Potential of tannins for exterior grade plywood.
Resins from Uncaria gambier and Acacia catechu tannins were prepared by copolymerization with phenol and formaldehyde at 100[degrees]C. Both tannins were used to substitute up to 50 percent of the phenol using 5, 8, and 11 percent alkali concentrations. Adhesive formulations and gluing conditions were tested by preparing three-ply Shorea robusta boards (53.34 by 53.34 cm). We found that U. gambier tannin can substitute up to 50 percent of the phenol, using 8 and 11 percent sodium hydroxide as a catalyst; A. catechu tannin can substitute up to 30 percent of the phenol, using 8 and 11 percent sodium hydroxide. The resultant boiling water resistance grade plywood meets the requirements laid down in Indian Standards (IS) 303-1989 for exterior grade plywood in all respects (i.e., glue shear strength in dry, water resistance, and mycological tests).
In most countries only phenolic adhesives are considered suitable for the manufacture of exterior grade wood products, particularly if exposure to extreme climatic conditions is anticipated (Pizzi et al. 1981). Due to the high cost of synthetic adhesives, there have been several attempts to replace a portion of the petroleum-derived compounds with phenolic-type compounds obtained from renewable resources. Principal among these efforts is the development of adhesives from tannin (Pizzi and Scharfetter 1978, Pizzi 1983). Tannin-based adhesives have in the past been heavily fortified with urea, urea-formaldehyde, phenol-formaldehyde (PF), and resorcinol-formaldehyde with encouraging results (Pizzi 1977, 1983, 2008; Pizzi and Roux 1978; Pizzi and Scharfetter 1978). However, very little work has been done with Acacia catechu and Uncaria gambier tannins. Tannins contained in vegetable extracts are polymers of flavonoid units or polyflavonoids fairly well diffused in various tree barks, wood, cones, and fruits. Tannins are broadly divided into hydrolyzable and condensed tannins. The former are simple mixtures of pyrogallols, gallic acid, and ellagic acid, all of which are simple phenols with low reactivity toward formaldehyde. However, they constitute only 5 to 10 percent of a total industrial production of tannin extracts manufactured in the world. The main tree species exploited to obtain these hydrolyzable or gallic tannins is chestnut (Castanea) (Pizzi 1980).
Condensed tannins are the polymerization of monomeric flavan-3-ol or flavan-3,4-diol precursors (Figs. 1 and 2). The structure and formation of condensed tannins are the topic of many speculative theories that have been summarized and criticized by many researchers. The "catechin hypothesis" was introduced by Freudenberg and De Lama (1958) and suggests that the complex polymeric structures of many of the condensed tannins are primarily derived by polycondensation of precursors of a flavonoid type.
The generic term catechin was first used by Freudenberg and De Lama (1958) to describe the colorless crystalline substances commonly located in plant tissues in association with the condensed tannins. Since the catechins were readily converted in vitro to amorphous tannin-like materials, the researchers regarded them as direct precursors of the tannins in nature.
Later work showed that the catechins are derivatives of the basic flavan-3-ol structure, and these compounds are currently referred to as flavan-3-ols to avoid confusion with trivial names (Haslam 1966). The first and perhaps most widely distributed compounds of this class to be isolated from natural sources were (+)-catechin from U. gambier and (-)-epicatechin from A. catechu; these are diastereoisomers of the 5,7,3',4'-tetrahydroxyflavan-3-ol structure (Figs. 3 and 4)
[FIGURE 1 OMITTED]
The tannins of U. gambier and A. catechu belong to the phloroglucinolic type. These types of tannins are difficult to handle because of their high molecular weight and extremely high reactivity toward formaldehyde (Hemingway and McGraw 1976, Schroeder 1976, Rossouw 1978). This reactivity causes premature curing, and the residual active centers become too far apart for formaldehyde molecules to bridge, resulting in incomplete cross-linking. This shortcoming results in brittleness, poor wood penetration, and poor wet strength (Sowunmi et al. 1996). This also prevents the formation of tannin-resols, tannin resins carrying methylol reactive groups, because the methylol reactive groups will condense with other tannin phenolic nuclei in a very short time. Thus resol resins, which dominate synthetic PF technology, are not a feasible alternative for tannins. In short, tannin-resols are not stable, and their shelf life is far too short to be of industrial or practical significance. This leads to tannins being added to PF resins to overcome the short pot life of tannin-formaldehyde resins.
