Polyester structural applications

Due to dieir compact, branched structure and to die resulting lack of chain entanglement, dendritic polymers exhibit much lower melt and solution viscosity dian their lineal" counterparts. Low a-values in die Mark-Houwink-Sakurada intrinsic viscosity-molar mass equation have been reported for hyperbranched polyesters.198 199 Dendrimers do not obey diis equation, a maximum being observed in die corresponding log-log viscosity-molar mass curves.200 The lack of chain entanglements, which are responsible for most of the polymer mechanical properties, also explains why hyperbranched polymers cannot be used as diermoplastics for structural applications. Aldiough some crystalline or liquid... 

Since unsaturated polyester resins alone would have insufficient strength for structural application, reinforcements are used to enhance the physical strength of such resins. Typically, tensile strength, impact strength and stiffness are the physical properties of most interest. Reinforcements can be regular particulates, as in glass microspheres, irregular particulates, as in flakes, or fibers. 

A combination of enhanced reactivity and reduced viscosity for alkyd resins has been achieved by using hyperbranched polyester structures as discussed in Sect. 4.2.3 [ 123]. This study clearly showed the benefits of using highly branched structures in coating applications to obtain improved properties. 

Another resin application based on the same hyperbranched polyester structure described herein is low-VOC alkyds, which have very low viscosity and high reactivity compared to conventional high-solid alkyds. Other resin structures are unsaturated polyesters, polyurethane dispersions, and epoxides. ... 

Perhaps the most widely utilized (and studied) lyotropic LCP is poly j -phenylene terephthalamide (PPTA), more commonly known as Kevlar (see Figure 1.70). Kevlar belongs to the class of aramids that are well known for their LCP properties. Because these polymers are crystalline in solution, they are often spun into filaments, from which the solvent is subsequently removed in order to retain the aligned polymer structure. The result is a highly oriented, strong filament that can be used for a wide variety of structural applications. Most thermotropic LCPs are polyesters or copolymers that can be melted and molded into strong, durable objects. 

Common uses for polyester resins are reinforced plastics automotive parts boat hulls foams encapsulation of electrical equipment protective coatings ducts flues and other structural applications low pressure laminates magnetic tapes piping bottles non-woven disposable filters and low-temperature mortars. 

One can classify fibers in a variety of ways. For example, one may divide the whole field of fibers into apparel and nonapparel fibers, i.e. based upon the final use of fibrous material. The apparel fibers include synthetic fibers such as nylon, polyester, spandex, and natural fibers such as cotton, jute, sisal, ramie, silk, etc. Nonapparel fibers include aramid, polyethylene, steel, copper, carbon, glass, silicon carbide, and alumina. These nonapparel fibers are used for making cords and ropes, geotextiles, and structural applications such as fiber reinforcements... 

The development of highly crosslinked rigid polyisocyanurate foams opens an excellent area of applications for polyester polyols [4-8]. The required polyols do not need high functionality and the plasticising effect of polyester structures is extremely beneficial for these highly crosslinked systems [6]. The first polyester polyols used for these applications were low viscosity polycondensation products of AA with ethyleneglycol (EG) or diethyleneglycol modified with phthalic anhydride or triols. 

We have successfully synthesized ATF which can be used with FPE up to 80% but no less than 20%. ATF improves processability. Cross-linked ATF provides flexibility and thermal stability to the fluorenone polyester. The fact that the polyester structure does not contain nitrogen is a potential advantage in fire-resistant fiber applications, since there is no likelihood of HCN generation during burning. Because of high glass transition temperature of fluorenone polyesters, these polymers can be used as heat-resistant fibers. 

