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CHARACTERISATION
OF POLYMERS BY
THERMAL ANALYSIS
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CHARACTERISATION
OF POLYMERS BY
THERMAL ANALYSIS
W.M. GROENEWOUD
Eerste Hervendreef 32, 5232 JK 's Hertogenbosch
The Netherlands
ELSEVIER
Amsterdam. Boston 9London 9New Y o r k - O x f o r d 9Paris
San Diego. San Francisco. Singapore- Sydney- Tokyo
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ISBN:
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T r a n s f e r r e d to digital p r i n t i n g 2 0 0 5
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To Vera
for 36 years of love, support and continuous inspiration.
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PREFACE
The development of the Linear Variable Displacement Transducer
(LVDT) was a first order technological break-through after
centuries in optical length-difference measurments. The first
LVDT's became commercially available in Holland in 1959. Our
research team (I was a junior member) bought one LVDT for the
development of a length dilatometer to measure the change in
length of a polymer sample during a heating or cooling
procedure. The LVDT signal and (sample temperature)
thermocouple signal were recorded on an XY-recorder. Indeed,
we were very proud of our first 'automated' measuring system.
We did not yet call our system a Thermal Mechanical Analyser
(TMA) nor described our activities as 'Thermal Analysis'.
Nowadays, computer controlled dynamic and static TMA systems
are supplied by several manufacturers and perform completely
automated the measuring and data handling procedures required.
This story illustrates the huge technological development
during the last forty years. Thermal Analysis (TA) has become
an indispensable family of analytical techniques in polymer
research. This increased importance of these techniques can be
seen as the result of three more or less parallel
developments:
a tempestuous development of TA measuring techniques in
combination with a high degree of automation,
- the strongly increased understanding of the underlying
theory, published by authors like Wunderlich, Hohne,
Richardson and Mathot [1,2] and
- the increasing knowledge of the relation between the
polymers' chemical structure and their physical properties.
These developments still continue and a lot of work has yet to
be done in the second and especially the third area.
Increasing knowledge of the dependence of physical properties
on chemical structure form the added value of accurate
thermoanalytical measurements and this knowledge is very
important for the development of new polymeric systems.
-
The table below lists the various TA techniques following the
notation of the ICTA (International Committee for Thermal
Analysis) nomenclature committee. The three "classic" TA
techniques are DSC, TGA and TMA of which DSC is still the
"workhorse". TA is also covering, however, a substantial
number of other techniques and applications and several of
these techniques are described in this book. This book is not
a comprehensive textbook about TA but more a survey of the
author's work during many years, at the Koninklijke Shell
Laboratorium in Amsterdam. It describes in six chapters the
use of the various TA techniques (printed in bold in the
table) for specific problems, illustrating the versatility of
TA. A technical description is only given for equipment of own
design.
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Thermal Analysis techniques
Differential Scanning Calorimetry
- high pressure DSC
- photo-DSC
- modulated DSC
Thermogravimetric Analysis
Thermodilatometry
length dilatometry
volume dilatometry
-
-
(DSC)
(TGA)
(TMA)
Dynamic Mechanical Analysis (DMA)
(low frequency) DMA
- u l t r a s o n i c (high frequency) analysis
-
s
t
a
n
d
a
r
d
Thermo-electrometry
dielectric analysis (DETA)
volume resistivity analysis
thermally stimulated discharge analysis
-
-
-
Simultaneous Techniques
- thermally stimulated discharge analysis/thermomechanical
analysis (TSD/TMA)
- thermogravimetric analysis/fourier transform infra red/mass
spectroscopy (TGA/FTIR/MS)
- thermogravimetric analysis/differential thermal analysis/
mass spectroscopy (TGA/DTA/MS)
- thermomechanical analysis/dielectric analysis (TMA/DETA)
Thermoluminosence
Thermomagnet ome try
Thermo-optometry
Thermosonimetry
Over the years, quantitative structure/property relationships
have been developed by various workers in the polymer research
field. Well known are for example the important contributions
made by D.W. van Krevelen in 'Properties of polymers' [3] and
by J. Bicerano in 'Prediction of Polymer Properties' [4]. An
endeavour is made in chapter seven (and eight) to improve some
of such correlations by using consistently measured,
reproducible TA data. Chapter nine shows the contribution of
TA to the characterisation effort necessary for the technical
and commercial development of a new polymer system. Chapter
ten finally, provides information about different polymers
obtained during special case studies. This book illustrates in
this way, applications of a wide variety of thermal analysis
techniques. The author hopes that this monograph will be
useful especially to those who are going to work in the
thermal analysis area in the context of polymer research.