The aim of this study therefore was to improve the adhesive properties of U. gambier and A. catechu tannin adhesives. Specifically, the objective was to modify the resulting structure with resol-type PF resin to reduce the tendency for premature curing and encourage a high degree of cross-linking.
Materials and Methods
Uncaria gambier tannin (Stiasny value 74.5%, hide powder tannin content 59.49%, nontannins 20.08%, and total solubles 79.57%) is a commercial product obtained after the separation of katha and was supplied by Chemistry Division, Forest Research Institute, Dehradun (patent no. 1484/DEL/98, 1485/DEL/98, P981302/98, 9804614/98). Acacia catechu tannin (Stiasny value 72.2%, hide powder tannin content 55.89%, nontannins 22.04%, and total solubles 77.93%) was supplied by the Mantu Khair Industry, Rangia Assam.
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
The chemicals used in this study included phenol (Qualigens, laboratory reagent [LR] grade), formalin (37% to 41%; Ranbaxy, LR grade), sodium hydroxide pellets (Ranbaxy, LR grade), hide powder (E. Merck AG), chrome alum (s d fine-chem Limited, LR grade), kaolin (CDH, LR grade), hydrochloric acid (Ranbaxy, LR grade), and methanol (Ranbaxy, LR grade).
Preparation of PF resin, using 5, 8, and 11 percent alkali as the catalyst.-One hundred grams of molten phenol (60[degrees]C to 65[degrees]C) was charged into the 500-mL round-bottom flask followed by 120 g of formalin (37% to 41% concentration) and 5 g of sodium hydroxide dissolved in 10 mL of distilled water. The condensation reaction was carried out for 30 minutes at a refluxing temperature of approximately 100[degrees]C. When the viscosity of the resin syrup was about 100 cps and the water tolerance was about 1:5, the resin was discharged from the round bottom flask and cooled to room temperature by keeping the container in cold circulating water (George 1977).
The procedure for the manufacture of PF resin using 8 and 11 percent alkali concentration was similar to that described for the 5 percent alkali concentration, except for the increased amount of sodium hydroxide.
Preparation of phenol-tannin-formaldehyde (PTF) resin at 5, 8, and 11 percent alkali concentration.--The adhesive formulation was based on a constant molar ratio of phenol-tannin with formaldehyde. The molar ratio (P+T):F was 1:1.2. The replacement of phenol by tannin was successfully achieved up to 50 percent, above which gel formation of resins was observed.
Required amounts of molten phenol (grams) and formaldehyde (grams) were mixed together in a beaker. Tannins of U. gambier and A. catechu taken separately (grams, oven dry) were added into the phenol-formaldehyde mixture and stirred for 15 to 20 minutes at room temperature until the tannin was completely incorporated (Table 1). The reactants were transferred into a 500-mL round-bottom flask with aqueous sodium hydroxide (5%, 8%, and 1 I% to that of phenol and tannin) and experiments were carried out for 30 minutes at the refluxing temperature (100[degrees]C). The physicochemical properties of PF resin prepared after substitution of phenol with tannins of U. gambier using 5, 8, and 11 percent sodium hydroxide as the catalyst are reported in Tables 2 and 3.
[FIGURE 4 OMITTED]
Eighteen test specimens of 2.54 by 15.24 cm were cut along the grain of face veneers from each plywood panel and used for glue shear strength testing (Anonymous 1983, 1989) in dry, water resistance, and mycological environments (Table 4). The results are shown in Tables 5 and 6.
