General Concepts Chapter 2

1. General ConceptsChapter 2 Professor Joe Greene CSU, CHICO MFGT 144

2. Chapter 2 Objectives • Objectives • Monomers and Polymerization • Homopolymers • Amorphous State • Crystallinity • Cross-linking and Molecular Networks • Copolymers • Polyalloys • Fillers, Reinforcements • Additives

3. Bonding e- e- e- e- H H H H H C C e- e- e- e- e- e- e- e- e- e- H H e- H • Covalent bonding (most important for plastics) • Occurs when two nonmetal atoms are in close proximity. • Both atoms have a tendency to accept electrons, which results in shared outer electron shells of the two atoms. • Number of shared electrons is usually to satisfy the octet rule. • Resulting structure is substantially different that the individual atoms, e.g., C and H4 make CH4, a new and distinct molecule. • Atoms is covalent bonds are not ions since the electrons are shared rather than transferred as in ionic or metallic bonds. e-

4. Bonding • Secondary bonding: weaker than ionic, metallic, covalent • Hydrogen bonding • Occurs between the positive end of a bond and the negative end of another bond. • Example, water the positive end is the H and the negative end is O. • van der Waals • Occurs due to the attraction of all molecules have for each other, e.g. gravitational. Forces are weak since masses are small • induced dipole • Occurs when one end of a polar bond approaches a non-polar portion of another molecule.

5. Naming Organic Compounds • Basis for naming organic compounds • Indicate the family of organic compounds to which a molecule belongs (importance to polymers) • Dependent upon functional group, e.g. alcohol group, methanol or methyl alcohol. • Dependent upon the number of carbon atoms in the repeating molecule. Number Counting Carbons Counting functional groups • 1 C Meth mono • 2 C Eth Di • 3 C Pro Tri • 4 C But Tetra • 5 C Pent Penta • Example, • CH4 has one carbon and no functional groups (alkane), thus is meth ‘ane. • C2H2 has 2 carbons and has a double bond (alkene), thus is eth ‘ene.

6. Monomers and Polymerization H H H H H H Polyethylene polymer (powder or solid) H H C C C C C C C C …... H H H H H H H H • Polymers are formed from a • monomer, which is a small (low MW) molecules with inherent capability of forming • chemical bonds with the same or other monomers in such a manner that long chains (polymer chains or macromolecules) are formed • Typical polymer chains involves hundreds or thousands of monomeric molecules Ethylene Monomer (gas) Polymerization …... Heat, pressure, catalyst

7. Definition of Plastics • Plastics come from the Greek plastikos, which means to form or mold. • Plastics are solids that flow (as liquid, molden, or soften state) when heat is applied to material. • Polymers are organic materials that come from repeating molecules or macromolecules • Polymer materials are made up of “many” (poly) repeating “units”(mers). • Polymers are mostly based in carbon, oxygen, and hydrogen. Some have Si, F, Cl, S • Polymers are considered a bowl of spaghetti or a bag of worms in constant motion.

8. Polymerization Mechanisms • Chain Growth (Addition) Polymerization • Polymerization begins at one location on the monomer by an initiator • Instantaneously, the polymer chain forms with no by-products • Step-wise (Condensation) Polymerization • Monomers combine to form blocks 2 units long • 2 unit blocks form 4, which intern form 8 and son on until the process is terminated. • Results in by-products (CO2, H2O, Acetic acid, HCl etc.)

9. Condensation Polymerization Example • Polyamides • Condensation Polymerization • Nylon 6/6 because both the acid and amine contain 6 carbon atoms NH2(CH2)6NH2 + COOH(CH2)4COOH Hexamethylene diamene Adipic acid n[NH2(CH2)6NH2 ·CO(CH2)4COOH] (heat) Nylon salt [NH(CH2)4NH·CO(CH2)4CO]n + nH2O Nylon 6,6 polymer chain

10. Polymerization Methods • 4 Methods to produce polymers • Some polymers have been produced by all four methods • PE, PP and PVC are can be produced by several of these methods • The choice of method depends upon the final polymer form, the intrinsic polymer arrangement (isotactic, atactic, etc), and the yield and throughput of the polymer desired. • Bulk Polymerization • Solution Polymerization • Suspension Polymerization • Emulsion Polymerization

11. Formation of Polymers H H H H H H H H H H C C C C C C C C C C H H H Cl CH3 H H H H n n n n n • Polymers from Addition reaction • LDPE HDPE PP • PVC PS

12. Other Addition Polymers O O O O C n • Polyetheretherketone (PEEK) • Wholly aromatic structure • Highly crystalline • High temperature resistance

13. Other Addition Polymers O O O S S S Cl Cl CH2 CH2 • Polyphenylene • Polyphenylene oxide • Poly(phenylene sulfide) • Polymonochloroparaxylyene

