to assess the dimensional stability and decay resistance of treated wood, respectively. Blocks were conditioned, as described, for 2 weeks, and the dimensions of the blocks used in the swelling tests were measured using digital calipers. Wood blocks were weighed, ovendried at 105[degrees] [+ or -] 2[degrees]C overnight, cooled in a desiccator for 10 minutes, and then reweighed before treatment. The treatment procedure was changed from double diffusion used initially to treat veneers to a dual vacuum impregnation process. The concentrations of the solutions used for each treatment were:

* Sodium aluminate: alum (15%) and NaOH (2%);

* Aluminum hydroxide: alum (15%) and ammonia (28%);

* Magnesium aluminate: solution one (alum 15% and NaOH 2%) and magnesium chloride (20%); and

* Aluminum borate: alum (15%) and sodium tetraborate (10%).

In the first impregnation, ovendried blocks were placed in a beaker inside a desiccator. An initial vacuum of -95 kPa was drawn for 15 minutes to remove air from the dry blocks. The first treatment solution (150 mL at 50[degrees]C) was introduced into the beaker, and when the blocks were fully submerged in the solution the desiccator was vented to atmospheric pressure. The blocks were soaked in the solutions for 6 hours, with the exception of blocks treated with sodium hydroxide, which were soaked for 10 minutes. Blocks were then ovendried at 105[degrees] 2[degrees]C overnight to a constant weight, conditioned at 20[degrees] [+ or -] 1 [degrees]C and 65 [+ or -] 5 percent RH for 2 weeks and vacuum impregnated with the second solution. The blocks were soaked in the solutions for 6 hours, with the exception of blocks treated with ammonia, which were soaked for 10 minutes. After the second treatment the samples were ovendried and their dimensions remeasured. They were then reweighed, and weight gains due to treatments were calculated. A set of wood blocks were also impregnated under vacuum with a 2 percent solution of CCA containing a wax emulsion at 2.5 percent concentration (CCA-wax). Water-treated blocks (as described) and untreated conditioned blocks were used as controls. All samples were conditioned at 20[degrees] [+ or -] l[degrees]C and 65 [+ or -] 5 percent RH for a minimum of 3 weeks prior to measurement of their dimensional stability.

Measurement of dimensional stability

Specimens were placed in a galvanized steel container measuring 12 cm (length) by 9.5 cm (width) by 4 cm (depth) that was part of a measuring device built to continuously measure the radial and tangential swelling of wood blocks. Individual treated or untreated blocks were placed on a brass x-y stage within the steel container, and linear variable differential transducers attached to the side and top of the container were placed on the radial and upper tangential surfaces of the specimen. The container was filled with 500 mL of water and swelling of the wood block was measured. The voltage output of the transducers was converted to a digital form using an analog/digital card attached to a personal computer. After 23 hours, specimens were blotted dry, reweighed, and their dimensions remeasured using digital calipers, as described. The rate of swelling of treated and untreated blocks was compared using graphical plots of swelling (% of original treated dimensions) against time (min). The anti-swelling efficiency (ASE) of treated blocks and controls was also calculated according to the following formula (Stamm 1964):

ASE % = (([S.sub.2] - [S.sub.1]/[S.sub.2])) x 100

where: [S.sub.2] = volumetric swelling of untreated control and [S.sub.1] = volumetric swelling of treated specimen.

Blocks were subjected to leaching under running water for 48 hours. They were ovendried at 105[degrees] [+ or -] 2[degrees]C overnight to a constant weight, weighed, reconditioned for 2 weeks, and their dimensional stability remeasured.

Decay resistance

Nine wood blocks for each treatment type, including controls, were buried in a sandy loam soil to a depth of 70 mm in plastic containers (350 by 250 by 130 mm), with a minimum space of 30 mm between adjacent blocks, as well as between the blocks and the container walls. A small gap was left for ventilation. The position of the blocks in the containers was random. The containers were placed in a constant temperature room maintained at 20[degrees]C. The moisture content (MC) of the soil was adjusted to 90 percent of its water-holding capacity, and pieces of partially brown-rotted wood were mixed with the soil to encourage the activity of brown-rot fungi. Distilled water was added periodically to adjust soil MC to its original value. Treated blocks and untreated controls were removed from each container after 10, 20, and 30 weeks and the blocks were cleaned of soil. They were then ovendried overnight at 105[degrees] [+ or -] 2[degrees]C, reweighed on an analytical balance, and weight losses calculated.