In the water resistance test, the specimens were kept in boiling water for 8 hours. They were then cooled by submerging in cold water at room temperature and then tested for glue shear strength. For the mycological test, the specimens were kept in a porcelain dish filled with a 25-mm layer of sawdust obtained from the sapwood of a perishable timber like semul (Bombax ceiba) in its natural condition. The sawdust was moistened with 1 liter of water containing 15 g of sucrose (cane sugar was normally used), so that it was damp but not so wet that free water could be squeezed from it by hand pressure. To attain this condition with dry sawdust, it is generally necessary to add water at three times the mass of the sawdust. The dish was sealed against the glass with screws so that the atmosphere around the test ply samples remained saturated. The dish and contents were maintained at a temperature of 27[degrees]C [+ or -] 2[degrees]C for a period of 3 weeks, after which specimens were tested at room temperature for glue shear strength.
Results and Discussion
Properties of PTF adhesives prepared using different molar ratios of reactants and alkali concentrations are reported in Table 1; viscosity, pH, gelation time, and specific gravity of U. gambier and A. catechu tannins are reported in Tables 2 and 3, respectively.
With an increasing molar ratio of tannin in PF resin, the viscosity of adhesives increased sharply as with a simultaneous increase of catalyst from 5 to 11 percent in both cases. Adhesives made from A. catechu tannin had greater viscosity than those made from U. gambier tannin (Figs. 5 and 6). This may have been due to A. catechu tannin extract having more nontannins (22.04%) compared with U. gambier tannin extract (20.08%). The presence of nontannin compounds such as hydrocolloid gums, which are hydrophilic and highly branched polysaccharides, in A. catechu tannin extract tends to promote high solution viscosities and affects the properties of tannin-based adhesives, particularly their moisture resistance (Sowunmi et al. 1996). The pH of the adhesives prepared using both tannins remained alkaline yet it decreased with increasing catalyst and molar ratio of tannin. This was due to the acidic nature of tannins used. The effect of viscosity was clearly reflected in the gelation time of resin prepared from both of the tannins; the higher the viscosity, the lower the gelation time. Resins with more viscosity have higher polymerization because less time is required for complete polymerization during the determination of gelation time. The specific gravity of the resins prepared using both the tannins showed an increasing trend with an increase in molar ratio of tannins in PF as well as the catalyst. However, it was insignificant compared with the specific gravity of the control resin.
Glue shear strength
In IS 303 (Anonymous 1989), the average and the minimum values specified for boiling water resistance (BWR) grade plywood for glue shear strength are 135 and 110 kg in a dry state, 100 and 80 kg for the water resistance test, and 100 and 80 kg for the mycological test, respectively. Glue shear strength values of plywood prepared using different molar ratios of U. gambier and A. catechu tannins are reported in Tables 5 and 6.
Phenol-U. gambier tannin-formaldehyde resin.--Glue shear strength for dry, water resistance, and mycological tests of plywood samples using PF resin prepared by substituting phenol with 10 percent U. gambier tannin and 5 percent sodium hydroxide was found to be slightly lower (Table 5), except water resistance was slightly better compared with the average and minimum requirements for BWR grade plywood. Further, substitution of phenol with tannins not only lowered the glue bond in dry and mycological tests, but samples even delaminated in water resistance tests. These results may have been due to incomplete condensation of reactants, possibly due to the low concentration of the catalyst. With an increase in the catalyst from 5 percent to 8 and 11 percent (Table 5), glue bond improved considerably, to the extent that up to 50 percent phenol could be replaced with U. gambier tannin without any appreciable effect on glue bond.
Plywood prepared with a 50 percent substitution of phenol with U. gambier tannin also met the minimum and average requirements of glue shear strength specified for BWR grade of plywood in all respects.
Phenol-A. catechu tannin-formaldehyde resin.--Table 6 shows the results for glue shear strength in dry, water resistance, and mycological tests of plywood samples using PF resin prepared by substituting phenol with A. catechu tannin and 5 percent sodium hydroxide as the catalyst. The glue shear strength values were lower compared with the control, particularly in the dry state. Further, it was also observed that in the water resistance tests the values of glue shear strength met the requirements for BWR grade plywood made after 20 and 30 percent replacement of phenol with A. catechu tannin. Further, the replacement of phenol with tannin resulted in delamination of the plywood during testing. However, with 30 percent replacement of phenol with tannin, only in the mycological tests did glue shear strength meet the requirements for BWR grade plywood.
