Surface energy characterization of preservative-treated wood and E-glass/phenolic composites.
The effects of various wood preservative systems and treatment processes on the surface energy of wood and E-glass/phenolic pultruded composite material for wood reinforcement were characterized using surface energy methods. Southern yellow pine and pultruded E-glass/phenolic FRP (fiberglass reinforced plastic) composite sheet were treated with two common wood preservative chemicals (waterborne chromated copper arsenate [CCA] and organometallic copper naphthenate [CuN]). Surface energy of the preservative-treated and untreated wood and FRP composite material was determined by means of static contact angle analysis using the Good-Girifalco (geometric mean) and Chang approaches. It was found that the total surface energies of the surfaces of these materials were greatly affected by preservative treatments. As preservative retentions change, the surface energies of solids were also changed. The surface energy of CCA- and CuN-treated FRP composite decreased as a result of exposure to preservative treatments, while increased CCA retentions resulted in increases of surface energy in southern pine wood. This difference in surface energy behavior with CCA retention is attributed to the accumulation of high surface energy metallic salts on lumen surfaces in treated wood and the CSM layer of the FRP composite. Scanning electron microscopy showed deposits of metal oxides on the cell wall of CCA-treated wood. A discussion of surface energy changes and the possible effects on wettability and bondability of treated wood and FRP composite surfaces is presented.
Pressure treatment with wood preservatives has been known to interfere with the bond integrity of solid wood glued specimens. Vick et al. (1990), Vick (1994), and Vick and Kuster (1992) reported that the lumen surfaces of chromated copper arsenate (CCA, a waterborne wood preservative) treated southern yellow pine were completely covered by hemispherically shaped deposits ranging in diameter from around 1.0 [micro]m to essentially invisible at a magnification of 5,000X. Theoretically, these deposits reduce the molecular level contact between the adhesive and lignocellulosic wood material. They also proposed that in CCA-treated wood, the insoluble metal oxides tie up aromatic hydrocarbon functional groups, reducing hydrogen bonding and/or perhaps covalent bonding opportunities between the adhesive and lignocellulosic wood content.
The lack of information available in the literature directly related to surface energy characterization of wood and fiberglass reinforced plastic (FRP) composites, and the changes occurring as the result of preservative treatment, prompted the initiation of this study. In this research, two wood preservatives (acidic waterborne and organometallic oil-borne) at different retention levels with one wood species and one FRP composite type were evaluated.
When a pre-treatment (preservative application before lamination) method is used to produce reinforced wood composites, the individual wood laminates are exposed to preservative chemicals before the lamination process starts. Therefore, the determination of surface energy characteristics of treated wood and FRP surfaces can provide useful information related to the bonding properties of the treated material.
The objectives of this study were to:
1. determine the surface energy characteristics of preservative-treated wood and FRP composite surfaces and characterize the effect of the preservative type.
2. evaluate the relationship between surface energy and the active retention of preservative in treated wood and FRP composite surfaces, and
3. recommend compatible preservatives to the wood products industry for bonding FRP composite reinforcement in pre-treated (preservative treatment before lamination) applications.
Surface energy assesses the ability of material surfaces to 'wet out' and thereby promote adhesion. Material interfaces with high surface energy have improved bonding performance. Surface energy characterization can be achieved by evaluation of contact angles between the solid material and standard liquids of known surface tension. The contact angle defines the shape of an adhesive liquid drop resting on a solid material surface. Therefore, contact angle evaluation provides a measure of substrate surface energy that correlates to the wettability and bondability of different material surfaces.
Contact angle reflects the physical and chemical affinity between a surface and a liquid such as an adhesive. As a result, contact angle analysis has been used to characterize the wettability of wood surfaces and then to predict their performance when bonded with adhesives (Shen et al. 1998, Gardner et al. 1991, Collet 1972, Hse 1972).
