t2101 - 21.5 Recycling Issues in Materials Science and...

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Unformatted text preview: 21.5 Recycling Issues in Materials Science and Engineering ● S-375 Table 21.1 Recycle Codes, Uses of the Virgin Material, and Recycled Products for Several Commercial Polymers Recycle Code 1 Polymer Name Polyethylene terephthalate (PET or PETE) High-density polyethylene (HDPE) Uses of Virgin Material Plastic beverage containers, mouthwash jars, peanut butter and salad dressing bottles Milk, water and juice containers, grocery bags, toys, liquid detergent bottles Clear food packaging, shampoo bottles Bread bags, frozen-food bags, grocery bags Ketchup bottles, yogurt containers and margarine tubs, medicine bottles Videocassette cases, compact disc jackets, coffee cups; knives, spoons, and forks; cafeteria trays, grocery store meat trays, and fast-food sandwich containers Recycled Products Liquid-soap bottles, strapping, fiberfill for winter coats, surfboards, paint brushes, fuzz on tennis balls, soft-drink bottles, film, egg cartons, skis, carpets, boats Soft-drink bottle base caps, flower pots, drain pipes, signs, stadium seats, trash cans, recycling bins, traffic-barrier cones, golf bag liners, detergent bottles, toys Floor mats, pipes, hose, mud flaps Garbage can liners, grocery bags, multipurpose bags Manhole steps, paint buckets, videocassette storage cases, ice scrapers, fast food trays, lawn mower wheels, automobile battery parts License plate holders, golf course and septic tank drainage systems, desktop accessories, hanging files, food service trays, flower pots, trash cans, videocassettes 2 3 4 5 Polyvinyl chloride or vinyl (V) Low-density polyethylene (LDPE) Polypropylene (PP) 6 Polystyrene (PS) Source: American Plastics Council. identification code; for example, a ‘‘1’’ denotes high-density polyethylene (HDPE). Table 21.1 presents these recycling code numbers and their associated materials. Also included in the table are uses of virgin and recycled materials. Plastics recycling is complicated by the presence of fillers (Section 14.12) that were added to modify the original properties. The recycled plastic is less costly than the original material, and quality and appearance are generally degraded with each recycle. Typical applications for recycled plastics include shoe soles, tool handles, and industrial products such as pallets. The recycling of thermoset resins is much more difficult since these materials are not easily remolded or reshaped due to their crosslinked or network structures. Some thermosets are ground up and added to the virgin molding material prior to processing; as such, they are recycled as filler materials. Rubber materials present some disposal and recycling challenges. When vulcanized, they are thermoset materials, which makes chemical recycling difficult. In addition, they may also contain a variety of fillers. The major source of rubber scrap in the United States is discarded automobile tires, which are highly nonbiodegradable. Scrap tires have been utilized as a fuel for some industrial applications (e.g., cement plants), but yield dirty emissions. Recycled rubber tires that have been split and reshaped are used in a variety of applications such as automotive bumper guards, mud flaps, door mats, and conveyor rollers; and, of course, used ...
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