Wire Groenewoud
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ACKNOWLEDGMENTS
The results described in this book could only be obtained by
the expertise and the cooperation of many members of the
different skillgroups at the Koninklijke Shell Laboratorium in
Amsterdam (KSLA). The still unique possibilities of this
laboratory are mentioned with pleasure.
Without pretending to be complete, I have to mention a number
of colleagues:
For stimulating discussions and valuable insight provided by
Roel Jongepier, Bram Ghijsels, Toni Cervenka, John Wintraecken
and Piet Kooijmans.
An important part of the experimental work was performed by:
Arie van der Zwan, Nico Groesbeek, Ton Jakobs, Wouter de Jong,
Bob Oudhaarlem, Leo Sman and Karin Orzessek.
Bob van Wingerden read and discussed with me many of the
internal reports which formed the basic data source of this
book resulting in many, always improving, suggestions.
Regretting any unintentional omissions I finally thank the
management of KSLA for the permission to publish results of
our polymer research.
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CONTENTS
Preface
Acknowledgments
Chapter 1. Differential Scanning Calorimetry
I. 1 Introduction
I.I.I DSC calibration and stability
1.1.2 The Tg-value determination
1.1.2 Melting/recrystallisation determinations
1.2 Tg-values of car-tyre rubber systems
1.2.1 Introduction
1.2.2 The Tg-value of BR and SSBR rubbers
1.2.3 The Tg-value after blending and oil-extension
of BR and SBR rubbers
10
Ii
14
17
17
19
1.3 Recrystallisation and fusion of polypropylene
1.3.1 Introduction
1.3.2 Additives acting as nucleating agents for PP
1.3.3 Annealing experiments with i-PP
26
26
28
1.4 Side-chain crystallisation in poly(1-olefine) s
1.4.1 Introduction
1.4.2 Crystallisation in poly(l-olefin)s
36
36
1.5 Chemical reactions monitored by DSC
I. 5.1 Introduction
1.5.2 The determination of the cure conditions of
a powder coating system
1..5.3 Reactions of model compounds studied by DSC
1.6 Determination of the heat of vaporisation by DSC
1.6.1 Introduction
1.6.2 DSC modification for the AHvap.25 determination
1.6.3 Results of AHvap.25 determinations by DSC
Chapter 2. Thermogravimetrical
2.1 Introduction
Analysis
2.2 01igomers c o n t e n t and thermal stability of polypropylene
2.2.1 The non-isothermal thermal stability
determination
2.2.2 The isothermal thermal stability determination
2.3 The TG analysis of a PP catalyst system
2.3.1 A 'plastic wrapped' TGA
2.3.2 TG analysis of a MgCl2-supported, TiCI4/DIBP
catalyst
40
43
43
52
52
54
61
63
65
70
72
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Chapter 3. Thermodilatometry
3.1 Length dilatometry (TMA)
3. i. 1 Introduction
3.1.2 The l.e.c, determination of filled polymers
3.1.3 Shrinkage of PK terpolymer and nylon 6.6 due
to moisture loss
3.2 Volume
3.2.1
3.2.2
3.2.3
3.2.4
dilatometry
Introduction
The volume dilatometer
The measuring procedure
Isothermal crystallisation of IR rubbers
Chapter 4. Dynamic Mechanical Analysis
4.1 The standard DMA technique
4.1.1 Introduction
4.1.2 DMA analysis of PP/C2C3 rubber blends
4.1.3 Tg-value determination of aged, rigid PU
foams by DMA
4.2 Mechanical measurements at ultra-sonic frequencies
4.2.1 Introduction
4.2.2 The ultra-sonic measuring equipment
4.2.3 Results of ultra-sonic measurements on
car- tyre rubbers
Chapter 5. Thermo-electrometry
5.1 The DC and AC properties of polymers
5.1.i Introduction
5.1.2 DC properties of polymers
5. i. 3 AC properties of polymers
5.1.4 The AC and DC measuring system
