Nicholas P. Cheremisinoff,
We,hc.od, 11ew.l.ny, U.S.A.
Copyright 0 1996 by Noyes Publications
No part of this book may be reproduced or utilized in
any form or by any means, electronic or mechanical,
including photocopying, recording or by any information storage and retrieval system, without petmission
in writing from the Publisher.
Library of Congress Catalog Card Number: 96010912
Printed in the United States
Published in the United States of America by
369 Fairview Avenue
Westwood, New Jersey 07675
Library of Congress Cataloging-in-Publication
Cheremisinoff, Nicholas P.
Polymer characterization : laboratory techniques and analysis / by
Nicholas P. Cheremisinoff.
is a private consultant to industry,
academia, and government. He has nearly twenty years of
industry and applied research experience in elastomers,
synthetic fuels, petrochemicals manufacturing, and environmental control. A chemical engineer by trade, he has authored
over 100 engineering textbooks and has contributed extensively
to the industrial press. He is currently working for the United
States Agency for International Development in Eastern
Ukraine, where he is managing the Industrial Waste Management Project. Dr. Cheremisinoff received his B.S., M.S., and
Ph.D. degrees from Clarkson College of Technology.
Nicholas P. Cheremisinoff
To the best of our knowledge the information in this publication is accurate; however, the Publisher does not assume
any responsibility or liability for the accuracy or completeness
of, or consequences arising from, such information. This book
is intended for informational purposes only. Mention of trade
names or commercial products does not constitute endorsement
for use by the Publisher. Final determination of the suitability of any information or product for use
contemplated by any user, and the manner of that use, is the
sole responsibility of the user. We recommend that anyone intending to rely on any recommendation
of materials or procedures mentioned in this publication should satisfy himself as
to such suitability, and that he can meet all applicable safety
and health standards.
This volume provides an overview of polymer characterization
test methods. The methods and instrumentation described
represent modern analytical techniques useful to researchers,
product development specialists, and quality control experts
in polymer synthesis and manufacturing. Engineers, polymer
scientists and technicians will find this volume useful in
selecting approaches and techniques applicable to characterizing molecular, compositional, rheological, and thermodynamic properties of elastomers and plastics.
It is essential that both R&D laboratories as well as quality
control functions be versed in the various techniques described
in this book in order to properly design their products and to
ensure the highest quality polymers on the market place. This
volume is particularly useful in introducing standard polymer
characterization laboratory techniques to technicians and engineers beginning their careers in polymer manufacturing and
product development areas.
A large portion of this volume is comprised of appendices
providing definitions of testing and product characterization
terms. These sections are intended to provide the reader with
a practical source of fundamental information. The author
wishes to extend gratitude to Linda Jastrzebski for her
assistance in organizing and typesetting this book.
Nicholas P. Cheremisinoff
1. CHROMATOGRAPHIC TECHNIQUES ...............
Chromatography for Analytical Analyses ............
Gas Chromatography ..........................
Types of Gas Chromatography ..................
Liquid Chromatography ........................
Types of Liquid Chromatography ................
Type of Information Obtained ...................
Gel Permeation Chromatography ..................
Submitting Samples .........................
2. THERMAL ANALYSIS ..........................
General Principles of Operation ..................
Thermal Analysis of Polymers ...................
Differential Scanning Calorimetry(DSC) ..........
ThermogravimetricAnalysis (TGA) ..............
Thermomechanical Analysis (TMA) ..............
Dynamic Mechanical Thermal Analysis (DMTA) ....
MICROSCOPY FOR POLYMER
General Information ..........................
Non-Routine Techniques .......................
4. ELEMENTAL AND STRUCTURAL
CHARACTERIZATION TESTS ....................
Atomic Absorption Spectroscopy .................
Inductively Coupled Plasma Atomic Emission
Ion Chromatography (IC) ......................
Ion Selective Electrodes (ISE) ...................
Mass Spectrometry (MS and GC/MS) .............
