Plywood exposure tests (Sixth progress report)

Media

Part of Forestry Leaves

Title: Plywood exposure tests (Sixth progress report)
Language: English
Rights
Fulltext: Plywood Exposure Tests. (Sixth Progress Report) by EMILIO JARANILLA SUMMARY This report covers the results of tests and observations on red lauan and bagtikan plywood bonded with melamine-type adhesive after two years of exposure to outdoor conditions. The study showed that the adhesive was not durable and therefore could not be considered suitable for use in the manufacture of Type I plywood. INTRODUCTION The study presented in this report is a continuation of a previous study1 conducted on a melamine-type adhesive submitted bv a certain chemical company. As per original agreement, the adhesive was to be tested in accordance with the requirements for Type I plywood bond. This investigation was conducted to evaluate the performance. of this adhesive as it is exposed to the changing weather conditions in the Philippines. Its performance would indicate the extent to which it can be considered serviceable for exterior use. MATERIALS Laboratory-prepared panels, made of red lauan and bagtikan heartwood, were used. They were of the three-ply constructions, consisting of 1/16-inch veneer for faces and backs, and 1/8-inch for cores. The melamine-type adhesive used has the following components: 1 Manzo, P. M. and I. M. Laroya. 1962. A study on melamine-type adhesive for Type I plywood. MOVING-UP DAY ISSUE-1965 COMPONENTS PARTS BY WEIGHT Liquid _ _ _ _ _ _ _ 100 Powder _ _ _ _ _ _ 46 Total _ _ _ _ 146 EXPERIMENTAL PROCEDURE A panel was randomly taken from each of the triplicate panels previously manufactured under the following experimental variables: 1. Spread: 30 and 40 lbs/M sq. ft. SGL 2. Pressing time: 2 and 4 minutes 3. Assembly time: 10, 30 and 90 minutes 4. Moisture content: 6 and 12 per cent. Thus, a 2 x 2 x 3 x 2 factorial design was used, with each variable represented in the 24 panels that were studied. All the panels were nailed at two selected points on the center of each panel to a veritcal test fence facing south. The lowe-;t row was 24 inches above the ground. A distance of 2 inches separated each test piece. The test panels were removed after two years. It was observed that delamination was present in nearly all the test specimens. Delamination was measured. Bond strength was evaluated by means of the dry shear test. Analysis of results 1. The shear strength and wood failure (bond strength) obtained after two years was compared to the corresponding she.n Page 77 strength and wood failure after fabricatio1l. The comparison was expressed quantitativnly as the per cent reduction in bond strength given in the following formula: Bond strength reduction, per Original bond strength - bond strength after two years cent=-----------Original bond strength x 100 The formula was based on the assumption that the original bond strength was the maximum value that could be attained under the combination of variables used. The values obtained are tabulated in Table 2. 2. An analysis of variance was employed to test the hypothesis that the variables used have an effect on the amount of shear strength reduction. The F-test values are shown in Tables 3 and 4. 3. Delamination was evaluated by classifying the panels as either failed or have not failed. Failure was attained when the total delamination exceeded four inches in length, or 4 per cent of the glue line. The delamination presented in Table 1 was expressed as a per cent of the total glue line. RESULTS AND DISCUSSIONS The comparison between the panels which were originally fabricated and those exposed after 2 years showed that there was a significant reduction of bond strength after two years. On the average, the shear reduction of red lauan and bagtikan was 24 per cent and 18 per cent, respectively. The averagr~ reduction in wood failure was 77 per cent for red lauan and 69 per