Polyurethanes play a major role in today’s modern materials such as in composite wood, which is a combination of synthetic and natural materials. Polyurethane-based binders, typically used both with wood and rubber, are used in composite wood products to permanently glue organic materials into oriented strand board, medium-density fiberboard, long strand lumber, laminated veneer lumber, and even strawboard and particleboard.
What Is Oriented Strand Board?
Oriented Strand Board, also referred to as OSB, is manufactured from fast-growing trees such as the aspen poplar, southern yellow pine, mixed hardwoods and other suitable species. OSB is frequently made by coating wood chips (known as strands) with MDI, then arranging consecutive strand layers roughly perpendicular to each other, and finally pressing the strands under high temperature and high pressure to form boards. The MDI binds the strands together by reacting with water on the strands to form polyurea and reacting with hydroxyl groups in the wood lignin to form polyurethane. These bonds form a chemical matrix that serves to glue the strands together. The perpendicular orientation of the wood strands imparts strength properties to the panels. OSB panels measure 4’x8’ with thickness typically ¼” to 23/32”. OSB is widely used as construction sheathing, as the web material for wood I-joists, as structural membranes of structural insulated panels (SIPs) and in a growing number of other applications.
What Is Medium-Density Fiberboard?
Medium-Density Fiberboard, also referred to as MDF, is widely used in the manufacture of furniture, cabinets, door parts, moldings, millwork and laminate flooring. MDF panels are manufactured in a variety of dimensions and densities, providing the opportunity to design the end product with the specific MDF needed.
As with other composite wood products, MDF typically consists of cellulosic fibers combined with a synthetic resin or other suitable bonding system and joined together under heat and pressure. Additives may be introduced during manufacturing to impart additional characteristics. The surface of MDF is flat, smooth, uniform, dense and free of knots and grain patterns, all of which make finishing operations easier and more consistent. The homogeneous density profile of MDF allows intricate and precise machining and finishing techniques for superior finished products. Trim waste is significantly reduced when using MDF compared to other substrates. Stability and strength are important assets of MDF, and it holds precise tolerances in accurately cut parts.
What Is Long Strand Lumber?
Long Strand Lumber (LSL), also known as Oriented Strand Lumber (OSL), is similar to OSB, except for the following important differences. The strands used in LSL are longer than those used in OSB. Also, all of the strands are arranged parallel to each other, so that the product is very strong along its length. LSL is much thicker than OSB because its intended use is to serve as a substitute for dimension lumber. It is suitable to use in place of 2”x4” studs in residential construction applications. Another major use is the flange portions of wooden I-joist beams.
What Is Laminated Veneer Lumber?
Laminated Veneer Lumber (LVL), also known as Structural Composite Lumber (SCL), is an engineered wood product created by layering dried and graded wood veneers with waterproof adhesive into blocks of material known as billets. Cured in a heated press, LVL is typically available in various thicknesses and widths and is easily worked in the field using conventional construction tools.
In LVL billets, the grain of each layer of veneer runs in the same direction, rather than cross-lamination which is typical of other engineered wood products such as plywood. The resulting parallel-laminated lumber has excellent performance characteristics. LVL is a solid, highly predictable and uniform engineered wood product that is sawn to consistent sizes and is virtually free from warping and splitting.
One important benefit to LVL is that the veneering and gluing process enables large timbers to be made from relatively small trees of many species, thereby providing for efficient utilization of wood fiber resources. Some of the LVL’s many uses are headers and beams, hip and valley rafters, scaffold planking, and the flange material for prefabricated wood I-joists.