What are the differences between GRP and FRP in fiberglass-reinforced plastics

What are the differences between GRP and FRP in fiberglass-reinforced plastics?

Many fiberglass-reinforced plastic products exist. They include Molded FRP grating, FRP profiles, FRP pultruded round tube, FRP H beam, and FRP Angle. But, their abbreviations can be confusing. Let’s explain the differences between GRP and FRP in detail below.

GRP stands for Fiberglass Reinforced Plastic, or FRP. In Chinese, they call it Glass Reinforced Thermosetting Plastic or Fiberglass Reinforced Plastic.

It is a composite material consisting of two parts: the matrix and the reinforcement. The matrix of GRP material is resin, which serves as a binder and accounts for 30% to 40% of the total volume. Resin is a thermosetting plastic, like epoxy and phenolic resin. It is also an organic, non-metallic material. The reinforcement of GRP material is glass fiber, which serves as a strengthening agent. Glass fiber is an artificial, non-metallic inorganic fiber. It, along with carbon and Kevlar fibers, makes up 60% to 70% of the total volume. GRP is a plastic-based composite. They make it from organic and inorganic non-metallic materials.

GRP has good insulation and bonding. It has high strength, heat resistance, and is weavable. It resists acids, alkalis, solvents, and mold. GRP has a small molding shrinkage rate, with a volume shrinkage rate of 1% to 5%. After adding a curing agent, you must form it under heat and pressure, or cure it at room temperature under contact pressure.

FRP (Fiber Reinforced Plastics) is fiber-reinforced plastic. They are usually plastics with glass fibers and a resin matrix. You can use unsaturated polyester, epoxy, or phenolic as the resins. They are commonly known as fiberglass-reinforced plastic.

1. What is fiberglass-reinforced plastic?

Fiberglass reinforced plastic is a type of plastic. It is a plastic reinforced with glass fibers. The letters FRP can represent it. The literal meaning of plastic refers to a material that can be molded. People usually call synthetic plastics the materials made by adding different additives to resins. If manufacturers do not add any additives to the resin, they cannot call it plastic but only resin. Since resins are either thermoplastic or thermosetting, so are plastics. If glass fibers reinforce thermoplastic plastics, it’s called thermoplastic fiberglass reinforced plastic. If they reinforce thermosetting plastics, it’s called thermosetting fiberglass reinforced plastic. Currently, the production of fiberglass reinforced plastic mainly refers to thermosetting types. FRP is a composite material when we look at how it uses materials. You can also see it as a structure due to its own composite design.

2. What are the characteristics and shortcomings of FRP?

Answer: FRP has the following characteristics.

(1) It is lightweight and high-strength. Its density is 1.5 to 2.0. That’s only 1/4 to 1/5 of carbon steel. Its tensile strength is equal to or greater than that of carbon steel. Its specific strength is as high as that of high-grade alloy steel. So, it performs well in aviation, rockets, and spacecraft. It is also good for high-pressure containers and other lightweight products. The tensile, bending, and compressive strengths of certain epoxy FRP can reach over 400 MPa. Note: Specific strength is the strength divided by the density.

(2) Good corrosion resistance: FRP is highly corrosion-resistant. It resists the atmosphere, water, and various acids, alkalis, and oils. FRP has been widely used for chemical corrosion resistance. It is gradually replacing carbon steel, stainless steel, wood, and other nonferrous metals.

This material has excellent electrical properties. It is a great insulator. So, it allows for the creation of insulators. It has good dielectric properties at high frequencies and good microwave permeability. Thus, it is widely used in radar domes.

(4) Good thermal performance: FRP has low thermal conductivity, at 1.25 to 1.67 kJ/(m·h·K) at room temperature. This is only 1/100 to 1/1000 of that of metals. It is an excellent insulating material. At ultra-high, instant temperatures, it is an ideal thermal protection and ablation-resistant material. It can protect spacecraft from high-speed gas flows at over 2000 °C.

(5) Good designability:

Various structural products can be flexibly designed to meet needs. This ensures excellent product integrity.

You can choose materials to meet specific product performance needs. For example, they can be corrosion-resistant. They can also handle sudden high temperatures or have high strength in certain directions. They can also have good dielectric properties, among other features.

(6) Excellent processability:

Select a molding process based on the product’s shape, requirements, use, and quantity.

The process is simple, allowing for one-time molding, with outstanding economic benefits. This is true for complex-shaped, hard-to-mold, low-quantity products. It shows its process superiority.

One type of FRP cannot meet all requirements. FRP is not omnipotent and has the following shortcomings:

(1) Low elastic modulus: The elastic modulus of FRP is twice that of wood but 10 times lower than that of steel (E = 2.1×10^6). Thus, in product structures, it often feels insufficiently rigid and prone to deformation. We can compensate for this by using thin-shell or sandwich structures. We can also use high-modulus fibers or reinforcing ribs.

(2) Poor long-term temperature resistance: FRP does not suit high temps for long periods. Common polyester FRP loses strength above 50°C and is effective below 100°C. Common epoxy FRP loses strength above 60°C. High-temp resins can withstand 200 to 300°C.

(3) Aging phenomenon: Aging is a common defect of plastics, and FRP is no exception. It degrades in performance due to UV rays, wind, sand, rain, snow, chemicals, and stress.

(4) Low interlaminar shear strength: It is very low. The resin bears it. We can improve this by choosing processes and using coupling agents. Most importantly, avoid interlaminar shear in product design as much as possible.

3. What are the production methods of FRP?

We can split them into two main types: wet contact molding and dry compression molding.

Here are some process characteristics for molding:

• Hand layup molding

• Laminating

• RTM (Resin Transfer Molding)

• Pultrusion

• Compression molding

• Winding

Hand lay-up molding has various methods, including:

• Hand lay-up

• Bag molding

• Spray lay-up

• Low-pressure wet layup

• Moldless hand lay-up

Currently, the most widely used molding methods in the world are as follows:

① Hand lay-up: Mainly used in countries such as Norway, Japan, the United Kingdom, and Denmark.

② Spray lay-up: Mainly used in countries such as Sweden, the United States, and Norway.

③ Compression molding: Mainly used in countries such as Germany.

④ RTM: Mainly used in countries such as the United States, Europe, and Japan.

In China, manufacturers produce over 90% of FRP products using hand lay-up. Other methods include compression molding, winding, and laminating. In Japan, hand lay-up still accounts for 50%. Globally, hand lay-up still holds a considerable proportion, indicating its continued viability. Hand lay-up uses wet resin for molding. It has simple equipment and low costs. It can mold products over 10 meters in length at one time. The disadvantages are low mechanization, long production cycles, and unstable quality. In recent years, China has imported processes and equipment. These include pultrusion, spraying, and winding. With the development of the FRP industry, new process methods will continue to emerge.