Characteristics of Plastic Materials

1. Characteristics of Plastic Materials Chapter 10

2. Plastics – synthetic materials capable of being formed and molded to produce finished products. • Derived from many types of organic and inorganic materials • Most often from petroleum base stock or natural gas • Polystyrene – benzene and ethylene, both from petroleum

3. New plastics are constantly being developed • Many no longer depend on petroleum • Gargill Dow, LLC invented the first viable plastic made from sugar found in corn and sugar beets • Renewable resource • Corn is milled and starch is separated • Unrefined dextrose sugar is produced from starch • Dextrose is converted into lactic acid • Lactic acid is purified • Used in thermoforming, sheet and film extrusion, blown film processing, fiber spinning, and injection molding • Other plastics being developed using wheat, potatoes, green algae

4. Unique Characteristics of Plastics • Several characteristics that provide advantages over other materials: • About 1/8th the weight of steel (next slide) • Highly resistant to corrosion (do not deteriorate when exposed to environment) • Good thermals and electrical insulation (handles, electrical joints) • Minimal friction (when created with smooth surfaces, may never need lubrication) • Reduce energy consumption (use for insulation, saves millions of barrels of oil)

5. Weight Reduction Examples • 1977 – 2 liter plastic bottles weighed 68 grams • Today they weigh 51 grams • 25% reduction • 200-300 lbs of plastics in modern cars • If the 300 lbs of plastic were made of steel the car might weigh 2100 lbs more

6. The Development of Plastics • First synthetic plastic called Parkesine developed in 1862 • English chemist Alexander Parkes • Material could be heated and formed, then when cooled it retained it’s shape • Wanted to use it to replace rubber at a lower cost • Lost financial backing • New York, 1866 • Billiards company offered a $10,000 reward for a usable substitute for ivory to make billiards balls • John Hyatt discovered the same combination as Parkes • Patented celluloid in 1869 • Was used for dental plates, vehicle windshields and motion picture film • Unfortunately it was highly flammable

7. First real industrial application called Bakelite, introduced in 1907 • American chemist Dr. Leo Baekeland • Thermoset phenolic resin • Would not burn, boil, melt or dissolve in any known acid or solvent • Could not be remelted • Used through WWII • Telephone housings • Pan handles

8. By 1940, plastic had replaced metals, wood, glass, leather, paper and rubber in many products • Many new varieties of plastics introduced • 1981, Malden Mills and Patagonia create a synthetic sheep skin called Polar Fleece

9. Plastics made from petrochemical resources create disposal and recycling challenges • Biodegradable polymers (from starches) are designed to be more environmentally friendly • Uses for recycled plastics are growing rapidly • Demand for products greater than the amount of recycled plastics

10. Making Industrial Stock Resin - any of a class of solid or semi-solid organic products of natural or synthetic origin, generally of high molecular weight with no definite melting point Plastic – one of many natural or synthetic, high polymeric products (excluding rubber), that are capable of flowing under heat and pressure, into a desired shape • Often confused • Manufacturer starts with resin in liquid, pellet, granule, or powdered form, and uses it to form or create the plastic material that will be the final product

11. Commodity Resins • Standard grade resins • Includes most thermoplastic and thermoset resins • Used to make common day items • Containers • Toys • Household items

12. Engineering Resins • High performance resins in various grades • Advanced • Intermediate • Commodity • Advanced grades are most resistant to chemical attack, extreme heat, and impact • Scientific lab equipment • Helmets (sports) • Reheatable food containers

13. Structure of Plastic • Hundreds of resins and compounds • Each manufacturer is able to customize their product for specific applications • All plastics are polymers Polymer – long chain molecule made up of thousands of smaller molecules linked together called monomers Monomer – simple molecules Different combinations of monomers = different polymers

14. Major Classes of PlasticsThermoplastics • Long discrete chains of molecules that melt to a viscous liquid at a specific processing temperature (240°F - 700°F) • Softening and hardening cycles are reversible • Formed into desired shape, pellet, bar, tube, etc. • Then reformed into products

16. Thermosets • Chemically reactive in their fluid state and harden through further reaction called curing • Once cured, cannot be returned to a fluid state • Kept partially cured before final forming • High dimensional stability • High temperature resistance • Excellent resistance to solvents

18. Plastic Memory • The capability of a material to return to its original shape after it is bent or formed • Heat is applied after a material has been deformed to activate it’s memory • PVC has a very high plastic memory

19. Creep • The slow and continuous increase in length at the point of deformation, over a period of time, when a material is placed under a steady load and constant temperature • Cold flow – when creep takes place at room temp

20. How Creep Takes Place • A plastic bar, 2 inch square by 6 foot long • Ends are fastened to cement blocks • One pound weight is placed on the center of the bar • The plastic will naturally sag (called elastic deformation) • If the weight is removed quickly the bar will return to its original shape • If the weight is left on the bar for a period of time, the bar will continue to sag at a slow rate