小型秸稈壓塊機(jī)設(shè)計(jì),小型秸稈壓塊機(jī)設(shè)計(jì),小型,秸稈,壓塊機(jī),設(shè)計(jì) Wood Sci Technol (2004) 38: 93–107 DOI 10.1007/s00226-003-0207-3 ORIGINAL G. J. Goroyias ? M. D. Hale The mechanical and physical properties of strand boards treated with preservatives at different stages of manufacture Received: 5 May 2001 / Published online: 25 March 2004 Springer-Verlag 2004 Abstract The physical and mechanical properties of boards treated with a preservative at di?erent points during the manufacture process were evaluated to determine the best stage for the application of preservative. A copper boron tebuconazole amine water-based preservative was used in 3% PF-bonded strand boards to achieve ?ve di?erent retentions. Preservative addition was examined at di?erent stages of the manufacture cycle, namely, green strand di?usion, dry strand vacuum treatment, glue-line spray addition, heat and cold quench of manufactured board, and by post-manufacture vacuum treatment. The treatment methods had marked e?ects on the mechanical properties of some of the boards when the boards with the highest preservative retention were compared with their respective untreated controls. The best results were achieved where the preservative was applied by vacuum treatment of dry strands or by di?usion of green strands before board manufacture. Increasing preservative retention had minimal e?ects on board properties with these two methods but signi?cant deterioration was noted when the preservative was applied by spraying dry strands or by post-board-manufacture heat and cold quench. An increase of pressing temperature resulted in signi?cant improve- ments to the mechanical properties of the spray-treated boards. Post-manu- facture vacuum treatment of boards caused excessively high losses in internal bond strength. Introduction Oriented strand board (OSB) is a structural board widely used in building construction and other applications mainly for interior use or for short-term exterior out-of-ground contact exposure. The use of OSB in exterior conditions is restricted due to its low durability against decay fungi (Chung et al. 1999; Goroyias and Hale 2000a), swelling under high moisture conditions, and the resultant reduction in internal bond strength (Goroyias and Hale 2000a). Preservative treatment is readily applied to solid wood and may also be applied to improve the properties of panel products. In this context it is applied G. J. Goroyias ? M. D. Hale (&) School of Agricultural and Forest Sciences, University of Wales, LL57 2UW Bangor, U.K. E-mail: m.d.hale@bangor.ac.uk 94 for commercial use to plywood after manufacture. A product of this type, treated with a suitable preservative, shows su?cient decay resistance for ground contact use (AWPA C9 1999). However, the lower cost of production of OSB compared to plywood and solid wood gives a cost-competitive incentive to develop a system to improve decay resistance and the dimensional stability of OSB. Fluid preservative treatment of OSB after manufacture results in high swelling so alternative application stages in the manufacture cycle need to be investigated. For this, a series of factors, including time of treatment, stage of preservative addition, physical and mechanical properties of the treated board, resistance of the preservative to leaching, and decay resistance (with and without leaching) need to be considered. The combination of preservative and adhesive type and the stage of addition play an important role in the successful production of a preservative-treated board. Goroyias and Hale (1999, 2000a, 2000b) have recently reviewed the literature related to the e?ect of point of preservative application on board properties. Preservative addition to wood-based panel products has been shown to result in signi?cant losses to the mechanical and physical properties (Boggio and Ger- tjejansen 1982; Laks et al. 1988; Vick 1990; Vick et al. 1990; van Acker and Stevens 1993; Jeihooni et al. 1994; Barnes et al. 1996). Many preservatives were applied by several researchers to prevent wood- based panel products from decay. These include pentachlorophenol, didecyl dimethyl ammonium chloride (DDAC), DDAC with copper, DDAC with carbamate, sodium ?uoride, ammonium hydrogen bi?uoride, ammoniacal copper zinc arsenate (ACZA), borate preservatives, copper naphthenate (CuN), copper octoate, chlorpyrifos, zinc naphthenate. However, various problems may occur: substantial vapour losses of toxic preservatives may occur during pressing, preservatives may interfere with the adhesive, and the resultant sig- ni?cant loss of board mechanical properties result in restricted widespread commercial application (Huber 1958; Vintila et al. 1967; Deppe and Petrowitz 1969; Becker 1972; Laks et al. 1988; Vick 1990; Vick et al. 1990; Fushiki et al. 1993; Jeihooni et al. 1994). However, non-acidic preservatives (e.g. DDAC- based) and emulsi?ed CuN have shown fewer negative e?ects on board mechanical properties (Vick et al. 1990; Schmidt 1991). Azaconazole, applied as a powder to aspen wafers after the application of resin, had no signi?cant e?ect on the board properties tested (Schmidt and Gertjejansen 1988). Composite boards can be preserved at a variety of points during and after manufacture. Di?usion treatment using several preservative formulations [i.e. ammoniacal copper arsenate (ACA), copper-chromium-arsenic (CCA)] before blending has been shown to produce a panel with good properties, above standard speci?cations (Hall et al. 1982), but with poorer properties when compared to the untreated board (Boggio and Gertjejansen 1982; Jeihooni et al. 1994). Surface addition of preservative as a liquid (i.e. ACA, CCA) by spray or as a powder during, before, or after resin blending has been shown to result in a signi?cant decrease of board properties (Hall and Gertjejansen 1979; Jeihooni et al. 1994; Schmidt and Gertjejansen 1988). The extent of in?uence depends on the degree of compatibility of the preservative with the adhesive. It has been shown that several preservative formulations (chlorpyrifos-CP, dichlorophen- thion-ECP, sila?uofen-HOE, propetanphos-PP, IF-IF-100, IPBC) do not interfere with UF resins. However, UF is not suitable for exterior speci?cation 95 boards as UF-bonded boards fail dramatically when wetted (Becker and Deppe 1969; Deppe 1987; Subiyanto et al. 1994). Several types of powder preservative formulations have been applied with the resin before board manufacture (Schmidt and Gertjejansen 1988). This method gives good mechanical properties only when the preservative is heat-stable and compatible with the adhesive. Liquids may be applied post-manufacture by dipping, spraying, brushing, or vacuum or vacuum-pressure, but due to drying, conditioning, and mechanical strength limitations of such methods (Deppe 1967; van Acker and Stevens 1993; Barnes et al. 1996), approaches with vapour treatments (Turner et al. 1990) and supercritical ?uids (Acda et al. 1997) have been investigated. These novel approaches have given some promising results with no changes in board mechanical or physical properties. Brushing, dipping, and spraying frequently yields unsatisfactory depths of penetration and products treated with these methods are only suitable for out-of-ground use, because preservative pene- tration is limited only to the surface regions of the board. It can be concluded from the literature that a variety of isolated studies have looked at the preservation of di?erent types of panel products. These studies involve various preservatives, various formulation types (e.g. powder, oil, or waterborne), application of preservatives at di?erent stages in the manufacture process, and di?erent wood species, resins, and pressing conditions. These studies cannot be directly compared with each other to determine the best method for the application of preservation because they involve too many unrelated variables. However, they do give indications that some ground-con- tact preservatives are not suitable. This paper is a comprehensive study on numerous physical and mechanical properties of strand boards, preserved with a new generation ground-contact wood preservative formulation (Tanalith 3485) at di?erent stages of the manufacture process. Where di?erent pressing conditions have been used to achieve successful board production comparable controls have been included. The leach and decay resistance of these boards will be reported in a later publication. Experimental PF-bonded Scots pine unoriented strand boards treated with Tanalith 3485 (copper azole borate) were made under laboratory conditions to achieve ?ve )3 di?erent preservative retentions (0, 1.5, 3, 6, and 12 kg m ). The internal bond strength (IB), modulus of elasticity (MOE), modulus of rupture (MOR), thickness swelling (TSw), water absorption (Wabs), shear strength, and density of the boards were then evaluated. Board treatment Five di?erent treatment methods were evaluated: di?usion treatment of ‘‘green’’ strands, vacuum treatment of dried strands, spray treatment of dried strands in the resin blender, heat and cold quench (HCQ) of manufactured boards, and post-manufacture vacuum treatment of boards. Goroyias and Hale (1999, 2000a, 2000b) have described in detail the methods of preservative addition used in this study. 