USDA FOREST SERVICE RESEARCH PAPER FPL U.S. DEPARTMENT OF AGRICULTURE FOREST SERVICE, FOREST PRODUCTS LABORATORY MADISON, WISCONSIN

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1 DRY-FORMED, MEDIUM-DENSITY HARDBOARDS FROM URBAN FOREST MATERIALS USDA FOREST SERVICE RESEARCH PAPER FPL U.S. DEPARTMENT OF AGRICULTURE FOREST SERVICE, FOREST PRODUCTS LABORATORY MADISON, WISCONSIN

2 ABSTRACT Dry-formed, medium-density hardboards were made from various combinations of wastepapers separated from household trash, used pallets, dismantled railroad cars, diseased elm trees, aspen, and newsprint, using urea resin and high frequency curing. Such material has potential use for various products, particularly high quality furniture corestock. Most of the properties of the experimental boards were as good as or better than those required for medium-density, matformed wood particleboard but they were not as good as those obtained on three commercial boards made by the same process. Properties of these medium-density hardboards can be improved by the addition of more resin or by increasing the density of the boards. ACKNOWLEDGMENTS The authors gratefully acknowledge the technical and financial assistance provided by the Rust Engineering Co., Birmingham, Ala., and Hercules, Inc., Wilmington, Del. The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by the U.S. Department of Agriculture of any product or service to the exclusion of others which may be suitable.

3 DRY-FORMED, MEDIUM-DENSITY HARDBOARDS FROM URBAN FOREST MATERIALS By JAMES F. LAUNDRIE, Chemical Engineer and J. DOBBIN McNATT, Technologist FOREST PRODUCTS LABORATORY 1 FOREST SERVICE U.S. DEPARTMENT OF AGRICULTURE INTRODUCTION An excellent review of the problems and the collected raw materials were converted into potential solutions concerning the recycling of for- hardboard-type fiber using the pressurized refiner est products retrieved from urban solid waste was system at the pilot plant of C.E. Bauer, Springfield, recently given by Auchter (1) 2. He indicated that Ohio. The fiber was then shipped to the pilot plant reclaimed urban forest products have potential of Miller-Hofft, Richmond, Va., where it was utilization mainly in the area of reconstituted converted into dry-formed, medium-density hardproducts. One of the fastest growing markets is for boards using urea-type resins and high frequency hardboards, especially those made by the dry-form heat curing. The experimental boards were shipped process because of the absence of water pollution to the Forest Products Laboratory for the problems (2). The purpose of the work reported evaluation of mechanical and physical properties. here was to evaluate the potential of using a wide This report presents these properties and compares variety of reclaimed urban forest products and them with properties of (a) Type 1 medium-density, usual commercial practices to manufacture mat-formed wood particleboard (3) commonly used dry-formed, medium-density hardboards. for furniture corestock and (b) medium-density Two separate series of experimental dry- hardboards made by three different commercial formed, medium-density hardboard trials were manufacturers. (4). made during 1971 and In both series of trials, Raw Materials MATERIALS AND METHODS Household trash.- The household trash used in the first series of hardboard trials was collected from the city of Gary. Ind., and transported to Madison, Wis., for shredding there in the municipal vertical shaft hammermill. After shredding, the material was screened on a 1/2-inch diameter screen to remove tine dirt. During screening, rags and large rigid plastic containers were removed by hand picking. The material retained on the screen was then air-classified to separate the light paper-containing fraction away from the heavier fraction. The light fraction was transported to a nearby farm where it was dried in an agricultural crop dehydrator operating with an exhaust temperature of 170 F. Drying at this temperature did not affect the thermoplastic films present in the light fraction, and they therefore remained with the papers during subsequent processing. The average moisture content of the dried material was 6.5 percent. 1 Maintained at Madison, Wis , in cooperation with the University of Wisconsin. 2 Numbers in parentheses refer to References at the end of this report. 1

