Bending properties of particleboards made from soft maple, red oak, white oak, black cherry, beech, and yellow-poplar bark were obtained and compared with the specimen's density and thickness. Regression analyses indicated that the bending properties depend not only on species but also on density and/or specimen thickness. This dependence was not consistent among species

Blankenhorn, Paul R.

Murphey, Wayne K.

Rishel, Lester E.

English

Wood and Fiber Science (E-Journal)

A NOTE ON THE FLEXURAL PROPERTIES OF BARK BOARD' Lc.ster E. Rishel, Paul R. Blankenhorn Research Assistant and Associate Professor of Wood Technology School of Forest Resources. The Pennsylvania State University, University Park, Pennsylvania 16802 and Wuyne K .  Murphey Head of Forest Science Texas A&M University. College Station. Texas 77843 (Received 15 March 1979) ABSTRACT Bending properties of particleboards made from soft maple, red oak, white oak, black cherry. beech, and yellow-poplar bark were obtained and compared with the specimen's density and thick- ness. Regression analyses indicated that the bending properties depend not only on species but also on density andlor specimen thickness. This dependence was not consistent among species. Kr,yvc,ords: Bark board, flexural properties, density, specimen thickness. INTRODUCTION Bhagwat (1975) reviewed the utilization of bark residues particularly in the areas of chemistry, pulp products, soil additives, bark production, bark disposal, fuel, hardboard, particleboard, etc. Utilization of bark residue in particleboard would process large volumes of bark, and because of this possibility, some prop- erties of bark particleboards have been reported (Blankenhorn et al. 1977; Judd 1973; Murphey and Rishel 1969). Generally the data indicate that bark boards possess high swelling and low strength values. Previous research reported that flexural and compressive properties of red oak bark board were correlated with density (Blankenhorn et al. 1977). This corre- lation has not beer1 reported for other species. Also, data relating the effects of specimen thickness on the mechanical properties have not been reported. The objective of this study was to establish whether a relationship exists between the flexural properties, density, and specimen thickness of six bark species. EXPERIMENTAL Bark from soft maple (Acer spp.), red oak (Quercus rubra L.), white oak (Quer- CLIS alba L.), black cherry (Prunus serofina Ehrh.), beech (Fagus grandijbliu Ehrh.), and yellow-poplar (Liriodendron tul ipf ira L.) was obtained from a ros- serhead debarker and dried in a kiln to approximately 5% moisture content (oven- ' This research was supported by funds from McIntire-Stennis Project 231 I .  Paper No. 5708 in the Journal Series of the Pennsylvania Agricultural Experiment Station. Authorized for publication on 29 March 1979. Wood and I;,hrr. 11(4), 1980, pp. 233-236 (D 1980 h y  the Society of Wood Sclence and Technology 234 W 0 0 1 )  A N D  FIBER, WINI 'ER 1980. V .  1 l(4) MOE S~ec1e5  Y = MOE (mi): P = Density (Ih1ft"i. T = 'l'hlckncss (inch) R" Beech MOE = 79966.4 - 645.3P - 65776.1T 0.542 Soft maple MOE = 104141.8 - 1682.0P - 226782.3T + 5121.4PT 0.224 Black cherry MOE = 147535.5 - 2585.5P - 354555.1T + 8127.OPT 0.184 White oak MOE = 135104.2 - 21 15.7P - 39847.9'r 0.283 Red oak MOE = 7744.6 + 74054.7T 0.125 MOR Y - MOR (psi); P = Density (Iblft.'). T = 'Th~ckness (inch) Beech MOR = 1266.9 - 1379.2T 0.655 Soft maple MOR = 1633.4 - 15.9P - 3273.7T + 70.4PT 0.193 Black cherry MOR = 1212.7 - 4.27P - 3922.2T + 86.3PT 0.312 White oak MOR = 1255.7 - 6.4P + 1386.7T - 44.3PT 0.336 S~gn~f icant  at the (1 05 level dry basis). Each species was hammermilled and all particles passing a 0.25-inch but retained on a 0.06 inch screen were used in the preparation of the molded specimens. Bark from each of the six species was tumbled, coated, and mixed with 6% by weight of powdered phenol-formaldehyde resin, and placed i n  rect- angular molds of 0.25, 0.50, 0.75, and 1.00 inch square by selected lenglhs (20 times thickness). Targeted densities were 40, 50.60, and 70 Iblft"). The specimens were conditioned at 30% RH and 22 C prior to testing. Density measurelments, based on oven-dry weight and volume, were obtained after mechanical testing, while thickness measurements were obtained on all specimens prior to testing. Load deformation data were obtained using a Universal Tinius Olsen Testing Machine with a crosshead speed of 0. I inchlminute in accordance with ASTM D 1037-72A. Regression analyses for each species were conducted using the depender~t vari- ables of density, thickness, and interaction of density and thickness. Nonsignifi- cant variables were eliminated from the general regression equation. Additional regression analyses were performed on the data at the different thicknesses ('A, %. -%, and 1 inch) for each species. These analyses were conducted to observe if the MOE or MOR was a function of density at different thicknesses. RESULTS A N D  DISCUSSION Table 1 is a summary of the significant regression equations produced using the general model of the flexural properties versus the density, thickness, and