In composite materials, the main function of the resin is to transfer stress between the reinforcing fibers, and act as a role for fixing the fibers together, protecting the fibers from mechanical and environmental damage. The resin matrix generally used to reinforce polymer composites is thermoplastic or thermoset. This article briefly introduces the characteristics of several common thermosetting resin matrixes.
Most composite materials use thermosetting resins in the manufacturing process, and they are converted from liquid to solid through a process called polymerization or crosslinking. When used in the production of finished products, thermosetting resins are “cured” through the use of catalysts, heat or a combination of both. The cured thermosetting resin cannot be converted back to its original liquid form. Common thermosetting plastics are polyester, vinyl ester, epoxy and polyurethane.
Unsaturated polyester resin
Unsaturated polyester resin (UPR) is the main force in the composite material industry, accounting for about 75% of the total resin used. There are a variety of raw materials and processing techniques that can be used to formulate or process the required properties of polyester resins. Polyesters are versatile because they can be modified or customized in the process of building polymer chains. They are useful in almost all areas of the composite material industry.
The main advantage of these resins is to strike a balance between performance (including mechanical, chemical, and electrical), dimensional stability, cost, and ease of handling or processing. Polyester manufacturers can provide resins with the necessary properties to meet the needs of specific end users.
Epoxy resin can be used in various composite parts, structures and concrete repairs. By improving the structure of the resin, many products with different performance levels can be produced. Compared with unsaturated polyester resin, the main advantage of epoxy resin is its lower shrinkage.
Epoxy resins can also be formulated with different materials or blended with other epoxy resins to obtain specific performance characteristics. Epoxy resins are mainly used to manufacture high-performance composite materials that have excellent mechanical properties, corrosion resistance, excellent electrical properties, good performance at high temperatures, good adhesion to substrates, or a combination of these advantages. However, epoxy resin does not have particularly good UV resistance.
The development of vinyl esters combines the advantages of epoxy resins with better handling/faster curing, which is a typical feature of unsaturated polyester resins. These resins are prepared by reacting epoxy resin with acrylic or methacrylic acid. This provides sites of unsaturation, very similar to those created in polyester resins when maleic anhydride is used. The resulting material was dissolved in styrene to produce a liquid similar to polyester resin.
Vinyl esters can also be cured with conventional organic peroxides used with polyester resins. Vinyl ester has mechanical toughness and excellent corrosion resistance, and these enhanced properties can be obtained without complicated processing, handling or special workshop processing operations (usually epoxy resin).
Phenolic resins are a type of resin usually based on phenol (carbonic acid). Phenolic resin solidifies through condensation reaction to produce water, so it should be removed during processing. The application of coloring is limited to red, brown or black.
Phenolic composites have many desirable properties, including high temperature resistance, creep resistance, excellent heat and sound insulation properties, corrosion resistance, and excellent fire/smoke/smoke toxicity characteristics. Phenolic resin is used as an adhesive or matrix adhesive for engineered wood (plywood), brake linings, clutch plates, circuit boards, etc.
Polyurethanes are a family of polymers with a wide range of properties and uses, all of which are based on the exothermic reaction of organic polyisocyanates and polyols (alcohols containing more than one hydroxyl group). Several basic components with different molecular weights and functions can be used to produce the entire polyurethane material.
Polyurethane comes in surprisingly many forms. These materials are ubiquitous, and they play an important role in all aspects of our daily lives compared to any other single polymer. They are used as coatings, elastomers, foams or adhesives. When used as a coating for exterior or interior finishes, polyurethane is tough, flexible, chemically resistant and can cure quickly. Polyurethane is used as an elastomer in solid tires, wheels, bumper assemblies, or insulation.
There are many polyurethane foam formulations to optimize the density of insulation materials, structural sandwich panels and building components. Polyurethane is commonly used to bond composite structures together. The advantages of polyurethane adhesives are that they have good impact resistance, the resin can cure quickly, and can bond well to a variety of different surfaces (such as concrete).