1. PSE 406: Lecture 51 Wood Chemistry PSE 406 Lecture 5 Cellulose

2. PSE 406: Lecture 52 Ketoses α- D-fructopyranose β- D-fructofuranose

3. PSE 406: Lecture 53 Cellulose: the Basics Linear polymer made up of  -D glucopyranose units linked with  glycosidic bonds. lRepeating unit = glucose (cellobiose) lGlucopyranose units in chair form - most thermodynamically stable. Only less that 1% in other forms CH 2 OH and OH groups in equatorial positions  stability

4. PSE 406: Lecture 54 Cellulose: More Basics lCellulose is elongated and the glucose units in one plane for the following reasons:  linkages »The thermodynamic stability of the chair form Amylose (starch) occurs as a helix in solid state because of the  1-4 linkage.

5. PSE 406: Lecture 55 Reducing End Groups lEach cellulose chain has 1 reducing end group at the C1 position of the terminal glucopyranose unit lThe C4 position of the other terminal is not reducing. lDoes the reducing end mutarotate? »In fibers, probably not because of hydrogen bonding, etc. »In solution, probably Notes

6. PSE 406: Lecture 56 Cellulose: Molecular Weight Degree of Polymerization of Cellulose DP = molecular weight of cellulose molecular weight of one glucose unit l Determination of molecular weight requires isolation and solubilization of cellulose l Isolation procedures will modify (reduce) molecular weight l Various modification procedures used for isolation »Derivitize with a variety of agents »Metal complexes »Pulping »Solvent systems

7. PSE 406: Lecture 57 Degree of Polymerization Notes

8. PSE 406: Lecture 58 Carbons 6 x 12 = 72 Oxygen 6 x 16 = 96 Hydrogen 12 x 1 = 12 180 g/mole Molecular Weight Determination lDetermination of the molecular weight of the glucose molecule on the left is quite simple. lSimply count all of the atoms and add up the molecular weight.

9. PSE 406: Lecture 59 Molecular Weight of Mixtures 180g/mole 342g/mole 504g/mole 666g/mole lWhat if you have a mixture of 4 different chemicals and refer to it as a single compound like cellulose. What is the molecular weight?

10. PSE 406: Lecture 510 lThe simple answer to to question of molecular weight of mixtures is that you use an average of the molecular weights. This is known as the number average molecular weight. lAlthough this gives a number which is usable, it doesn’t completely describe the system. This is because you can obtain the same number average molecular weight with completely different mixtures. For example, a sample of all medium sized molecules and a mixtures of big and little molecules could give the same value. Molecular Weight of Mixtures Number Average Molecular Weight (Mn) Mn = weight # molecules =  NxMx  Nx

11. PSE 406: Lecture 511 Molecular Weight Equations Weight Average Molecular Weight (Mw) Mw =  CxMx  Cx =  NxMx)(Mx)  NxMx =  NxMx 2  NxMx lThe second method for determining molecular weight is the weight average method. This method gives values which are influenced by the amount of larger molecules. This equation is developed from the number average equation by replacing the number of molecules Nx by the weight of the molecules Cx. For examples on calculating molecular weight, see the end of this lecture.

12. PSE 406: Lecture 512 Polydispersity lPolydispersity is the ratio of the weight average molecular weight to the number average molecular weight. This value provides information on the distribution of molecular weights. Larger values indicate that you have a wide range of molecular weights while low values mean a narrow distribution. Polydispersity Polydispersity = Mw/Mn

13. PSE 406: Lecture 513 Lecture 5 Example Problems

14. PSE 406: Lecture 514 Molecular Weight: Example 1 1g/mole5g/mole10 g/mole Note: These values represent the molecular weight of each of spheres

15. PSE 406: Lecture 515 Cellulose Molecular Weight: Example 1 1. Number Average Mn Mn =  NxMx  Nx = (5)(1) + (5)(5) + (5)(10) 5+5+5 = 5.33 2. Weight Average Mw Mw =  CxMx  Cx = (5)(1) + (5)(5) + (5)(10) (5)(1)(1) + (5)(5) 2 + (5)(10) 2 = 7.875 3. Polydispersity = Mw Mn = 1.477

16. PSE 406: Lecture 516 Cellulose Molecular Weight: Example 2 1g/mole5g/mole10 g/mole

17. PSE 406: Lecture 517 Cellulose Molecular Weight: Example 2

18. PSE 406: Lecture 518 Cellulose Molecular Weight: Example 3 1g/mole5g/mole10 g/mole

19. PSE 406: Lecture 519 Cellulose Molecular Weight: Example 3

20. PSE 406: Lecture 520 Cellulose Molecular Weight: Example 4 1g/mole5g/mole10 g/mole 25 x

21. PSE 406: Lecture 521 Cellulose Molecular Weight: Example 4