5.1.5 AC and DC properties of a cured resin system
5. i. 6 Time/temperature superposition of dielectric
results
5.1.7 The dielectric constant of rigid PU foam
5.2 Effect of moisture on the electrical properties
of polymers
5.2.1 Introduction
5.2.2 Influence of moisture on the dielectric
properties of resin castings and laminates
5.2.3 Effect of seawater and cargo on the electrical
properties of a tankcoating system
5.2.4 The determination of the Ki-value of PVC cable
insulation
5.3 Conduction improvement of epoxy resins by carbon
black addition
5.3.1 Electrostatic safety criteria
5.3.2 DC properties of experimental epoxy resin/
carbon black systems
5.3.3 DC properties of anti-static epoxy GFR pipes
77
77
81
85
85
89
91
94
99
105
109
112
114
123
124
128
132
134
140
145
151
153
158
163
171
172
177
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5.4 Thermally Stimulated Discharge analysis
5.4.1 The TSD technique
5.4.2 Bucci's TSD theory
5.4.3 Results of TSD experiments
181
181
184
Chapter 6. Coupled thermal analysis techniques
6.1 Introduction
188
6.2 Simultaneous TSD/TMA measurements
6.2.1 The TSD/TMA system
6.2.2 TSD/TMA results
191
192
6.3 The TGA - coupled - FTIR/MS technique
6.3.1 Introduction
6.3.2 The TGA/FTIR and TGA/MS coupling
6.3.3 The heated capillaries tip temperatures
6.3.4 Single component calibration
6.3.5 Investigation of the thermal decomposition
of Cobaltphthalocyanine by TGA - coupled FTIR/MS
6.3.6 Investigation of the released vapours during
the cure of epoxy resin system by TGA coupled - FTIR/MS
222
Chapter 7. Chemical structure/physical
correlations
7.1 Introduction
230
195
196
200
201
209
properties
7.2 The Tg-value estimation
7.2.1 Introduction
7.2.2 The 'modified cohesion energy' method
7.2.3 The Tg-value of crosslinked polymeric systems
232
233
245
7.3 The Tm-value estimation
7.3.1 Introduction
7.3.2 The reduced Tg/Tm correlations
253
254
7.4 The Hf-value estimation
264
7.5 The thermal stability estimation
7.5.1 Introduction
7.5.2 The semi-static Td, o-value determination
7.5.3 Thermal stability estimation based on
Td, o-values
268
269
269
7.6 The moisture sensitivity estimation
274
7.7 Estimation of the key-properties
277
of a new polymer
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Chapter 8. Tg-values of polymers with double bonds in the main
chain and Tg-values of non-polar polymers with side
chains
8.1 Introduction
282
8.2 Experimental BR systems
8.2.1 BR with a high 1,4 trans content
8.2.2 BR with a high syndiotactic
1,2 BR content
282
286
8.3 Experimental
288
IR systems
8.4 A Tg/structure correlation
systems with side-chains
for non-polar polymer
293
Chapter 9. Characterisation of polyketone polymer systems
by Thermal Analysis Techniques
9.1 Introduction
9.2 Investigation of the crystalline phase of PK co- and
terpolymers
9.2.1 PK copolymer and PK terpolymer
9.2.2 The Tm(o)- and Hf(max.)-values of PK copolymer
9.2.3 Alpha- and beta-crystallinity in PK copolymer
9.2.4 Alpha- and beta-crystallinity in PK copolymer
after a common processing procedure
9.2.5 Alpha- and beta-crystallinity in PK terpolymers
297
297
299
302
308
310
9.3 Investigation of the amorphous phase of PK terpolymer
by DMA/DSC
9.3.1 Amorphous phase transition effects
312
9.3.2 Ageing and moisture absorption effects
312
9.3.3 Determination of the Tg-value of PK terpolymer
by DSC
318
9.4 TMA measurements on PK terpolymer systems
9.4.1 The linear thermal expansion coefficient of
long glassfibre reinforced PK terpolymers
9.4.2 The repeatability of the l.e.c, determination