Thermal resistance

The samples used for thermogravimetric and differential thermal analyses consisted of wood flour (6 to 8 mg) obtained from small treated wood samples (25 by 25 by 6 mm). Thermogravimetric analyses were carried out using a Shimadzu TGA-50. Air was passed over and around the sample at a rate of 50 mL/min to remove the pyrolysis or combustion products, and the temperature was raised from ambient to 800[degrees]C at a heating rate of 20[degrees]C/min. Weight losses (%) were recorded as a function of temperature and time. Differential thermal analyses were carried out using a Shimadzu DTA-50, under the same airflow rate and temperature parameters used for thermogravimetric analyses. Plots of residual weight losses (%) against temperature ([degrees]C) and of differential heat flow (uV) against reference temperature ([degrees]C) were generated for the samples tested in the thermogravimetric and differential thermal analysis machines, respectively.

Results and discussion

Infrared spectroscopy

FTIR-PAS spectra of oxy-aluminum-treated veneers showed changes, suggestive of chemical modification, of the wood matrix (Fig. 1). The extent of such modification can be assessed with reference to the spectra for the untreated and chromium trioxide modified wood (Fig. 1). The changes in the infrared spectrum of veneers as a result of treatment with chromium trioxide were similar to those reported previously (Evans et al. 1992, Pandey and Khali 1998). The major change was loss of peaks at wavenumbers of 1600 [cm.sup.-1] (benzene ring stretching in lignin), 1660 [cm.sup.-1] (keto-carbonyl conjugated with benzene ring), and 1730 [cm.sup.-1] (C=O stretching in xylan) due to the introduction of a broad band centered at 1590 [cm.sup.-1] (Fig. 1 and Table 2). There was also weakening of the band at a wavenumber of 1505 [cm.sup.-1] (benzene ring stretching in lignin). These changes in the infrared spectrum of wood following treatment with chromium trioxide were similar to those observed in the spectra of aqueous mixes of the lignin model guaiacol or lignosulphonate and chromium trioxide (Michell 1993) and provide evidence for substantial modification of lignin by chromium trioxide. In addition to these changes, the spectrum of chromium trioxide modified veneers also showed weakening of bands at wavenumbers of 2900 (C-H stretching), 1230 (C=O stretching in xylan), 895 (C1 group frequency in cellulose and hemicellulose), 810 (1, 3, 4--substituted benzene ring in softwoods), and 680 (COH out-of-plane bending in cellulose). These changes suggested that chromium trioxide modified hemicelluloses as well as lignin. The spectrum of veneers treated with sodium aluminate (sodium hydroxide and alum) showed the introduction of a broad band at 1590 [cm.sup.-l] that obscured the peaks at 1730 and 1660 [cm.sup.-1] and caused significant diminution of the peak at 1600 [cm.sup.-1]. Similar changes have been noted in wood treated with sodium hydroxide, which was part of the sodium aluminate treatment developed here, and have been ascribed to band shifting from 1730 [cm.sup.-1] as a result of salt formation associated with the carboxyl group (Michell et al. 1965). This band shifting caused the spectrum of sodium aluminate-treated veneers to resemble that of chromium trioxide-treated veneers, but there are important differences between the two spectra. Firstly, the spectrum for sodium aluminate-treated veneers showed a smaller change in the peak at 1505 [cm.sup.-1] suggesting less modification of lignin by sodium aluminate than chromium trioxide. Secondly, veneers treated with sodium aluminate showed weakening of peaks at wavenumbers of 1050 (C-O stretching in cellulose and hemicellulose), 1160 (C-O-C asymmetric band in cellulose and hemicellulose), and 1370 [cm.sup.-1] (C[H.sub.2] bending in cellulose and hemicellulose). These changes may be caused by degradation of hemicelluloses by sodium hy droxide and suggest that the sodium aluminate treatment modified hemicelluloses to a greater extent than chromium trioxide. Evidently the degradation of hemicellulose was not pronounced as there was no strengthening of peaks associated with various characteristics of cellulose (1200, 1170, 1160, 1050, 895, 680 [cm.sup.-1]), which has been reported to be an effect of the removal of hemicelluloses during the pulping of wood with sodium hydroxide (Kuo et al, 1988). Veneers treated with aluminum hydroxide showed weakening of peaks at 1730, 1660, and 1600 [cm.sup.-1], but the changes were less pronounced compared to those observed for wood treated with chromium trioxide or sodium aluminate. There was no weakening of peaks assigned to various characteristics of hemicelluloses suggesting that there was little degradation of hemicellulose by the alum or ammonia that were used in the aluminum hydroxide treatment. The spectra of veneers treated with magnesium aluminate or aluminum borate were similar to that of the untreated control with the exception of slight weakening of peaks at 1730, 1160, 1370, 1160, and 680 [cm.sup.-1], possibly caused by degradation of hemicelluloses.

