The process of forming plastics into various shapes typically involves the steps of melting, shaping, and solidifying. As an example, polyethylene pellets can be heated above Tm, placed in a mold under pressure, and cooled to below Tm in order to make the final product dimensionally stable. Thermoplastics in general are solidified by cooling below Tg or Tm. Thermosets are solidified by heating in order to carry out the chemical reactions necessary for network formation.
Plastics are everywhere – in food containers and toys, in cosmetics packaging and household utensils. While some plastics are eco-friendly and may be safe for kids, others contain harmful chemicals or cause dangerous pollution during manufacturing.
Polyethylene terephthalate (PET or PETE); a strong, stiff synthetic fibre and resin, and a member of the polyester family of polymers. PET is spun into fibres for permanent-press fabrics, blow-molded into disposable beverage bottles, and extruded into photographic film and magnetic recording tape.
Pasteurization heat-treatment process that destroys pathogenic microorganisms in certain foods and beverages. It is named for the French scientist Louis Pasteur, who in the 1860s demonstrated that abnormal fermentation of wine and beer could be prevented by heating the beverages to about 57° C (135° F) for a few minutes. Pasteurization of milk, widely practiced in several countries, notably the United States, requires temperatures of about 63° C (145° F) maintained for 30 minutes or, alternatively, heating to a higher temperature, 72° C (162° F), and holding for 15 seconds (and yet higher temperatures for shorter periods of time). The times and temperatures are those determined to be necessary to destroy the Mycobacterium tuberculosis and other more heat-resistant of the non-spore-forming, disease-causing microorganisms found in milk. The treatment also destroys most of the microorganisms that cause spoilage and so prolongs the storage time of food.
Light, versatile synthetic resin made from the polymerization of ethylene. Polyethylene is a member of the important family of polyolefin resins. It is the most widely used plastic in the world, being made into products ranging from clear food wrap and shopping bags to detergent bottles and automobile fuel tanks. It can also be slit or spun into synthetic fibres or modified to take on the elastic properties of a rubber.
(a) Improved consumer health and safetyPlastics contribute to the health and safety of consumers in food and water packaging applications. Water has become a critical focus in urban areas, and plastics provide the mechanism for the supply and storage of clean drinking water. Additionally, plastics are lightweight, easy to manufacture and are installed in a range of diverse water control and distribution systems (e.g. sewerage, storm water, land drainage and irrigation). Plastic food packaging allows safe, time-dependent storage of fresh produce and other food, using temperature and atmosphere control inside the package (using gas-flush packaging and oxygen scavenger technology). In addition, the quality of packaged foods (especially time–temperature history) can be monitored with low-cost indicator labels built into the packaging (M. A. Neal 1990–1995, personal communication).