Nuclear Magnetic Resonance Spectrometer ..........
Established Methods by ‘H NMR ...............
Fourier Transform Infrared (FI’IR) ...............
Ultraviolet, Visible, and Infrared Spectrometry
(UV, Vis, IR) ..............................
X-Ray Fluorescence Spectrometry ................
Potentiometric Titrations .......................
Neutron Activation Analysis .....................
5. RHEOMETRY .................................
Rheometrics System IV ........................
Capillary Rheometry ..........................
Torque Rheometry ...........................
6. CHEMICAL ANALYSIS OF POLYMERS ............
Comminution, Separation, and Identification ........
Stabilizer Identification .......................
Polymer Identification ........................
APPENDIX A: ABBREVIATIONS OF POLYMERS . . . . . . . 105
APPENDIX B: GLOSSARY OF POLYMERS
AND TESTING . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . 107
APPENDIX C: PROFESSIONAL AND TESTING
ORGANIZATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
American National Standards Institute (ANSI) . . . . . . 117
American Society for Testing and
Materials (ASTM) .........................
Food and Drug Administration (FDA) ............
National Bureau of Standards (NBS) .............
National Electrical Manufacturers
Association (NEMA) ........................
National Fire Protection Association (NFPA) .......
National Sanitation Foundation (NSF) ............
Plastics Technical Evaluation Center (Plastec) ......
Society of Plastics Engineers (SPE) ...............
Society of Plastics Industry (SPI) ................
Underwriters Laboratories (UL) .................
APPENDIX D: GLOSSARY OF ENGINEERING AND MATERIALS
TERMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
FOR ANALYTICAL ANALYSES
Chromatography may be defined as the separation of molecular mixtures
by distribution between two or more phases, one phase being essentially
two-dimensional (a surface) and the remaining phase, or being a bulk
phase brought into contact in a counter-current fashion with the twodimensional phase. Various types of physical states of chromatography
are possible, depending on the phases involved.
Chromatography is divided into two main branches. One branch is
gas chromatography, the other is liquid chromatography.
chromatography can be further subdivided as shown in Figure 1.
The sequence of chromatographic separati.on is as follows: A sample
is placed at the top of a column where its components are sorbed and
desorbed by a carrier. This partitioning process occurs repeatedly as the
sample moves towards the outlet of the column. Each solute travels at
its own rate through the column, consequently, a band representing each
solute will form on the column. A detector attached to the column’s
outlet responds to each band. The output of detector response versus
time is called a chromatogram. The time of emergence identifies the
component, and the peak area defines its concentration, based on
calibration with known compounds.
If the moving phase is a gas, then the technique is called gas
chromatography (GC). In gas chromatography the sample is usually
Figure 1. Shows types of chromatographic operations.
_ .- _ -
injected at high temperature to ensure vaporization. Obviously, only
materials volatile at this temperature can be analyzed.
Types of GC
If the stationary phase is a solid, the technique is referred to as gas-solid
chromatography. The separation mechanism is principally one of adsorption. Those components more strongly adsorbed are held up longer
than those which are not.
If the stationary phase is a liquid, the technique is referred to as gasliquid chromatography and the separation mechanisms is principally one
of partition (solubilization of the liquid phase).
Gas chromatography has developed into one of the most powerful
analytical tools available to the organic chemist. The technique allows
separation of extremely small quantities of material (lO+jgrams).
The characterization and quantitation of complex mixtures can be
accomplished with this process. The introduction of long columns, both
megabore and capillary, produces a greater number of theoretical plates
increasing the efficiency of separation beyond that of any other available
The technique is applicable over a wide range of temperatures (-40-35072) making it possible to chromatograph materials
covering a wide range of volatiles. The laboratory uses packed columns
along with megabore and capillary. In this way the broadest range of
chromatographic problems can be addressed.
The detector used to sense and quantify the effluent provides the
specificity and sensitivity for the analytical procedure.
summarizes significant detector characteristics.
