FRP, fiberglass reinforced plastic, is a composite made from fiberglass reinforcement in a plastic (polymer) matrix. A construction analogy would be the steel reinforcing bars in a concrete matrix for highways.
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. These variations allow an incredible range of strength and physical properties to be obtained. FRP composites can be developed specifically for the performance required versus traditional materials: wood, metal, ceramics, etc.
Engineers can design the FRP composite to provide the needed characteristics, and avoid cost penalties of an over-engineered product.
What is Fiberglass?
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 chopped into short strands, woven into a cloth or used as continuous roving.
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.
What are Plastic/Polymers?
There are two basic types of plastics/polymers: thermoplastic and thermoset. In general, FRP composites utilize a thermoset plastic.
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. 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.
In addition to these basic characteristics, polymers provide the FRP composite designer with a myriad of characteristics that can be selected, depending on the application. Combined with reinforcement of the polymer matrix, a vast range of characteristics are available for FRP composites.