Applications of Unsaturated Polyesters

Using the building blocks shown in Table 12.1, resin producers may prepare unsaturated polyester formulations to meet a broad spectrum of critical end-use requirements.The estimated 1979 consumption of unsaturated polyester resins in the United States by end-use areas (percentage by weight) is shown in Fig. 12-1. The fortunes of unsaturated polyesters production and consumption closely follow the gross national product of the United States, with a correlation coefficient 90% all through the 1970s. The present United States capacity for MA production is about 1.9 billion lb. 

Marine applications are estimated to be the largest end-use category for polyesters, with the major use being in pleasure boats. This market has been experiencing percentage slippage due to the pleasure boat market 

The procedure provides a cost efficiency bonus that helps satisfy tightening OSH A requirements. 

In the construction industry the largest use of polyester resins is centered about flat and corrugated sheet, unitized tub-wall units, shower stalls, and sanitary ware. The sheet materials (panels) are useful for room dividers, roofing and siding, awnings, skylights, fences, and other applications. The major share of the base resins used in these applications may have limited 

Corrosion-resistant resins for construction are experiencing an annual growth rate greater than 18%, due to environmental rules and regulations. These resins are used in process equipment and pollution control apparatus, such as ducts, storage tanks, tubing, pipes, hoods, and related items for industrial applications. In the corrosion-resistant equipment area 

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Table 9.1 highlights the properties, products and applications of unsaturated polyesters. 

The main sectors for magnesium hydroxide use are in elastomers and thermoplastics, since they cause excessive thickening in the main thermoset application of unsaturated polyester systems. It is also much more expensive than ATH with which it shares comparable properties and flame retardancy, and so ATH will be preferred by processors wherever possible. As a result the principle opportunities are in applications where the extra thermal stability is essential, mainly in PP and polyamides. 

In coatings, one of the main applications of unsaturated polyester resins is in furniture and wood finishes. They are also used in gel coats for boats and bathroom fixtures. Another important area of application is in automotive fillers and putties. Unsaturated polyesters are also widely used in chemical resistant coatings and linings for chemical and petrochemical storage tanks. 

Unsaturated polyesters prepared from the intermediates in Table 12.1, formulated with various vinyl-type unsaturated monomers such as styrene, have been widely studied, patented, and discussed in the literature.Bjork-sten s book gives a good presentation of the early studies on the chemistry, production, and applications of unsaturated polyesters. 

At about the same time, an allyl resin known as CR39 was introdueed in the United States as a low-pressure laminating resin. This was followed in about 1946 with the introduction of unsaturated polyester laminating resins which are today of great importance in the manufaeture of glass-reinforced plasties. Alkyd moulding powders were introduced in 1948 and have since found specialised applications as electrical insulators. 

World production of unsaturated polyester resins in 1997 was of the order of 1.7 X 10 tonnes, with the USA accounting for about 45% and Western Europe 27%. Over 75% is used in reinforced plastics, with the rest being used for such diverse applications as car repair putties, cultured marble , wood substitution and surface coatings. The pattern of consumption in 1993 of reinforced polyesters in the USA was reported as ... 

For example, the molecular weight of unsaturated polyesters is controlled to less than 5000 g/mol. The low molecular weight of the unsaturated polyester allows solvation in vinyl monomers such as styrene to produce a low-viscosity resin. Unsaturated polyesters are made with monomers containing carbon-carbon double bonds able to undergo free-radical crosslinking reactions with styrene and other vinyl monomers. Crosslinking the resin by free-radical polymerization produces the mechanical properties needed in various applications. 

Polyester resins. The fire-performance characteristics of unsaturated polyester resins are of utmost importance in many application areas, particularly in the construction, transportation and electronics industries ( 1 3). Consequently, these plastics represent one of the major growth areas for fire retardants in recent years ( 1 4). 

P.B.15 3, like stabilized a-Copper Phthalocyanine Blue, markedly affects the hardening of unsaturated polyester cast resins. The list of applications also includes PUR foam materials, office articles, such as colored pencils, wax crayons, and water colors, as well as spin dyeing of polypropylene, polyacrylonitrile, secondary acetate, polyamide, polyester, and viscose. Used in polyester spin dyeing, P.B.15 3 satisfies the thermal requirements of the condensation process (Sec. 1.8.3.8). 1/3 and 1/25 SD samples equal step 7-8 on the Blue Scale for lightfastness. Textile fastnesses, such as stability to wet and dry crocking are perfect. 

