Unsaturated polyesters polyester molding compounds

Aromatic polyester Unsaturated polyester Alkyd molding compounds ... 

Rydes, M. (1993) Aspects of the Rheology of Unsaturated Polyester Dough Molding Compounds, London University of West London and National Physical Laboratories. 

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. 

Sheet molding compound (SMC) is a composite material that has been used as an alternative to steel for more than 30 years. SMC consists of a glass-fiber-filled unsaturated polyester and vinyl ester resin that has been compacted into a sheet. These sheets are then placed into compression molds and formed into body panels, and these panels are then coated mainly by dual-cure coatings. ... 

Sheet and Bulk Molding Compounds. The activity with SMC and and BMC is based on resin technology which was known more than 20 years ago (3). The key concept involves increasing the viscosity of the unsaturated polyester resin. The polyester resin with an initial viscosity of several thousand centipoise is advanced chemically to a viscosity of several million centipoise. 

Again, as in many other fields covered in the book, modified epoxies are the most studied systems (toughened epoxies for adhesive coatings and composites). But also rubber-modified phenolics and low-profile unsaturated polyesters for sheet and bulk molding compounds have been extensively studied. 

The matrix can be either a thermoset or thermoplastic. The oldest and still widest used material for compression molded products is phenolic. The thermoset materials used to manufacture fiber reinforced compression molded articles is unsaturated polyester sheet or bulk, reinforced with glass fibers, known as sheet molding compound (SMC) or bulk molding compound (BMC). In SMC, the 25 mm long reinforcing fibers are randomly oriented in the plane of the sheet and make up for 20-30% of the molding compound s volume fraction. 

Alkyds. Alkyd resins consist of a combination of unsaturated polyester resins, a monomer, and fillers. Alkyd compounds generally contain glass fiber filler, but they may also include clay, calcium carbonate, alumina, and other fillers. Alkyds have good heat, chemical, and water resistance, and they have good arc resistance and electrical properties. Alkyds are easy to mold and economical to use. Postmolding shrinkage is small. Then-greatest limitation is extremes of temperature (above 175°C) and humidity. 

Unsaturated polyester resins are one of the most important thermosetting resins used for preparing molding compounds for hot-press matched molding, cold molding, eind contact molding. 

On the other heind, the linear unsaturated polyester resins find use in memy commercial applications, such as in producing solventless lacquers, and thermosetting molding compounds. The resin is normally prepcured by the reaction of a saturated diol with a mixture of an unsaturated dibasic acid and a modifying dibasic acid or its corresponding anhydride. It is commonly referred to as... 

Alkyd resins have been the workhorse for the coatings industry over the last half century. The term alkyd was coined to define the reaction product of polyhydric alcohols and polybasic acids, in other words, polyesters. However, its definition has been narrowed to include only those polyesters containing monobasic acids, usually long-chain fatty acids. Thus thermoplastic polyesters typified by polyethylene terephthalate (PET) used in synthetic fibers, films, and plastics and unsaturated polyesters typified by the condensation product of glycols and unsaturated dibasic acids (which are widely used in conjunction with vinylic monomers in making sheet molding compounds or other thermosetting molded plastics) are not considered as part of the alkyd family and are beyond the scope of the present discussion. 

FRP fine powder was made from waste septic tanks, which were formed by Sheet Molding Compound (SMC) method. The SMC was a composite of resin, inorganic filler and glass fiber (GF). The resin was unsaturated-polyester resin. The inorganic filler was fine powder of calcium carbonate. These two materials compose 70% of the weight and the rest of the weight (30%) was GF. 

The technique is also applicable to cross-linked polyesters made from unsaturated polyesters and styrene, as in the sheet-molding compounds used in cars and boats.165 The ester linkages were broken by treatment with ethanolic potassium hydroxide or by ethanolamine. The latter was preferred, because no waste salts were formed by neutralization, as they were with the potassium hydroxide. The filler and glass fibers could be removed at this stage, if desired. The alcohol-soluble product was suitable for use in new bulk-molding compounds. A method that allows the cross-linked polyester to recycled back into the same use... 

Some new types of S-B block copolymers are now being used as low-shrink/low-profile additives in sheet molding compounds made from unsaturated polyesters. 

Presently, epoxy resins sell for 81< /lb. Compared to unsaturated polyesters at 38< /lb., phenollcs at 40d/lb. and urea molding compounds at 56< /lb., epoxy resins are still more expensive and perhaps will continue to be so. A brief breakdown of the reported uses for these resin in 1978 is given. 

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