Commercial product or performance standards for wood-based composites

The primary component of wood-based composites is the wood element, often 94% or more by mass. Common ele-ments for conventional wood-based composites include veneers, strands, particles, and fbers. The physical charac-teristics of common elements can be seen in Figure 11–5. Properties of wpc products materials can be changed by chang-ing the size and geometry of the elements and by combin-ing, reorganizing, or stratifying elements.

Bonding in most conventional wood-based composites is provided by thermosetting (heat-curing) dhesive resins. Chapter 9 provides a more thorough discussion of thermoset adhesive resins. Commonly wood plastic composite fence gate used resin–binder systems include phenol-formaldehyde, urea-formaldehyde, melamine-formaldehyde, and isocyanate.Phenol-Formaldehyde Phenol-formaldehyde (PF) resins are typically used in the manufacture of construction plywood and oriented strand-board where exposure to weather during construction is a concern. Other moisture exposure situations, such as tem-porary weather exposure, occasional plumbing leaks, or wet foot traffc, may also necessitate the use of PF resins. PF resins are commonly referred to as phenolic resins. Phenolic resins are relatively slow-curing compared with other ther-mosetting resins.

In hot-pressed wood-based composites, use of phenolic resin necessitates longer press times and higher press temperatures. Hot-stacking of  wood plastic composite rail fence pressed material shortly after emergence from the press is a fairly common industrial practice, used to attain adequate resin cure with-out greatly extending press time. Signifcant heat exposure associated with pressing of phenolic-bonded composites commonly results in a noticeable reduction in their hygro-scopicity. Cured phenolic resins remain chemically stable at elevated temperatures. Their bonds also are sometimes referred to as being “boil-proof” because of their ability to maintain composite dimensional and mechanical properties under wet conditions. The inherently darker color of PF res-in compared with other resins may make them aesthetically unsuitable for product applications such as interior paneling and furniture.