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Properties of unsaturated polyester resin

Jan 25, 2019

Resin is a common name and refers to the polymer raw materials used in the manufacture of plastic products. Any high polymer that is not processed can be called a resin. Polyester refers to a polymer obtained by polycondensation of a dicarboxylic acid and a diol. Polyester resins can be divided into two categories: one is a saturated polyester resin, and its molecular structure has no non-aromatic unsaturated bonds, such as polyethylene terephthalate. This is a thermoplastic resin that can be injection molded into a "polyester" fiber by a spinneret, or a film, that is, a "polyester" film. The other type is an unsaturated polyester resin which has a non-aromatic unsaturated bond in its molecular structure and can be crosslinked by a suitable initiator to form a thermosetting plastic. The unsaturated polyester resins described herein are of this type and are often referred to as polyesters for convenience. Unsaturated polyester molecules are long-chain molecules before curing, and their relative molecular mass (hereinafter referred to as molecular weight) is generally 100 to 3000. Such long-chain molecules can be crosslinked with unsaturated monomers to form complex The massive network of molecules. This network of molecules has three forms. (a) is a substantially uniform continuous network structure; (b) is a non-uniform continuous network structure, and a chain of lower density chains is connected to each other between the dense networks having a higher density; (c) is discontinuous The network structure, the denser continuous web is dispersed among the unbonded components. The unsaturated polyester resin mainly forms a macromolecule of the second network structure after curing. This structural form can be studied by an electron microscope or by observing the swelling process of the resin. Unsaturated polyester is the most commonly used resin in reinforced plastics. In the field of reinforced plastics, the amount of thermosetting resin is about 75%, and the amount of thermoplastic resin is increasing. There are many types of thermosetting resins, in which the amount of unsaturated polyester is much higher than that of other various resins because unsaturated polyesters have particularly advantageous processing conditions and are inexpensive. For example, although the price of phenolic resin is lower than that of polyester, it is necessary to discharge water during processing and solidification to form steam, and it is necessary to adopt a high molding pressure (generally 8 to 30 MPa) and a temperature rising condition, so that a large press is required to produce. Unsaturated polyesters do not vent moisture or other by-products during processing and can be formed at lower pressures and temperatures. In fact, unsaturated polyesters are used in large quantities at various temperatures and contact pressures to form various articles, which are unmatched by other resins. The performance comparison between polyester and two other commonly used thermosetting resins after curing is shown in Table 1-1. Although the unsaturated polyester resin can be an insoluble or infusible thermosetting material after curing, its mechanical properties are low and cannot meet most of the requirements for use. If it is reinforced with glass fiber, it becomes a composite material, commonly known as glass reinforced plastic. It has many excellent properties such as light weight, high strength, chemical corrosion resistance, electrical insulation, microwave penetration, etc., and the molding method is simple, and it can form various large-sized or complex configuration products at one time, which has become a great advantage. New Materials.

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