Poly(Propylene Fumarate) (PPF) is a linear, unsaturated, hydrophobic polyester (Structure 12) containing hydrolyzable ester bonds along its backbone. PPF is highly viscous at room temperature and is soluble in chloroform, methylene chloride, tetrahydrofuran, acetone, alcohol, and ethyl acetate [66]. The double bonds of PPF can form chemical crosslinks with various monomers, such as W-vinyl pyrrolidone, poly(ethylene glycol)-dimethacrylate, PPF-diacrylate (PPF-DA), and diethyl fumarate [67,68]. The choice of monomer and radical initiator directly influence the degradative and mechanical properties of the crosslinked polymer. Once crosslinked, PPF forms a solid material with mechanical properties suitable for a range of bone engineering applications. 

A. Atiqah, M.A. Maleque, M. Jawaid, and M. Iqbal, Development of kenaf-glass reinforced unsaturated polyester hybrid composite for structural applications. Compos. B 56, 68-73 (2014). 

Polyester and vinyl esters. Polyester matrices have had the longest period of use, with wide application in many large structural applications. (See Table 2.31.) They will cure at room temperature with a catalyst (peroxide) which produces an exothermic reaction. The resultant polymer is nonpolar and very water resistant, making it an excellent choice in the marine construction field. The isopolyester resins, regarded as the most water-resistant polymer in the polymer group, has been chosen as the prime matrix material for use on a fleet of U.S. Navy mine hunters. 

Mylar Mylar is a tradename for a polyterephthalate film produced by Du Pont. It is manufactured from the polyester of ethylene glycol and terephthalic acid (dimethyl terephathalate). Mylar films are commonly used in the electrical/ electronic industries for their excellent electrical properties and also as high-strength film for structural applications. 

Polyester resins are widely used due to their versatility and economic cost. Polyester exhibits a good combination of resistance to softening and deformation at elevated temperatures, good electrical properties and high resistance to corrosion as well as excellent weatherability [30, 31]. Structural applications, such as reinforced polyester containing glass fibre, comprise more than 80% of the market. Table 2.6 illustrates some of the physical parameters of polyester. 

A typical SMC contains about 30-50% of fiber (25-75 mm long, frequently E-glass fiber 25.4 mm), 25% resin (usually unsaturated polyester), and 25-45% filler (usually, calcium carbonate, alumina or clay) by the weight fraction. In the case of structural applications, 50-70 wt% of fibers can be used in SMCs. In general, fillers are not added if the SMC contains more than 60 wt% of fiber (see Table 3.1, Mallick, 1990). 

The previously described properties of the resin types make thermosetting resins much more useful for civil engineering structural applications, and in fact they have been used in almost all commercially available FRP pultruded products. Table 9.2 presents the basic properties of the thermoset resins most commonly used in pultrusion polyester, vinylester, epoxy and phenolic. 

In structural applications for plastics, which generally include those in which the part has to resist substantial static and dynamic loads, one of the problem design areas is the low modulus of elasticity of polymeric materials. Even when such rigid polymers as the ladder types of polyesters and polyamides are considered, the elastic moduli of unfilled polymers are under one million psi as compared to metals where the range is usually 10 to 40 million psi. Ceramic materials also have high moduli. Since shape integrity under load is a major consideration for structural parts, plastics parts must be designed for efficient use of material to afford maximum stiffness. 

Epoxy resins are widely used as protective coatings and adhesives, for structural applications such as adhesives to bulk out structural components, with extensive use in the aerospace, dental and other medical fields. Moreover, epoxies are widely used as insulating and structural materials in manufacturing microelectronic devices and components such as computer chip packing and circuit boards, due to their excellent combination of chemical and corrosion resistance and good electrical properties. On the other hand, unsaturated polyester (UPE) resin, a resin prepared from a polyester synthesized by esterification of glycol, unsaturated acid and saturated acid dissolved in styrene monomers, is widely used in many applications, such as electronic equipment, containers, automobiles, and cultured marble because of its clarity, and excellent chemical and corrosion resistance. 

Flame retarded polyesters cured, as prepregs, at 135 - 163 C for vacuum-bag or low pressure press cure. Suitable for laminate or sandwich panel construction in aircraft and other secondary structural applications requiring good mechanical performance, low flammability and excellent electrical properties. 

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