cent for bagtikan. This reduction in bond strength indicates that tension and compression stresses, set up on the width and thickness of the plywood panels, were sufficiently great to cause degradation of the glue line. The analysis of variance showed that th·~ main variables used during the fabrication of the panels have no effect on the reduc~Page i8 lion of shear strength. This also includes their first order . and second order intera<> tions. The result shown by the analysis of. variance could be interpreted in two ways .. The first inlerpretation assumes that the effect of the variables has been confined only to the manufacturing operation and that the variables have no more effect as far as th~ service performance of the plywood is concerned. The second interpretation assumt>s that the effects of other factors, such as weathering, stressing of the glue line due to moisture content changes, were far greater than the effects of the variables used in the study, in degrading the glue line. The latter interpretation is believed to be better because of the physical and chemical changes that is inherent in weathering which probably occurred simultaneously with mechanical degradation. Wood failure was not treated statistically in the same manner as the shear strength because of the semi-subjective method o)f evaluating it from the shear specimens. No conclusion as to the effect of the processing variables on the reduction of wood failure could thercf ore be made. The evaluation of delamination showed that 17 out of 24 or about 71 per cent delarninated in red lauan. In bagtikan, 16 out of 24 or 67 per cent delaminated. The specimens which failed were 10 out of 24 or about 42 per cent for red lauan and 9 out of 24 or about 38 per cent for bagtikan. These results show that there was excessive delamination after only two years of exposure to outdoor conditions. CONCLUSIONS In assessing the performance of an adhesive, both its strength and durability mmt be taken into consideration. In most cases, durability is considered as the better criterion. FORE~TRY LEAVES The results of the exposure test showt)d that the service performance of the melamine-type adhesive submitted by the chemical company concerned was not satisfactory The reduction in bond strength is moderate, but the excessive number of delaminated panels and the number of specimens that failed because of delamination within a span of only two years, pointed out that the adhtsive was not durable. Hence, the adhesive is considered not suitable for use in the manufacture of Type I plywood based on the aforementioned findings. Table 1. Bond strength and delamination of red lauan and bagtikan panels after two years outdoor exposure. RED LAU AN BAGTIKAN TREATMENTS Shear Wood Delami- Shear Wood strength failure nation I strength failure (psi) (per cent) (per cent) I (psi) (per cent) ' M1A1S1t1 169 4 3.1 249 20 M1A1S1t2 231 44 1.0 280 23 M1A1S2t1 172 10 None 274 25 M1A1S2t 2 189 10 None 241 32 M1A2S1t1 179 8 5.7 245 12 M1A2S1t2 236 18 None 240 12 M1A2S2t1 209 14 None 242 38 M1A2S2t2 179 10 None 266 60 M1AaS1t1 156 23 0.5 256 34 M1A 3 S1 t2 181 18 2.1 236 26 M1AaS2t1 210 31 None 283 39 M1A 3 S2t2 211 43 None 274 35 M 3 A1S1t1 240 41 26.0 238 17 M 3 A1S1t 2 172 11 26.0 273 28 M 3 A1S2t1 204 18 18.2 270 59 MaA1S2t2 225 34 19.8 280 36 M 3 A2S1t1 215 27 26.0 266 12 MaA2S1t2 254 25 9.4 274 14 MaA2S2t1 203 21 3.1 250 22 M3 A2S2t2 192 22 '12.5 236 19 MaAaS1t1 160 6 26.0 275 51 MaAaS1t2 165 9 7.3 242 29 MaAaS2t1 206 26 0.8 262 16 MaAaS2t2 203 19 1.5 279 40 Legend: M = 1 6 per cent moisture content S 1 = 30 lbs. spread, MSGL M 3 = 12 per cent moisture content S 2 = 40 lbs. spread, MSGL A 1 = 10 minutes assembly time t 1 = 2 minutes pressing time A 2 = 30 minutes assembly time t 2 = 4 minutes pressing time A 3 = 90 minutes assembly time MOVING-UP DAY ISSUE - 1965 Delamination (per cent) 1.0 13.5 4.2 None 1.0 0.5 None 1.0 9.4 26.0 1.0 None 14.5 14.5 None