The resin protects the fibers, maintains their alignment, and distributes the loads evenly among them. The FRP composite may also contain fillers, additives and core materials. None of the elements in a composite dissolve or merge completely into each other, but act together to offer benefits ideal for structural applications. The FRP significantly increases the members' load carrying capacity. According to the American Composites Manufacturing Association, FRP composites deliver more strength per unit of weight than most metals and are 1/5th the weight of steel.

Fiberglass. Many FRP panels are made from a polyester resin with a chopped glass fiber reinforcement. Chopped glass is used because of its added cross-directional reinforcement.

Fiberglass fibers are made from molten glass extruded at a specified diameter. The fibers are gathered into bundles and the bundles combined create a roving. Rovings are a continuous rope, similar to twine, and are wound on a mandrel to form a ball called a doff. Reinforcements for FRP are made from rovings that are either chopped into short strands or woven into a cloth.

There are many factors that affect the reinforcement characteristics of fiberglass:

• Fiber and bundle diameter and type of glass
• Direction of the fiberglass reinforcement
• The amount of fiberglass reinforcement
• The physical contact (wetout) of the fiber with the polymer

All of these factors must be taken into account when designing an FRP composite so that the required physical property strengths are met.

Photo: Crane Composites, Inc. FRP panels are commonly found in the food preparation area of many restaurants.

Plastics/Polymers.There are two basic types of plastics/polymers: thermoplastic and thermoset. In general, FRP composites utilize a thermoset plastic, and are not to be confused with a thermoplastic, which is a plastic material that can be readily softened and reformed by heating and rehardened by cooling.

A plastic in which the polymer molecules are not crosslinked (not chemically bonded to other polymer molecules) is a thermoplastic. Since the molecules are not connected by crosslinks, it allows the molecules to spread farther apart when the plastic is heated. This is the basic characteristic of a thermoplastic; the plastic will soften, melt, or flow when heat is applied. Melting the plastic and allowing it to cool within a mold will form the finished product. Typical thermoplastics are: polyethylene (PE) - used in making garbage bags; polyvinyl chloride (PVC) - used for house siding; and polypropylene (PP) - used as carpet fibers, packaging, and diapers.

A plastic in which the polymer molecules are crosslinked (chemically bonded) with another set of molecules to form a "net like" or "ladder-like" structure is a thermoset plastic. Once crosslinking has occurred, a thermoset plastic does not soften, melt, or flow when heated. However, if the crosslinking occurs within a mold, the shape of the mold will be formed. Typical thermoset plastics are: unsaturated polyester (UP) -used for bowling balls and boats; epoxy− used for adhesives and coatings; and polyurethanes (PURs) - used in foams and coatings.

Many FRP wall and ceiling panels are made of thermoset plastic, that is, a material that undergoes a
chemical reaction in which it is formed into a solid and cannot be reformed. By reinforcing the plastic matrix, a wide variety of physical strengths and properties can be designed into the FRP composite. Additionally, the type and configuration of the reinforcement can be selected, along with the type of plastic and additives within the matrix. FRP composites can be developed specifically for the performance required versus traditional materials such as wood, metal, ceramics, and the like. A key advantage of FRP is that engineers can design the FRP composite to provide the needed characteristics, and avoid cost penalties of an over-engineered product.

Food processing requires the rugged performance of FRP panels. Photo: Crane Composites, Inc.

A thermoset FRP wall panel provides a long-term, durable, sanitary finish that meets the rugged performance needed in food processing, health care and storage environments. The primary advantage of this type of FRP panel is its long-term resolution of these performance needs.

On the other hand, non-reinforced thermoplastic panels such as those made of PVC, PE or PP, or combinations thereof, may be lower in cost but have inferior performance characteristics. Because of their lack of reinforcement, they are particularly difficult to install properly. Both PE- and PP-based panels may be more difficult to use with water-based latex adhesives because of high-surface tension properties. That is, during installation, latex adhesives can tend to "bead" and resist spreading, possibly causing delamination early after installation. The high surface tension, combined with thermal expansion up to three times higher than that of FRP panels, can cause bubbles and bulges in wall panels within weeks of installation. Further, only a small temperature change will result in a relatively large expansion of the non reinforced thermoplastic panels-a property that will cause failure and need for replacement in refrigerated and cooking areas.

The soft surface of the thermoplastics makes them poor performers in cleanability and abrasion. Surface hardness tests show that FRP panels are over three times harder than non-reinforced thermoplastics which tend to stain easily and become difficult to clean. This applies to graffiti, food stains and yellowing and color change. In terms of durability, the thermoplastic panels display only 24 percent of the stiffness provided in FRP panels. While often touted as environmentally friendly, non-reinforced thermoplastics contain a small percentage of recycled plastic. The higher the recycled plastic component, the lower the performance characteristics, and use of recycled content contributes to premature aging and yellowing.

In selecting thermoset FRP panels, which have no recycled plastic at this point, architects should note that they do vary in strength based on the amount of fiberglass reinforcement. Less expensive panels tend to have less reinforcement. The panels are generally utilitarian, rather than aesthetic, and have a tendency to yellow with age, though this can be somewhat offset by use of a special sealant. An installation crew experienced with FRP panels is advisable.

The Manufacturing Process

Photo: Crane Composites, Inc. Chopped fiberglass is laid onto the resin and film.

In making the fiberglass-reinforced plastic panels, first fiberglass is fed into the machine. Glass doffs provide the reinforcement. Embossed film is fed into the process, and resin poured onto the polyester film. Chopped fiberglass is laid onto the resin and film. The panel is cured prior to trimming, which is done by water jets. Finished panels are then inspected for quality and packaged, ready to be shipped to a job site.