Most of the literature available in this area focuses on CCA-treated wood since until recently, CCA has been the most commonly used preservative worldwide. A significant body of research exists on surface properties of recycled CCA-treated wood. Maldas and Kamden (1998a, b) have reported on the modification of red maple surface properties following treatment with CCA as follows:
a. Wood cell walls are covered with 1 to 5 [micro]m solid deposits, which are rich in chromium, copper, and arsenic;
b. The O/C ratio of CCA-treated samples is increased due to the added oxygen atoms from the CCA on the surface, and at the same time reduced presence of carbon or C1;
c. The surface pH of untreated wood was 6.6 ([+ or -]0.13) compared to 5.9 ([+ or -]0.17) for CCA-treated wood; and
d. The surface roughness profiles for CCA-treated wood changed considerably compared with those of untreated wood. The average roughness found for water-treated wood was 1.72 Ra, where for CCA-treated wood was 2.48 Ra, where Ra is average roughness, i.e., deviation from the mean peak and expressed in [micro]m.
In another similar study on artificially weathered CCA-treated southern pine (Zhang et al. 1997), CCA treatment resulted in improved resorcinol formaldehyde (RF) resin wettability, as expressed by the lower contact angle of RF with the CCA-treated wood, compared to untreated southern pine surfaces. Total surface tension of the CCA-treated wood was greater than the untreated southern pine. Interestingly, Zhang et al. (1997) also noted that the total surface tension of both the CCA-treated and untreated southern pine increased as a result of the exposure to accelerated-weathering cycles that caused surface oxidation. Zhang et al. (1997) discussed findings that CCA-treated wood had been shown to be coated with deposits of metallic oxides (Vick and Kuster 1992) causing a microscopically rough surface. This roughness, coupled with some polar affinity of the oxides with RF resin, may result in the improved wetting of CCA surfaces beyond that occurring with untreated wood surfaces. The wax content of some commercial CCA treatments has previously been offered as an explanation for the higher water contact angle of CCA-treated wood as compared to untreated wood. But a greater magnitude contact angle change for water than for RF adhesive indicated that CCA treatment affects water repellency more than the adhesive wettability of the wood. In terms of bond strength evaluation, Zhang et al. (1997) reported an approximately 20 percent shear strength loss as the result of CCA treatment. The percent of wood failure was not significantly affected when CCA-treated and untreated wood were compared. Accelerated weathering did not greatly reduce the bonding properties of the CCA-treated southern pine. Zhang et al. (1997) concluded that aged CCA-treated southern pine should have reasonable bonding properties assuming that the proper adhesive and bonding technology were employed.
In a scanning electron microscopy (SEM) study of CCA-treated southern pine wood, Vick and Kuster (1992) and Vick (1994) found that the lumen surfaces were coated by a heavy deposits of hemispherically shaped material ranging in diameter from around 1.0 [micro]m to essentially invisible at a magnification of 5,000X. Theoretically this would allow little opportunity for molecular-level contact of the adhesive with lignocellulosic constituents of the cell walls. Phenolic components of adhesives are rich in polar hydroxyl groups that can form hydrogen bonds with polar functional groups on lignocellulosic constituents in the cell walls. But in the case of treated wood, as proposed by Vick and Kuster, the insoluble CCA metal oxides that already occupy functional sites may block hydrogen or perhaps covalent bonding sites that normally might bond with the resin. Despite the presence of insoluble deposits blocking contact between the adhesive and the wood, Vick and Kuster (1992) concluded that mechanical interlocking by a deep-penetrating phenolic adhesive can produce delamination-free bonds to CCA-treated southern pine even after severe cyclic aging tests.
Materials and methods
Wood species and FRP composite material
All specimens were manufactured from southern yellow pine (SYP) lumber. Generally, specimen material was cut from nominal 50 by 153 mm, medium density, flat-sawn sapwood boards. The boards were straight-grained and free of defects.