If the moving phase is a liquid, then the technique is called liquid
chromatography (LC). In liquid chromatography the sample is first
dissolved in the moving phase and injected at ambient temperature. Thus
there is no volatility requirement for samples. However, the sample
must dissolve in the moving phase. Note that LC has an important
advantage over GC: The solubility requirement can usually be met by
SUMMARY OF DETECTOR CHARACTERISTICS
conductivity of gas
6 x 10.lo
10esgm of CH,
per vol. of
H, - 0, Flame
organic compounds, not to
Hz0 or fixed
9 x lo5 for alkane
2 x lo-” gm for
N2 + B+ee- + Sample +
2 x lo-l4 for CCL 4
iMinimum detectable quantity.
In halogen mode
1 x lOI g cllsec
changing the moving phase. The volatility requirement is not so easily
Types of LC
There are four kinds of liquid chromatography, depending on the nature
of the stationary phase and the separation mechanism:
Liquid/Liquid Chromatography (LLC)--is partition chromatography or solution chromatography. The sample is retained by
partitioning between mobile liquid and stationary liquid. The
mobile liquid cannot be a solvent for the stationary liquid. As
a subgroup of liquid/liquid chromatography there is paper
Liquid/Solid Chromatography (LX)--is adsorption chromatography. Adsorbents such as alumina and silica gel are packed in
a column and the sample components are displaced by a mobile
phase. Thin layer chromatography and most open column chromatography are considered liquid/solid chromatography.
Zon-ExchangeChromatography--employszeolites and synthetic
organic and inorganic resins to perform chromatographic
separation by an exchange of ions between the sample and the
resins. Compounds which have ions with different affinities for
the resin can be separated.
Exclusion Chromatography--is another form of liquid
chromatography. In the process a uniform nonionic gel is used
to separate materials according to their molecular size. The
small molecules get into the polymer network and are retarded,
whereas larger molecules cannot enter the polymer network and
will be swept our of the column. The elution order is the largest
molecules first, medium next and the smallest sized molecules
last. The term “gel permeation chromatography” has been
coined for separations polymers which swell in organic solvent.
The trend in liquid chromatography has tended to move away from open
column toward what is called high pressure liquid chromatography
(HPLC) for analytical as well as preparative work. The change in
technique is due to the development of high sensitivity, low dead volume
detectors. The result is high resolution, high speed, and better sensitivity
Type of Information Obtained
The output of a chromatographic instrument can be of two types:
A plot of areas retention time versus detector response. The
peak areas represent the amount of each component present in
A computer printout giving names of components and the
concentration of each in the sample.
The units of concentration are reported in several ways:
Weight percent or ppm by weight.
Volume percent or ppm by volume.
Size--A few milligrams is usually enough for either GC or LC.
1. For GC, the sample can be gas, liquid, or solid. Solid samples are
usually dissolved in a suitable solvent; both liquid or solid samples
must volatilize at the operating temperature.
2. For LC, samples can be liquid or solid. Either must be soluble in
Moderately fast quantitative analyses (0.5-l .5 hours per sample).
Excellent resolution of various organic compounds.
Not limited by sample solubility.
Separation of high boiling compounds.
Not limited by sample volatility.
Moving phase allows additional control over separation.
Limited by sample volatility.
Less sensitive than GC.
Detectors may respond to solvent carrier, as well as to sample.
Interferences in chromatography can generally be overcome by finding
the right conditions to give separation. However, this might be costly,
since development of separations is largely a trial-and-error process.
For common linear homopolymers, such as PIB, PE, PS.. . , GPC analysis can be performed with a single DRI detector. Figure 2 shows the
basic component of a GPC/DRI System. Most often, a PS calibration
curve is generated from narrow molecular weight PS standards
(Figure 3), which can then be converted to the desired polymer (i.e.,
PIB, EP.. .) if the appropriate calibration constants are available. These
constants, known as the Mark-Houwink parameters or k and alpha, are
used to calculate the intrinsic viscosity of the polymer as a function of
molecular weight (which is needed to relate the size of one type of
polymer to another). If the Mark-Houwink parameters are not available,
the molecular weights can be used for relative comparison but will not
be correct on an absolute basis. If the sample is branched, the molecular
weights will be biased low, and a secondary detector (LALLS or VIS)
is needed for accurate results.