14. Other Addition Polymers H H H Y C C C C H H X X H H H Cl C C C H Cl H Cl H H C C H OCOCH3 • Vinyl- Large group of addition polymers with the formula: • Radicals (X,Y) may be attached to this repeating vinyl group as side groups to form several related polymers. • Polyvinyls • Polyvinyl chloride • Polyvinyl dichloride (polyvinylidene chloride) • Polyvinyl Acetate (PVAc) or C

15. Formation of Polymers • Condensation Polymerization • Step-growth polymerization proceeds by several steps which result in by-products. • Step-wise (Condensation) Polymerization • Monomers combine to form blocks 2 units long • 2 unit blocks form 4, which intern form 8 and son on until the process is terminated. • Results in by-products (CO2, H2O, Acetic acid, HCl etc.)

16. Common Polymer Synthesis • Polyamides • Condensation Polymerization • Nylon 6/6 because both the acid and amine contain 6 carbon atoms NH2(CH2)6NH2 + COOH(CH2)4COOH Hexamethylene diamene Adipic acid n[NH2(CH2)6NH2 ·CO(CH2)4COOH] (heat) Nylon salt [NH(CH2)4NH·CO(CH2)4CO]n + nH2O Nylon 6,6 polymer chain

17. Nylon Family • The repeating -CONH- (amide) link is present in a series of linear, thermoplastic Nylons • Nylon 6- Polycaprolactam: • [NH(CH2)5CO]x • Nylon 6,6- Polyhexamethyleneadipamide: • [NH(CH2)6NHCO (CH2)4CO]x • Nylon 12- Poly(12-aminododecanoic acid) • [NH(CH2)11CO]x

18. Polycarbonate O CH3 CH2 C CH2 OH Phenol + Acetone Bisphenol-A + water OH OH C 2 CH2 • Polycarbonates are linear, amorphous polyesters because they contain esters of carbonic acid and an aromatic bisphenol (C6H5OH) • Polymerized with condensation reaction + H2O +

19. Polycarbonate nCOCl2 + CH2 O CH2 Bisphenol-A + Phosgene Polycarbonate + salt OH OH C C O O C CH2 CH2 n + NaCl

20. Condensation Polymerization O O • Polyhydroxyethers (Phenoxy)- Reaction of Bisphenol A and epichlorohydrin. Similar to polycarbonate. Sold as thermoplastic epoxide resins. H H H CH2 C C C C H OH H CH2 n

21. Other Condensation Polymers O O O O R C R C O O R C R C • Thermoplastic Polyesters • Saturated polyesters (Dacron). • Linear polymers with high MW and no crosslinking. • Polyethylene Terephthalate (PET). Controlled crystallinity. • Polybutylene Terephthalate (PBT). • Aromatic polyesters (Mylar)

22. Other Condensation Polymers O SO2 • Polysulfones- Repeating unit is benzene rings joined by sulfone groups (SO2), an isopropylidene group (CH3CH3C), and an ether linkage (O). CH3 O C CH3 n

23. Characteristics of Addition and Condensation • Table 2.4

24. Polymerization by other than Addition or Condensation • Ring opening • Epoxy is created via ring opening to generate active species and initiate polymerization. • Epoxy plus amine produces epoxy polymerization • Nylon 6 is formed when caprolactam ring is opened. • Acetal polymer is made by the opening of the trioxane ring.

25. Polymer Length • Polymer notation represents the repeating group • Example, -[A]-DP where A is the repeating monomer and DP represents the number of repeating units. • Molecular Weight • Way to measure the average chain length of the polymer • Defined as sum of the atomic weights of each of the atoms in the molecule. • Example, • Water (H2O) is 2 H (1g) and one O (16g) = 2*(1) + 1*(16)= 18g/mole • Methane CH4 is 1 C (12g) and 4 H (1g)= 1*(12) + 4 *(1) = 16g/mole • Polyethylene -(C2H4)-1000 = 2 C (12g) + 4H (1g) = 28g/mole * 1000 = 28,000 g/mole =MW • Polystyrene -(C2H3)(C6H5) 1000 = 8C (12g) +8H(1g) = 104 g/mole *1000 Then MW = 104,000 = DP x M1 = 1000 * 104 = 104,000

26. Molecular Weight • Average Molecular Weight • Polymers are made up of many molecular weights or a distribution of chain lengths. • The polymer is comprised of a bag of worms of the same repeating unit, ethylene (C2H4) with different lengths; some longer than others. • Polyethylene -(C2H4)-1000 has some chains (worms) with 1001 repeating ethylene units, some with 1010 ethylene units, some with 999 repeating units, and some with 990 repeating units. • The average number of repeating units or chain length is 1000 repeating ethylene units for a MW of 28*1000 or 28,000 g/mole .

