Download - Characterizing Polymers
Mechanical Properties of Polymers
Characterizing Polymers
Mini-tutorial
First step in characterizing a polymer:
Use your senses (take pictures to document)What color? Does it
fluoresce Transparent or opaque?Homogeneous in appearance?Solid or
liquidTacky or sticky or brittle or toughMass compare with
theoretical yield
Describe the material below
Describe the material below
Second, try and dissolve the polymer in different solvents
Water, ethanol, benzene, methylene chloride, tetrahydrofuran,
acetonitrile, hexane, acetone, diethyl ether, dimethyl sulfoxide,
N-methyl pyrrolidone (NMP)Leave it at room temp overnight. Look for
swelling if not dissolved.Boil solvent for 4 hours.If it doesnt
dissolve its probably cross-linked or really crystalline
Types of Polymers & solubility
Wont dissolve
Will dissolve
Third, Structural Characterization of soluble polymers
1H & 13C & 29Si Nuclear Magnetic Resonance and infrared
spectroscopyMolecular weight by gel permeation
chromatographyComposition by combustion analysesX-ray diffraction
on film or powderViscosity of dilute solutions- shape of
polymer
X-ray diffraction
Semi-crystalline polymer shows diffraction rings
amorphous polymer shows diffuse band
Or third, Structural Characterization of insoluble
polymers
Harder to characterizeSolid state 1H & 13C & 29Si Nuclear
Magnetic Resonance and infrared spectroscopyComposition by
combustion analysesX-ray diffraction on film or powder
Morphological Characterization of polymers
If opaque or transluscent, SEM and optical microscopy
(bifringence)-crystalline or amorphous & more.Fracture polymer
and look at fracture surfacesLook for phase separation (like
immiscible block copolymers)Look for long range orderLook for
pores
Thermal characterization of polymers
Thermal gravimetric analyses (TGA) determines decomposition
temperature
Differential scanning calorimetry (DSC) detects phase changes
(melting or glass transition temperatures) or chemical
reactions
DSC analysis
Thermal gravimetric analysis
Mechanical characterization of polymers
Stress-strain curves:Youngs modulus (brittleness)Tensile
strength-pull sample appart Flexural strength- bend until it
breaksCompressive strength-crush sample Dynamic mechanical analyses
(same info as above but with cyclic application of stress or
strain.Generate modulus temperature curvesFatigue studies to
predict failure under cyclic stress
Elongation by extension of neck
Chains in neck align along elongation direction:
strengthening
Stress-Strain Analysis
Tensile strength = pull sample appart
27
Stress relaxation test:
--strain to eo and hold.--observe decrease in stress with
time.
Relaxation modulus:
Data: Large drop in Er for T > Tg.
(amorphouspolystyrene)
Sample Tg(C) values:
PE (low Mw)PE (high Mw)PVCPSPC
-110- 90+ 87+100+150
Adapted from Fig. 15.7, Callister 6e. (Fig. 15.7 is from A.V.
Tobolsky, Properties and Structures of Polymers, John Wiley and
Sons, Inc., 1960.)
Selected values from Table 15.2, Callister 6e.
TIME DEPENDENT DEFORMATION
Not every polymer needs all of these analyses, but structure is
the most basic and important
Known (described in literature) polymers need less structural
characterization. Often just IR and Mw from GPC.
New polymers need complete structural characterization: NMR, IR,
Combustion analysis, GPC, solubility, glass transition temp and/or
melting point.
Morphological and Mechanical studies are dependent on research
interests.
If you are interested in strong polymers, then morphological,
mechanical & thermal studies are importantOther applications
requiring morphological, mechanical & thermal studies would
include preparation and testing of 1) membranes, 2) coatings, 3)
paint, 4) polymer foams, 5) organic photovoltaics, 6) OLEDs, 7)
adhesives and 8) low friction coatings
Other polymer properties that are important for specialty
polymers
Coatings, packaging, membranes, Photovoltaics & OLEDs; gas and
water permeability should be measured.Battery and fuel cell
membranes: gas & water permeability and ion
conductivityDielectrics, wiring insulation: dielectric and
electrical conductivityFabrics & building materials: fire
resistanceAny polymer used in sunlight or radiation or in the
presence of chemicals: resistance to oxidative
degradation.