ENGR-45_Lec-30_Polymer-Apps.ppt 1 Bruce Mayer, PE Engineering-45: Materials of Engineering Bruce Mayer, PE Licensed Electrical & Mechanical Engineer Engineering 45 Polymer Applications

ENGR-45_Lec-30_Polymer-Apps.ppt 2 Bruce Mayer, PE Engineering-45: Materials of Engineering Learning Goals – Polymer Apps  Learn How Microstructure affects Room Temperature Tensile Stress Behavior  Understand Hardening, Anisotropy, and Annealing in Polymers  How the elevated-temperature mechanical-response for PolyMers compares to Ceramics and Metals

ENGR-45_Lec-30_Polymer-Apps.ppt 3 Bruce Mayer, PE Engineering-45: Materials of Engineering PolyMer Tensile σ-ε Response  PolyMers Exhibit 3 Basic Types of Tensile Response A.Brittle → Glass-Like Linear-Elastic Very Small Strain at Fracture B.Elastic-Plastic → Metal-Like Well-Defined Yielding Significant Strain at Fracture C.Elastomeric → Rubber-Like Completely Elastic; all the way to fracture Very Large Strains

ENGR-45_Lec-30_Polymer-Apps.ppt 4 Bruce Mayer, PE Engineering-45: Materials of Engineering Tensile Response – Brittle & Plastic 0 unload/reload 0 brittle failure plastic failure  (MPa)  x x semi- crystalline case amorphous regions elongate crystalline regions align crystalline regions slide 8 onset of necking aligned, cross- linked case networked case Initial Near Failure near failure

ENGR-45_Lec-30_Polymer-Apps.ppt 5 Bruce Mayer, PE Engineering-45: Materials of Engineering Tensile Response – Elastomers  Compare Elastomers to responses of other polymers: BRITTLE response (aligned, cross-linked & networked case) PLASTIC response (semi-crystalline case) initial: amorphous chains are kinked, heavily cross-linked. final: chains are straight, still cross-linked  (MPa)  8 x x x elastomer plastic failure brittle failure Deformation is reversible!

ENGR-45_Lec-30_Polymer-Apps.ppt 6 Bruce Mayer, PE Engineering-45: Materials of Engineering T & StrainRate - ThermoPlastics  DEcreasing Temp Increases E Increases TS Decreases %EL  INcreasing Strain Rate... Same effects as decreasing Temperature °C 20°C 40 60°C to 1.3  (MPa)  Data for the semicrystalline polymer: PMMA (Plexiglas)

ENGR-45_Lec-30_Polymer-Apps.ppt 7 Bruce Mayer, PE Engineering-45: Materials of Engineering PreDeformation by Drawing  Drawing stretches the polymer prior to use aligns chains to the stretching direction  Results of drawing Increases the elastic modulus (E) in the stretching direction Increases the tensile strength (TS) in the stretching direction Decreases ductility (%EL)

ENGR-45_Lec-30_Polymer-Apps.ppt 8 Bruce Mayer, PE Engineering-45: Materials of Engineering Vulcanization  Chemically Induced Cross-Linking Process in Elastomers is called VULCANIZATION An Irreversible Chemical Reaction Performed at Elevated Temperature Thru a Cross Linking Agent; Typically Sulfur  Typically Requires More than ONE S-atom per Cross-Link  Vulcanization at the 1-5 wt%-S level improves Elastomer Properties Including Wear & Strength (e.g., Tires)

ENGR-45_Lec-30_Polymer-Apps.ppt 9 Bruce Mayer, PE Engineering-45: Materials of Engineering Time Dependent Deformation  Stress Relaxation Test Rapidly deform to Strain ε 0, and Hold Measure Hold-Stress as a Function of Time  The Hold-Stress Decreases with Time Due to “unkinking” of the PolyMer chains Where –σ 0  Stress at time-0 –   Time Constant; i.e., the time required for the stress to drop by 63%

ENGR-45_Lec-30_Polymer-Apps.ppt 10 Bruce Mayer, PE Engineering-45: Materials of Engineering Relaxation Modulus  Given Stress Relaxation  Next Pick a BaseLine time, Say 10s, and Vary Temperature to  Define a Time- Dependent RELAXATION Modulus

ENGR-45_Lec-30_Polymer-Apps.ppt 11 Bruce Mayer, PE Engineering-45: Materials of Engineering Relaxation Modulus vs Temperature  Glassy State Material is RIGID and BRITTLE ELASTIC Stretching of Bonds  Leathery State some Sliding of chains over one another some Permanent deformation deformation will be time- dependent and not totally recoverable

ENGR-45_Lec-30_Polymer-Apps.ppt 12 Bruce Mayer, PE Engineering-45: Materials of Engineering Relaxation Modulus vs Temp cont.1  Rubbery Plateau deforms in a rubbery manner both elastic and viscous behavior straightening out of polymer chains gives large strains strain is reversible due to crosslinks and entanglements

ENGR-45_Lec-30_Polymer-Apps.ppt 13 Bruce Mayer, PE Engineering-45: Materials of Engineering Relaxation Modulus vs Temp cont.2  Rubbery flow and Viscous flow high temperature states polymer chains slide over each other permanent deformation is possible (molding)

ENGR-45_Lec-30_Polymer-Apps.ppt 14 Bruce Mayer, PE Engineering-45: Materials of Engineering Glass Transition Temperature  Notice on the E r vs T curve the almost VERTICAL Slope at the Center of the Leathery, or Tough Regime  This marks the Transition from a Brittle, amorphous State to a ViscoElastic Condition

ENGR-45_Lec-30_Polymer-Apps.ppt 15 Bruce Mayer, PE Engineering-45: Materials of Engineering The Glass Transition Temp Temperature Specific Volume = 1/ρ (cu-m/kg) TgTg TmTm Note Change in Slope  NonCrystalline Material T < Tg → Rigid, Glass-Like Tg < T < Tm → Rubbery or Leathery T > Tm → Melted, Liquid

ENGR-45_Lec-30_Polymer-Apps.ppt 16 Bruce Mayer, PE Engineering-45: Materials of Engineering Structure-Property Relationships  Ease of MOVEMENT of molecular chains affects properties crystallinity (ability to pack efficiently) Tg (onset of large-scale molecular motion) Glass-forming ability Strength vs. Flexibility

ENGR-45_Lec-30_Polymer-Apps.ppt 17 Bruce Mayer, PE Engineering-45: Materials of Engineering Structure-Property Relns cont.  STRUCTURAL factors that inhibit molecular motion: Complexity of the Mer Size of Side Groups Branching, Crosslinking Configuration Bonding Entanglements Possible organization of PolyEthylene polymer chains Crystalline Region Amorphous Tie Region

ENGR-45_Lec-30_Polymer-Apps.ppt 18 Bruce Mayer, PE Engineering-45: Materials of Engineering WhiteBoard Work  Prob Similar to  Vulcanize P olyIsoPrene with Sulfur Given –57 wt%-S combined with the polymer –Six Sulfur atoms per CrossLink on Average Determine CrossLinks per Isoprene Mer Natural rubber (cis- polyisoprene) before vulcanizing with sulfur

ENGR-45_Lec-30_Polymer-Apps.ppt 19 Bruce Mayer, PE Engineering-45: Materials of Engineering IsoPrene Polymerization

ENGR-45_Lec-30_Polymer-Apps.ppt 20 Bruce Mayer, PE Engineering-45: Materials of Engineering σ-ε vs. T for FluoroPolymer