The use of unsaturated polyester resins in structural applications is well documented. There are, however, significant quantities of unsaturated polyester resins used in specialist compounded products, which are more likely to be unreinforced. The most well known of these technologies are formulated gel-coats, a technology that has been changing rapidly in recent years with improvements in gloss retention, color retention, and volatile organic compound emissions.
The introduction of granite effect coatings and solid surface material is a further example of the versatility of unsaturated polyester resins. Although these materials have been predominantly used for interior applications, their potential for exterior use on buildings provides exciting possibilities for a new and varied range of composite building materials providing stone effects at a fraction of the weight of conventional building materials.
Other compounded resins that are especially important to the building and construction market are those with fire resistant characteristics. In addition, the improvements in smoke reduction from unsaturated polyester resin systems make such materials attractive for cladding applications. Combining the advantages of these resins with decorative coatings and sandwich construction provides the basis for structural, insulating components.
Markets
The markets for reinforced plastics are frequently split into a number of generally accepted sectors, such as marine, land transport, building and construction, and chemical containment. There are, of course, subdivisions in each sector, for example, powered pleasure boats, powered work boats, sailboats, and offshore applications in the marine market, but most of the discussion in the literature is about the use of fiber-reinforced composites in these market sectors and market subgroups. In general, unfilled resins with good mechanical properties are preferred, but there are, very often, requirements for compounded products to provide special characteristics to meet specific performance requirements. Obviously, compounded fire-resistant materials fall into such a category and are used to impart resistance to ignition, resistance to surface spread of flame, and, increasingly, reduction in emissions of smoke and toxic fumes. Although such materials are often highly filled, they are used with fiber reinforcement for the manufacture of structural and semistructural components. The importance of these resins and their developments together with two other important compounded unsaturated polyester resin-based products has been disclosed. These latter materials are not used in conjunction with fiber reinforcement but are usually simply filled or pig-mented; they are gel-coats and are mainly used as "in-mold" coatings and solid surface materials for the manufacture of synthetic granite-type products.
Resin concrete and repair putties are also large consumers of unsaturated polyester resin in non-fiber-reinforced compounds.
Resistance to Fire
The use of glass-fiber-reinforced plastics (GRP) in applications where fire resistance was particularly important was introduced into the building industry five decades ago. Generally, the structural performance of the material was not questioned for building applications because it had been well proven for the construction of boats. However, as with most plastic materials, its ability to perform under fire conditions was in question for use in buildings even though it had been documented that fires in buildings originate from the contents and in a vast majority of circumstances the structure does not contribute to loss of life.
One of the most successful means to improve the resistance of plastics to fire is by the incorporation of fillers, which break down with heat to produce heavy vapors to prevent oxygen reaching the surface of the material and hence reduce the possibility of burning. The major problem associated with the high levels of filler required to render resins fire retardant is the increase in their viscosity, which results in handling difficulties when manufacturing structural components.
The use of halogenated additives, which work synergistically with some fire-retardant fillers, help to overcome handling problems but result in the potential for toxic fume production under fire conditions.
The availability of improved viscosity modifiers is now enabling resins filled with high levels of nontoxic fillers, such as alumina tri-hydrate, to be used to manufacture laminates containing reasonable levels of reinforcement to produce, at least, semistructural components.
Such systems will meet the new International Maritime Organization (IMO) requirements for use on passenger ships. Under the test conditions, the material has to exhibit low surface spread of flame characteristics, low smoke emissions, and low emissions of carbon monoxide.
Gel-Coat Protection
In the early days of the GRP industry, the need for resin-rich surfaces was established to:
• Improve the durability of components
• Protect the laminate from the environment
• Reduce fiber pattern
• Provide a smooth aesthetic finish
• Eliminate the need for painting
As a result of these requirements, a market for ready-formulated coatings was established and gel-coat product ranges became established.
The availability of quality "in-mold" coatings, such as gel-coats, to fabricators saves labor and wastage in the workshop and improves the quality of molded components. Gel-coats are available in brush and spray versions with a variety of properties and performance characteristics to meet a range of needs. They must be applied carefully and correctly to avoid faults.
Gel-Coat Developments
Over the years the need for improved gloss and color retention in gel-coats has been recognized and developments in ultraviolet (UV) resistance and color fastness have resulted in a range of gel-coats that can be weathered under the severest tropical weather conditions without changes in appearance.
Solid Surfaces
Resins have often been used to bind together fillers and aggregates to produce materials such as resin concrete and synthetic cultured and onyx marble. For decorative surfaces a clear (translucent) gel-coat is used to improve the quality of the surface finish and remove the effects of surface porosity. Although the gel-coat used is usually based on good quality, water-resistant resins, the inferior quality of the backing systems often results in a material that is susceptible to crazing, cracking, poor water resistance, and poor thermal resistance. Because the gel-coat surface is too thin for repairs to be effectively carried out, the problems cannot be easily rectified.
The monopoly of the acrylic-based solid surface material has been gradually eroded by the introduction of unsaturated polyester-based solid surface, which offer a much wider range of colors to provide improved customer choice. Raw materials and manufacturing processes have been designed to eliminate voids in polyester-based solid surfaces.
Traditionally, solid surface materials have been used for the manufacture of kitchen surfaces, sinks, and bathroom units. However, there is increasing interest in more diverse applications such as furniture, table tops, tiles, paneling, cutlery, and pens. It is also possible to use the material as a 2- to 3-mm-thick coating for other materials and the granite effect finish is reviving interest in GRP for cladding for buildings.
The unsaturated polyester resin-based material comprises of three components:
1. Chips. The colored fillers or chips, used to provide the granite effect, can be based on thermoplastic or thermo-set materials.
2. Resins. Resin must be clear and near "water white" to allow the depth of color of the chips to be appreciated. The resin must also be resistant to elevated temperature, water, staining, UV light, and cigarette burns. Hence, typical formulations giving an acceptable level of performance are based on isophthalic acid and neopentyl glycol (NPG).
3. Fillers. Only alumina trihydrate can be used in addition to the colored "chips" because it is translucent. It also offers fire-retardant characteristics.
Solid surface systems are nonreinforced and can be machined and cut with conventional woodworking equipment. Patterns can be routed in solid surface materials and cast resin "in laid" to provide a variety of customized finishes.
It is important to ensure when manufacturing solid surface that the resin is formulated to accept high filler loading without air entrapment and will develop hardness rapidly. The final product must be resistant to chipping, cracking, hot-cold water cycling, "blushing," and UV light. It must also be easy to machine for shaping and finishing.
Future
Unsaturated polyester resin-based compounded products provide a range of materials with tailored performance characteristics for a variety of markets.
Gel-coats are essential for most applications for GRP, providing aesthetic finishes in the marine, transport, building, and construction markets. They have well-proven durability but improvements in gloss and color retention will ensure their position as the major coating for fiber-reinforced composite materials in the future.
Fire-retardant resins with exceptionally low smoke production under fire conditions are becoming a reality with unsaturated polyester resin-based systems. New standards are providing new challenges, which are being met successfully to ensure materials meet new requirements for surface spread of flame for materials for use in construction applications.
