Since many of the terms used in the composites industry are confusing, we will try to clarify everything in a few lines.

A “composite” is an engineering material that consists of two or more different components. These components are usually classified into two categories: matrix and reinforcement. The matrix can be a plastic or polymer, metal or ceramic, and the reinforcement can be particles or fibers. Metal-ceramic matrix composites are usually referred to as MMC or CMC. But in reality, most composites are polymer-based and fiber-reinforced, which we call FRP (Fibre Reinforced Plastics). The fiber part can be glass, carbon, aramid, etc., and the plastic part usually uses a thermosetting resin such as polyester, vinyl ester, or epoxy. If the reinforcing fiber is glass, the composite is called “GFRP” or “GRP”. Although the terms “composite” and “FRP” are generally synonymous, meaning that they both mean fiber reinforced polyethylene or polymer, the term “composite” is usually used for carbon fiber reinforcing fibers and in high-value industries such as aerospace, and the term “FRP” is usually used in the materials engineering industry. On the other hand, “GRP” is a term that is usually used in the industry for low-value applications such as swimming pools, shower enclosures, covers, enclosures, etc. Finally, although these words are almost synonymous, they are different. In fact, GRP is a type of FRP and FRP is a type of composite.

Epoxy resins

Vinyl ester resins

Polyester resins

Unsaturated polyester resins are classified into two general categories based on the type of phthalic acid used

Iso phthalic unsaturated polyester resins and ortho phthalic unsaturated polyester resins. If the phthalic acid used is of the ortho type, the resin is called ortho phthalic unsaturated polyester resin, and if iso phthalic acid is used, the resin is called iso phthalic unsaturated polyester resin. A high percentage of unsaturated polyester resins used in the composite industry are ortho phthalic unsaturated polyester resins. Iso phthalic unsaturated polyester resins are used in products that require use against chemicals and corrosive materials and in gel coats. Orthophthalic resins are used for general applications, while isophthalic unsaturated polyester resins have specialized and specific applications. The advantage of orthophthalic unsaturated polyester resins is low price, good flexural and tensile strength, and high hardness. The advantage of isophthalic unsaturated polyester resins is high tensile and flexural strength, good resistance to water and chemicals.

The top layer of composite surfaces, which looks like a colored and shiny coating, is called gelcoat.

In addition to playing an aesthetic role for the part, gelcoat is responsible for protecting the surface of composite parts from abrasion, corrosion, chemicals, weather, and ultraviolet rays of sunlight.

In other words, gelcoat is the most vital part of a composite part. Although gelcoat is the least consumed compared to other raw materials used to produce a composite part, the lifespan of composite parts and their proper performance depend on the correct selection of gelcoat and its application method.

The main material used to produce gelcoat is resin, which determines the physical and chemical properties of gelcoat based on its chemical composition. Gelcoats are often produced from unsaturated polyester, vinyl ester and epoxy resins, and the appropriate gelcoat is selected and produced according to the required application of the final part.

Knowing the properties of the various resins used in the production of gelcoats is a great help in choosing the right one and, as a result, achieving the desired quality in the manufacture of a composite part, especially when the final part must provide specific resistances such as resistance to water, sunlight, mechanical strength, etc.

Today, anti-fouling paints are very common and widely used in the marine industry. These anti-fouling paints are used to apply to various parts of the ship that are in contact with water, and they disrupt the process of fouling in the hull of ships through mechanisms. To understand anti-fouling paints, we must first have information about mosses. Sea mosses are formed by the adhesion of barnacles, macro algae, and microbial slimes. This adhesive layer causes many problems such as increased surface roughness, increased friction between seawater and the moving ship, increased fuel costs, destruction of the hull coating and its repair, increased corrosion and the resulting losses, and increased downtime in the special repair area for the ship’s hull for all fixed and moving marine surfaces. Barnacles are hard to attach to the hull of a ship after about 48 hours. These organisms do not need sunlight to survive, so they can live in all parts of a ship that are in contact with seawater. Another factor affecting the growth of algae is the speed of the ship. If the ship is stationary for a longer period of time, the growth of these algae increases.

The fight against algae has existed since ancient times. In the past, bitumen was used for anti-moss coating on wooden boats, but with the advancement of the maritime industry and the expansion of science, arsenic and tin compounds were used as anti-moss marine paints. Among the tin compounds, the following can be mentioned:

• Tributyltin oxide (TBTO)
• Tributyltin fluoride (TBTF)
• Triphenyltin fluoride (TPTF)
• Tributyltin acrylate (TBTA)
• Tributyltin methyl methacrylate (TBTMMA)

According to the environmental laws adopted by the International Maritime Organization in 2008, the use of anti-moss marine paints containing tin compounds was prohibited.

Copper compounds such as copper (II) oxide, copper thiocyanate, and copper sulfide are also used as anti-moss. Of course, the use of these compounds is also limited, but they pose far fewer environmental risks than tin compounds.

These products are a range of coatings that have a variety of shades and high beauty. Polyurethane topcoat paints have high tolerance to sunlight. Alkyd topcoat paints are also a good option for staining and application in limited areas due to their single-component nature and ease of application. The shelf life of these paints is up to 5 years if applied correctly to the hull of the vessels, and if standard marine paints with high polish and gloss are used, after each year, by applying a special marine polish and wax, the paint will regain its gloss and freshness.