[FIGURE 5 OMITTED]
Test results reported in Table 6 for glue shear strength in dry, water resistance, and mycological tests of plywood samples using PF resin with up to 30 percent of the phenol substituted with tannin and using 8 percent alkali as the catalyst indicate that the samples met the requirements for BWR grade plywood in all aspects.
Further, by increasing the concentration of alkali (the catalyst) to 11 percent, up to 40 percent of the phenol can be substituted with tannin without affecting the glue bond quality; this plywood meets the requirements for BWR grade plywood (i.e., minimum and average specified for glue shear strength in dry, water resistance, and mycological tests).
[FIGURE 6 OMITTED]
The substitution of phenol with tannin beyond 30 percent with 8 percent catalyst and 40 percent with 11 percent catalyst affected the glue bond adversely. It was also evident that an increase in catalyst from 5 to 11 percent in partially substituted PTF resin helped in the completion of the condensation reaction to a great extent. Further, the glue bond quality also improved with an increase in partial substitution of phenol with tannin and also with an increase in the catalyst concentration as with the U. gambier tannin based adhesives.
The data of various parameters, dry testing failing load (DTFL), boiling water resistance failing load (BWRFL), and mycological testing failing load (MTFL), were subjected to analysis of variance (ANOVA) for 5, 8, and 11 percent alkali concentrations. From this analysis, we found a significant difference for 5 and 8 percent alkali concentrations from the standard (control) for all parameters in all effects. However, for 11 percent alkali concentration, the glue bond quality of treated plywood was on par with the standard for DTFL and BWRFL; for MTFL it was significantly different from the standard (Table 7). To evaluate the differences among alkali concentrations, all data were pooled excluding the performance of standard and analyzed. From this analysis it was observed that all major effects (i.e., alkali concentration, species, molar ratio), all possible two-factor interactions, and three-factor interactions were significantly different for all three parameters except the main effect of species for the BWR test (Table 8).
We observed that U. gambier tannin can be substituted for up to 50 percent of the phenol using 8 and 11 percent sodium hydroxide as catalyst, and in the case of A. catechu, tannin can be substituted for up to 30 percent of the phenol using 8 and 11 percent sodium hydroxide as the catalyst for making BWR grade plywood meeting the requirements of IS 303 (Anonymous 1989) in all respects (i.e., glue shear strength in dry, water resistance, and mycological tests). We prepared PTF resin at 5, 8, and 11 percent alkali concentrations. The effect of pH on the rate of curing and polymerization of phenolic resin is well known. It is also widely accepted that at alkaline pH, the curing rate of phenolic nuclei as nucleophiles is strengthened by ionization of the phenol to form phenolate ions. PF resins are used as thermosetting wood adhesives, an application for which only PF resins of very high alkalinity, generally at pH values between 10 and 13, are used to impart faster reactivity and shorter pressing time to the adhesive. Further, it is also observed that U. gambier tannin is a better partial substitute of phenol compared with A. catechu tannin. This may be because of the presence of more nontannin compounds in A. catechu such as hydrocolloid gums that promote high solution viscosity and poor moisture resistance of tannin-based adhesives (Sowunmi et al. 1996).
Resin from both of these tannins with 8 percent alkali used as the catalyst results in glue bond quality of the plywood meeting the Indian Standard; thus, these tannins can be used for making resin. The use of 11 percent sodium hydroxide as the catalyst will increase the cost of resin; however, the statistical analysis of the results showed that 8 and 11 percent sodium hydroxide can be used as the catalyst. In the case of U. gambier tannin, up to 50 percent of the phenol can be replaced, and in the case ofA. catechu tannin, up to 30 percent of the phenol can be replaced. Both yield comparable results for plywood meeting the IS 300 requirement. However, if 11 percent sodium hydroxide is used as the catalyst (with both tannins), results are comparable to the control and better than those with resin prepared using 8 percent sodium hydroxide as the catalyst. As shown in Table 7, results of treated plywood (both tannins) are comparable to those of the control at 8 and 11 percent sodium hydroxide using all parameters. Consequently, tannins of U. gambier and A. catechu are successful partial substitutes for phenol in PF resin for making three-ply S. robusta boards.
