Wood and plywood

Good compression properties for cores made of honeycombs, wood and plywood. Low compression properties for foamed cores. The compression strength and modulus of a lOOkg/m foam are roughly as low as 2 MPa and 0.1 GPa, respectively. On the other hand, pinpoint impact is distributed across the whole surface facing, provided it is sufficiently resistant. 

Phenolics are used in bonding wood and plywood. They are also good adhesives for automobile brake linings. A phenolic plus poly(vinyl butyral) is used to bond copper to paper or glass fiber for printed circuits. 

In D-3024 (see wood adhesive specifications), samples of laminated wood and plywood are tested both before and after water exposure and variously evaluated for shear strength and/or wood failure. These procedures could have applications in other wood glue testing as well. 

Plywood furniture core panels, also about 19 mm (3/4 in.) thick, were normally made of a number of layers of relatively thick, 1.5—3.0 mm (1 /16—1 /8 in.) lower value wood veneers combined with thin surface pHes of the decorative veneer. These assembhes were laid-up from glued veneers and then pressed while the bonding occurred. Both lumber core and plywood core have been almost totally displaced in recent years by particleboard or medium-density fiberboard, both discussed herein. This change resulted from the increasing availabiHty and improved finishing characteristics of composites and from decreasing suppHes of core lumber or veneer of suitable quaHty. 

Amino and Phenolic Resins. The largest use of formaldehyde is in the manufacture of urea—formaldehyde, phenol—formaldehyde, and melamine—formaldehyde resins, accounting for over one-half (51%) of the total demand (115). These resins find use as adhesives for binding wood products that comprise particle board, fiber board, and plywood. Plywood is the largest market for phenol—formaldehyde resins particle board is the largest for urea—formaldehyde resins. Under certain conditions, urea—formaldehyde resins may release formaldehyde that has been alleged to create health or environmental problems (see Amino RESINS AND PLASTICS). 

Early phenoHc resins consisted of self-curing, resole-type products made with excess formaldehyde, and novolaks, which are thermoplastic in nature and require a hardener. The early products produced by General BakeHte were used in molded parts, insulating varnishes, laminated sheets, and industrial coatings. These areas stiH remain important appHcations, but have been joined by numerous others such as wood bonding, fiber bonding, and plywood adhesives. The number of producers in the 1990s is approximately 20 in the United States and over 60 worldwide. 

Pressures on forest resources and competing uses of fresh wood have resulted in greater recovery of sawlogs from trees that are formerly considered a fiber resource. On the west coast of North America, the larger trees are primarily used for lumber and plywood, leaving only the residues for pulp chips. In order to minimize butt damage, many operations use sawheads rather than shears on the feUer-bunchers. 

Softwood veneer and plywood 2439 Structural wood members, n.e.c. ... 

The insulation was 3.5-in.- (90-mm-) thick, unfaced, glass-fiber insulation (friction-fit). Walls with insulation also had a 4-mil clear polyethylene vapor barrier on their interior side. All wood and gypsum materials were conditioned at 23°C and 50 percent relative humidity, resulting in moisture content of 9 to 10 percent in wood materials. Figure 1 is a diagram of the wall frame construction. The hardboard siding was on the exterior side of the 5/8-in. (16-mm) plywood (not shown). 

Musical Instruments (painted wood), Pablo Picasso, 1914 Target with Four Faces (canvas and plaster), Jasper Johns, 1955 Radiant White 952 (cardboard and plywood), Robert Rauschenberg, 1971... 

To reduce the contribution of wood to fire losses, much research through the years has gone into development of fire-retardant treatments for wood. A total of 21.3 million pounds of fire-retardant chemicals were reported used in 1974 to treat 5.7 million cubic feet of wood products (2). The amount of wood treated was about one tenth of 1 percent of the total domestic production of lumber and plywood and has increased ninefold in 20 years. 

Effective fire-retardant treatments for wood for exterior uses under conditions of leaching and weathering have been needed for many years. For wood shingle or shake roofing, a commercial treatment system has been developed (61) in the United States that meets acceptance requirements of Underwriters Laboratories, Inc. Lumber and plywood are also available with this exterior-type treatment. 

In 1971, Marra and Maloney of Washington State University were interviewed regarding their pilot-plant research on bark board (45). They predicted that a shortage of easy-to-use sawmill and plywood plant wood-type residues would lead composition board manufacturers to seek bark, logging slash, and reclaimed waste paper as a source of furnish. Some potential problems with bark were discussed, especially that bark naturally possesses lower strength properties than wood of the same species. 

Despite the many consumer and wood gluing uses mentioned here, an estimated 75% of casein production went into paper coatings until World War II (4). Casein use for adhesives reached its peak in 1973, at about 121 million dry pounds (5). Today, very little casein glue is used by household consumers, paper coaters, and plywood manufacturers. In 1986, nearly all U.S.-casein adhesive production was used by the door manufacturing industry, where the total volume was less than 10 million pounds. 

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