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Polymer Science and Engineering - مطالب ابر plastic
If you’re after basic information on plastic materials, this is the place to find it. Here you’ll learn the definition and properties of polymers, another name for plastics


The simplest definition of a polymer is a useful chemical made of many repeating units. A polymer can be a three dimensional network (think of the repeating units linked together left and right, front and back, up and down) or two-dimensional network (think of the repeating units linked together left, right, up, and down in a sheet) or a one-dimensional network (think of the repeating units linked left and right in a chain). Each repeating unit is the “-mer” or basic unit with “poly-mer” meaning many repeating units. Repeating units are often made of carbon and hydrogen and sometimes oxygen, nitrogen, sulfur, chlorine, fluorine, phosphorous, and silicon. To make the chain, many links or “-mers” are chemically hooked or polymerized together. Linking countless strips of construction paper together to make paper garlands or hooking together hundreds of paper clips to form chains, or stringing beads helps visualize polymers. Polymers occur in nature and can be made to serve specific needs. Manufactured polymers can be three-dimensional networks that do not melt once formed. Such networks are called THERMOSET polymers. Epoxy resins used in two-part adhesives are thermoset plastics. Manufactured polymers can also be one-dimensional chains that can be melted.  These chains are THERMOPLASTIC polymers and are also called LINEAR polymers. Plastic bottles, films, cups, and fibers are thermoplastic plastics.

Polymers abound in nature. The ultimate natural polymers are the deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) that define life. Spider silk, hair, and horn are protein polymers. Starch can be a polymer as is cellulose in wood. Rubber tree latex and cellulose have been used as raw material to make manufactured polymeric rubber and plastics. The first synthetic manufactured plastic was Bakelite, created in 1909 for telephone casing and electrical components. The first manufactured polymeric fiber was Rayon, from cellulose, in 1910. Nylon was invented in 1935 while pursuing a synthetic spider silk.

The Structure of Polymers

Many common classes of polymers are composed of hydrocarbons, compounds of carbon and hydrogen. These polymers are specifically made of carbon atoms bonded together, one to the next, into long chains that are called the backbone of the polymer. Because of the nature of carbon, one or more other atoms can be attached to each carbon atom in the backbone. There are polymers that contain only carbon and hydrogen atoms. Polyethylene, polypropylene, polybutylene, polystyrene and polymethylpentene are examples of these. Polyvinyl chloride (PVC) has chlorine attached to the all-carbon backbone. Teflon has fluorine attached to the all-carbon backbone.

Other common manufactured polymers have backbones that include elements other than carbon. Nylons contain nitrogen atoms in the repeat unit backbone. Polyesters and polycarbonates contain oxygen in the backbone. There are also some polymers that, instead of having a carbon backbone, have a silicon or phosphorous backbone. These are considered inorganic polymers. One of the more famous silicon-based polymers is Silly Putty®.

Molecular Arrangement of Polymers

Think of how spaghetti noodles look on a plate. These are similar to how linear polymers can be arranged if they lack specific order, or are amorphous. Controlling the polymerization process and quenching molten polymers can result in amorphous organization. An amorphous arrangement of molecules has no long-range order or form in which the polymer chains arrange themselves. Amorphous polymers are generally transparent. This is an important characteristic for many applications such as food wrap, plastic windows, headlight lenses and contact lenses.

Obviously not all polymers are transparent. The polymer chains in objects that are translucent and opaque may be in a crystalline arrangement. By definition, a crystalline arrangement has atoms, ions, or in this case, molecules arranged in distinct patterns. You generally think of crystalline structures in table salt and gemstones, but they can occur in plastics. Just as quenching can produce amorphous arrangements, processing can control the degree of crystallinity for those polymers that are able to crystallize.  Some polymers are designed to never be able to crystallize. Others are designed to be able to be crystallized. The higher the degree of crystallinity, generally, the less light can pass through the polymer. Therefore, the degree of translucence or opaqueness of the polymer can be directly affected by its crystallinity.  Crystallinity creates benefits in strength, stiffness, chemical resistance, and stability.

Scientists and engineers are always producing more useful materials by manipulating the molecular structure that affects the final polymer produced. Manufacturers and processors introduce various fillers, reinforcements and additives into the base polymers, expanding product possibilities.

Characteristics of Polymers

The majority of manufactured polymers are thermoplastic, meaning that once the polymer is formed it can be heated and reformed over and over again. This property allows for easy processing and facilitates recycling. The other group, the thermosets, cannot be remelted. Once these polymers are formed, reheating will cause the material to ultimately degrade, but not melt.

Every polymer has very distinct characteristics, but most polymers have the following general attributes.

