Polyester Resin and Its Applications

Polymers are substances whose molecules consist of a large number of units from several types. The units composed of a set of atoms are generally called polymer segments. In the polymerization of a mixture consisting of two monomers, the structure of each macromolecule contains units belonging to both monomers. Such a polymer is called a copolymer, and the process of its synthesis is called copolymerization. Polyesters are versatile synthetic copolymers with widely varying applications. Polyesters are produced worldwide in high volumes exceeding EUR 30 billion annually. UP (Unsaturated Polyester) resins consist of at least two separate components: reinforcing fiber and embedding matrix. Other additives can be used to improve properties and characteristics. Carbon, aramid or, most commonly, glass fibers can be used to produce FRP (Fiber Reinforced Plastic) or specifically GRP (Glass Reinforced Plastics). Materials essentially fill the gap between conventional commodity plastics and specialist engineering plastics. Production of the resin is carried out by reinforcing reinforcement while the resin is uncured, that is, in liquid form. Such materials are widely used in a number of applications where advantages can be taken of mechanical properties, corrosion resistance and low weight. Commercially, they are frequently seen in fiber, plastic, composites and coating applications. Polyester resins are most often used as composite materials. Innovations related to these materials make it possible to develop exciting new applications, particularly in aviation, transport and construction markets. The first polyester resins were mentioned in Berzelius's work in 1847 and in the work of Gay-Lussac and Pelouze in 1883. Unsaturated polyester resins used in today's reinforced plastics (RP) are combinations of reactive monomers.

Carleton Ellis proposed the combination idea in the 1930s. Ellis discovered that unsaturated polyester resins formed by the reaction of glycols with maleic anhydride could be improved to insoluble solids by adding a peroxide catalyst.

In 1936 he filed a patent for this idea. Ellis later discovered that by combining unsaturated polyester alkyd with reactive monomers such as vinyl acetate or styrene, a more useful product could be made by facilitating the addition of catalyst and application of the resin. Glass fiber reinforced polyester composites were first used in aircraft and boat hulls. The invention of the pultrusion line allowed unsaturated polyester-based materials to be developed in new application areas such as oil wells and electrical insulation devices. The filament winding process further expanded the potential market for unsaturated polyester resins. This technique was initially developed for the manufacture of military rocket casings and nozzles, but the potential for use in pipe and storage vessel manufacturing was discovered shortly after. In the 1960s and following these BMC (Bulk Moulding Compounds) and DMC (Dough Moulding Compounds) techniques, PMCs (Polyester Moulding Compounds) were also adopted by the industry. Systems of this structure are applied in many fields ranging from simple material packages to molding of complex details.

Processing

The structure of unsaturated polyester depends on the materials used for a particular application and the curing conditions. Contact molding is the dominant processing technique for unsaturated polyesters. More traditional methods for processing polyester materials represent open mold systems, namely hand and spray placement. The hand placement market represents approximately two-thirds of all contact molding operations. Compression molding, on the other hand, has begun to be used more in recent years. Additionally, highly automated processes such as SMC/DMC Molding, Resin Transfer Molding and pultrusion are also used to create elements from UP (Unsaturated Polyester) resins.

Applications

Polyester resin is a synthetic material produced by reaction between organic acids and alcohols. It can take various forms such as liquid, gel and film and has different properties that make it a useful material in many industries. Architects, builders, engineers and designers take advantage of polyester resin's light weight and weather resistance in various applications. UP Resins are widely used in a number of applications where benefits can be taken of good mechanical properties, corrosion resistance and low weight. Unreinforced versions are most commonly seen in cast resins, coatings, buttons, volume fillers, work surfaces (such as polyester marble), polyester concrete (for applications such as road drainage) and gel coats (to improve surface finish of composite materials).

Automotive, Aviation, Marine

UP resins have significant use in the transportation field. The materials are widely used in aircraft, trucks and buses for lower volume applications. Applications include bumper beams, body panels, sunroof frames, catalytic converter heat shields, dashboard carriers, seat structures, battery supports and spring systems. In addition to weight reduction, polyester parts also have the potential to reduce painting costs. Polyester parts provide good corrosion resistance properties. The adhesive properties of polyester resin are used to bond glass fiber layers in the production of body panels for automobiles, aircraft and boats. Rail cars, railway vehicles and shipping containers are also manufactured using UP resin composites. The marine market is also dependent on UP resins, primarily for the production of luxury yacht hulls. Its lightness is ideal for racing cars and light aircraft. Steel body panels are sometimes even coated with a polyester resin-based colorant for decorative purposes.  

Construction Materials

The largest market for reinforced polyester resin (composite materials) is the building and sanitary ware market. Here composite material is used in applications such as structural parts (e.g., replacing concrete-coated steel), cladding panels, covering (e.g., for prefabricated buildings), roof tiles, pipes and also bathroom fixtures (such as bathtubs and shower trays). Many building materials contain polyester resin as a lightweight resin source. Prefabricated shower trays and cabinet parts are often polyester resin and acrylic mixtures, and decorative metal parts are typically gel coated with a polyester resin-based colorant to match the decor. Many decorative details such as columns and railings are reinforced with glass fiber and polyester resin after being carved from rigid foam and made weather resistant, and can also be painted to suit the building.

Luggage, Packaging and Storage

The ability of polyester resin to be dried into film form and remain transparent while being made into sheets makes it an ideal packaging material. When vacuum forming and heat-sealing technology were developed, new packaging methods using polyester resin as the base material came to the fore and remain the most common form of small product packaging today. The same advantages that make polyester resin excellent for packaging also make it ideal for luggage. Suitcases and briefcases mostly contain polyester resin panels reinforced with fabric or leather to make them attractive. UP resins are commonly used in storage containers (where the chemical resistance of the material is high).

Tools and Furniture

Polyester resin is often used to bond fiberglass inside many "wet" appliances, including dishwashers and washing machines. Despite its relationship to economy models, fiberglass and resin linings have advantages compared to stainless steel interiors and do not rust. The same light strength that makes polyester resin popular in many other applications is also useful in the production of patio furniture. It has qualities such as weather resistance and low replacement cost.

References: • https://cdn.intechopen.com/pdfs-wm/39416.pdf • Dow, Resins--Polyester Resin. • Frbiz, Domestic Gel Coat Resin with Glass Fiber Reinforced Plastic Industry. • Bharat Dholakiya, Unsaturated Polyester Resin for Specialty Applications.