Polymer Characterization - Laboratory Techniques and Analysis-03

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3 MICROSCOPY FOR 
POLYMER CHARACTERIZATION 
GENERAL INFORMATION 
This chapter provides general information on the use of microscopic 
techniques for polymer characterization. For polymer blends a minimum 
domain size of 1 pm can be examined in the optical microscope using 
one or more of the following techniques. A schematic of a typical 
optical microscope is shown in Figure 1. 
1. 
2. 
3. 
4. 
Phase contrast--Thin sections (100-200 nm) in thickness (and 
having refractive indices which differ by approximately .OOS) are 
supported on glass slides and examined “as is” or with oil to 
remove microtoming artifacts, e.g., determination of the number 
of layers in coextruded films, dispersion of fillers, and polymer 
domain size. (Figures 2 and 3) 
Polarized light--Is used if one of the polymer phases is 
crystalline or for agglomeration of inorganic filters, (e.g., 
nylon/EP blends and fillers such as talc. (Figure 4) 
Incident--Is used to examine surfaces of bulk samples, e.g., 
carbon black dispersion in rubber compounds. (Figure 5) 
Bright Jield--Mainly used to examine thin sections of carbon 
black loaded samples, e.g., carbon black dispersion in thin films 
of rubber compounds. 
When the domain size is in the range of < 1 pm to lOrmr, scanning 
electron microscopy (SEM) and/or transmission electron microscopy 
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26 Polymer Characterization 
(TEM) are necessary. A schematic of a scanning electron microscope is 
shown in Figure 6. 
Samples in the SEM can be examined “as is” for general 
morphology, as freeze fractured surfaces or as microtome blocks of solid 
bulk samples. Contrast is achieved by any one or combination of the 
following methods: 
1. Solvent etching--When there exists a large solubility difference 
in a particular solvent of the polymers being studied, e.g., 
PP/EP blends. 
2. 0,0, Staining--There exists at least 5% unsaturation in the 
polymers being investigated, e.g., NR/EPDM, BIIR/Neoprene. 
(Figure 7) 
3. RuO, Staining--When there is no solubility differences or 
unsaturation this possibility is explored, e.g., knit explored line 
between two DVA’s (dynamic vulcanized alloys). (Figure 8) 
In addition, the SEM can be used to study liquids or temperature 
sensitive polymers on a Cryostage. 
The SEM is also used to do X-ray/elemental analysis. This 
technique is qualitative. X-ray analysis and mapping of the particular 
elements present is useful for the identification of inorganic fillers and 
their dispersion in compounds as well as inorganic impurities in gels or 
on surfaces and curatives, e.g., aluminum, silicon, or sulfur in rubber 
compounds and Cl and Br in halobutyl blends. (Figure 9) 
TEM (schematic shown in Figure 10) is used whenever a more in- 
depth study (when domain sizes are less than 1 micron or so) is required 
on polymer phase morphologies such as dynamically vulcanized alloys 
(Figure 11) and Nylon/EP (Figure 12) filler location as in carbon black 
in rubber compounds (Figure 13) and also in the morphology of block 
copolymers (Figure 14). Thin sections are required and take anywhere 
from one hour to one day per sample depending on the nature of the 
sample. They must be - 100 run in thickness and are prepared usually 
by microtoming with a diamond knife at near liquid nitrogen 
temperatures (-150°C). The same contrasting media for SEM apply to 
TEM. In addition, PIB backbone polymers scission and evaporate in the 
TEM which helps locate these polymers domains in blends. 
Microscopy for Polymer Characterization 27 
NON-ROUTINE TECHNIQUES 
Solvent casting when microtoming is not desirable as a method 
of sample preparation. 
SZ73W-Used for elemental composition study in thin films when 
better resolution is required than X-ray analysis in the SEM on 
bulk samples. 
Cryostage - SEM--To study liquid samples at low temperatures, 
e.g., butyl slurry. 
Fluorescence microscope--Useful in examining polymer/asphalt 
blends or any sample which is fluorescent. 
OM/Hot stage--To observe melting point of either an impurity or 
other moiety in a compound. 
28 Polymer Characterization 
Light Source (Lamp) 
Condenser Lens 
Specimen 
Objective Lens 
Optical Microscope 
Figure 1. Schematic of an optical microscope. 
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30 Polymer Characterization 
CIIR = Crey Areas 
PP = White Areas 
Neoprene (CR) = Dark Areas 
Figure 3. Light microscopy phase contrast polymer domains chlorobutyl I 
polypropylene / neoprene blend (CIIR/PP/CR). 
Microscopy for Polymer Characterization 31 
; EP is light, 
, Dispersed Phase 
j Nylon is Dark 
Matrix 
Polarized Light 
(Shows Spherultic Structures) 
Figure 4. Light microscopy phase contrast nylon/EP blends. 
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Microscopy for Polymer Characterization 33 
illuminating Source 
(Electron Gun) 
Condenser Lens 
Obiective Lens A 
SpecimenF&2 V 
IJfhvtnr --m 
(/tide0 Amplifier 
Deflection Coils 
Figure 6. Schematic of a scanning electron microscope (SEM). 
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36 Polymer Characterization 
SEM image Si X-Ray Map 
Al X-Ray Map K X-Ray Map 
Figure 9. X-ray mapping of surface impurity. 
Microscopy for Polymer Characterization 37 
Light Source 
(Lamp) 
Condenser Lens 
- Illuminating Source 
(Electron Gun) 
Specimen * 
Objective Lens - 
Objective Lens 
Aperture 
Intermediate Lens 
Projector Lens 
Fluorescent 
Screen 
Figure 10. Schematic of a transmission electron microscope (TEM). 
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Microscopy for Polymer Characterization 39 
Figure 12. Phase morphology in a nylon/EP-MA blend by TEM. 
40 Polymer Characterization 
Figure 13. Location of carbon black in a blend of chlorobutyl and natural 
rubber & EPDM. 
Microscopy for Polymer Characterization 41 
Figure 14. REM-Ruthenium tetroxide stained graft copolymer.