GEL PERMEATION CHROMATOGRAPHY
Gel Permeation Chromatography (GPC), also known as Size Exclusion
Chromatography (SEC), is a technique used to determine the average
molecular weight distribution of a polymer sample.
appropriate detectors and analysis procedure it is also possible to obtain
qualitative information on long chain branching or determine the
composition distribution of copolymers.
As the name implies, GPC or SEC separates the polymer according
to size or hydrodynamic radius. This is accomplished by injecting a
small amount of (100-400 ~1) of polymer solution (O.Ol-0.6%) into a set
of columns that are packed with porous beads. Smaller molecules can
penetrate the pores and are therefore retained to a greater extent than the
larger molecules which continue down the columns and elute faster.
This process is illustrated in Figure 4.
One or more detectors is attached to the output of the columns. For
routine analysis of linear homopolymers, this is most often a Differential
Refractive Index (DRI) or a UV detector. For branched or copolymers,
however, it is necessary to have at least two sequential detectors to
determine molecular weight accurately. Branched polymers can be
analyzed using a DRI detector coupled with a “molecular weight
sensitive” detector such as an on-line viscometer (VIS) or a low-angle
laser light scattering (LALLS) detector. The compositional distribution
of copolymers, i.e., average composition as a function of molecular size,
can be determined using a DRI detector coupled with a selective detector
( DETECTOR(S) 1
Figure 2. Basic components of GPC/DRI.
Figure 3. Typical calibration curve using a polystyrene (PS) standard.
Figure 4. Polymer solution flow through GPC column.
such as UV or FTIR. It is important to consider the type of polymer and
information that is desired before submitting a sample. The following
outline describes each instrument that is currently available.
One can use two instruments with sequential LALLS and DRI detectors.
The unit is operated using TCB at 135°C and is used to analyze PE, EP,
and PP samples. The other, operating at 60°C is for butyl type
polymers which dissolve in TCB at lower temperatures.
consists of two chromatograms, plots of detector mV signal (LALLS and
The DRI trace corresponds to the
concentration profile whereas the LALLS signal is proportional to
concentration *M, resulting in more sensitivity at the high molecular
weight end. An example of the output is shown in Figure 5 for
polyethylene NBS 1476. The LALLS trace shows a peak at the high
molecular weight end (low retention time) which is barely noticeable on
the DRI trace. This suggests a very small amount of high molecular
weight, highly branched material. This type of bimodal peak in the DRI
trace is often seen in branched EP (ethylene-propylene polymers) or
LDPE (low density polyethylene) samples. The report consists of two
result pages, one from the DRI calibration curve as described above, and
the second from the LALLS data. An example of a report page is shown
in Figure 6. At the top of the page should be a file name and date of
analysis. The header also includes a description of the method and
detector type, which in this case is the DRI detector and EP calibration
curve. Following the header are the parameters integration (i.e., start
and end times for integration and baseline) and a slice report (i.e.,
cumulative weight percent and molecular weight as a function of
retention time). This section gives details about the distribution, such as
the range of molecular weights for the sample and the fraction of
polymer above a particular molecular weight. At the bottom of the page
is a summary of the average molecular weights, whereas Z denotes the
Z average molecular weight or Mz, etc.
For a linear polymer (if all the calibration constants are known), the
molecular weights from both pages should agree within 10%. A LALLS
report that gives higher molecular weights than the DRI suggests that the
sample is branched, and the values from the LALLS report should be
used (again, assuming that the calibration constants are correct).
Occasionally, some of the sample, gel or insolubles, is filtered out during
the sample preparation and analysis. The percentage should be indicated
on the report.
GPC with an on-line viscometer can be used instead of a
detector to analyze branched polymers.
