Engineered wood

From Wikipedia, the free encyclopedia

Engineered wood, also called composite wood, includes a range of derivative wood products which are manufactured by binding together wood strands, particles, fibers, or veneers with adhesives to form composite materials. These products are engineered to precise design specifications which are tested to meet national or international standards.

1966 photo shows that wood waste was routinely burned for fuel in Oregon.

Typically, engineered wood products are made from the same hardwoods and softwoods used to manufacture lumber. Sawmill scraps and other wood waste can be used for engineered wood composed of wood particles or fibers, but whole logs are usually used for veneers, such as plywood. Alternatively, it is also possible to manufacture similar engineered cellulosic products from other lignin-containing materials such as rye straw, wheat straw, hemp stalks, or sugar cane residue, in which case they contain no actual wood but rather vegetable fibers.

[edit] Characteristics

Engineered wood products are used in a variety of ways, often similarly to solid wood. Engineered wood products are preferred over solid wood in many applications due to a certain comparative advantages:

Because engineered wood is man-made, it can be designed to meet application-specific performance requirements.
Large panels of engineered wood may be constructed from small trees.
Small pieces of wood and wood that has defects can be used in many engineered wood products, especially particle and fiber-based boards.
Engineered wood products are often stronger and less prone to humidity-induced warping than equivalent solid woods, although most particle and fiber-based boards readily soak up water unless they are treated with sealant or at least paint.

Engineered wood products are more expensive to produce than solid lumber in terms of time, money, and energy, but enjoy economic advantages when manufactured in large sizes due to the rarity of trees suitable for cutting large solid-wood panels.

Although engineered wood products use the resource of wood efficiently and therefore promote natural resource conservation, the required adhesives may be toxic. A concern with some resins is the release of formaldehyde in the finished product, often seen with urea-formaldehyde bonded products.

Adhesives types are:

Urea-formaldehyde resins, (UF), most common and cheapest, not waterproof
Phenol-formaldehyde resins, (PF), a yellow-brown adhesive commonly used for exterior exposure products
Melamine-formaldehyde resin, (MF) a white, heat and water resistant resin, often used in exposed surfaces in more costly designs
Methylene diphenyl diisocyanate (MDI) or ethyl carbamate (urethane) resins which are expensive and generally waterproof do not contain formaldehyde

Many non-wood products are finding their way into traditional wood products. As example in "types" below, gypsum board and cement board usually contain no wood or cellulose but have been designed to replace plywood in some applications demanding wet strength or fire proofing. A wider term used is "structural composites". As example, fiber cement siding is a construct of cement and wood fiber, while cement board is a low density cement panel, often with added resin, faced with fiberglass mesh. Plastic extrusion mixes of wood fiber and thermoplastic, such as polyproplyene, has given rise to decking and railing material resistant to weather and is steadily replacing rot-resistant wood.