Anonymous. 1983. Methods of test for plywood. IS 1734 (Parts I-XX). Bureau of Indian Standards, New Delhi. pp. 1-5.
Anonymous. 1989. Specification for plywood for general purposes. IS 303. Bureau of Indian Standards, New Delhi. pp. 1-7.
Freudenberg, K. and J. M. A. De Lama. 1958. Tannin catechins. Annalen 612:78-80.
George, J. 1977. Economics of production of synthetic resin adhesives. IPIRI J. Indian Plywood Ind. Res. Inst. 7(2):48-71.
Haslam, E. 1966. Condensed tannins analysis of extracts. In: Chemistry of Vegetable Tannins. Academic Press Inc., London. pp. 14-64.
Hemingway, R. W. and G. W. McGraw. 1976. Southern pine bark polyflavonoids: Structure, reactivity and use in wood adhesives. Appl. Polym. Syrup. 28:1349-1364.
Pizzi, A. 1977. Hot-setting tannin-urea-formaldehyde exterior wood adhesives. Adhes. Age 20(12):27-35.
Pizzi, A. 1980. Tannin-based adhesives. J. Macromol. Sci. C 18(2): 247-315.
Pizzi, A. (Ed.). 1983. Wood Adhesives: Chemistry and Technology. Marcel Dekker Inc., New York. pp. 105-178.
Pizzi, A. 2008. Tannins: Major sources, properties and applications. In: Monomers, Polymers and Composites from Renewable Resources. M. N. Belgacem and A. Gandini (Eds.). Elsevier, Amsterdam. pp. 179-199.
Pizzi, A. and D. G. Roux. 1978. The chemistry and development of tannin-based weather- and boil-proof cold-setting and fast-setting adhesives for wood. J. Appl. Polym. Sci. 22:1945-1954.
Pizzi, A. and H. O. Scharfetter. 1978. The chemistry and development of tannin-based adhesives for exterior plywood. J. Appl. Polym. Sci. 22:1745.
Pizzi, A., H. Scharfetter, and E. W. Kes. 1981. Adhesives and techniques open new possibilities for the wood processing industry. Holz Roh-Werkst. 39:85-89.
Rossouw, D. du T. 1978. Outwikkeling van dennelooistoffe. Special Report Hout 137. CSIR, Pretoria, South Africa.
Schroeder, H. 1976. Pine tannin adhesives. Special Report Hour 120. CSIR, Pretoria, South Africa.
Sowunmi, R., O. Ebewele, A. H. Conner, and H. River. 1996. Fortified mangrove tannin-based plywood adhesives. J. Appl. Polymer Sci. 62:577 584.
The authors are, respectively, Research Associate, Research Officer, Scientist (Retired), and Scientist (Retired), Chemistry Div., Forest Research Inst. (Indian Council of Forestry Research and Education), Dehradun, India (email@example.com [corresponding author], firstname.lastname@example.org [corresponding author]). This paper was received for publication in June 2012. Article no. 12-00060.
