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Materials Engineering
Published in Quamrul H. Mazumder, Introduction to Engineering, 2018
These molding techniques used with thermoplastic polymers include injection molding, blow molding, and extrusion. Injection molding uses a cylinder to force pelletized or powdered raw material through a heated chamber toward a mold. The heat from the walls of the heating chamber melts the thermoplastic material. Then the cylinder forces the viscous liquid polymer into the mold chamber. Pressure is maintained until the parts have cooled. Blow molding is widely used for making plastic bottles. In blow molding, a length of polymer tube is joined at the bottom to form something like a heavy-walled bag. This bag, called a parison, is moved while still hot to a mold. The mold is formed in two pieces around the parison. Then air or steam is used to pressurize the inside of the parison; this forms the exterior of the parison to the interior of the mold. When the bottle is cooled, the mold is opened.
Static Systems for Producing Gas Mixtures
Published in O. Nelson Gary, Gas Mixtures, 2018
The materials chosen for construction should be such that the walls are smooth and do not cause excessive adsorption or reaction. Glass bottles are generally used, but phenolic,7 epoxy,18 Teflon, stainless steel,17,24,25 and polyvinyl chloride26 materials have been used.
Solid Waste Source Reduction and Recycling
Published in Charles R. Rhyner, Leander J. Schwartz, Robert B. Wenger, Mary G. Kohrell, Waste Management and Resource Recovery, 2017
Charles R. Rhyner, Leander J. Schwartz, Robert B. Wenger, Mary G. Kohrell
Plastic containers range from egg cartons to plastic soda bottles, detergent bottles, and tubs for butter. The use of recycled resins in plastic food containers is controlled by the Food and Drug Administration (FDA). The FDA is concerned about possible contaminants from recycled resins affecting the quality of the food. For this reason, little recycled resin was used in food containers prior to the mid-1990s, although technological advances indicate more will be used in the future. Plastic egg cartons and soda bottles are two of the more common exceptions granted by FDA. The FDA has decided that egg shells protect eggs from any possible contaminants. Other exceptions, granted to soft drink companies, allows them to use recycled soda bottles. In one case the bottles are made from recycled PET that has been broken down into its basic chemical monomers and then reprocessed into a new bottle using a process called methanolysis (see chemical processing below). Another process used is the production of a layered soda bottle with a center layer of recycled resin and a virgin plastic outer layer. Finally, the FDA has approved a process whereby recycled PET is cleaned to meet all standards, and can be used directly in the manufacture of new soda bottles.
Effect of stretch ratio on the induced crystallinity and mechanical properties of biaxially stretched PET
Published in Phase Transitions, 2020
The mechanical properties of plastics are a major factor of consideration when selecting them for both industrial and domestic applications. Most times, owing to the application, different sections of a piece of plastic have different degrees of processing. For instance, studies in the stretch blow moulding process have shown that the top and bottom of the bottles are the least stretched and are therefore the most brittle [1]. These, therefore, are bound to have different mechanical properties compared to the longitudinal section of the bottle. It is worthy of note that there are many different types of plastics with the essential similarity in their viscoelastic nature [2]. However, each type of plastic is unique in its fundamental, microstructural, physical and mechanical properties and changes in these after processing. Moreover, designers and producers in the plastic industry require comprehensive knowledge of the specific changes that occur following certain processing of the very plastic they are using. One of the most common plastics in the industry today is polyethylene terephthalate, PET, which is used in most bottled drinks. This paper investigates and reports the changes that occur in PET after a processing which involves heating it to a temperature above its glass transition temperature and biaxially stretching it to known stretch ratios. The results are compared to the original (unprocessed) PET sample.