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IAT 336 (11)
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Interactive Arts & Tech
IAT 336
Ken Zupan

Plastics Plastics are among the most versatile and useful of all materials known to man Plastics can be made to look like, and take the place of various materials like wood, glass, china (porcelain), cloth, rubber, jewels, varnish, etc. -for this reason, plastics find wide use in industry and for craftwork Polymers Although nature’s polymer-woods, wools, leathers are the older of the world’s materials, the main polymers of today have little that is natural about them -they are derived from the imagination of the chemist -almost all are synthesized from oil (although they don’t have to be) -they are composed of the simplest atoms: carbon, hydrogen, oxygen, chlorine, and sometimes nitrogen and fluorine) The First Plastics The first plastic, cellulose nitrate (Celluloid) was developed by John Wesley Hyatt, an American printer -this was the only plastic of commercial importance until Casein plastics were introduced about 1900 in France and Germany Leo Baekeland, a Belgian scientist developed the phenolic plastic Bakelite in 1909 -that discovery marked the real beginning of the plastics industry; during and after WWII, the growth of the plastics industry was phenomenal Plastics Naming Conventions In most cases plastics are named for their basic chemical compounds Plastics produced by more than one manufacturer (GE, Monsanto) are given a trade name -Lucite and Plexiglas are trade names for the plastic polymethylmethacrylate The Plastics Industry From chemical companies, the manufacturer of plastic raw materials obtains the ethers, alcohols, esters, acids, and other raw materials for resins The processors of plastic convert the basic plastic compounds into useful forms. Processors include the molders, the extruders, and the coaters -fabricators convert the various forms into finish products The Composition of Plastics All plastics are synthetic organic compounds. They are synthetic because they are man-made and organic because they contain carbon Other elements including hydrogen, oxygen, chlorine, and sulfur unite with the carbon to form various compounds suitable for use in plastics The basic materials used to produce plastics come from common sources including coal, petroleum, and cellulose of cotton fiber Two Main Classifications of Plastic Most plastics are described as being either thermosetting or thermoplastic. These terms indicate a reaction of plastic to heat Thermosetting plastics soften with heat but stay soft for only a short time. They set or harden if the heat continues. No amount of heat will make them soft again Thermoplastic plastics are soften with heat but remain soft if they heat continues. They set only when cooling and can be softened again by reheating Manufacturers choose plastics for these qualities They select thermosetting plastics for objects that must withstand heat -plastics of this type can be heated to temperatures of almost 500 degrees Fahrenheit before they begin to char Thermoplastic resins are used for articles not subjected to unusual temperature changes -these plastics soften or even melt at temperatures near 200 degrees Fahrenheit Thermosets: Elastomers Elastomers were originally called rubbers because they were used to erase pencil marks Unlike other solids, elastomers remember their shape when they are stretched some to five or more times their original length -they allows for conformability lending their use in engine gaskets and seals High dampening elastomers recover slowly whereas low dampening recover quickly and are ideal for springs, catapults, etc. Elastomer Properties There are more than 100 grades of elastomer While conformable, elastomers are subject to UV and chemical degradation. For this reason, they are mixed with carbon-black (soot) to protect against UV Conversely, rubber is vulcanized (mixed with sulphur) Ironically, some tire makers have added colors to their tire compounds Because they are thermosets, tires cannot be re-melted into raw material -they are usually grounded up into roof shingle material Casting and Molding Epoxy, phenolic, polyester, and polyurethane are the most often cast thermosets Identifying Thermosets/Thermoplastics Most plastics can be recycled, but they have to be separated into their different polymer types -because of the difficulty and expense of sorting, collecting, cleaning and reprocessing, at the moment it is only economically viable to recycle, PETE, HDPE, and PVC Thermoplastics can be re-melted but thermosetting plastics can only be crushed and used as insulation Nylon and acrylic are the most common thermoplastics used in casting Thermoplastics: Polymers Polyethylene (PE) PE was first synthesized in 1993 PE is commercially produced as film, sheet, rod, foam, and fiber Drawn PE has strong mechanical stiffness and strength, used in textile and structural uses PE is cheap, easy to mold, and fabricate Uses include oil containers, milk bottles, toys, beer crates, food packaging, squeeze tubes. Low density PE (LDPE) is used for film and packaging Polypropylene (PP) PP was first produced commercially in 1958 is the younger sibling of PE and can be used at higher temperatures PP has exceptional strength and resilience; it is also resistant to water Uses include ropes, automobile ducts, garden furniture, artificial turf, thermal underwear Polystyrene (PS) PS in its simplest form is brittle PS can be made in a high-impact variant or as polystyrene foam It is easy to mold, has the ability to be colored and has extreme clarity like glass PS has a weak tensile strength and can be cracked easily Common uses include food containers and packaging, ceiling tiles, molded parts (e.g. refrigerator trays) Acrylonitrile-butadiene-styrene (ABS) ABS is tough, resilient, and easily molded It takes on an opaque form although some forms can be transparent and pigment. It can even take on integral metallic finishes ABS-PVC alloys are stronger than standard ABS and can be used in casings for power tools and equipment ABS has good chemical and temperature resistance as well as high-impact pressure ABS also has good transparent qualities (up to 90%) Typical uses include cases for computers and TVs, telephones, food mixers, vacuum cleaners, bath trays, plumbing pipes, RV parts, shower stalls, sports equipment Resin Forming Processes In antiquity, resin forming was exclusively used for ceremonial purpose. The first resins were burned as incense in pyres. Early forms were made from wood ashes, charcoal and even dried cow dung The Composition of Plastics Plastic chemists specify the amounts of various ingredients needed for each type of plastic The raw plastic that result are made in various forms including syrup, powder, flakes, and pellets Raw plastics are called resins Casting and Molding Casting is a limited production process most often used for part evaluation or pre-production parts -although mold costs are low, labour production-time costs are fairly high Molds can be rigid or flexible materials Casting is usually done with a two part mixture of a monomer and a catalyst plus additives such as pigments, fillers, and reinforcements Thermoplastics are usually heated before being poured into the mold Thermoset materials usually generate their own heat in reaction to the catalyst Foam molding is used to produce cushions and other forms in flexible polyurethane resins for the furniture industry Rigid foam materials are also used to produce insulating blocks and foam core interior and exterior building products for the construction industry Foam density depends on the pressure created by the volume of the mixture of the mold and the amount of gas injected into the mold Hand lay-up or contact molding is a labour intensive process typically used in low to moderate production of small to large parts -the process makes use of molds of plastic, wood, and plaster to make boat hulls, tub, and shower units, and other large housings A reinforcement normally woven of mat fibers of glass is combined with a thermoset polyester resin mixture in an open mold A roller is used to compress the reinforcements and distribute the materials in the mold Resin Molding Types Reaction Injection Molding (RIM) is the process in which a resin and catalyst mixture is combined in and chemically reacts in the mold cavity -glass or graphite reinforcements are usually added to improve part strength Because the pressures are low, the most costs are inexpensive As with most thermoset processes, the wall thickness can vary but only the bottom of the mold side is smooth RIM is used to make automo
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