1. Pull thin polymer rod in tension 1 1 2 2 3 3 4 4 5 5 Get alignment of crystalline regions

2. Polymer fibers have aligned crystalline regions - alignment gives greater strength to fiber Polymer fibers have aligned crystalline regions - alignment gives greater strength to fiber

3. Kevlar is highly aligned Polymer fibers have aligned crystalline regions - alignment gives greater strength to fiber Polymer fibers have aligned crystalline regions - alignment gives greater strength to fiber

4. Breaking strength of polymer fibers (tenacity) 1.measure denier (wt. in grams of 9000 meters of fiber) 2.run tensile test Breaking strength of polymer fibers (tenacity) 1.measure denier (wt. in grams of 9000 meters of fiber) 2.run tensile test

5. Tenacity increases w/ chain length - fewer crystal defects

6. Polymer stiffness, strength and toughness vary over extraordinary range Stress/strain characteristics of polymers

7. Polymer stiffness, strength and toughness vary over extraordinary range Due to structure - ranges from purely amorphous states to chain folded semi- crystalline to highly oriented (fibers) Polymer stiffness, strength and toughness vary over extraordinary range Due to structure - ranges from purely amorphous states to chain folded semi- crystalline to highly oriented (fibers) Stress/strain characteristics of polymers

8. Polymer stiffness, strength and toughness vary over extraordinary range Due to structure - ranges from purely amorphous states to chain folded semi- crystalline to highly oriented (fibers) Polymers plastically deform readily, esp. if temp raised (often less than 100 0 C ) Polymer stiffness, strength and toughness vary over extraordinary range Due to structure - ranges from purely amorphous states to chain folded semi- crystalline to highly oriented (fibers) Polymers plastically deform readily, esp. if temp raised (often less than 100 0 C ) Stress/strain characteristics of polymers

9. x x x Glassy polymer or semi-crystalline polymer below Tg Semi-crystalline polymer above Tg Rubber Stress (  ) Strain (  )

10. Yielding in flexible semi-crystalline polymers Yielding in flexible semi-crystalline polymers Flexible semi- crystalline polymers such as polyethylene (T g of amorphous domains is below rm temp) usually display considerable amount of yielding if not stretched too quickly Stress Yield Point Strain

11. Relaxation Yielding due to relaxation Time dependent molecular transition or rearrangement, such as change in conformation of a chain, crystalline slip, chain sliding, usw. Yielding due to relaxation Time dependent molecular transition or rearrangement, such as change in conformation of a chain, crystalline slip, chain sliding, usw.

12. Yielding in rigid polymers Stress Yield Point Strain Rigid polymers usually don't have yield point May yield by crazing Rigid polymers usually don't have yield point May yield by crazing

13. Crazing Microscopic cracks form perpendicular to applied stress

14. Crazing Microscopic cracks form perpendicular to applied stress Tiny fibrils span cracks - hold material together Microscopic cracks form perpendicular to applied stress Tiny fibrils span cracks - hold material together

15. Crazing Microscopic cracks form perpendicular to applied stress Tiny fibrils span cracks - hold material together Polymer whitens Microscopic cracks form perpendicular to applied stress Tiny fibrils span cracks - hold material together Polymer whitens

16. Polymers aren’t very stiff

17. Stiffness dictated by structure

18. Stiffness depends on crystallinity crosslinking T g Stiffness depends on crystallinity crosslinking T g

19. For fibers, stiffness depends on draw ratio For fibers, stiffness depends on draw ratio

20. Tensile strength

21. Glass transition temperature (T g )

22. Molecular wt.

23. Glass transition temperature (T g ) Chemical structure

24. Glass transition temperature (T g ) Chain stiffness

25. Glass transition temperature (T g ) Chain stiffness

26. Glass transition temperature (T g ) Bulky side groups