One type of FRP material was used in this experiment: E-glass/phenolic pultruded composite. This FRP material, identified as K-1, was developed by the Advanced Engineered Wood Composites Center at the University of Maine (Dagher et al. 1998) and manufactured by Strongwell Corporation, Minnesota. The FRP material consisted of reinforced unidirectional (0[degrees]) E-glass continuous fiber rovings, and E-glass chopped strand mat (CSM) 0.023 g/[cm.sup.2] (0.75 oz./ft.[.sup.2]) made of randomly oriented short fibers (Fig. 1). The short-fiber CSM was initially bonded with melamine resin binder to form a mat suitable for the pultrusion process. In the pultrusion process, the continuous fiber rovings were oriented in the core and integrated with the exterior CSM layers using a phenolic resin matrix. A variation of the pultrusion process was applied in which the continuous rovings were impregnated in phenolic resin, while the CSM mats were pulled dry into the heated die. As a result of this processing scheme, a resin-starved surface layer that improves bonding to wood was produced. The corresponding average volume contents for the fabricated FRP composite sheet were:
[V.sub.f] = 54 percent,
[V.sub.m] = 21 percent, and
[V.sub.v] = 25 percent,
[V.sub.f] = fiber volume fraction,
[V.sub.m] = matrix volume fraction, and
[V.sub.v] = void volume fraction.
Two wood preservative systems (acidic waterborne and organometallic dissolved in mineral spirits) were tested (Table 1). CCA is currently facing severe restrictions and will be phased out of many commercial uses in the United States and in other areas of the world (Vlosky and Shupe 2002). However, it currently is still the most widely used acidic waterborne preservative in the world and was used in this work at several loadings targeting ground contact and marine application retentions for southern pine.
The other preservative was copper naphthenate (CuN), an organometallic wood preservative, dissolved in mineral spirits at several concentrations. CuN is currently being promoted as a replacement for CCA since it does not contain arsenic and chromium, which are of concern from an environmental standpoint.
[FIGURE 1 OMITTED]
Preparation of specimens
Five wood specimens (19 by 50 by 250 mm) were cut from nominal 50 by 153 mm, medium density, flat-sawn SYP sapwood boards. All surfaces were planed prior to the preservative treatment. Five 10- by 100-mm strips were cut from the same pultruded FRP sheet (254 by 121 mm). Prior to the pressure-treatment process, both faces of the pultruded sheets were wiped with acetone and ethanol to remove possible surface oils and other contaminants, which might interfere with wood preservative chemical effects.
All pressure treatments were performed in a cylindrical pressure treatment vessel with dimensions 3 m in length by 0.5 m in diameter. Two different pressure-treatment schedules were used. For the waterborne preservative (CCA) a full-cell process that included an initial vacuum of 635 mm of Hg for 10 minutes followed by a pressure of 1.034 MPa for 15 minutes was applied. For the oil-borne preservative (CuN), an empty cell process that included only 15 minutes of 1.034 MPa pressure was used. Because of the very high retentions obtained in preliminary full-cell treatments with oil-borne preservatives, to reach required retentions the empty cell process was utilized. Both treatments took place at ambient temperature. The total contact time of the specimens with the solutions was approximately 60 minutes. Retention levels for each board or FRP composite strip were monitored by weighing before and after the treatment. All samples (both FRP composite and SYP strips) were then exposed to a three-day period of wet fixation. This period was followed by air-drying and conditioning at 21[degrees]C (70[degrees]F) and 60 percent relative humidity (RH) (an equilibrium moisture content [EMC] of approximately 11%) until the specimens reached an equilibrium weight. The preservative-treated and untreated SYP blocks were planed prior to surface energy measurement. The FRP composite strips were not primed to measure the effects of the wood preservative systems alone. All contact angle measurements were completed within three hours after surface preparation. The untreated wood and FRP composite controls were also conditioned at the same EMC.
