Composite boards

Phenol, in its various purity grades, is used for phenol—formaldehyde resins to bond constmction materials like plywood and composition board (40% of the phenol produced), for the bisphenol A employed in making epoxy resins (qv) and polycarbonate (qv) (30%), and for caprolactam (qv), the starting material for nylon-6 (20%). Minor amounts ate used for alkylphenols (qv) and pharmaceuticals (10). 

Clarke, M., Steiner, P.R. and Anderson, A.W., United States patent USP 4,824,896. Phenol formaldehyde adhesives for bonding wood pieces of high moisture content and composite board and veneers bonded with such adhesive. Assigned to the inventors, 1989. 

Four different methods (vapour-phase acetylation using acetic anhydride, acetylation using ketene gas, liquid phase acetylation using acetic anhydride/xylene, or neat acetic anhydride) were used to acetylate pine wood chips to a variety of WPGs for the production of MUF-bonded particleboards (Nilsson etal., 1988). Composite boards were exposed to unsterile soil in fungal cellar tests. Boards made from ketene acetylated chips were not found to be resistant to decay at the maximum WPG level achieved (17 %) with a liquid acetic anhydride modification, no decay was recorded at a WPG level of c. 18 % after 12 months exposure, whereas with a vapour-phase treatment at the same WPG, evidence for decay was found. 

Chow, P., Harp, T., Meimban, R., Youngquist, J.A. and Rowell, R.M. (1994). Biodegradation of acetylated southern pine and aspen composition board. International Research Group on Wood Preservation, Doc. No. IRGAVP 94 0020. 

Clemons, C., Young, R.A. and Rowell, R.M. (1992). Moisture sorption properties of composite boards from esterified aspen fiber. Wood and Fiber Science, 24(3), 353-363. 

Rowell, R.M., Dawson, B.S., Hadi, Y.S., Nicholas, D.D., Nilsson, T., Plackett, D.V., Simonson, R. and Westin, M. (1997). Worldwide in-gronnd stake test of acetylated composite boards. International Research Gronp on Wood Preservation, Doc. No. IRGAVP 97 0088. 

Deck plank vinyl profiles or composite boards are used to form the base of the walking surfaces or stairs. 

This review of composition boards containing bark will not include references on the use of bark or bark extracts in the role of bonding agents for composition boards. That subject has been covered in the paper by Dr. A. B. Anderson. 

An appropriate beginning is an attempt to answer the question, "How much bark might be available for composition board furnish " Estimates of total bark available in the United States have been difficult to obtain, and the published estimates have shown considerable variation. 

A recent estimate made by Ellis (1) is based upon four regional compilations in 1973. Ellis estimated 17 million tons (ovendry) of bark are produced annually, of which 7 million tons presently are unused (Table I). At least 1 million tons presently are unused in each region. The entire amount, of course, would not be available for composition boards as other potential uses, such as fuel and mulch, would siphon off part of the unused bark. 

From the above, we can conclude that sufficient bark still is available for use as composition board furnish. The amounts available, however, vary greatly from one geographical region to another. Potential volumes are large enough to be a source of furnish for production of composition boards. 

An excellent comprehensive compilation of the literature on all phases of tree bark was prepared by Marian and Wissing and published over a span of 2 years (1956-1957) in 11 different issues of Svensk Papperstidning (3). Their bibliography lists the subject under 12 different major subheadings bark composition boards may be found under the subheading "The Utilization of Bark Fibers. ... 

Another excellent bibliography by Roth and coworkers (4) lists 1,339 references with a concise abstract for each. Since the original compilation was published in 1960, two supplements have appeared, I in 1968 (5) and II in 1973 (6). References to bark composition boards are listed under the subheading "Utilization. ... 

The Chemical Utilization Division of the Forest Products Research Society published a "Review of Chemical Utilization in I960 (7). The authors, Pearl and Rowe, included a section titled "Bark, and its use in composition boards was reviewed. This review was followed up by another published 3 years later by Rowe (8). 