Table 21.2 provides a general guide to the effect that chemical constituents can have on unsaturated polyester resin end-use performance. The routes to change an unsaturated polyester resin for a particular application is normally apparent and there can be several pathways available to achieve the desired properties. As the unsaturated polyester resin markets are highly competitive, raw material cost usually reduces the number of available routes available to the formulator. As noted previously, there are three main types or families of unsaturated polyesters, namely general purpose orthophthalic, isophthalic and DCPD resins. However, within each of these families, there are hundreds of variants that incorporate these various chemical constituents in different combinations and permutations to achieve the desired results. 

As discussed previously, there are thousands of unsaturated polyester resins based on the available chemical constituents. However, major application areas require specific performance and the unsaturated polyester resins used can be broadly categorized by the major chemical constituents that deliver the specific performance necessary. Table 21.5 contains such a categorization. This should be used as a general reference because discrete, end-product performance may dictate a departure from these general categorizations. 

Consumption of unsaturated polyesters in the marine industry consists of broad usage for hulls, decks and numerous small parts such as hatch and engine covers. Hulls and decks are generally produced with unsaturated polyester resins and multiple layers of fiberglass cloth knits and chopped fibers. Most marine applications require the use of unsaturated polyester resin gel coats for exterior appearance and for protection from the elements. 

The driving forces for the establishment of unsaturated polyester resin pipe, tank and fittings applications were environmental regulations, on-site labor savings and corrosion resistance. 

Sheet molding compounds (SMCs) and bulk molding compounds (BMCs) are the dominant materials used in automotive applications. These composites of unsaturated polyester resin, fillers and fiberglass have advantages of high stiffness, heat resistance and low coefficient of expansion. Coupled with low creep resistance, which is a distinct advantage over thermoplastic competition, and low-profile additives, which can yield Class A surfaces, these materials are well suited for applications from exterior body panels to under the hood components. 

The growth of unsaturated polyesters will continue to be fueled by their versatility and their ability to provide cost-effective solutions to end-use requirements. Unsaturated polyester composites will continue to provide solutions to engineering demands for corrosion resistance, strength-to-weight and cost performance. Marine, transportation and construction opportunities currently identified and being developed will provide growth beyond the existing applications presented. Some examples are as follows ... 

The crosslinking copolymerization of unsaturated polyesters with styrene is utilized industrially for the production of surface coatings. More extensive are applications in fiber-reinforced plastics where the unsaturated polyesters are used as a matrix for inorganic and organic fibers (see Example 5-20). Areas of application are (large) parts in boats, vehicles, and sport equipment construction. 

The weatherability and hydrolytic stability of unsaturated polyesters based on neopentyl glycol have made it a popular intermediate for use in formulations exposed to severe conditions, eg, in gel coats for cultured marble and marine applications (see Coatings, MARINE) (13). 

Diacyl peroxides are used in a broad spectmm of applications, including curing of unsaturated polyester resin compositions, cross-linking of elastomers, production of poly(vinyl chloride), polystyrene, and polyacrylates, and in many nonpolymeric addition reactions. 

Whereas the BPO—DMA redox system works well for curing of unsaturated polyester blends, it is not a very effective system for initiating vinyl monomer polymerizations, and therefore it generally is not used in such applications (34). However, combinations of amines (eg, DMA) and acyl sulfonyl peroxides (eg, ACSP) are very effective initiator systems at 0°C for high conversion suspension polymerizations of vinyl chloride (35). BPO has also been used in combination with ferrous ammonium sulfate to initiate emulsion polymerizations of vinyl monomers via a redox reaction (36). 

Lecithin has some catalytic or cocatalytic effects in multiphase systems because of its surface-active properties. Lecithin is reported to be useful as an emulsifier in the curing of aqueous dispersions of unsaturated polyesters (337). The products are more easily removed from their molds and have improved mechanical properties when lecithin is used. In a fermentation application, 1.5% soybean lecithin acts as an inducer in the preparation of cholesterol esterase using a strain of Pseudomonas bacteria (338). Aside from its role as a catalyst, initiator, or modifier, lecithin may have ancillary uses in catalyst systems as part of a protective coating (339). 

Polymer concretes show excellent mechanical properties and chemical resistance compared with conventional cement concretes. Polymer concretes can be cured quickly by the use of curing agents. Thus, the applications of polymer concretes are being increased. One of the popular polymers for polymer concretes is unsaturated polyester (UPE) resin. The properties of UPE resin can be modified by changing its molecular features. For the synthesis of the resin, phthalic anhydride or isophthalic acid as well as maleic anhydride can be employed to modify the mechanical properties or hydrothermal resistance. Terephthalic acid which is also used for the synthesis of poly ethylene terephthalate (PET) enhances the thermal resistance of the cured UPE resin. However, the synthesis of unsaturated polyester resin from terephthalic acid is difficult. One method to synthesize unsaturated polyester from terephthalic acid is the use of recycled PET. 

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