Oriented strandboard

Specifications, Standards, Quality Control, and Health and Safety Factors. APA-The Engineered Wood Association represents the softwood plywood and oriented strandboard industries in the areas of specification, standards, and quaHty control (QC). An APA product standard, PSl-95 (6), discusses the above areas in detail. The following listing summarizes plywood characteristics covered in PSl-95. 

In 1932, the first plywood hot press was installed in the United States. This marked the advent of the large market for phenolic wood adhesives [51]. By 1962, the volume of phenolic wood adhesives had reached about 33 kt (solids) in the U.S. Growth was accelerated in 1962 with the development of Southern pine plywood. By 1979, the consumption of phenolic plywood adhesives exceeded 220 kt or about 25% of phenolic resin production [51]. Phenolic adhesive demand for wood products took another jump in 1964 with the commencement of waferboard production. The first oriented strandboard (OSB) plants were built in 1981 [52]. OSB soon replaced most of the waferboard production and began a period of... 

Oriented strandboard (OSB) resins are quite similar to plywood resins, though they tend to be lower in alkalinity and higher in solids. Sinee OSB resins are sprayed onto dry wood in small discrete droplets rather than applied in glue lines, the problems associated with holding the glue on the wood surfaee are not usually issues of coneem. Adhesive dry-out and loss of flow displace over-penetration as major difficulties. 

Adhesives based on isocyanate (especially PMDl, polymethylene diisocyanate, more exactly polymeric 4,4 -diphenylmethane diisocyanate) have been used for more than 25 years in the wood-based panel industry [88], but still have a low market value in the wood-working industry compared to systems based on UF-, MUF- or PF-resins. The main application is the production of waterproof panels, but also the production of panels from raw materials that are difficult to glue, like straw, bagasse, rice shells or sugar cane bagasse. They can be used as adhesives for wood-based products like particleboard, oriented strandboard (OSB), laminated strand lumber (LSL), medium-density fiberboard (MDF) or... 

Sprayable exterior adhesives of competitive performance for structural panels such as flakeboards, waferboards, and strandboards based on renewable resources. (A blood-lignin adhesive for oriented strandboard or waferboard would be an example.)... 

Interest in pine bark as a source of adhesive components began to accelerate following the oil crisis of 1973. Sodium hydroxide extracts of southern pine bark were successfully used in replacing up to 40% of the phenolic resin for bonding of particleboards, oriented strandboards, and composites with a flakeboard core and veneer facing (50f51). Similar results were obtained with extracts from patula pine (52). Encouraged by results of this type, the New Zealand Forest Products Ltd. Corporation expanded their radiata pine bark tannin pilot plant to full-scale operation in 1981 to produce an extract trademarked Tannaphen. This material was crosslinked with paraformaldehyde and used as an adhesive... 

Figure 10.19. Prefabricated I-joists with laminated veneer lumber flanges and structural panel webs, (a) With an experimental hardboard web. (b) With commercially produced oriented strandboard web. (c) With a plywood web.

Carlson FE, Phillips EK, Tenhaeff SC, et al. 1995. A study of formaldehyde and other organic emissions from pressing of laboratory oriented strandboard. For Prod J 45 71-77. 

Isocyanates are used in the forest products industry to adhesively bond wood chips, which are then pressed to form particleboard and oriented strandboard. Urethanes are also used to fill knotholes and surface defects in finished plywood boards ( plywood patch ). These filled systems must cure rapidly and be sanded easily. 

The various aminoplastic resins are the most important class of adhesives in the wood-based panels industry, especially for the production of particleboards and medium density fibreboard (MDF), and partly also for oriented strandboard (OSB), plywood, block-boards, and some other types of wood panels. They are also used in the furniture industry as well as in carpenters shops. 

Table 12 Examples of PF Glue Mixes for Particleboard, Oriented Strandboard, and Pl5rwood Parts by Weight...

Oriented strandboard (OSB) Strand, flake, wafer PP, pMDI S Roof, floor, wall sheathing, floor underlayment, siding, I-beams web stock, hybrid products 6-32(1-11/8) 580-700(36-44)... 

The principal wood composite products currently in use in the United States and Canada, based on volume, are plywood (17.5 million cubic meters), oriented strandboard (16.8 million cubic meters), particleboard (10.3 milHon cubic meters), medium density fiberboard (3.4 million cubic meters), hardboard (2.0 million cubic meters), hardwood plywood (1.0 million cubic meters), and laminated veneer lumber (1.2 million cubic meters) (13). These products are described below. While all of these composites occupy an important place in the market now, some of these products are gaining in importance while others appear to be losing market share to other composite products. 

Oriented Strandboard (OSB). Oriented strandboard (OSB) panels have been developed as an alternative to plywood in building construction. The emergence of OSB was driven in part by a decreased supply of large diameter logs suitable for veneer production, and by innovation and productivity changes in the North American wood products industry over the past few decades as well as the structural performance of OSB products, which are suitable for use in most plywood applications but at a much lower cost. In addition, OSB manufacture allows small, low grade timber resources to be processed into a marketable product. This effectively saves raw materials that are in short supply and promotes efficient utilization of wood (3,5,6). 

LSL is another type of engineered wood prodnct in which all the strands are aligned in one direction, ie, LSL is an oriented strand Inmber. The strands in LSL are shorter than in PSL and prodnced from strand wood rather than veneer. The strands are typically longer than strands utilized in oriented strandboard. Pressing includes steam injection rather than radio-freqnency heating, and isocyanate resin is typically used rather than PF adhesive. LSL is nsed in indnstrial and light strnctural applications (Table 2). 

These adhesives performed equally well when used for bonding of oriented strandboards made from Douglas-fir flakes. In addition, composites made from oak or southern pine flakeboards to which southern pine veener was bonded on the face and back passed the 6-cycle durability test of the American Plywood Association when the core was bonded with the peanut hull-based adhesives, even when the 0.64-cm cores were pressed for only 75 seconds. Chen s work on these adhesives is described further in a series of four U.S. Patents (41-44). 

MDI is mostly used in polyurethane chemistry. About 80% of MDI is used to make polyurethane foams, both flexible and rigid. Half of all the foam produced with MDI is rigid foam. This rigid foam is used in the insulation, construction, refrigeration, and packaging industries. Also, MDI is used in the production of spandex fibers. MDI is used as a wood binder and in foundry cores. The binding of wood flakes into oriented strandboard is replacing plywood in construction. 

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