Table 1.--Partial substitution of phenol with tannins of Uncaria gambier and Acacia catechu in phenol-formaldehyde resin. Resin sample code P:T:F molar ratio (a) 5% Catalyst U1, Al 90:10:120 U2, A2 80:20:120 U3, A3 70:30:120 U4, A4 60:40:120 U5, A5 50:50:120 8% Catalyst U6, A6 90:10:120 U7, A7 80:20:120 U8, A8 70:30:120 U9, A9 60:40:120 U10, A10 50:50:120 11% Catalyst Ull, All 90:10:120 U12, A12 80:20:120 U13, A13 70:30:120 U14, A14 60:40:120 U15, A15 50:50:120 (a) P:T:F = phenol:tannin:formaldehyde; U = Uncaria gambler; A = Acacia catechu. Gelation of resin was observed at a molar ratio of 40:60:120. Table 2.--Physicochemical properties of phenol-formaldehyde (PF) resin with phenol partially substituted with Uncaria gambier tannin. (a) Viscosity Resin or Shear rate Viscosity resole ([s.sup.-1]) (cps) pH 5% Catalyst PF1 9.3 110 9.89 Ul 9.3 135 9.09 U2 9.3 175 9.05 U3 9.3 255 9.01 U4 3.4 300 8.95 U5 2.8 350 8.19 8% Catalyst PF2 9.3 145 10.75 U6 9.3 190 10.6 U7 9.3 200 10.53 U8 9.3 210 10.52 U9 2.8 600 10.49 U10 2.5 7,700 9.22 11 % Catalyst PF3 9.3 170 11.55 Ull 2.5 900 11.42 U12 2.5 1,200 11.39 U13 2.5 2,500 11.24 U14 2.5 3,800 10.78 U15 2.5 10,600 10.5 Gelation time Resin or at 100 [degrees]C Specific resole (h:min:s) gravity 5% Catalyst PF1 >10:0:0 1.15 Ul 2:59:00 1.15 U2 2:07:00 1.16 U3 1:50:00 1.20 U4 1:05:00 1.20 U5 0:45:00 1.21 8% Catalyst PF2 >10:0:0 1.16 U6 1:18:00 1.18 U7 1:02:00 1.19 U8 0:48:04 1.20 U9 0:34:14 1.22 U10 0:17:00 1.24 11 % Catalyst PF3 >10:0:0 1.17 Ull 1:58:00 1.184 U12 1:30:00 1.19 U13 0:53:42 1.22 U14 0:23:46 1.23 U15 0:09:09 1.25 (a) cps = counts per second; U = Uncaria gambler. Table 3.--Physicochemical properties of phenol-formaldehyde (PF) resin with phenol partially substituted with Acacia catechu tannin. (a) Viscosity Resin or Shear rate Viscosity resole ([s.sup.-1]) (cps) pH 5% Catalyst PF1 9.3 110 9.89 Al 9.3 305 9.2 A2 9.3 400 9.08 A3 9.3 550 9.03 A4 3.4 775 8.99 A5 2.8 1,250 8.92 8% Catalyst PF2 9.3 145 10.75 A6 9.3 510 10.65 A7 9.3 600 10.58 A8 9.3 630 10.55 A9 2.8 1,900 10.51 A10 2.5 15,400 9.41 11% Catalyst PF3 9.3 170 11.55 All 2.5 2,100 11.45 A12 2.5 3,400 11.40 A13 2.5 6,900 11.26 A14 2.5 9,100 10.06 A15 2.5 28,200 10.8 Gelation time Resin or at 100 [degrees]C Specific resole (h:min:s) gravity 5% Catalyst PF1 >10:0:0 1.15 Al 2:10:00 1.15 A2 1:56:00 1.16 A3 1:35:00 1.16 A4 0:55:00 1.18 A5 0:35:00 1.20 8% Catalyst PF2 >10:0:0 1.16 A6 1:05:00 1.18 A7 0:50:00 1.19 A8 0:39:01 1.20 A9 0:23:47 1.20 A10 0:07:38 1.22 11% Catalyst PF3 > 10:0:0 1.17 All 1:51:00 1.17 A12 1:25:00 1.18 A13 0:51:40 1.21 A14 0:20:36 1.22 A15 0:02:45 1.24 (a) cps = counts per second; A = Acacia catechu. Table 4.--Basic gluing conditions for different resins prepared with Uncaria gambier and Acacia catechu tannins. (a) Plywood parameters Processing conditions Veneer species Sal (Shorea robusta) Veneer thickness 1.5 mm Veneer moisture content 7%-9% Glue spread for: U. gambler 195-218 g/[m.sup.2], double glue line, solid basis A. catechu 193-218 g/[m.sup.2], double glue line, solid basis Panel assembly 3-ply Pressing temperature 150 [degrees]C [+ or -] 5 [degrees]C Pressing time 12 min Pressing pressure 14 kg/[cm.sup.2] (a) Plywood panels of 53.34 by 53.34 cm were made under the indicated laboratory conditions. Table 5.