27. Molecular Weight • Average Molecular Weight • Distribution of values is useful statistical way to characterize polymers. • For example, • Value could be the heights of students in a room. • Distribution is determined by counting the number of students in the class of each height. • The distribution can be visualized by plotting the number of students on the x-axis and the various heights on the y-axis.

28. Molecular Weight • Molecular Weight Distribution • Count the number of molecules of each molecular weight • The molecular weights are counted in values or groups that have similar lengths, e.g., between 100,000 and 110,000 • For example, • Group the heights of students between 65 and 70 inches in one group, 70 to 75 inches in another group, 75 and 80 inches in another group. • The groups are on the x-axis and the frequency on the y-axis. • The counting cells are rectangles with the width the spread of the cells and the height is the frequency or number of molecules • Figure 3.1 • A curve is drawn representing the overall shape of the plot by connecting the tops of each of the cells at their midpoints. • The curve is called the MolecularWeight Distribution (MWD)

29. Molecular Weight • Average Molecular Weight • Determined by summing the weights of all of the chains and then dividing by the total number of chains. • Average molecular weight is an important method of characterizing polymers. • 3 ways to represent Average molecular weight • Number average molecular weight • Weight average molecular weight • Z-average molecular weight

30. Gel Permeation Chromatography • GPC Used to measure Molecular Weights • form of size-exclusion chromatography • smallest molecules pass through bead pores, resulting in a relatively long flow path • largest molecules flow around beads, resulting in a relatively short flow path • chromatogram obtained shows intensity vs. elution volume • correct pore sizes and solvent critical

31. Gel Permeation Chromatography

32. Number Average Molecular Weight, Mn • where Mi is the molecular weight of that species (on the x-axis) • where Ni is the number of molecules of a particular molecular species I (on the y-axis). • Number Average Molecular Weight gives the same weight to all polymer lengths, long and short. • Example, What is the molecular weight of a polymer sample in which the polymers molecules are divided into 5 categories. • GroupFrequency • 50,000 1 • 100,000 4 • 200,000 5 • 500,000 3 • 700,000 1

33. Molecular Weight • Number Average Molecular Weight. Figure 3.2 • The data yields a nonsymmetrical curve (common) • The curve is skewed with a tail towards the high MW • The Mn is determined experimentally by analyzing the number of end groups (which permit the determination of the number of chains) • The number of repeating units, n, can be found by the ratio of the Mn and the molecualr weight of the repeating unit, M1, for example for polyethylene, M1 = 28 g/mole • The number of repeating units, n, is often called the degree of polymerization, DP. • DP relates the amount of monomer that has been converted to polymer.

34. Weight Average Molecular Weight, Mw • Weight Average Molecular Weight, Mw • Favors large molecules versus small ones • Useful for understanding polymer properties that relate to the weight of the polymer, e.g., penetration through a membrane or light scattering. • Example, • Same data as before would give a higher value for the Molecular Weight. Or, Mw = 420,000 g/mole

35. Z- Average Molecular Weight • Emphasizes large molecules even more than Mw • Useful for some calculations involving mechanical properties. • Method uses a centrifuge to separate the polymer • Example Calculations • Mn and Mw and Polydispersity = Mw/Mn

36. Molecular Weight Distribution • Molecular Weight Distribution represents the frequency of the polymer lengths • The frequency can be Narrow or Broad, Fig 2.3 • Narrow distribution represents polymers of about the same length. • Broad distribution represents polymers with varying lengths • MW distribution is controlled by the conditions during polymerization • MW distributions can be symmetrical or skewed.

37. Physical and Mechanical Property Implications of MW and MWD • Higher MW increases • Tensile Strength, impact toughness, creep resistance, and melting temperature. • Due to entanglement, which is wrapping of polymer chains around each other. • Higher MW implies higher entanglement which yields higher mechanical properties. • Entanglement results in similar forces as secondary or hydrogen bonding, which require lower energy to break than crosslinks.

38. Physical and Mechanical Property Implications of MW and MWD • Higher MW increases tensile strength • Resistance to an applied load pulling in opposite directions • Tension forces cause the polymers to align and reduce the number of entanglements. If the polymer has many entanglements, the force would be greater. • Broader MW Distribution decreases tensile strength • Broad MW distribution represents polymer with many shorter molecules which are not as entangled and slide easily. • Higher MW increases impact strength • Impact toughness or impact strength are increased with longer polymer chains because the energy is transmitted down chain. • Broader MW Distribution decreases impact strength • Shorter chains do not transmit as much energy during impact