In this case the
viscosity is measured so that the Mark-Houwink parameters
needed. It is complementary to the LALLS instrument in
The UV detector is used to analyze chromophores. Its most common use
is for graft or block copolymers containing PS or PMS. The data from
this instrument consists of two chromatograms, the UV and DRI traces.
An example is shown in Figure 7 for an EPg-PS coploymer (peak 1)
with risidual PS homopolymer (peak 2). The UV absorption relative to
the DRI signal corresponds to the copolymer composition, which is why
the relative UV absorption is higher for the pure PS in peak 2. The
results report consists of two pages. One is the molecular weight report
from the DRI calibration curve as described above. Note that the
molecular weights are reported as if the sample is a homopolymer not
The other page using the UV data gives an effective
extinction coefficient E’ which is the UV/DRI ratio. A higher E’
3 Apr 1990
High Speed GPC
Detector - DRI
30 Mar 1990
Peak Parameters - Time, min
INST B EP TCB
Average Mol Wts
Peak Area, mv-set
Molecular Weight at Peak Max
Cum Wt Pet
Ratios of Averages
Cum Mol Pet
Time Iut Std Peak, min
Figure 6. Example of a report page.
indicates a higher composition of the UV active chromophore (for
example, more PS in the graft copolymer). This technique is also used
to determine the compositional distribution of ENB (ethylidene
norbonene) in EPDM, i.e., whether the ENB is evenly distributed across
the molecular weight distribution or concentrated in the low or high
molecular weight end. The GPC/DRI/UV instrument can be used to
analyze samples that dissolve in THF at 30-45°C.
The GPC/DRI/FTIR instrument is complementary to the UV detector for
compositional distribution. It runs at 135°C in TCB and can be used for
EP analysis. Typical applications include ethylene content as a function
of molecular weight, maleic anhydride content in maleated EP, or PCL
content in caprolactone-g-EP copolymers. The FTIR detector is off-line
so that 5-10 fractions of the eluant are collected on KBr plates and
analyzed. This procedure gives calibration of IR absorption bands. This
method is much more labor intensive than the other techniques and
should be used with discretion.
Samples should be weighed out (typically 30-120 pg) in bottles. The
submitter should check which is the appropriate amount for a particular
test. The sample should be labeled with the contents, exact amount of
polymer, and test type. Any other information, such as expected
molecular weight range, ENB or other monomer content, dissolution
temperature.. . , is helpful for optimizing the analysis. Typically, a single
GPC run takes approximately 2% hours, except for GPC/FTIR which
can take five hours for the fractionation and additional time for the FTIR
Thermal analysis refers to a variety of techniques in which a property of
a sample is continuously measured as the sample is programmed through
a predetermined temperature profile. Among the most common techniques are thermal gravimetric analysis (TA) and differential scanning
In TA the mass loss versus increasing temperature of the sample is
recorded. The basic instrumental requirements are simple: a precision
balance, a programmable furnace, and a recorder (Figure 1). Modern
instruments, however, tend to be automated and include software for data
reduction. In addition, provisions are made for surrounding the sample
with an air, nitrogen, or an oxygen atmosphere.
In a DSC experiment the difference in energy input to a sample and
a reference material is measured while the sample and reference are
subjected to a controlled temperature program. DSC requires two cells
equipped with thermocouples in addition to a programmable furnace,
recorder, and gas controller. Automation is even more extensive than in
TA due to the more complicated nature of the instrumentation and
A thermal analysis curve is interpreted by relating the measured
property versus temperature data to chemical and physical events
occurring in the sample. It is frequently a qualitative or comparative
In TA the mass loss can be due to such events as the volatilization
of liquids and the decomposition and evolution of gases from solids. The
onset of volatilization is proportional to the boiling point of the liquid.
The residue remaining at high temperature represents the percent ash
content of the sample. Figure 2 shows the TA spectrum of calcium
oxalate as an example.
Shows the TA spectrum
of a TA instrument.