Gregory and Root in 1961 (9) prepared what they termed a "statistical analysis" of the literature covering bark utilization and, in addition, reviewed examples of commercial and pilot plant operations. They found 52 references on use of bark in composition boards. The report concludes with sections covering "Limitations and Hurdles in Bark Utilization" and a discussion of "Future Opportunities."... 

Ross (10) in 1966 compiled references that have been published since Roth et al. (4) reported on the bark literature in 1960. Ross categorized the latest references under one of 12 headings bark composition boards were included under the title, "Bark Fiber, Cork, and Dust Products, Boards, Panels, Adhesives, and Tiles."... 

The same year (1969), Walters (12) prepared a report specifically reviewing the current status of bark used for board products. Information was given regarding potential maximum amounts of bark utilizable in various types of composition boards, based on research up to that time. 

A short review by Currier and Lehmann (13) on use of bark in composition boards was contained in the proceedings from a conference in 1971 on "Converting Bark into Opportunities."... 

Another review of utilizing a single bark species in composition boards was presented by Scroggins and Currier for western redcedar bark (15). 

Another interesting report by Anderson and Runckel discussed use of Douglas-fir branchwood in wet-process hardboard (25). This is one of the earliest references to utilizing this type of material as composition board furnish satisfactory boards were made from 100% branchwood. No binder was added. Actual percentage of bark in the furnish was not disclosed. 

Up until 1952, all references found on bark in composition board were based upon wet-process softboard or hardboard. The first mention of a dry process came in a one-page article published by the British Columbia Research Council (30). The brief report indicated a dry process had been developed for making an interior wallboard possessing good strength and moisture resistance. No binder was necessary for the cedar mill residues, which included bark. Apparently, the process never was tried commercially. 

Lewis in 1961 discussed why composition boards containing bark seldom had found commercial application (37). He believes the reasons are that... 

One of today s fastest growing segments of the wood composition board industry is production of medium density fiberboard (MDF) using a dry process similar to that used for particleboard. First mention of the possibility of utilizing bark for MDF came in a presentation by Brooks in 1971 (43). He described a process in which a homogenous board with superior properties could be made from such raw materials as mixed, unbarked hardwood pulp chips unbarked pine chips, if bark content was less than 30% forest thinnings, branches, and so on and hardwood bark. Furnish was prepared by double-disk pressurized refiners. Brooks concluded a plant could be built to operate on 100% hardwood bark. 

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. 

The thermal properties of composite boards were the subject of a recent report by Place and Maloney (58). Thermal conductivity tests were made on three-layer boards with surfaces of white pine wood flakes and cores of either Douglas-fir or grand fir bark. Density was varied at 34, 42, and 52 pounds per cubic foot. The composite boards containing bark proved to be better insulators than wood particleboard of comparable density. Douglas-fir bark cores had lower thermal conductivity than did grand fir. 

Wood Composites—these are resin-bonded composite boards where the particles are wood shavings, flakes, chips, or fibers bonded with thermosetting adhesives that can be urea formaldehyde, melamine formaldehyde, phenol formaldehyde, or diisocyanate. In recent years, the markets for OSB and MDF board have been rapidly increasing. Most particle board production uses urea-formaldehyde as a binder that is acid setting. Hence, sodium borates (alkaline) can interfere with the setting. As a result, boric acid has been the major boron compound used as the flame retardant in particle board.28 29 Typically, a loading of 12%-15% of boric acid in MDF is required to meet the ASTM E-84 Class A rating. If sodium borate is used as a flame retardant, phenol-formaldehyde binder, that is compatible with alkaline chemicals, is commonly used. 

Decorative laminate is defined in ISO 472 but in common usage has come to mean sheet materials consisting of decorative surface papers impregnated with melamine resin and consolidated under heat and pressure with plies of core paper permeated with phenolic resin. In a wider sense the term can be applied to many associated products—including laminates in solid colour laminates with facings such as metal foils, textiles, or wood veneers polyester laminates direct faced boards and composite boards comprising thin laminates bonded to substrates of various kinds. 

When describing in more detail the characteristics and methods of manufacture of laminated sheet materials of different types it is helpful to use the classifications below, each of which is covered by a British Standard High-pressure laminates Decorative continuous laminates Direct-faced boards Composite boards. 

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