  1. Polymers can be very resistant to chemicals. Consider all the cleaning fluids in your home that are packaged in plastic. Reading the warning labels that describe what happens when the chemical comes in contact with skin or eyes or is ingested will emphasize the need for chemical resistance in the plastic packaging. While solvents easily dissolve some plastics, other plastics provide safe, non-breakable packages for aggressive solvents.

  2. Polymers can be both thermal and electrical insulators. A walk through your house will reinforce this concept, as you consider all the appliances, cords, electrical outlets and wiring that are made or covered with polymeric materials. Thermal resistance is evident in the kitchen with pot and pan handles made of polymers, the coffee pot handles, the foam core of refrigerators and freezers, insulated cups, coolers, and microwave cookware. The thermal underwear that many skiers wear is made of polypropylene and the fiberfill in winter jackets is acrylic and polyester.

  3. Generally, polymers are very light in weight with significant degrees of strength. Consider the range of applications, from toys to the frame structure of space stations, or from delicate nylon fiber in pantyhose to Kevlar, which is used in bulletproof vests. Some polymers float in water while others sink.  But, compared to the density of stone, concrete, steel, copper, or aluminum, all plastics are lightweight materials.

  4. Polymers can be processed in various ways. Extrusion produces thin fibers or heavy pipes or films or food bottles. Injection molding can produce very intricate parts or large car body panels. Plastics can be molded into drums or be mixed with solvents to become adhesives or paints. Elastomers and some plastics stretch and are very flexible. Some plastics are stretched in processing to hold their shape, such as soft drink bottles. Other polymers can be foamed like polystyrene (Styrofoam™), polyurethane and polyethylene.

  5. Polymers are materials with a seemingly limitless range of characteristics and colors. Polymers have many inherent properties that can be further enhanced by a wide range of additives to broaden their uses and applications. Polymers can be made to mimic cotton, silk, and wool fibers; porcelain and marble; and aluminum and zinc. Polymers can also make possible products that do not readily come from the natural world, such as clear sheets and flexible films.

  6. Polymers are usually made of petroleum, but not always. Many polymers are made of repeat units derived from natural gas or coal or crude oil.  But building block repeat units can sometimes be made from renewable materials such as polylactic acid from corn or cellulosics from cotton linters. Some plastics have always been made from renewable materials such as cellulose acetate used for screwdriver handles and gift ribbon.  When the building blocks can be made more economically from renewable materials than from fossil fuels, either old plastics find new raw materials or new plastics are introduced.

  7. Polymers can be used to make items that have no alternatives from other materials.  Polymers can be made into clear, waterproof films. PVC is used to make medical tubing and blood bags that extend the shelf life of blood and blood products. PVC safely delivers flammable oxygen in non-burning flexible tubing.  And anti-thrombogenic material, such as heparin, can be incorporated into flexible PVC catheters for open heart surgery, dialysis, and blood collection. Many medical devices rely on polymers to permit effective functioning




طبقه بندی: اطلاعات پلیمری،
برچسب ها: پلیمر، polymer، plastic، monomer، polymers، plastics،

تاریخ : دوشنبه 21 فروردین 1396 | 08:31 ق.ظ | نویسنده : Arash Sadeghi | نظرات
  • Construction Waste

AluminumWood
  • Electronics

Cell PhoneElectronicsPrinter Cartridges
  • Glass

Glass
  • Hazardous Waste

AutoChemicalsBatteries

Light BulbsMotor Oil

Paint
Car Tire
  • House Chemicals

  • Household Items


BicycleBooks

ChipBagFurniture

MattressMedical

Makeup
Video
Water Filter
  • CD DVD

  • Organic Waste

Food ScrapsGarden ChemicalsGarden Waste
  • Metal

AluminumBeverageCan

ScrapMetalTins
  • Paper

Food CartonsCardboardPaper
Paper TowelsTissuesPaperboard
  • Plastic

BankCardsBottleCaps

PlasticPlastic Bags

Polystyrene BlockYogurt Pots
  • Plastic Wraps

  • Textiles

/CarpetClothes












reference: www.recyclingnj.com



طبقه بندی: اطلاعات پلیمری،
برچسب ها: polymer، recycling، plastic،

تاریخ : سه شنبه 19 بهمن 1395 | 10:28 ب.ظ | نویسنده : Arash Sadeghi | نظرات

Bottle Caps

Bottle caps are removed and discarded prior to the recycling of plastic or glass bottles and most refuse companies require you to remove the bottle cap before putting the bottle in your recycling box.

Plastic bottles are made from either polyethylene terephthalate (plastic #1) or high density polyethylene (plastic #2) but the plastic caps themselves can be made from high density polyethylene (plastic #2), low density polyethylene (plastic #4) or most often from polypropylene (plastic #5).