Application of the static contact angle method
The sessile drop contact angle method with four probe liquids (Table 2) was used to measure the surface energy of treated SYP and FRP composite surfaces. Probe liquids (10 [micro]l, 0.010 ml) were transferred with a micropipette onto the surfaces of the differentially treated wood and FRP. Two seconds after placement of the liquid droplet, a digital (pseudostatic) image of the droplet was captured utilizing a computer-based digital image acquisition card (frame grabber) and a charge-coupled device (CCD) camera. Using the digitally recorded images, the contact angles of the drops on both sides (left and right) were measured and averaged with digital image analysis software (Fig. 2). Each drop was placed on an earlywood portion of a growth ring on the tangential surface for wood and on the CSM surface for the FRP composite specimens. After each drop, the experimental strips were moved to obtain a new surface under the pipette tip for repetitive measurements (Shen et al. 1998).
The Good-Girifalco (geometric mean) and Chang equations were used to calculate the surface energy of the treated wood and FRP composite surfaces (Gardner et al. 1999).
The work of adhesion based on the Geometric Mean Model results in:
W = (1 + cos[theta])[[gamma].sub.L] = 2[([[gamma].sub.L.sup.d][[gamma].sub.s.sup.d])[.sup.1/2] + ([[gamma].sub.L.sup.p][[gamma].sub.s.sup.p])[.sup.1/2]] 
[theta] = contact angle,
[[gamma].sub.L] = surface tension of the liquid (mJ/[m.sup.2]),
[[gamma].sub.s] = surface energy of the solid,
d = non-polar (dispersive) component of surface energy, and
d = polar component of surface energy.
The work of adhesion based on the Chang model results in:
W = (1 + cos[theta])[[gamma].sub.L] = [P.sub.L.sup.d][P.sub.S.sup.d] - [P.sub.L.sup.a][P.sub.S.sup.b] - [P.sub.L.sup.b][P.sub.S.sup.a] 
[P.sub.L.sup.d] = dispersive parameter of liquid,
[P.sub.S.sup.d] = dispersive parameter of solid,
[P.sub.L.sup.a] = principle acid value of liquid, and
[P.sub.L.sup.b] = principle base value of solid.
All of the chemicals used in this study were high performance liquid chromatography (HPLC) grade with 99 percent purity or higher.
Results and discussion
Since two different treatment schedules (full-cell for waterborne CCA and empty-cell for oil-borne CuN) were used, the retentions values (Table 3) varied among the speciments. As expected, full-cell treatments resulted in greater retentions for both wood and FRP specimens. It was known from a previous experimental study (Tascioglu et al. 2002) that the void content of the FRP composite sheet affects the preservative retention values. As a result, the solution concentrations were adjusted for both preservatives to match the targeted retentions for FRP composite sheets.
Surface energy characterization
The average measured contact angles obtained from differentially treated SYP and FRP composite surfaces utilizing a series of probe liquids is summarized in Table 4. In general, CuN treatment, an organometallic preservative, resulted in an increase in contact angle of water while CCA-C-treated surfaces reduced the contact angle of water on SYP surfaces. This was expected due to the different physical and chemical characteristics of both surfaces tested. In the case of preservative-treated FRP composite surfaces, however, both types of treatment (water- and oil-borne) caused increases in water contact angles. The increase in contact angle on surfaces tested represents a reduction of surface energy (Pocius 1997).
[FIGURE 2 OMITTED]
Known values of [[gamma].sub.L], [[gamma].sub.L.sup.d], [[gamma].sub.L.sup.p] for the probe liquids used (Table 2) and their actual measured contact angles on wood and FRP composite surfaces (Table 4) were used to calculate the total surface energy ([[gamma].sub.S]) of solid surfaces, acid-base surface tension ([[gamma].sub.ab]), and the dispersive component (Table 5), as described by Gardner et al. (1999).