[FIGURE 1 OMITTED]

Dimensional stability

The radial and tangential swelling of Scots pine blocks after treatment with oxy-aluminum compounds, CCA-wax, and untreated controls are shown in Figures 2 and 3, respectively. As expected, water-treated and untreated blocks swelled rapidly and swelling was essentially complete after 100 and 400 minutes, respectively. It was clear that magnesium aluminate-treated blocks showed the greatest dimensional stability, and there was even some shrinkage of wood blocks when they were immersed in water (Figs. 2 and 3). This may be due to loss of salts from the treated blocks during the test. Blocks treated with the other oxy-aluminum compounds were less dimensionally stable than those treated with magnesium aluminate, possibly because of the lower weight gains achieved with these treatments (Table 3). The dimensional stability of oxy-aluminum-treated Scots pine blocks exceeded that of blocks treated with CCA-wax (Figs. 2 and 3). Magnesium aluminate-treated blocks showed the highest anti-swelling efficiency (105.4%), followed by sodium aluminate (70.8%), aluminum hydroxide (68.9%), and aluminum borate-treated (55.0%) blocks (Table 3). Miyafuji and Saka (1997) showed that wood-inorganic composites with higher weight gains had higher anti-swelling efficiencies, and this effect was partially supported by our findings. Magnesium aluminate-treated wood had the highest weight gains and the highest anti-swelling efficiency. On the other hand, the weight gain of samples containing aluminum borate was higher than that of samples containing sodium aluminate or aluminum hydroxide, but the anti-swelling efficiency of aluminum borate-treated samples was lower (Table 3). Differences in the microdistribution of the inorganic end products of the different treatments may explain why there was not a precise correlation between weight gain due to treatment and anti-swelling efficiency. Aluminum borate was the least effective of the treatments at reducing swelling of wood, but the treatment was the least affected by leaching (Table 3). This suggests that aluminum borate was fixed to a greater extent than the compounds generated by the other treatments. Samples containing the other oxy-aluminum compounds still retained significant dimensional stability after leaching, although leaching reduced their effectiveness (Table 3). Magnesium aluminate-treated blocks showed the highest dimensional stability after leaching (58.6%), although their anti-swelling efficiency was only a little more than half that of the unleached blocks. Interestingly, the anti-swelling efficiency values obtained here after leaching were still equal or higher than those obtained in previous studies for different wood-inorganic composites. Saka (1998) tested several wood-inorganic composites prepared by a sol-gel process and found anti-swelling efficiencies no higher than 50 percent (for wood containing Si[O.sub.2] and [B.sub.2][O.sub.3]). The results obtained here suggest that oxy-aluminum treatments dimensionally stabilize wood by bulking the wood cell wall, and therefore their effectiveness is probably related to their ability to penetrate cell walls and maintain them in a permanently swollen condition.

[FIGURES 2-3 OMITTED]

Decay resistance in soil

The effect of the oxy-aluminum treatments on the weight losses of Scots pine blocks exposed in soil is shown in Table 4. Sodium aluminate- and aluminum borate-treated blocks showed similar overall weight losses, and magnesium aluminate-treated blocks were the least resistant to microbiological deterioration, despite their high initial weight gains. Blocks treated with aluminum hydroxide were the most resistant to decay, but none of the treatments was as effective as CCA-wax at preventing decay. The higher ability of aluminum hydroxide to retard microbial attack might be related to its capacity to modify the carbohydrate portion of the wood cell walls, as suggested by infrared spectroscopy (Fig. 1). The bulking effect of inorganic compounds in the cell wall may also explain the enhanced decay resistance of oxy-aluminum-treated wood, since aluminum is not a biocide.