The polyethylene caps are the caps that you can deform easily if you squeeze or bend them with your fingers. These can be included with the plastic bottles in your recycling collection. An example of a polyethylene cap, is the flat cap commonly found on the top of plastic milk jugs. These caps push on to the top of the bottle rather than having a screw thread. Caps with a screw thread are usually made from polypropylene.

Polypropylene caps are much harder and more rigid than polyethylene caps, often with a screw on thread, and should not be included in your curbside recycling collection. If you try to bend these caps with your fingers the plastic will only bend a small amount. Polypropylene cap examples are detergent bottle caps, screw caps on soda, water bottles and toothpaste tubes or the flip top caps on shampoo bottles or other cosmetics products.

If you are not sure what type of plastic the cap is made from then place the cap in your general trash and recycle just the bottle.


reference : http://www.recyclingnj.com/



طبقه بندی: پلاستیک ها،
برچسب ها: Bottle Caps، Bottle، Caps، plastic، pp، polymer،

تاریخ : سه شنبه 19 بهمن 1395 | 10:25 ب.ظ | نویسنده : Arash Sadeghi | نظرات

What Are Synthetic Polymers?

Check out these images of useful, everyday items. Do you notice anything that they have in common? For one, all these compounds are super strong, cheap, and easy to make. Secondly, they are all examples of this video's topic: synthetic polymers! But what is a synthetic polymer?

Let's break the term apart to discover the definition. To start, a compound that is synthetic is man-made and produced by chemical reactions. Synthetic compounds may be made as exact replicas of naturally occurring compounds like vitamin C, or they may be unique compounds like plastic.

To talk about polymers, imagine a paperclip chain. If you've got time (and lots of paperclips), you can just make one instead of thinking about it! A paperclip chain is like a polymer. It is a long, strong chain made of many paperclips hooked together. By definition, a polymer is a compound that is made of many small repeating units bonded together. In our case, the small repeating units are the paper clips.

We use the scientific term 'monomer' to describe the small, repeating units used to make up a polymer. Polymers usually consist of tens of thousands of monomers, all bonded together. Huge molecules like these are often referred to as macromolecules. Our world is loaded with naturally occurring polymers, like cellulose (the stuff in plant fibers), DNA (the molecule that contain our genes), and silk.

Now, we can put our two terms together! A synthetic polymer is a man-made macromolecule that is made of thousands of repeating units. Sometimes these polymers are straight-chained, like our paperclip chain example, and consist of one long chain of monomers bonded end to end.

Sometimes polymers are both straight-chained and branched. This means that neighboring chains will bond with each other and make vast, net-like structures. This type of bonding between chains is called crosslinking.

Synthetic polymers are lightweight, hard to break, and last a long time. They are quite cheap to make and easy to form into shapes.

One of the most common and versatile polymers is polyethylene. It is made from ethylene (also known as ethene) monomers. In polymer form, the double bond between the carbons is lost and a chain is formed between repeating units of two carbons, each bonded to two hydrogens.

Polymer chain
Polymer chain

Sometimes for brevity's sake, the polymer chain is represented like the image you see here, with a large pair of parentheses around the monomer. You'll notice that there is an n in the bottom right hand corner outside the parenthesis. This n can represent any number. It could be 5 or 10,000! Often times, it is just left as a simple n to show it is a polymer of varying length.

Polyethylene is used to make plastics of all sizes and shapes, from piping to bottles to toys. And if you've ever dealt with these pesky things, then you know polyethylene!

Examples

Polyethylene has a pretty popular cousin, named polyethylene terephthalate (abbreviated PET or PETE). You might recognize PET from our intro! PET is commonly used for packaging liquids, especially sodas. PET is also used to make plastics that need to tolerate extreme temperatures.

PET is a great example of a thermoplastic. Thermoplastics are solid until heated to a certain temperature. When they get to that special temperature, they can be molded into any shape. Once they cool, their shape is set. Thermoplastics can be melted down once they are used up or no longer needed, and reshaped! This process is known as recycling.

Maybe you've seen these symbols on some plastics? They tell you several things. First, the item is a thermoplastic. Also, the number represents the type of polymer. And lastly, this symbol lets you know that this is very recyclable! Next time you are using something in a plastic bottle, look for one of these symbols. Then when you're finished using the plastic bottle, make sure to recycle it




طبقه بندی: اطلاعات پلیمری،
برچسب ها: polymer، monomers، material، plastic، synthetic، polymers،

تاریخ : سه شنبه 7 دی 1395 | 12:43 ق.ظ | نویسنده : Arash Sadeghi | نظرات
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