The dispersive energy was determined using the geometric mean (Equation ). Diiodomethane was used to determine [[gamma].sub.S.sup.d]. Assuming ([[gamma].sub.L.sup.p][[gamma].sub.S.sup.p])[.sup.1/2] = 0, Equation  simplifies as:
(1 + cos[theta])[[gamma].sub.L] = 2([[gamma].sub.L.sup.d][[gamma].sub.S.sup.d])[.sup.1/2] 
Rearranging terms results in:
[[gamma].sub.S.sup.d] = 1/4[[gamma].sub.A](1 + cos[theta])[.sup.2] 
[[gamma].sub.L] = [[gamma].sub.L.sup.d] for non-polar liquids.
The calculated dispersive surface energy was inserted into the Chang model (Eq. ) to compute the dispersive parameter [P.sub.S.sup.d]:
[P.sub.S.sup.d] = (2[[gamma].sub.S.sup.d])[.sup.1/2] 
The Chang model takes into account not only the attractive interactions between acidic and basic molecules, but also the repulsive interaction of a solid or a liquid surface.
The acid-base surface tension results in:
[[gamma].sub.S.sup.AB] = -[P.sub.S.sup.a][P.sub.S.sup.b] 
And the total surface energy results in:
[[gamma].sub.S.sup.Total] = [[gamma].sub.S.sup.d] + [[gamma].sub.S.sup.AB] 
[[gamma].sub.s.sup.d] = non-polar dispersive component.
The computed values are listed in Table 5.
[FIGURE 3 OMITTED]
Surface energy calculations based on the contact angle data from Tables 4 and 5, reveal that the surface chemistry of SYP and FRP was altered by preservative treatments (Figs. 3,4, and 5). The total surface energy of SYP decreased by about 1 mJ/[m.sup.2] when CuN retention increased from 0 to 0.97 kg/[m.sup.3] and 10 mJ/[m.sup.2] when CuN retention increased from 0.97 kg/[m.sup.3] to 4.00 kg/[m.sup.3] (Fig. 3). This decrease in surface energy was expected because of the oily non-polar nature of CuN wood preservative. Increased CCA retention conversely, increased the total surface energy of SYP. The total surface energy of untreated SYP increased from 42.16 to 44.97 mJ/[m.sup.2] with a retention of 5.93 kg/[m.sup.3] of CCA. Approximately a ten-fold further increase in CCA retention increased the total surface energy of SYP to 48 mJ/[m.sup.2] (Fig. 4). These findings are in agreement with Zhang et al. (1997). They reported a total surface energy of 43.35 mJ/[m.sup.2] for commercial CCA-C-treated SYP at a 6.4 kg/[m.sup.3] retention level. The increased surface energy was attributed to the chemical modification of the wood surface by the high surface energy metallic salts (Zhang et al. 1997). An accumulation of these high surface energy metallic salts utilizing a SEM microscope were observed (Fig. 6).
FRP composite surfaces, unlike the SYP, responded similarly to both CCA and CuN treatment. The total surface energy of the pressure-treated FRP composite was reduced with increased retentions of CCA-C and CuN, suggesting that adhesion performance would be negatively altered by these treatments (Fig. 5). Somewhat different changes were expected since the chemical interactions between preservative chemicals and surfaces are different. These findings are important for long-term durability of pre-treated FRP composite reinforced glulam beams if the composite sheets are also to be treated before lamination. The results presented show that CCA-C and CuN treatments of wood laminates or FRP composite sheets will directly affect the physiochemical surface properties, the total surface energy of these materials and consequently, the bondability of wood and FRP composite laminates.
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
[FIGURE 6 OMITTED]
In parallel studies, pressure treatment of individual wood laminates with oil-borne preservatives (such as creosote, CuN, and PCP) resulted in high delamination values for wood/FRP interfaces (Tascioglu et al. 2003, Herzog et al. 2003). The present surface energy analysis supports these findings with total surface energy reductions up to 23 percent for SYP surfaces and up to 40 percent for E-glass/phenolic pultruded surfaces.