Thermal resistance

The thermal properties of oxy-aluminum-treated wood were assessed using thermogravimetric analysis and differential thermal analysis. The literature indicates that untreated wood begins to thermally degrade at approximately 250[degrees]C, but decomposition of its principal structural constituent, cellulose, does not commence until a temperatue of 300[degrees]C is reached (LeVan 1984, Rowell and LeVan-Green 2005). Beyond this temperature, cellulose begins to depolymerize via transglycosylation, and this is followed by fragmentation of sugar units and the production of non-combustible and combustible volatiles. When the latter reach their ignition temperature, exothermic combustion occurs and visible radiation is emitted. This is known as flaming combustion. As pointed out by Rowell and LeVanGreen (2005), "the high rate of heat released upon flaming combustion provides the energy needed to gasify the remaining wood elements," further accelerating thermal decomposition of the wood. Oxidation of residual char after flaming combustion results in glowing combustion, which occurs at a temperature of approximately 440[degrees]C. Figure 4 shows the results of thermogravimetric analysis of untreated and oxyaluminum-treated wood. The oxyaluminum treatments lowered the initial temperature of thermal degradation and increased the amount of non-combustible residual char. These findings are similar to those obtained for wood treated with inorganic fire-retardants (LeVan 1984, LeVan and Winandy 1990, Rowell and LeVan-Green 2005). Such compounds modify the thermal properties of wood by inhibiting the production of volatile combustible materials and increasing the production of char and its thermal stability (Rowell and LeVan-Green 2005). It is possible that the oxy-aluminum treatments developed here modified the thermal properties of wood through similar effects.

[FIGURE 4 OMITTED]

Figures 5 and 6 show the differential thermal analysis plots obtained for the oxy-aluminum composites and CCA-wax-treated and untreated wood. The peaks obtained for oxy-aluminum-treated wood (with the exception of magnesium aluminate) were broadened compared to the untreated control (Figs. 5 and 6), indicating that the treatments moderated the generation of heat during thermal degradation of wood. This may be explained by the presence of inorganic materials in wood, which would probably reduce the amount of wood substance ex posed to heat, thereby lowering the heat liberated. This effect was most pronounced for aluminum borate-treated wood (Fig. 6). Miyafuji and Saka (1997) and Miyafuji et al. (1998) also found a weakening of the differential thermal analysis peaks of wood containing Si[O.sub.2]-[P.sub.2][O.sub.5]-[B.sub.2][O.sub.3] or Ti[O.sub.2]. The reduction in the intensity of the exothermic peaks of oxyaluminum-treated wood was particularly noticeable during the glowing stage (Figs. 5 and 6), with the exception of magnesium aluminate. The very high intensity of the glowing peak for magnesium aluminate-treated wood indicates that most of its degradation occurs during the glowing stage, although the peak was shifted to a higher temperature (Fig. 6). This type of behavior has been attributed to increased dehydration reactions in cellulose caused by inorganic additives (LeVan 1984). The differential thermal analysis curve for CCA-wax-treated wood (Fig. 6) and the low residual weights obtained at the flaming stage (not shown) confirm the poor fire resistance of CCA-treated wood, as suggested by previous studies (Evans et al. 1994). The shapes of the thermogravimetric and differential thermal analysis curves found for oxyaluminum-treated Scots pine (with the exception of magnesium aluminate) suggest that the main mechanism of fire resistance for oxy-aluminum composites occurs through the increased production of char and reductions of volatiles produced during the burning process.

[FIGURES 5-6 OMITTED]

Conclusions

The oxy-aluminum treatments developed in this study improved dimensional stability as well as decay and fire resistance of wood to various degrees. The treatments were better than CCA-wax at increasing the dimensional stability and fire resistance of wood, but less effective at increasing the decay resistance of wood. The magnesium aluminate treatment was particularly effective at increasing the dimensional stability of wood, but the anti-swelling efficiency of the treated wood decreased after leaching (albeit to a level higher than that imparted by the other treatments), and the treatment was less effective than the other treatments at restricting decay. The aluminum hydroxide-treated wood showed better decay resistance in soil than sodium aluminate-, magnesium aluminate-, and aluminum borate-treated wood, and the treated wood had good dimensional stability and thermal resistance. There was evidence that the sodium aluminate and aluminum hydroxide treatments modified the wood matrix. Results indicate that oxy-aluminum treatments have potential as wood protection agents, but further research on a larger scale is needed to optimize and further evaluate the treatments including their effects on the mechanical properties of wood and the corrosion of fasteners.

