Presentation on theme: "POLYMERS “Plastics” Third Generation CAPT Science Preparation for"— Presentation transcript:
1POLYMERS “Plastics” Third Generation CAPT Science Preparation for Strand II: Chemical Structures and Properties
2What 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.
3PolymerizationPolymerization is the process of combining many small molecules known as monomers into a covalently bonded chain.
6Fractional 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.
7CrackingWe 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)
9Resin Identification Code Symbol Abbreviation Polymer TypePET or PETE Polyethylene TerephthalateHDPE High Density PolyethylenePVC Polyvinyl Chloride or VinylLDPE Low Density PolyethylenePP PolypropylenePS PolystyreneOther Polymers or blends of polymers that do not fall intothe other 6 classifications.
10Properties 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.
11Testing Plasticstensile strength - the amount of pulling force placed upon a material before it breaksabrasion resistance - toughness of material against scraping, scuffing or scarringpuncture resistance - ability of a material to keep moving objects from perforating the surface
12Properties 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.
13Three factors that influence the degree of crystallinity (or “stiffness”) are: Chain lengthChain branchingInterchain bondingThe importance of the first two factors is nicely illustrated by the differences between HDPE and LDPE.
14HDPE: High Density Polyethylene and LDPE: Low Density Polyethylene produced in greater quantity than any other synthetic polymer resistant to chemical attack, cheap to produce
15HDPE vs LDPEHDPE 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.
17Cross-linkingCross-linked Polymers have a web-like pattern as in a net or hammockProperties: extremely strong and difficult to tearEx’s like Threaded bottle caps, and Rubber tires are Thermoset Polymers
18Rubber 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.
19Thermoset PolymersA 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.
20Thermoplastic 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.
21The End Life of Polymers Durables 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.
22What do we do with Polymers when they are no longer useful What do we do with Polymers when they are no longer useful? Three Options and their consequencesDisposal in a landfillIncinerateRecycle
23Disposal in a landfillPolymers 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.
24IncinerateThe burning (combustion) of polymers produces harmful gases that are toxic to the environment.
25Recycle - The best choice! Mechanical RecyclingFeedstock RecyclingSource Reduction
26Mechanical RecyclingOnce 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.
27Feedstock RecyclingPyrolysis (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.
28Source 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.
29What is the first question you are asked at the grocery store checkout: paper or plastic?
31Paper bags can be recycled 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.
32Convinced 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.