4 The household trash used in the second series of hardboard trials was collected from the city of Madison, Wis. The shredded material was air-classified to separate the light fraction away from the heavy fraction without prior screening. The light fraction was transported to a different nearby farm, where this material was also dried in an agricultural crop dehydrator. Between collection of the first and second batches of paper from household trash, other work had shown that, by operating the dryer at a minimum exhaust temperature of 250 F., the film plastics are contracted upon themselves, thereby making them easy to separate from the papers by either air-classification or screening (5,6). Hence, the second batch of paper from household trash was dried with a minimum dryer exhaust temperature of 250 F. The dried material was then air-classified to separate the contracted thermoplastic films away from the paper followed by screening on a 1/2-inch-diameter screen to remove fine dirt. The average moisture content of the dried material was 10.7 percent. Used pallets. - Over a period of years, a large number of used wood pallets were accumulated by the Laboratory as a result of research studies made to evaluate various pallet construction techniques and species. Approximately 1 ton of these pallets, along with about 500 pounds of bin-type pallets obtained from a nearby glass retailer, were converted into chips by shredding in the City of Madison's vertical shaft hammermill. The shredded pallet chips were screened through a 1-inchsquare-holed screen, passed over a magnetic separator to remove ferrous fastenings, and converted into fiber in the pressurized disk refiner. The various wood species found in this mixture consisted predominantly of oaks (Table 1). The average moisture content of these chips was 11.3 percent. Dismantled railroad cars. - A metal salvage company of Chicago recently expanded into dismantling of railroad cars. Many of these, such as refrigeration cars, contain a high percentage of wood. Because this company had found no market for the wood, they were chipping it in a ring crusher normally used to compact and chip metal turnings, and were stockpiling the wood chips. One-and-ahalf tons of these chips were processed following the same procedure used with the chips from the pallets, and were converted into fiber in the pressurized disk refiner. The various wood species in the mixture consisted predominantly of southern pines and Douglas-fir (Table 2). The average moisture content of these chips was 10.3 percent. Elm branches. - Approximately 1,000 pounds of elm branches were obtained from the City of Madison Forestry Department. Branches 4 inches in diameter and smaller, with bark but without leaves, were chipped in the city's brush chipper. The chips passing through a 1-1/4-inchsquare-holed screen contained 27.9 percent bark and were used to make fiber in the pressurized disk refiner. The average moisture content of these chips was 26.4 percent. Table 1.-- Wood species in waste pallets Species Percent (by weight) Red oak 38.5 Aspen 23.4 White oak 16.6 Hickory 9.4 Elm 5.3 Red gum 3.1 Beech 2.5 Tupelo.9 Red maple.3 Table Wood species in dismantled railroad cars Species Percent (by weight) Southern pines 48.8 Douglas- fir 41.2 Spruce 6.7 Red oak 2.1 Aspen.7 White pine.3 Hemlock.2 Elm bolewood. - In the first series of trials, approximately 2 tons of unbarked bolewood and branches over 4 inches in diameter were converted into nominal 1/2-inch-length chips in a commercial 2