Literature cited

Evans, P.D. 1988. A note on assessing the deterioration of thin wood veneers during weathering. Wood and Fiber Sci. 20(4):487-492.

--, A.J. Michell, and K.J. Schmalzl. 1992. Studies of the degradation and protection of wood surfaces. Wood Sci. and Tech. 26(2):151-163.

--, P. Beutel, R.B. Cunningham, and C.F. Donnelly. 1994. Fire resistance of preservative-treated slash pine fence posts. Forest Prod. J. 44(9):37-39.

Furuno, T. 1992. Studies on combinations of wood and silicate and their properties. Bulletin 176 (Chemical Modification of Lignocellulosics). Forest Res. Inst., Rotorua, New Zealand, pp. 190-196.

-- and Y. Imamura. 1998. Combinations of wood and silicate Part 6. Biological resistances of wood-mineral composites using water glass-boron compound system. Wood Sci. and Tech. 32(3):161-170.

--, T. Uehara, and S. Jodai. 1991. Combinations of wood and silicate 1. Impregnation by water glass and application of aluminum sulfate and calcium chloride as reactants. Mokuzai Gakkaishi 37(5):462-472.

Kimura, Y. 1991. Reaction of aluminium potassium sulfate with bases in aqueous solution. Kagaku to Kyoiku 39(3):326-329.

Kuo, M.-L., J.F. McClelland, S. Luo, P.-L. Chien, R.D. Walker, and C.-Y. Hse. 1988. Applications of infra-red photoacoustic spectroscopy for wood samples. Wood and Fiber Sci. 20(1): 132-145.

LeVan, S.L. 1984. Chemistry of fire retardancy. In: The Chemistry of Solid Wood. R.M. Rowell, Ed. American Chemical Soc., Washington D.C. pp. 531-574.

LeVan, S.L. and J.E. Winandy. 1990. Effects of fire retardant treatments on wood strength: A review. Wood and Fiber Sci. 22(1):113-131.

Markstrom, D.C., L.A. Mueller, and L.R. Gjovik. 1970. Treating resistant Rocky Mountain species by regular and modified double-diffusion methods. Forest Prod. J. 20(12):17-20.

Mayer, P., G. Sampson, A. Gasbarro, and L. Alen. 1995. Service life of posts from Alaska tree species treated by non-pressure methods. Forest Prod. J. 45(11/12):53-56.

Michell, A.J. 1993. FTIR spectroscopic studies of the reactions of wood and lignin model compounds with inorganic agents. Wood Sci. and Tech. 2711):69-80.

--, A.J. Watson, and H.G. Higgins. 1965. An infrared spectroscopic study of delignification of Eucalyptus regnans. Tappi 48(9): 520-532.

Miyafuji, H. and S. Saka. 1997. Fire-resisting properties in several Ti[O.sub.2] wood-inorganic composites and their topochemistry. Wood Sci. and Tech. 31(6):449-455.

--, --, and A. Yamamoto. 1998. Si[O.sub.2]-[P.sub.2][O.sub.5]-[B.sub.2][O.sub.3] wood-inorganic composites prepared by metal alkoxide oligomers and their fire-resisting properties. Holzforschung 52(4):410-416.

Pandey, K.K. and D.P. Khali. 1998. Accelerated weathering of wood surfaces modified by chromium trioxide. Holzforschung 52(5):467-471.

Preston, A.F. 2000. Wood preservation: Trends of today that will influence the industry tomorrow. Forest Prod. J. 50(9): 12-19.

Rowell, R.M. 1983. Chemical modification of wood. Forest Products Abstracts 6(12):363-382.

-- and S.L. LeVan-Green. 2005. Thermal properties. In: Handbook of Wood Chemistry, and Wood Composites. R.M. Rowell, Ed. CRC Press, Washington, D.C. pp. 121-138.

Saka, S. 1998. Recent progress in topochemistry of wood-inorganic composites as prepared by the sol-gel process, ln: Proc. of the Fourth Pacific Rim Bio-Based Composites Symp., Bogor, Indonesia. pp. 386-404.

Sposito, G. 1989. The Environmental Chemistry of Aluminum. CRC Press. Florida. p. 222.

Stamm, A.J. 1964. Wood and Cellulose Sci. The Ronald Press Company, NY. pp. 248-263.