--Test results of glue shear strength of plywood made using phenol-formaldehyde (PF) and phenol-tannin-formaldehyde resins (Uncaria gambier). (a) Glue shear strength failing load (kg) Water resistance Mycological Dry test test test Catalyst Resin (%) Avg. Min. Avg. Min. Avg. Min. PF1 5 137 122 110 97 104 90 A1 5 125 106 108 100 95 85 A2 5 69 48 dl dl 54 45 A3 5 99 95 dl dl 85 85 A4 5 86 70 dl dl 85 72 A5 5 83 60 dl dl 83 72 PF2 8 141 132 112 97 105 97 A6 8 139 132 108 103 106 95 A7 8 136 130 115 95 112 97 A8 8 153 135 113 100 105 92 A9 8 138 130 118 109 107 100 A10 8 143 132 121 107 114 103 PF3 11 145 139 115 101 112 99 All 11 138 128 117 107 105 102 A12 11 141 132 139 122 113 104 A13 11 137 127 102 95 97 92 A14 11 161 154 137 128 113 107 A15 11 158 151 110 92 107 102 IS 303 135 110 100 80 100 80 BWR grade (a) Avg. = average; Min. = minimum; U = Uncaria gambler; dl = delamination; BWR = boiling water resistance. Table 6.--Test results of glue shear strength of plywood made using phenol-formaldehyde (PF) and phenol-tannin-formaldehyde resins (Acacia catechu). (a) Glue shear strength failing load (kg) Water resistance Mycological Dry test test test Catalyst Resin (%) Avg. Min. Avg. Min. Avg. Min. PF1 5 137 122 110 97 104 90 Al 5 106 82 95 90 95 85 A2 5 120 105 105 94 90 88 A3 5 110 95 103 85 101 98 A4 5 80 65 dl dl 78 65 A5 5 85 72 dl dl 79 72 PF2 8 141 132 112 97 105 97 A6 8 139 132 105 92 103 92 A7 8 136 129 104 93 100 92 A8 8 135 127 118 110 117 111 A9 8 123 100 88 82 87 75 A10 8 86 78 79 67 79 72 PF3 11 145 139 115 101 112 99 All 11 141 134 112 98 107 100 A12 11 135 122 101 88 98 91 A13 11 139 122 116 92 100 89 A14 11 140 132 106 92 101 96 A15 11 123 117 96 89 94 86 IS 303 135 110 100 80 100 80 BWR grade (a) Avg. = average; Min. = minimum; A = Acacia catechu; dl = delamination; BWR = boiling water resistance. Table 7--Mean values for comparison between control and treated samples. (a) 5% Catalyst 8% Catalyst Sample DTFL BWRFL MTFL DTFL BWRFL MTFL Control 136.50 110.17 104.17 140.83 112.00 104.50 Treated 96.32 41.08 84.50 132.82 106.7 102.92 11% Catalyst Sample DTFL BWRFL MTFL Control 144.00 115.00 111.67 Treated 141.07 113.18 103.47 (a) DTFL = dry testing failing load; BWRFL = boiling water resistance failing load; MTFL = mycological testing failing load. Table 8.--ANOVA for different parameters. (a) MSS (b) Source df DTFL BWRFL MTFL Replication 5 149.72 190.25 392.51 All treatments 29 Catalyst 2 34,028.75 * 95,538.84 * 6,992.11 Species 1 2,304.09 * 259.20 579.61 Molar ratio 4 1,829.61 * 9,174.79 * 612.41 Catalyst X species 2 2,540.91 * 15,101.02 * 1,611.17 * Species x molar ratio 4 2,423.45 * 6,312.60 * 1,199.91 * Catalyst X molar 8 1,037.81 * 3,368.15 * 484.99 * ratio x species Error 145 108.26 77.66 50.34 (a) MSS = mean sum of squares; DTFL = dry testing failing load; BWRFL = boiling water resistance failing load; MTFL = mycological testing failing load. (b) * Significant at 5 percent.
|Printer friendly Cite/link Email Feedback|
|Author:||Mathur, Smita; Sharma, Pradeep; Shukla, K.S.; Soni, P.L.|
|Publication:||Forest Products Journal|
|Date:||Aug 1, 2012|
|Previous Article:||Formaldehyde emissions from urea-formaldehyde- and no-added-formaldehyde-bonded particleboard as influenced by temperature and relative humidity.|
|Next Article:||Twenty-year performance of decking with two levels of preservative penetration.|