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Engineered Composite Sciences
FS-FPL-4706
Wood Handbook
Chapter 10, Wood-Based Composites and Panel Products
This and the web pages listed in the table of contents below are sections out of chapter 10, Wood-Based Composites and
Panel Products, of the wood handbook. The entire Chapter 10 is available for downloading and
is in Adobe Acrobat Reader portable document format (.pdf). The Adobe Acrobat Reader (preferably version 3.0 or higher) must be installed on
your system to view or print a PDF document. The Acrobat Reader may be part of your Web browser, or you may download it from Adobe free of charge.
Introduction
Because wood properties vary among species, between trees of the same species, and between pieces from the same tree, solid wood cannot match
reconstituted wood in the range of properties that can be controlled in processing. When processing variables are properly selected, the end
result can sometimes surpass nature's best effort. With solid wood, changes in properties are studied at the molecular level. With
reconstituted wood materials, changes in properties are studied at the fiber, particle, flake, or veneer level. Properties of such materials
can be changed by combining, reorganizing, or stratifying these elements.
The basic element for composite wood products may be the fiber, as it is in paper, but it can also be larger wood particles composed of many
fibers and varying in size and geometry. These characteristics, along with control of their variations, provide the chief means by which
materials can be fabricated with predetermined properties.
In any discussion of the strength properties of wood-based panels and other glued wood composites, the first consideration is the
constituents from which these products are made (O'Halloran and Youngquist 1984; Youngquist 1987, 1988).
The basic wood elements that can be used in the production of wood-based panels are shown in Figure 10-1.
The elements can be made in a great variety of sizes and shapes and can be used alone or in combination. The choice is almost unlimited.
Currently, the term composite is being used
to describe any wood material glued together. This product mix ranges from
fiberboard to laminated beams and components. Table 10-1 shows
a logical basis for classifying wood composites proposed by
Maloney (1986). For the purposes
of this chapter, these classifications were slightly modified from those in
the original version to reflect the latest product developments. Composites
are used for a number of structural and nonstructural applications in product
lines ranging from panels for interior covering purposes to panels for exterior
uses in furniture and support structures in many different types of buildings.
Figure 10-2 provides a useful way to further classify wood-based composite materials. This chart presents an overview of the
most common types of products discussed in this chapter as well as a quick reference to how these composite materials compare to solid wood
from the standpoint of density and general processing considerations. The raw material classifications of fibers, particles, and veneers are
shown on the left vertical axis (y axis). Specific gravity and density are shown on the top and bottom horizontal axis (x axis). The right
y-axis, wet and dry processes, describes in general terms the processing method used to produce a particular product. Note that both roundwood
and chips can serve as sources of fiber for wet-process hardboard. Roundwood or wood in the form of a waste product from a lumber or planing
operation can be used for dry-processed products. For medium-density fiberboard (MDF), resin is usually applied to the fiber after the fiber
is released from the pressurized refiner. The fiber is then dried, formed into a mat, and pressed into the final product. For other dry-processed
products, the material is fiberized and dried and then adhesive is added in a separate operation prior to hot pressing into the final
composite product. Figure 10-3 shows examples of some composite materials that are represented in schematic form in
Figure 10-2.
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Scope of Chapter
Although there is a broad range of wood composites and many applications for
such products, for the purposes of this chapter, wood composites will be grouped
into three general categories: plywood, particle and fiber composites, and
wood-nonwood composites. Books have been written about each of these categories,
and the constraints of this chapter necessitate that the discussion be general
and brief. References are provided to more detailed information. Information
on glued-laminated (glulam, timbers, and structural composite lumber, including
laminated veneer lumber) and glued members with lumber and panel products are
presented in Chapter 11 of this handbook. Many composite materials, like fiberboard,
medium-density fiberboard, and particleboard, can be made from wood alone or
in combination with agricultural fibers (Youngquist
and others 1993a, 1994; Rowell and others 1997).
The first category, plywood, is covered in some detail because the process
for manufacturing this kind of material is quite different from that used for
other composite materials and because there are many different classes and
grades of plywood in the marketplace. The second category, composite materials,
includes oriented strandboard (OSB), particleboard, and fiberboard. These types
of composites undergo similar processing steps, which is discussed in general
terms for all the products in the Particle and Fiber Composites section. The
first and second categories of composite materials are further generally classified
as conventional composite materials. The third category, wood-nonwood composites,
discusses products made from combining wood fibers with agricultural fibers,
with thermoplastics, and with inorganic materials.
Back to top
Types of Conventional Composite Materials
Conventional wood composite materials fall into five main categories based
on the physical configuration of the wood used to make the products: plywood,
oriented strandboard, particleboard, hardboard, and, cellulosic fiberboard.
Within limits, the performance of a conventional type of composite can be tailored
to the end-use application of the product. Varying the physical configuration
of the wood and adjusting the density of the composites are just two ways to
accomplish this. Other ways include varying the resin type and amount and incorporating
additives to increase water or fire resistance or to resist specific environmental
conditions.
Table 10-1.
Classification of wood-based compositesa
|
Veneer-based material |
Plywood |
Laminated veneer lumber
(LVL) |
Parallel-laminated veneer
(PLV) |
Laminates |
Laminated beams |
Overlayed materials |
Wood-nonwood compositesb |
Composite material |
Cellulosic fiberboard |
Hardboard |
Particleboard |
Waferboard |
Flakeboard |
Oriented strandboard
(OSB) |
COM-PLYc |
Edge-glued material |
Lumber panels |
Components |
I-beams |
T-beam panels |
Stress-skin panels |
Wood-nonwood composites |
Wood fiber-plastic composites |
Inorganic-bonded composites |
Wood fiber-agricultural
fiber composites |
aMaloney,
1986.
bPanels or shaped materials combined with nonwood
materials such as metal, plastic, and fiberglass.
cRegistered trademark of APA-The Engineered
Wood Association. |
Figure 10-1. Basic wood elements, from
largest to smallest (Marra 1979).
Figure 10-2.
Classification of wood
composite boards by particle size, density, and process type (Suchsland and
Woodson 1986).
Figure
10-3. Examples of various composite products
(from left to right: plywood, OSB, particleboard,
MDF, and hardboard).
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