96 Board manufacture Boards were produced to a target thickness of 15 mm and a target density of )3 650 kg m , using commercial Scots pine OSB strands with an average density )3 of 400 kg m . Board manufacture variables are presented in Table 1. Four di?erent types of control (untreated) boards were made (Table 1). Board testing Sampling and cutting of the large-sized boards (Table 1) was based on standard EN 326–1:1993. When this was not possible, due to the smaller size of the boards, the sampling and cutting was based on a speci?c pattern which was determined from the results of an analysis of variance (one way ANOVA and Tukey’s pairwise comparisons) of properties (IB, MOR, MOE, TSw, Wabs) between replicate boards. For this purpose small untreated (400·400 mm) boards were produced and tested. The sample variance of each property tested was then analysed using ANOVA (p=0.05) and Tukey’s pairwise comparisons between replicate boards. The results showed that there was no signi?cant di?erence in properties tested between the replicate small- sized boards. Samples were then tested for various mechanical and physical properties and the variances for each property between the boards were analysed (ANOVA, p=0.05, Tukey’s pairwise comparisons). The density pro?le of the boards was measured by using an ATR density pro?le machine (software v2.09) and average densities were calculated. MOE, MOR, IB, TSw, and Wabs were tested according to EN 310:1993, EN 319:1993, EN 317:1993. In addition, a modi?ed, non-standard shear strength test was performed on blocks with 50·25·15-mm thickness (Fig. 1). Load was applied parallel to the strand direction along the sample length in specially designed steel jigs. The load versus displacement curves are shown in Fig. 2. 3 Table 1 Process variables for the manufacture of the test boards Treatment method Resin content content time Wax Blending Temp. Press Sizeb Number of boards cyclea (s) (m) (%) (%) (min) (C) Di?usion 3 3 3 3 3 3 3 3 3,4,6,10 1.2 30 30 30 30 30 30 30 30 30 210 210 210 210 210 210 230 210 210 360 360 360 1·1 5 5 2 32 8 5 2 2 2 4 · Heat and cold quench (HCQ) Control (di?usion and HCQ) Vacuum-pressure Control (vacuum-pressure) Spray 1 Spray 2 Spray Control Post-manufacture vacuum 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1·1 1·1 360 0.4·0.4 360 0.4·0.4 660 540 0.4·0.4 660 1·1 360 0.2 0.2 1·1 3 · c a Pressing cycle includes 90 s press close time and 30 s decompression Board untrimmed size is displayed For post-manufacture vacuum treatment the controls used were the same boards but were untreated. The replicates in this case were two boards for each resin content. b c 97 Fig. 1 Block shear test Fig. 2 Load versus displacement curves for eight specimens using the block shear test The assessment of results was based on comparisons of the properties of the )3 highest retention preservative-treated boards (12 kg m ) with their appropri- ate untreated controls (ANOVA, p=0.05, Tukey’s pairwise comparisons using Minitab version 11). Fifteen replicates were tested for each property, except for the boards produced with vacuum-pressure-treated strands where 30 replicates were tested. To examine for the e?ect of increasing preservative retention on board properties, a correlation test (Pearson correlation, Minitab version 11) between preservative retention and each property was performed. The MOR and MOE )3 tests for the boards treated to the intermediate retentions (1.5, 3, 6 kg m ) included four replicates from the core, and the density pro?le, IB, shear, TSw, and Wabs tests included six core replicates. 98 Results Results for the e?ect of resin concentration on IB and TSw of the post-man- ufacture vacuum-treated boards are presented in Table 2. Results for the dif- ferent treatment methods on the physical and mechanical properties at each preservative level and their correlations are shown in Table 3. Discussion )3 The null hypothesis that the 12 kg m -treated boards do not di?er signi?cantly from their respective controls was tested using ANOVA and Tukey’s pairwise comparisons. When no signi?cant di?erence is shown, preservative addition did not result in a change of board properties, but where there is a signi?cant di?erence, an improvement or a reduction of board properties occurred. Post-manufacture vacuum treatment Post-manufacture treatment was not a successful treatment method in a board containing only 3% resin as high IB loss (42%) and TSw (34%) oc- curred and sub-standard boards resulted. Higher resin content boards (4– 10%) were made and tested for IB and TSw after treatment. Increasing the resin content from 3 to 4% resulted in boards of su?cient IB (Table 2) to )2 pass standards (EN 300, 0.30 N mm ) but even these had high IB losses (50– 56% as compared to their control values, Table 2) and showed no improvement in TSw after treatment. Further increases in resin content above 4% did not result in proportionately higher IB values after treatment. Irre- versible TSw was observed even at high resin contents (Table 2). This dete- rioration is in accordance with work by Hall et al. (1982) who examined aspen waferboards treated under vacuum. Table 2 Mean IB (mean of 4 samples) before and after post-manufacture vacuum treatment, IB loss (%), and percentage thickness swelling (TSw) immediately after post-manufacture vacuum treatment and after the drying (102C) of boards made with di?erent resin contents. Standard deviations are shown in brackets Resin content (%) IB (EN 319) TSw Untreated )2 Preservative-treated )2 Loss (%) Wet (%) Dry (%) (N mm ) (N mm ) 3 0.38 (0.0) 0.57 (0.01) 0.72 (0.02) 0.69 (0.04) 0.16 (0.04) 0.32 (0.02) 0.36 (0.03) 0.38 (0.01) 42 56 50 55 34.2 25.19 (9.70) 28.45 (5.5) 27.76 (1.85) 31.90 (2.32) (8.48) 35.79 (4.50) 39.85 (0.07) 33.97 (5.25) 4 6 10 99 100 101 ‘‘Green’’ strand di?usion Green strand di?usion proved to be a successful method for board manufac- ture, producing a board with good properties, although slightly inferior to boards made from vacuum-treated strands. There were no signi?cant di?er- –3 ences between the control and the 12 kg m -treated boards for the IB, MOE, Wabs (2 h), TSw (2 h and 24 h), and shear, but the intermediate preservative loading boards were marginally worse (Table 3) for the MOR and Wabs (24 h). )3 However the 3 kg m loading appears to have reduced the Wabs (2 h) (Ta- )3 ble 3). The lower MOR value with the 12 kg m loading board is an edge e?ect of the test samples. Similar works (Hall and Gertjejansen 1979; Boggio and Gertjejansen 1982) using di?usion into wet strands with di?erent kinds of copper-based preser- vatives showed pronounced negative e?ects on a variety of mechanical and physical properties of the boards. This is in contrast with the results of our study in terms of severity. No correlations were found between preservative retention and board properties (Table 3). The lack of correlation shows that the preservative addition did not a?ect the board properties and poor results (e.g. )3 12 kg m ,MOR) can be explained by other factors, e.g. edge e?ects. Vacuum pressure treatment of dry wood strands Vacuum-pressure-treated strands produced boards with better properties than all of the other treatment methods. The mechanical and physical testing results are no di?erent from their respective controls although signi?cantly less Wabs (2 h) and consequently less TSw (2 h) occurred (Table 3). However, with pro- longed soaking (24 h) these di?erences were no longer signi?cant. No other correlations were found between preservative retention and board properties with this treatment method (Table 3). This shows that this method of pre- servative application does not have any signi?cantly negative e?ects on board properties. Vick et al. (1990) found that vacuum preservative treatment of boards with ACA and CuN did not interfere with PF resin bonding as assessed by a lap shear test. Similar results are seen here as both IB and shear test data show no e?ect of preservative. The vacuum treatment method gives a good distribution of preservative within the wood strands and the preservative is encouraged to ?x with the wood, which may reduce preservative interference. Spray application Boards produced by spraying the preservative at the glue-line stage showed poor properties when compared to their respective controls; these were signif- icant for every property tested except MOE and MOR (Table 3). Boards treated to intermediate levels showed better values for MOE. High correlations between preservative retention and board properties are noted for spray treatment (Table 3). However, the correlations for the MOE and MOR are much lower than those for the other properties, especially IB and shear. This shows that in strand board the MOE and MOR are not directly related to the quality of wood–resin bond. The orientation and the large size of strands proved a key factor for the board bending strength. 102 Table 4 Mechanical and physical properties of spray-treated (12 kg m)3) boards pressed at 230C. Standard deviations are shown in brackets Property Spray (230C) IB (N mm)2 ) 0.50 (0.08) 9575 (991) )2 MOE (N mm MOR (N mm ) ) )2 46.62 (7.37) 24.42 (3.69) 29.66 (4.07) 60.55 (13.59) 74.23 (12.61) 2.51 (0.24) a TSw (2 h) % a TSw (24 h) % b Wabs (2 h) % b Wabs (24 h) % )2 Shear (N mm ) a Thickness swelling after 2- and 24-h immersion. Water absorption after 2- and 24-h immersion. b As the spray-treated boards pressed at 210C were so inferior, another series of boards were pressed at 230C. Preserved boards pressed at 230C (Table 4) had very good mechanical properties but these boards initially absorbed faster (Wabs, 2 h) than the 210C untreated controls and also showed increased initial swelling (TSw, 2 h). Rapid ?uid uptake during the immersion test and rapid subsequent swelling may have been caused by cell wall damage, i.e. crack for- mation, although other possibilities, such as increased resin–wood bond sti?- ness (low ?exibility resin unable to accommodate swelling), cannot be ruled out. Preservative addition by spraying resulted in an increase in mattress moisture content from 5 to 9%. This alone had a signi?cant negative e?ect on board prope