5 size, four-knife chipper. The chips passing through a 1-1/4-inch-square-holed screen contained 11.5 percent bark and were used to make fiber in the pressurized disk refiner. The average moisture content of these chips was 8.0 percent. Water was added to a portion of these chips in order to determine the effect of chip moisture content on board quality. The average moisture content of the wetted chips was 38.9 percent. Two 500-pound batches of chips were used in the second series of hardboard trials. One batch was made from unpeeled bolewood and contained 8.7 percent bark. The average moisture content of these chips was 31.9 percent. The other batch was made from bark-free bolewood and had an average moisture content of 40.1 percent. Both batches were chipped and screened the same as the elm bolewood used in the first series of trials. Aspen. - Fifteen hundred pounds of bark-free aspen chips with an average moisture content of 36.9 percent were obtained from a commercial manufacturer of hardboard for the second series of hardboard trials. Newsprint. - Five hundred pounds of over-issue newspapers with an average moisture content of 8.0 percent were shredded and used to produce fiber in the pressurized disk refiner for the second series of hardboard trials. Boards Received The first series of panels received at the Forest Products Laboratory for evaluation were made from one or a combination of the following raw materials: (1) Gary household trash (2) Used pallets (3) Dismantled railroad cars (4) Elm branches (5) Elm bolewood This shipment consisted of at least one full-sized panel (approximately 32 inches square) and one-half panel of each type. These panels were made at target densities of 42, 45, or 50 pounds per cubic foot (pcf) using 8 or 10 percent urea resin and 1 percent wax size. The second series of panels were made from one or a combination of the following raw materials: (1) Madison household trash (2) Elm bolewood with and without bark (3) Aspen (4) Newsprint With one exception, this shipment included a single full-size panel (approximately 32 inches square) of each type. Only a half panel was received of panel No Most of the panels were made at a target density of 50 pcf. Ten percent urea resin and 1 percent wax size were used in all panels. Nominal thickness of all panels from both series was 3/4-inch. A detailed breakdown of raw material content for each panel is presented in Tables 3 through 6. Test Methods Testing of all panels was based on their use as corestock (7) and included the tests listed in Table 7. Evaluations were made using test procedures specified in ASTM Standard D a (7) with some variation in procedure for screw withdrawal and water absorption, as discussed below. Direct screw withdrawal - A 1-inch No. 10 type A sheet metal screw was threaded to a depth of 2/3-inch into one edge and one face of each of the 3- by 10-inch specimens. Preliminary trials showed that some board types split when the screw was threaded into the edge using the recommended 7/64-inch diameter lead hole (0.109 inch). To prevent splitting, the lead hole diameter had to be increased to inch. Consequently, this lead hole size was used for all screw-withdrawal tests, both edge and face. 24-Hour water absorption and thickness swelling. - For the first series of panels, standard 12-inch-square specimens were prepared. In the second series, the specimens were cut 10 inches square because of the limited material available. The specimens were submerged vertically in water so that the top edge was 1 inch below the surface of the water. This was done so all could be evaluated at the same time in the same soaking tank. Normally, specimens are submerged horizontally which would result in somewhat lower absorption values. However, since all specimens were treated the same, the values from vertical submersion are acceptable for comparing absorption between the specimens. Edge thickness swelling (disk method). For the first series of panels, 1-inch-diameter disks were prepared with a special cutter. For the second series of panels, however, 1-inch-square specimens were cut because undamaged 1 -inch-diameter disks could not be prepared with the cutter available at that time. 3

6 Table 3. --Mechanical properties of dry- formed, medium-density hardboards from various urban wood wastes

7 Table 4.--Moisture related physical properties of dry-formed, medium-density hardboards from various urban wood wastes

8 Table 5.--Mechanical properties of dry-formed, medium-density hardboards containing various paper wastes

9 Table 6. --Moisture related physical properties of dry-formed, medium density hardboards containing various paper wastes

