Polyethylene terephthalate blow molding

Polyethylene terephthalate is injection blow molded to make water and carbonated drink bottles, and other liquid food packages. High stiffness, excellent clarity, and good resistance to carbon dioxide permeation are the principal attributes of these bottles. We carefully control molding conditions to promote transparency and surface gloss, which are prized for food... 

Polyethylene terephthalate is most often extruded into films or fibers, or blow molded into bottles. Polybutylene terephthalate is primarily found in injection molded parts. Such parts are highly crystalline, which makes them opaque. Polybutylene terephthalate is often modified with glass fibers or impact modifiers. Table 24.1 contains applications by processing method and resin. 

Polyesters exhibit excellent high temperature strength and electrical properties making them a good choice for many demanding applications. They also are physiologically inert allowing them to be used in food contact applications. The two common polyesters, polyethylene terephthalate and polybutylene terephthalate, are both used in injection molded products. Polyethylene terephthalate is often used in both extrusion and blow molded processes also. 

Polyesters Right now, you are probably using at least five things that are made from polyesters. Your clothes probably have some Dacron polyester fiber in them, and they are almost certainly sewn with Dacron thread. Ancient computers used floppy disks made of Mylar , and the optical film in your DVD is made of Mylar . Some of the electronics in your cell phone are probably potted (covered and insulated from shock) in Glyptal polyester resin. The soft drink in your hand probably came in a plastic bottle that was blow-molded from polyethylene terephthalate) resin, better known as PET. 

Dacron fiber is used to make fabric and tire cord, and Mylar film is used to make magnetic recording tape. Mylar film is strong, flexible, and resistant to ultraviolet degradation. Aluminized Mylar was used to make the Echo satellites, huge balloons that were put into orbit around the Earth as giant reflectors in the early 1960s. Polyethylene terephthalate) is also blow-molded to make plastic soft-drink bottles that are sold by the billions each year. 

Thennoset polyesters, such as Glyptal, alkyds and glass reinforced unsaturated polyesters have been available for several decades but Injection moldable polyaryl esters are relatively new. Whinfield and Dickerson extruded polyethylene terephthalate (PET) fibers (Dacron) in the 194O s. ( )pET was also extruded as film (Mylar) in the 1950 s but this polymer was not blow molded commercially until the 1970 s. 

Extrusion blow molding process (a) single-screw extruder, (b) die with a gas supplier, and (c) mold. The blow molding condition of high-density polyethylene (HOPE) was set as typically used in industry. The maximum extrusion temperature of a single-screw extruder was set at 220°C for HDPE and 250°C for HDPE/polyethylene terephthalate (PET) blend. 

Blown bottles (500 ml detergent bottle) by extrusion blow molding (a) high-density polyethylene (HOPE) and (b) HDPE/polyethylene terephthalate (PET) blend. 

Multilayer injection blow-molded containers have been available for a much shorter time than multilayer extrusion blow-molded containers, as development of the process was more difficult. However, these too are now available. A prominent example is multilayer polyethylene terephthalate (PET)-based ketchup bottles, which contain three layers of PET, and two layers of ethylene vinyl alcohol (EVOH) as an oxygen barrier. 

Polyethylene terephthalate, PET, is a thermoplastic polyester made by condensation reaction of ethylene glycol with either terephthalic acid or dimethyl terephthalate (Margolis, 1985). By the end of the 1920s J.R. Whinfield and J.T. Dickson discovered PET (BP 578079). It was first commercialized by Du Pont in 1930 (Brydson, 1982) as Dacron , followed by ICI with Terylene Films and blow-molded articles have become very important commercially. 

Polyethylene terephthalate (PET, polyethylene glycol terephthalate) n. A saturated, thermoplastic polyester resin made by condensing ethylene glycol, and terephthalic acid, used for textile fibers, water-clear, biaxially oriented film (e.g., Mylar ) and, more recently, for extruded, thermoform-able sheet (TV-dinner trays), injection-molded parts, and large, blow-molded, soft-drink bottles. It is extremely hard, wear- and chemical-resistant, dimensionally stable, and has good dielectric properties. See also polyester, saturated and crystallized polyethylene terephthalate (See image). 

In addition to bottles, a rapidly growing application for blow molding is the production of technical parts, such as automotive components—bumpers, ducts, and fluid containers. Common thermoplastic materials suited to blow molding include high-density polyethylene, polyvinyl chloride, polypropylene, and polyethylene terephthalate. 

Applicable materials for the injection blow molding process include high-density polyethylene (HOPE), low-density polyethylene (LDPE), polystyrene (PS), styrene acrylonitrile (SAN), ethylene vinyl acetate (EVA), polypropylene (PP), polycarbonate (PC), and polyurethane (PU). Polyethylene terephthalate (PET) and polyacrylonitrile (PAN) are less commonly used in the injection blow molding processes. 

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