Fabiano A. Ximenes

Philip D. Evans

The authors are, respectively, Research Officer, Forests R&D Division, New South Wales Dept. of Primary Industries, Beecroft, NSW, Australia (fabianox@sf.nsw.gov.au) and Professor, Centre for Advanced Wood Processing, Univ. of British Columbia, Vancouver, Canada (phil.evans@ubc.ca). F. Ximenes acknowledges a scholarship provided by The Australian National Univ., and both authors acknowledge the assistance of Denes Bogsanyi and Dr. John Broomhead of The Australian National Univ. during the initial stages of the work. This paper was received for publication in June 2005. Article No. 10075.

[c] Forest Products Society 2006. Forest Prod. J. 56(11/12):116-122.
Table 1.--Solutions and main products formed by oxy-aluminum
treatments.

Treatment (a) Solution 1 Solution 2

SA Sodium hydroxide Alum, Acetic acid
AH Alum Ammonia
MA Alum + sodium hydroxide Magnesium chloride
AB Sodium tetraborate Alum

Treatment (a) Main product

SA Sodium aluminate NaAl[(OH).sub.4]
AH Aluminum hydroxide [Al.sub.2][O.sub.3]x[H.sub.2]O
MA Magnesium aluminate Mg [(OH).sub.2][Al.sub.2]
 [(OH).sub.6]
AB Aluminum borate AlB[O.sub.3]

(a) SA = sodium aluminate; AH = aluminum hydroxide; MA magnesium
aluminate: and AB = aluminum borate.

Table 2.--Assignments of bands in the infrared spectrum of wood.

Peak number Wavenumber Assignment

 ([cm.sup.-1])

1 3300 Bonded O-H stretching
2 2900 C-H stretching
3 1730 C=O stretching in xylan
4 1660 Keto-carbonyl conjugated with benzene
 ring
5 1600 Benzene ring stretching in lignin
6 1505 Benzene ring stretching in lignin
7 1460 C[H.sub.3] deformation in lignin and
 C[H.sub.2] bending in xylan
8 1425 C[H.sub.2] scissor vibration in
 cellulose
9 1370 C[H.sub.2] bending in cellulose and
 hemicellulose
10 1325 C[H.sub.2] wagging vibration in
 cellulase
11 1275 Guaiacyl nuclei in lignin
12 1230 Syringyl nuclei in lignin and C=O in
 xylan
13 1160 C-O-C asymmetric band in cellulose
 and hemicellulose
14 1110 O-H association band in cellulose and
 hemicellulose
15 1050 C-0 stretching in cellulose and
 hemicellulose
16 895 Cl group frequency in cellulose and
 hemicellulose
17 870 l, 3, 4--substituted benzene ring in
 softwood lignin
18 810 1, 3, 4--substituted benzene ring in
 softwood lignin
19 680 COH out-of-plane bending in cellulose

Table 3.--Weight gains and anti-swelling efficiency of
oxy-aluminum-and CCA-wax-treated Scots pine blocks before
(ASE 1) and after (ASE 2) a leaching procedure.

Treatment WPG ASE 1 ASE 2

 (%)

Sodium aluminate 12.9 70.8 45.7
Aluminum hydroxide 12.2 68.9 45.5
Magnesium aluminate 28.1 105.4 58.6
Aluminum borate 15.2 55.0 48.5
Chromated copper arsenate 2.2 18.9 --
Water -0.35 5.5 --

Table 4.--Weight losses (%) of treated blocks and untreated controls
during a 30-week soil burial bioassay.

Treatments Exposure (weeks)

 10 20 30

 (%)

Sodium aluminate 2.9 4.6 3.5
Aluminum hydroxide -0.6 2.6 2.4
Magnesium aluminate 3.5 4.7 4.9
Aluminum borate 0.9 5.4 4.0
Chromated copper arsenate -2.6 -0.7 -1.4
Untreated 1.8 9.3 36.6
COPYRIGHT 2006 Forest Products Society
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2006 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Ximenes, Fabiano A.; Evans, Philip D.
Publication:Forest Products Journal
Geographic Code:1USA
Date:Nov 1, 2006
Words:5117
Previous Article:Increasing mold resistance of strand boards with spruce heartwood.
Next Article:Degradation of a wood-plastic composite exposed under tropical conditions.
Topics:

Terms of use | Privacy policy | Copyright © 2021 Farlex, Inc. | Feedback | For webmasters