The following conclusions have been drawn from this study:
1. Analysis of surface energy characteristics with contact angle measurements revealed that the surface energy of preservative-treated SYP and E-glass/phenolic FRP composite surfaces was affected by an average of 43 percent due to the preservative treatments (CCA-C and CuN) used in this study.
2. As CuN retention was increased in both wood and the FRP composite, the surface energies of both specimens decreased. This implies that the oily nature of the CuN and mineral spirit carrier reduced the wettability of the surfaces regardless of their chemical nature. This should be taken into account when wood or FRP composite laminates are treated with CuN before lamination (pretreated applications).
3. The CCA retention increases, on the other hand, resulted in increased total surface energy of SYP specimens only. The FRP composite surfaces reacted differently and showed decreased total surface energy with increased CCA retention, which should be also considered when pre-treatment applications are utilized. It is hypothesized that this difference in behavior is due to the different chemical fixation mechanisms of the preservatives on wood and FRP composite surfaces.
4. Surface energy characterization through static contact angle measurement proved to be a useful technique for characterizing the wettability and bondability of wood/FRP composite interfaces.
Table 1. -- Type and percent concentrations (w/w) of preservative used. Composition and Concentration (%) concentration FRP Preservative by weight Carrier SYP composite CCA-C Chromated copper arsenic Distilled 1 (a) 1 (a) type C; Arsenic acid water 10 (b) 5 (b) 17.0%, chromic acid 23.75%, copper oxide 9.25% Cu-N Copper naphthenate; Mineral 0.25 (a) 1 (a) naphthenic acid, copper spirits 1 (b) 2.50 (b) salt 60% to 80%, mineral spirits 15% to 25% (a) Targeting ground contact retention level. (b) Targeting marine retention level. Table 2. -- Values of surface tension components of the probe liquids used in the contact angle analysis (from Tze and Gardner 2001). (a) Probe liquid [[gamma].sub.L] [[gamma].sub.L.sup.d] (mJ/[m.sup.2]) Diiodomethane 50.8 50.8 Ethylene glycol 48 29 Formamide 58 39 Water 72.8 21.8 Probe liquid [[gamma].sub.L.sup.p] [P.sub.L.sup.p] (mJ/[m.sup.2]) ([mJ.sup.1/2]/m) Diiodomethane 0 11.6 Ethylene glycol 19 7.5 Formamide 19 7.3 Water 51 6.6 Probe liquid [P.sub.L.sup.a] [P.sub.L.sup.b] ([mJ.sup.1/2]/m) Diiodomethane -4.11 -4.12 Ethylene glycol 3.69 -5.44 Formamide 6.92 -4.64 Water 6.88 -7.4 (a) [gamma]=surface free energy (surface tension), the subscript L refers to liquid and superscripts d, p, a, and b refer to dispersive, polar, acid, and base forces, respectively. Table 3. -- The range of preservative retentions for the preservative systems used in this study. Retention (kg/[m.sup.3]) Preservative SYP FRP composite CCA-C 5.93 (a) 1.60 (a) (full-cell) 66.60 (b) 8.33 (b) Cu-N 0.97 (a) 1.92 (a) (empty cell) 4.00 (b) 5.28 (b) (a) Targeting ground contact retention level. (b) Targeting marine retention level. Table 4. -- Measured contact angle averages of the probe liquids used on differentially treated SYP and FRP composite surfaces (five replicates for each liquid). Mean contact angle ([theta]) (a) Surface material/ Probe liquids treatment Diiodomethane Ethylene glycol SYP/untreated 36.4 (2.67) 41.86 (4.42) SYP/0.25% Cu-N 38.21 (4.99) 56.21 (4.30) SYP/1% Cu-N 47.76 (3.52) 68.48 (3.8) SYP/1% CCA 33.34 (3.93) 41.9 (3.04) SYP/10% CCA 27.38 (1.33) 37.46 (4.40) FRP/untreated 20.28 (13.3) 27.16 (3.53) FRP/1% CCA 39 (13.6) 84.07 (4.56) FRP/5% CCA 48.24 (5.39) 90.35 (15.39) FRP/1% Cu-N 45.97 (2.38) 80.34 (5.23) FRP/2.5% Cu-N 43.88 (5.31) 74.67 (6.10) Mean contact angle ([theta]) (a) Surface material/ Probe liquids treatment Formamide Water SYP/untreated 34.58 (2.51) 85.17 (9.01) SYP/0.25% Cu-N 48.63 (6.92) 63.33 (5.33) SYP/1% Cu-N 58.43 (6.14) 111.7 (3.52) SYP/1% CCA 48.87 (9.53) 65.53 (5.84) SYP/10% CCA 41.49 (4.19) 59.89 (4.26) FRP/untreated 24.51 (2.11) 24.01 (14.9) FRP/1% CCA 91.87 (7.07) 112.9 (6.98) FRP/5% CCA 75.75 (7.56) 115.6 (3.07) FRP/1% Cu-N 83.23 (7.58) 90.79 (11.6) FRP/2.5% Cu-N 84.23 (4.97) 107.6 (9.98) (a) Values in parentheses are standard deviations. Table 5. -- Surface tension components for untreated, CCA-, and Cu-N- treated SYP and FRP composite after exposure to post-treatment conditioning. (a) Surface Material Treatment Retention preparation (kg/[m.sup.3]) SYP Untreated 0 Freshly planed Cu-N 0.97 Freshly planed Cu-N 4.00 Freshly planed CCA 5.93 Freshly planed CCA 66.60 Freshly planed FRP composite Untreated 0 Unprimed Cu-N 1.92 Unprimed Cu-N 5.28 Unprimed CCA 1.60 Unprimed CCA 8.33 Unprimed Material Treatment [[gamma].sup.AB] [[gamma].sub.S.sup.d] (mJ/[m.sup.2]) SYP Untreated 0.790 41.37 Cu-N 0.692 40.49 Cu-N -2.895 35.51 CCA 2.188 42.78 CCA 2.846 45.09 FRP composite Untreated 3.732 50.42 Cu-N -2.366 40.45 Cu-N 1.036 37.60 CCA -1.557 40.10 CCA -2.982 35.25 Material Treatment [[gamma].sub.S] (mJ/[m.sup.2]) SYP Untreated 42.16 Cu-N 41.19 Cu-N 32.61 CCA 44.97 CCA 47.94 FRP composite Untreated 54.16 Cu-N 38.08 Cu-N 36.57 CCA 38.55 CCA 32.26 (a) [[gamma].sup.AB] = acid-base component of solid surface; [[gamma].sub.S.sup.d] = dispersive component of solid surface; [[gamma].sub.S] total surface energy of the surface.
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The authors are, respectively, Assistant Professor, College of Forestry, Dept. of Wood Products Engineering, Abant Izzet Baysal Univ., Duzce, Turkey; Professor, Wood Science and Technology, Forest Prod. Lab., Univ. of Maine, 5755 Nutting Hall, Orono, ME 04469-5755; Assistant Professor, Dept. of Civil and Environmental Engineering, Univ. of Maine, 5711 Boardman Hall, Orono, ME 04469-5711; and Professor, Wood Science and Technology, Univ. of Maine, 208 AEWC Building, Orono, ME 04469-0001. The National Science Foundation--EPSCoR Program on Advanced Engineered Wood Composites at the University of Maine and the New England Wood Utilization Research Program provided funding for the study presented in this paper. This is paper 2766 of the Maine Agricultural and Forest Experiment Station. This paper was received for publication in June 2003. Article No. 9693.
*Forest Products Society Member.
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|Author:||Tascioglu, Cihat; Goodell, Barry; Lopez-Anido, Roberto; Gardner, Douglas|
|Publication:||Forest Products Journal|
|Date:||Dec 1, 2004|
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