| MadSci Network: Engineering |
Karl, The answer is "yes, all those materials do what you ask". Before you can begin to solve a problem or someone can give you helpful information about specific materials the problem must be outlined and then defined. Do so; then go to the supermarket or MacDonalds to see how a particular situation is solved. What materials are used and which particular properties of these materials are exploited to achieve a certain end. Polystyrene is a hydrocarbon polymer, a polyvinyl polymer with a phenyl pendant group; Acrylics of which Perspex; aka Lucite, Plexiglas according to who makes it, is one, are polyvinyl polymers with ester pendant groups [polymethylmethacrylate[PMMA]]. They have similar properties, costs, recyclability. Since these have rather bulky pendant groups and atactic [random] polymerization their strong points are lack of crystallinity and good optical properties. They can be made clear. The acrylics are more resistant to oils, etc than polystyrene because the ester groups are more polar; the polystyrene resists water and alcohols better. In any case a particular application must be tested for suitability. Aluminum is a metal. Metals have diverse properties which plastics can emulate. In general metals are opaque, conduct heat well by conduction, can be made stronger than plastics[esp Al, Fe, Ti] but a given application can usually be done by either material. It gets down to Specific needs and properties. Plastics are usually poorer heat conductors than metals, but heat conduction is best controlled by construction; see the thermos bottle and polystryene cups for examples. The properties of metals and polymers can be nicely combined: steel belted tires; the aluminum-Mylar space blanket; the paper-plastic-aluminum juice containers and many others. Aluminized glass or plastic for mirrors. Another property of metals; they can be highly reflective of light and heat. What properties do you need? Any material is subject to corrosion, wear and breakdown, chemical reaction, and physical trauma and breakage. these all must be evaluated critically in any application. Costs have to be evaluated critically on a case by case basis. Examples: the steel-tin can has not been replaced by polymer cans altho some are used. The glass milk bottle has been replaced by the polymer[polyethylene] bottle and the paper carton. Soda, beer come in glass and cans but beer doesn't come in plastic comtainers while soda does. Wine is just starting to sell in plastic jugs but glass is preferred even tho glass is not perfect as a container. Cellophane and waxed paper have been replaced by polymer substitutes in many cases. Costs, properties and results are intertwined. Recycling: Any material can be[and should be] potentially recycled. This is a political problem. Metals are heavily recycled. polystyrene and acrylics are not usually recycled put can be and should be. The Perspex company states it will do so for its material. I, for one, feel that manufacturers of any product should be responsible establishing a recycling protocol for that product. If you have specific questions please email them or send them in. Jim Griepenburg
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