inter- action of density and thickness. Yellow-poplar bark specimens did not produce significant equations for the variables measured. While the equations in Table 1 were significant, they generally had a low coefficient of determination. Generally, a relationship exists for the species for density andlor thickness, but it is not highly correlated. In fact, trends among species were not evident. Table 2 lists the average flexural properties for the six species investigated. Yellow-poplar bark boards were highly fibrous, and they produced specimens with the highest average MOE, while beech bark boards were highly particulate R ~ \ l r < l  <,I ol -RARK BOARD P R O P t R T I E S  235 MOE MOR Llensity Species (10' psi) (PW) (Iblft") Yellow-poplar 48.5 853 48.4 Red oak 48.4 819 47.6 Black cherry 31.1 966 46.4 Soft maple 29.1 838 44.8 White oak 23.5 743 42.4 Beech 19.2 600 44.8 - and produced specimens with the lowest MOE and MOR. Regression analysis for average MOE versus average MOR for all species indicated that generally as the average MOE decreases the average MOR also decreases, although the cor- relation coefficient (r) for this relationship is only 0.5 1 .  The average densities of the specimens listed in Table 2 for each species were less than 50 Iblft:' indicating that the targeted densities of 40, 50.60 and 70 Iblft:' were not achieved, particularly the higher targeted densities of 60 and 70 Iblft". Since the target densities were not achieved during fabrication. additional regression analyses centered around the individual molded thicknesses. Table 3 lists a summary of the regression equations that resulted in the highest coefficient of determination values (R" for bending properties of bark boards and the mea- sured density at selected thicknesses after fabrication. Other thicknesses pro- duced significant equations. but the R2 values were lower than those given in Table 3. Additional significant equations were obtained for bending properties of the six species versus density at the following thicknesses: red oak at 1.00 and 0.25 inch for MOE and l .OO for MOR; soft maple, 1.00, 0.75, and 0.25 inch for TABLE 3. Slttnmury ($ r~ ,yr ( ,~ .s ion ( , q ~ t ( ~ t i o ~ ~ ~ * f o r  bending propc.rtias rrnd dan;\ity. & *  MOE Thickness S p e c ~ e \  ( ~ n c h l  Y = MOE (psi): P = Denrity (lhlft'l R' Yellow-poplar 0.75 Y = -275000 + 7784P 0.859 Red oak 0.75 Y = - 295000 + 7477P 0.661 Soft maple 0.50 Y = 38234 - 515P 0.748 Black cherry 0.75 Y = -317000 + 7416P 0.618 White oak 0.25 Y = 162000 - 2056P 0.304 Beech 0.50 Y = 28302 - 363P 0.634 MOR 'l'h~ckness ( ~ n c h )  Y = MOR (psi): P = Denally (IbIft'J Yellow-poplar 0.75 Y = -3639 + l00P 0.65 1 Red oak 0.75 Y = - 1188 + 42.7P 0.630 Soft maple 1 .OO Y = 2083 - 33.2P 0.654 Black cherry 0.75 Y = -4688 + 117P 0.725 White oak 0.50 Y = 192 + 3.92P 0.347 Beech - - - -  - -  N o n e  - - - - - - - -  - - - - - - - - - - -  - ~ - - -  - * Significant at the 0.05 level " *  Density wa\ hased on oven-dry mas\ and vulumc measurements ohtained after the 5pecimens were tested In flexure. 236 WOOD 4 N D  FIBER, WINTER 1980. V .  1 l(4) MOE and 0.75 inch for MOR; black cherry, 0.50 and 0.25 inch for MOE; and beech, 0.25 inch for MOE. It is evident from this analysis that thickness influ- enced the bending properties and density relationships differently for the selected species. Results of this study indicated that the bending properties of bark board de- pended on specimen density and/or thickness differently for the six species in- vestigated. Comparisons among species were difficult. Targeted densities, partic- ularly the higher densities, were difficult to obtain during fabrication. Significant relationships, except for yellow-poplar, were obtained with low coefficients of determination, indicating that the relationship between the bending properties and density and/or thickness exists. Subsequent regression analyses of the bend- ing properties versus density at different thicknesses produced regression equa- tions with higher coefficients of determination implying specimen thicknesses for each species that produce the best relationship between flexural properties and density. The thickness producing the highest correlation for each species was not generally consistent among species. This study indicates that not only specimen density but also specimen thickness must be accounted for in flexural testing of bark board specimens of different species. REFERENCES BHAFWAT. SUDA G .  1975. Utilization of bark. For. Prod. J .  25(2):13-15. BLANKENHORN. P. R . .  W.  K .  MURPHEY, L. E.  RISHEL, A N D  D. E. KLINE. 1977. Some mechanical properties of impregnated bark board. For. Prod. J .  27(6):31-38. JUDD. F. S .  1973. The bark brick. a bark-resin composite building block. M.S. Thesis. The Penn- sylvania State Univ., University Park, PA. MURPHEY, W .  K . ,  A N D  L. E.  RISHEL. 1969. Relative strength of boards made from bark of several species. For. Prod. J .  19(1):52. 

A Note on the Flexural Properties of Bark Board

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A Note on the Flexural Properties of Bark Board

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