POLYMERS “Plastics”

1. POLYMERS“Plastics” Third Generation CAPT Science Preparation for Strand II: Chemical Structures and Properties

2. What is a Polymer? Any of numerous natural and synthetic compounds of usually high molecular weight consisting of up to millions of repeated linked units (monomers), each a relatively light and simple molecule.

3. Polymerization • Polymerization is the process of combining many small molecules known as monomers into a covalently bonded chain.

4. Natural Polymers(Biopolymers) Examples: • Cellulose • Shellac • Amber • Proteins • Nucleic Acids

5. Synthetic Polymers Examples: • Nylon • Neoprene • PVC • Polystyrene • Silicone • Silly Putty ®

6. Fractional Distillation • Plastics (synthetic polymers) can come from crude oil. Within crude oil are many different substances such as gasoline, jet fuel, heating fuel etc. To separate these the fractions or parts the mixture is heated. When each part or fraction’s boiling point is reached, that part comes off as a vapor and is separated from the mixture.

7. Cracking • We do not obtain enough gasoline from fractional distillation but the yield can be increased by cracking. In cracking, longer-chain hydrocarbons like lubricants (16+ carbon atoms) are broken into shorter chained fractions like gasoline with 5 to 12 carbons (ex. Octane = C8H18)

8. Some Common Synthetic Polymers

9. Resin Identification Code Symbol AbbreviationPolymer Type PET or PETE Polyethylene Terephthalate HDPE High Density Polyethylene PVC Polyvinyl Chloride or Vinyl LDPE Low Density Polyethylene PP Polypropylene PS Polystyrene Other Polymers or blends of polymers that do not fall into the other 6 classifications.

10. Properties of Polymers • Polymers can be very resistant to chemicals. • Polymers can be both thermal and electrical insulators. • Generally, polymers are very light in weight with significant degrees of strength.

11. Testing Plastics • tensile strength - theamount of pulling force placed upon a material before it breaks • abrasion resistance - toughness of material against scraping, scuffing or scarring • puncture resistance - ability of a material to keep moving objects from perforating the surface

12. Properties of Polymers cont. • Polymers can be processed in various ways. • Polymers are materials with a seemingly limitless range of characteristics and colors. • Polymers are usually made of petroleum, but not always. • Polymers can be used to make items that have no alternatives from other materials.

13. Three factors that influence the degree of crystallinity (or “stiffness”) are: • Chain length • Chain branching • Interchain bonding The importance of the first two factors is nicely illustrated by the differences between HDPE and LDPE.

14. HDPE: High Density Polyethyleneand LDPE: Low Density Polyethylene • POLYETHYLENE • produced in greater quantity than any other synthetic polymer • resistant to chemical attack, cheap to produce

15. HDPE vs LDPE • HDPE is composed of very long unbranched hydrocarbon chains. These pack together easily in crystalline domains that alternate with amorphous segments, and the resulting material, while relatively strong and stiff, retains a degree of flexibility. • In contrast, LDPE is composed of smaller and more highly branched chains which do not easily adopt crystalline structures. This material is therefore softer, weaker, less dense and more easily deformed than HDPE. As a rule, mechanical properties such as ductility, tensile strength, and hardness rise and eventually level off with increasing chain length.

17. Cross-linking • Cross-linked Polymers have a web-like pattern as in a net or hammock • Properties: extremely strong and difficult to tear • Ex’s like Threaded bottle caps, and Rubber tires are Thermoset Polymers

18. Rubber Tires: Example of Cross-linking • Vulcaniztion involves cross-linking rubber. By adding sulfur, rubber becomes more durable and prevents the polymer from moving independently so that when a stress is applied the rubber deforms but reverts back to its original shape when the stress is released.

19. Thermoset Polymers A Thermoset is a polymer that solidifies or “sets” irreversibly when heated or cured. A thermoset polymer can’t be softened once “set”. Thermosets are valued for their durability and strength and are used extensively in automobiles and construction including applications such as adhesives, inks, and coatings. The most common thermoset is the rubber truck and automobile tire.

20. Thermoplastic Polymers A Thermoplastic is a polymer in which the molecules are held together by weak secondary bonding forces that soften when exposed to heat and return to its original condition when cooled back down to room temperature. When a thermoplastic is softened by heat, it can then be shaped by extrusion, molding, or pressing. Examples include milk jugs and carbonated soft drink bottles.

21. The End Life of PolymersDurables vs. Non-Durables • Products with a useful life of three years or more are referred to as durables. They include appliances, furniture, consumer electronics, automobiles, and building and construction materials. • Products with a useful life of less than three years are generally referred to as non-durables. Common applications include packaging, trash bags, cups, eating utensils, sporting and recreational equipment, toys, medical devices and disposable diapers.

22. What do we do with Polymers when they are no longer useful?Three Optionsand their consequences • Disposal in a landfill • Incinerate • Recycle

23. Disposal in a landfill Polymers are fairly resistant to chemicals and therefore would take a very long time to decompose if just buried in a landfill. In the meantime, the waste polymers take up a lot of space and could possibly decompose or react with other materials that might eventually result in compounds that could be potentially harmful to the environment.

24. Incinerate The burning (combustion) of polymers produces harmful gases that are toxic to the environment.

25. Recycle - The best choice! • Mechanical Recycling • Feedstock Recycling • Source Reduction

26. Mechanical Recycling Once collected, reclamation is the next step where the plastics are chopped into flakes, washed to remove contaminants and sold to end users to manufacture new products such as bottles, containers, clothing, carpet, plastic lumber, etc.

27. Feedstock Recycling Pyrolysis (heating without oxygen) and other chemical recycling is a special case where condensation polymers such as PET or nylon are chemically reacted to form starting materials.

28. Source Reduction Use less! • Redesign products and packaging that uses less polymer material. • Reduce the amount the amount of polymer products that are purchased. • Clean and Reuse the polymer products that have been purchased.

29. What is the first question you are asked at the grocery store checkout: paper or plastic?

31. Paper bags can be recycled. Plastic bags are being recycled in many places, with about 50% of supermarkets now having recycling programs for plastic bags. However, a stack of 1,000 paper bags is 46 inches high and weigh 140 pounds. A stack of 1,000 plastic bags is only 4 inches tall and weighs 16 pounds. That is a 124 pound savings. When you translate these weight and volume differences into transportation efficiencies, it takes seven trucks to haul the same number of paper bags as can be hauled by only one truck carrying plastic ones.

32. Convinced you should stick with plastic bags ? • Extra credit points to attend the 5:30 pm showing of the movie “Bag-It” at the Darien Library, this Sunday March 5. • There will be a sign-in sheet.