10 Table 7.--Panel tests and replications the water absorption and thickness swell in 24-hour periods were substantially greater. This indicates that more wax size would be needed when manufacturing boards of wet elm bolewood. Only slight differences were noted in strength and stiffness between the dry and wet bolewood. The wet elm branches produced stronger boards than the bolewood, with no noted difference in linear movement. Mixtures of Different Urban Wood Waste Fibers The dry elm bolewood, dismantled railroad car and used pallet waste fibers were blended in various proportions with no marked effect on board properties. These properties were quite similar to those noted for boards from 100 percent dismantled railroad car waste. No noticeable differences in board properties were noted in fiberizing an equal blend of chips or in blending the pulps after fiberizing individually. DISCUSSION OF RESULTS The properties of medium-density hardboards are given in Tables 3 through 6. Single Urban Wood Waste The boards made from the used pallets (hardwoods) and dismantled railroad cars (primarily softwoods) were superior in strength and stiffness to those made from elm bolewood and branches. Those from the used pallets were 1-1/2 to two times stronger in bending and tension and had over three times the internal bond strength of the elm bolewood. The 24-hour water absorption and thickness swell were also more favorable for the board from used pallets but at an equilibrium moisture condition they exhibited greater linear movement. Boards from dismantled railroad cars were more linearly stable with changes in moisture than those from used pallets but were generally not as strong. These differences in properties between boards made from used pallets and those made from dismantled railroad cars are probably due to differences in the wood species involved. Other combinations of wood species might be expected to give different results. The wet elm bolewood gave boards with better linear stability than did the dry elm bolewood, but U.S. GOVERNMEMT PRINTING OFFICE Elm Bolewood and Bark The boards made from elm bolewood without bark had somewhat better dimensional stability, bending, tension parallel properties than those made from elm bolewood with bark. The other board properties were either not affected by the bark or enhanced only slightly. Addition of Paper Waste to Aspen and Elm Bolewood Fiber Additions of newsprint or Madison household trash to aspen fiber adversely affected the mechanical properties of boards. For example, with 25 percent of the Madison household trash, the internal bond strength of the aspen board was reduced 50 percent and the bending and tensile strengths 10 to 20 percent. With 15 percent Madison household trash added to the elm bolewood furnish, the loss in these properties was even greater. Acid was added to one of the elm bolewood fiber furnishes to lower its ph, but this did not improve the board properties. Linear stability of the boards was not affected by the trash additions. Addition of Paper Waste to Blend of Three Urban Wood Wastes The Gary household trash when added to the wood waste blend affected board strength similar to the addition of wastepaper to aspen and elm bolewood fiber. This material still had much of the plastic contaminant present which adversely affected the appearance of the board surface

11 These plastic spots would present problems in the printing of a decorative pattern on the board surface. Amount of Resin and Board Densification Experimental boards made with the blends of wood and fibrous wastes had lower mechanical properties than those of three commercial urea-bonded medium-density boards (4). Properties of the experimental boards were increased, however, by increasing the amount of resin or the board density. With a blend of three wood waste types and Gary household trash, increasing the resin content from 8 to 10 percent resulted in substantial increases in mechanical properties. This may be seen by comparing data in Table 6 for panels 1838 and 1840 (8 percent resin) and for 1832 and 1833 (10 percent resin). Similarly, increasing the density from 42.4 to 51.8 pcf, panels and resulted in marked improvements in strength properties. The linear stability of the boards remained essentially the same when these factors were altered. Comparison With Mat-Formed Particleboard and Three Commercial Medium-Density Hardboards Most of the boards made from the different urban forest materials showed strength properties as good as or better than those required by CS (3) for Type 1 medium-density particleboard typically used for furniture corestock. However, only half the board types were at or below the maximum allowable linear expansion of 0.35 percent between 50 and 90 percent relative humidity. Also, compared with the three commercial boards (4) the mechanical properties were generally substantially less. A wide variety of urban forest materials can be used io produce dry-formed, medium-density hardboards with properties as good as or better than those required for such boards made from mat-formed wood particleboard but not as good as CONCLUSIONS REFERENCES those obtained on three commercial hardboards made by the same process. Properties of these medium-density hardboards can be improved by the addition of more resin or by increasing the density of the boards. (I) Auchter, R.J Recycling forest products retrieved from urban waste. Forest Prod. Jour. 23 (2) : (2) Lampert, H Board production shipments reflect boom in all construction fields. Forest Industries 99 (8) : (3) U.S. Department of Commerce Mat-formed wood particleboard. Commercial Standard CS National Bureau of Standards, Washington, D.C. (4) Superfesky, M.J. and Lewis, W.C Basic properties of three medium-density hardboards. USDA Forest Service Research Paper FPL 238, Forest Products Laboratory, Madison, Wis. (5) Laundrie, J.F. and Klungness, J.H Effective dry methods of separating thermoplastic films from wastepapers. USDA Forest Service Research Paper FPL 200, Forest Products Laboratory, Madison, Wis. (6) Laundrie, J.F U.S. Patent 3,814,240. (7) American Society for Testing and Materials Standard methods of evaluating properties of wood-base fiber and particle panel materials. ASTM Desig. D a, Philadelphia, Pa.