Department of Chemistry CHEM1020 General Chemistry ***********************************************

1. Department of Chemistry CHEM1020 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 Tel: 931-6325 Email: hzhang@tntech.edu

2. CHEM1020/General Chemistry_________________________________________Chapter 10. (L11)-Organic Chemistry • Today’s Outline ..Properties of polymers crystalline and amorphous polymers glass-transition temperature fiber-forming properties ..Disposal of plastics incineration degradable plastics recycling ..Plastics and fire hazards ..Plasticizers and pollution ..Plastics and future

3. Chapter 10. (L11)-Organic Chemistry • Properties of polymers …Crystalline polymers: Their molecules line up neatly to form long fibers of high tensile strength. -good for synthetic fibers …Amorphous polymers: Composed of randomly oriented molecules that get tangled up with one another. -good for elastomers

4. Chapter 10. (L11)-Organic Chemistry • Properties of polymers …Glass transition temperature A property of most thermoplastic polymers …Glass transition temperature, Tg, is the temperature above which the polymer is rubbery and tough, but below which the polymer is like glass, hard, stiff, and brittle. Each polymer has its won characteristic glass transition T. at Troom > Tg, polymer is rubbery and tough at Troom < Tg, polymer is glassy, hard, stiff, brittle

5. Chapter 10. (L11)-Organic Chemistry • Fiber-forming properties of polymers …Synthetic fibers are much better in many ways than natural fibers such as wool, silk, cotton. stronger, chemical and biological resistant, durable, less expensive, non-shrinking, easy to care, etc.

6. Chapter 10. (L11)-Organic Chemistry • Disposal of plastics …Downsides of plastics: Persistently existing in the environments after dumped, causing many environmental problems. …Where plastic trash go? -landfills, ~8% of solid waste is plastics by mass but, ~21% by volume -incineration, burning plastics (to generate energy in some cases). But, burning can generate hazardous emissions, e.g., PVC burning can lead to toxic HCl gas.

7. Chapter 10. (L11)-Organic Chemistry • Disposal of plastics …Degradable plastics Make plastic package materials biodegradable or photodegradable, thus naturally decomposed in nature. Most biodegradable plastics are starch-based synthetic polymers. Photodegradable plastics usually contain a light-sensitive additive.

8. Chapter 10. (L11)-Organic Chemistry • Disposal of plastics …Recycling Probably the best way to handle the plastic trash problem The plastics are collected, sorted, chopped, melted, and then remolded. Separation of plastics trash by coding At present, HDPE milk jugs are recycled at large scales

9. Chapter 10. (L11)-Organic Chemistry • Disposal of plastics …Recycling, you can do it, please do it. Separation of plastics trash by coding PlasticsCode PET 1 HDPE 2 PVC 3 LDPE 4 PP 5 PS 6 All others 7

10. Chapter 10. (L11)-Organic Chemistry • Plastics and fire hazards …flammable fabrics, potential hazards burning plastics also generate toxic emissions. development of heat-resistant fabrics. details on pp. 296 of the book.

11. Chapter 10. (L11)-Organic Chemistry • Plasticizers and pollution …Plasticizer is a chemical that can make polymers more flexible and less brittle by lowing the glass transition temperature. Plasticizers are liquids of low volatility and are generally lost lost by diffusion and evaporation as a plastic article ages.

12. Chapter 10. (L11)-Organic Chemistry • Plasticizers and pollution …Examples of plasticizers -PCBs, polychlorinated biphenyls. -The structures of PCBs are similar to that of DDT. -PCB is electric resistant. -PCBs are degrading very slowly in the environment. -PCBs are soluble in non-polar media, making them easily accumulate in food chain. PCBs residues have been found in fish, birds, water, sediments, and in air. -The toxicity of PCB may be similar to DDT. -Monsanto Co. is the only company making PCBs in USA, discontinued its production in 1977, but they are still in the environment today.

13. Chapter 10. (L11)-Organic Chemistry • Plastics and future …More polymers are coming. …Environmental consequences of polymers in our life …Restriction of the resources. Most synthetic polymers are made from petroleum or natural gas, which are non-renewable natural resources. The big question, when petroleum and natural gas are used up, then what? …Sustainable development. Conservation.

14. Chapter 10. (L11)-Organic Chemistry • Plastics and future …For us ourselves or for our children of generations to come? …For today, or for tomorrow, centuries to come? …Lots of debate and thinking and reasoning.

15. Chapter 10. (L11)-Organic Chemistry Quiz Time The glass transition temperature is the temperature (a) at which a piece of glass becomes hot; (b) at which a piece of glass is broken; (c) above which the polymer is rubbery and tough, but below which the polymer is like glass, hard, stiff, and brittle; (d) at which a piece of glass becomes cold.

16. Chapter 10. (L11)-Organic Chemistry Quiz Time Burning plastics by means of incineration can cause (a) a slower turning of the earth; (b) no environmental pollution at all; (c) release of toxic substances into the environment through emissions; (d) none of above is relevant.

17. Chapter 10. (L11)-Organic Chemistry Quiz Time PCB in polymer chemistry refers to (a) pizza cutting board; (b) public climate broadcasting; (c) personal computer board; (d) polychlorinated biphenyls.

18. Chapter 10. (L11)-Organic Chemistry Quiz Time PCB is (a) an inorganic chemical; (b) an easily degradable chemical; (c) a plasticizer; (d) a chemical of no use.