None 15.6 6.2 None None 7.0 2.6 3.1 None Page 7Q Table 2. Reduction in bond strength after two years . exposure. RED LAU AN I BAGTIKAN I I Panel Reduction in---/ No.1 Reduction in Reduction in Reduction in shear strength wood failure shear strength wood failure (per cent) (per cent) (per cent) (per cent) -------1 35.5 95.9 25.4 78.9 2 8.7 55.6 15.2 74.7 3 36.8 89.9 19.6 72.8 4 22.2 89.6 26.5 63.6 5 26.0 91.9 21.5 87.6 6 16.9 81.8 21.0 87.8 7 21.4 85.8 27.3 57.8 8 26.0 89.8 18.4 37.5 9 39.3 76.0 11.7 64.2 10 27.6 81.6 27.2 71.7 11 20.4 67.7 6.9 59.8 12 14.2 56.6 17.7 62.0 25 0 40.6 22.2 81.5 26 38.3 87.8 18.8 70.5 27 28.4 77.5 12.S. 37.2 28 18.5 63.4 9.1 63.2 29 19.5 70.6 11.9 87.2 30 8.3 70.9 13.8 85.1 31 2~l7 78.4 20.9 77.3 32 31.4 76.l 22.4 80.2 33 38.9 93.9 18.6 45.7 34 28.6 90.0 22.7 67.8 35 16.2 64.9 15.2 83.0 36 24.0 80.0 17.0 58.8 1 Panel numbers designate the same treabnents as shown in Table 1. Table 3. Analysis of variance of red lauan. Source of Variation D.F. Sum of squares Mean square F M 1 9.88 9.88 N.S. s 1 14.72 14.72 N.S. t 1 34.08 34.08 N.S. A 2 99.07 49.53 N.S. M x s 1 46.9.'3 46.93 N.S. M x T 1 224.48 224.48 N.S. MxA 2 37.04 18.52 N.S. s x T 1 2.16 2.16 N.S. s x A 2 535.57 267.78 N.S. A x T 2 41.94 20.97 N.S. M x S x T 1 43.58 43.58 N.S. M x S x A 2 134.00 67.00 N.S. M x T x A 2 431.58 215.79 N.S. s x T x A 2 277.50 138.75 N.S. Error 2 473.67 236.83 Total 23 2406.20 (Continued on page 84) Page 80 FORESTRY LEAVES 1"45,000.00 worth of fancy articles made of ipil-ipil seeds every month. She said that these articles have become a craze among the American ladies. Necklaces, earrings and bracelets sell like hot cakes at $10.00 to $20.00 a set. The cones of Mindoro pine and Benguet pine can be painted and sold as decorations. These are good substitutes for mistletoes for Christmas trees. There is indefinite number of articles and novelties that can be made out of these seeds. Perhaps, the only limit to this is the inventive ingenuity and resourcefulness of man. The profitableness of seed collection has been proven in Arayat, Pampanga and Mount Makiling, Laguna. There are persons who would prefer to collect seeds rather than be employed temporarily at 'P'4.00 a day. These people claim that they are earning much more in seed collection and on top of this, they are not under the command of anybody. In other words, they are their own boss. Plywood Exposure . . . (Continued from page 80) Those who are interested to make additional income. by. coltecting seeds of forest tree species, they are we!Come for consultation at the Reforestation Administration in Diliman, Quezon City, or any of the Reforestation projects which is nearest their place. They will be told what to do, what seeds to collect, and how much they are going to be paid for the seeds that they will be able to collect. They will also be instructed how to treat, dry and store these seeds so that what they will collect will be fresh and viable. This coming dry season, many people will have nothing to do. At the same time, many economic trees will also be bearing fruits. They could make their spare hours profitable by collecting forest tree seeds. It will not only be financially rewarding but they will also feel a sense of accomplishment in the thought that they are also doing their share in helping restore the forest that have been destroyed by unthinking people. Table 4. Analysis of variance of bagtikan. - - - - - - ----· - -- - -- ---------- · - Source of Variation D.F. Sum of squares Mean square F -------- - - - - - - - M 1 44.01 44.01 N.S. s 1 10.27 10.27 N.S. T 1 9.75 9.75 N.S. A 2 23.56 11.78 N.S. M x s 1 1.76 1.76 N.S. M x t 1 4.09 4.09 N.S. M x A 2 83.71 41.85 N.S. s x T 1 0.27 0.27 N.S. s x A 2 142.43 71.22 N.S. T x A 2 138.23 69.11 N.S. M x s x T 1 2.3..'3 2.33 N.S. M x s x A 2 102.82 51.41 N.S. M x T x A 2 73.10 36.55 N.~. s x T x A 2 50.88 25.44 N.S. Error 2 40.20 20.10 Tota! 23 727.41 Pa!e 84 FORESTRY LEAVES