39. Thermal Property Implications of MW & MWD • Higher MW increases Melting Point • Melting point is a measure of the amount of energy necessary to have molecules slide freely past one another. • If the polymer has many entanglements, the energy required would be greater. • Low molecular weights reduce melting point and increase ease of processing. • Broader MW Distribution decreases Melting Point • Broad MW distribution represents polymer with many shorter molecules which are not as entangled and melt sooner. • Broad MW distribution yields an easier processed polymer Melting Point Mechanical Properties * Decomposition MW MW

40. Melt Index • Melt index test measure the ease of flow for material • Procedure • Heat cylinder to desired temperature (melt temp) • Add plastic pellets to cylinder and pack with rod • Add test weight or mass to end of rod (5kg) • Wait for plastic extrudate to flow at constant rate • Start stop watch (10 minute duration) • Record amount of resin flowing on pan during time limit • Repeat as necessary at different temperatures and weights

41. Melt Index and Viscosity • Melt index is similar to viscosity • Viscosity is a measure of the materials resistance to flow. • Viscosity is measured at several temperatures and shear rates • Melt index is measured at one temperature and one weight. • High melt index = high flow = low viscosity • Low melt index = slow flow = high viscosity • Example, (flow in 10 minutes) PolymerTempMass • HDPE 190C 10kg • Nylon 235C 1.0kg • PS 200C 5.0Kg

42. Melt Index and Molecular Weight • Melt index is related closely with average molecular weight • High melt index = high flow = small chain lengths = low Mn • Low melt index = slow flow = long chain lengths = high Mn • Table 3.1 Melt Index and Average Molecular Weight MnMelt Index* (g/10min) • 100,000 10.00 • 150,000 0.30 • 250,000 0.05 * Note: PS at T= 200C and mass= 5.0Kg

43. States of Thermoplastic Polymers • Amorphous- Molecular structure is incapable of forming regular order (crystallizing) with molecules or portions of molecules regularly stacked in crystal-like fashion. • A - morphous (with-out shape) • Molecular arrangement is randomly twisted, kinked, and coiled

44. Amorphous Materials • PVC Amorphous • PS Amorphous • Acrylics Amorphous • ABS Amorphous • Polycarbonate Amorphous • Phenoxy Amorphous • PPO Amorphous • SAN Amorphous • Polyacrylates Amorphous

45. States of Thermoplastic Polymers • Crystalline- Molecular structure forms regular order (crystals) with molecules or portions of molecules regularly stacked in crystal-like fashion. • Very high crystallinity is rarely achieved in bulk polymers • Most crystalline polymers are semi-crystalline because regions are crystalline and regions are amorphous • Molecular arrangement is arranged in a ordered state

46. Crystalline Materials • LDPE Crystalline • HDPE Crystalline • PP Crystalline • PET Crystalline • PBT Crystalline • Polyamides Crystalline • PMO Crystalline • PEEK Crystalline • PPS Crystalline • PTFE Crystalline • LCP (Kevlar) Crystalline

47. Factors Affecting Crystallinity Course Fine • Crystallization is time-dependent process • Several factors affect the speed at which it takes place (kinetics), but also the resulting morphology which can occur as course or fine grains. (Fig 2.10) • Density increases with increased crystallinity • Factors • Cooling Rate from mold temperatures • Barrel temperatures • Injection Pressures • Drawing rate and fiber spinning: Manufacturing of thermoplastic fibers causes Crystallinity • Application of tensile stress for crystallization of rubber Density Semi-cryst Amorphous Crystalline Crystallinity

48. Form of Polymers Melt Temp Tm Rubbery Increasing Temp Tg Glassy Polymer Form • Thermoplastic Material: A material that is solid, that possesses significant elasticity at room temperature and turns into a viscous liquid-like material at some higher temperature. The process is reversible • Polymer Form as a function of temperature • Glassy: Solid-like form, rigid, and hard • Rubbery: Soft solid form, flexible, and elastic • Melt: Liquid-like form, fluid, elastic

49. Glass Transition Temperature, Tg • Glass Transition Temperature, Tg: The temperature by which: • Below the temperature the material is in animmobile(rigid) configuration • Above the temperature the material is in a mobile (flexible) configuration • Transition is called “Glass Transition” because the properties below it are similar to ordinary glass. • Transition range is not one temperature but a range over a relatively narrow range (10 degrees). Tg is not precisely measured, but is a very important characteristic. • Tg applies to all polymers (amorphous, crystalline, rubbers, thermosets, fibers, etc.)

50. Glass Transition Temperature, Tg Amorphous Modulus (Pa) or (psi) Crystalline Tg Tg Tg -50C 50C 100C 150C 200C 250C -50C 50C 100C 150C 200C 250C Temperature Temperature • Glass Transition Temperature, Tg: Defined as • the temperature wherein a significant the loss of modulus (or stiffness) occurs • the temperature at which significant loss of volume occurs Vol.