on PK terpolymer systems
322
325
9.5 Determination of electrical properties of PK
terpolymers
9.5.1 The influence of moisture on the dielectric
properties
9.5.2 The frequency dependency of the dielectric
properties
9.5.3 The specific volume resistivity determination
of PK terpolymer
334
9.6 Survey of PK terpolymer thermal analytical
characterisation results
337
327
331
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9
Chapter i0. Thermo-analytical case studies
i0.i Introduction
339
10.2 The effect of the presence of a solvent during the
cure of a thermoharding system
339
10.3 The thermal transitions of a liquid crystalline
polymer
342
10.4 The optimal crystallisation temperature of
diphenylolmethane
345
10.5 The dynamic stiffness of ultra-high molecular
weight polypropylene in its melt
350
10.6 The effect of an anti-static additive on the
electrical resistivity of a polystyrene foam
354
10.7 The dielectric constant of polyethylene foil
356
10.8 The volume resistivity of epoxy based moulding
powder systems during immersion in hot water
359
10.9 The determination of the composition of a cartyre
rubber
364
I0.I0 The thermal stability of ASB
366
I0.ii The thermo-analytical characterisation of a maize
based, 'green' polymer
371
Index
377
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DIFFERENTIAL S CANNING
CALORIMETRY
CHAPTER 1
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I0
CHAPTER i: D I F F E R E N T I A L SCANNING C A L O R I M E T R Y
i. 1 Introduction
1 , 1 , 1 The D$C
Differential scanning calorimetry is, according to the ICTA I
n o m e n c l a t u r e committee, a technique in which the heat flux
(power) to the sample is monitored against time or temperature
while the temperature of the sample, in a specified
atmosphere, is programmed. In practice, the difference in heat
flux to a pan containing the sample and an empty pan is
monitored. The instrument used is a differential scanning
calorimeter or DSC. The DSC is commercially available as a
p o w e r - c o m p e n s a t i n g DSC or as a heat-flux DSC.
The p o w e r - c o m p e n s a t i n g DSC has two nearly identical (in terms
of heat losses) measuring cells, one for the sample and one
reference holder. Both cells are heated with separate heaters,
their temperatures are measured with separate sensors. The
temperature of both cells can be linearly varied as a function
of time being controlled by an average-temperature control
loop. A second-differential-control loop adjusts the power
input as soon as a temperature difference starts to occur due
to some exothermic or endothermic process in the sample. The
differential power signal is recorded as a function of the
actual sample temperature.
One single heater is used in the heat-flux DSC to increase the
temperature of both the sample cell and the reference cell.
Small temperature differences occurring due to exothermic/
endothermic effects in the sample are recorded as a function
of the programmed temperature. Both systems are extensively
described in the literature, more recently by Wunderlich [i].
The DSC is used (after proper calibration, see 1.1.2) in
polymer research for mainly three different types of
experiments.
a) glass-rubber transition temperature (Tg-value)
determinations, see 1.1.3,
b) m e l t i n g / r e c r y s t a l l i s a t i o n temperature and heat (Tm/Tcvalue and Hf/Hc-value) determinations, see 1.1.4,
c) measurements on reacting systems (cure measurements).
An example of m o n i t o r i n g chemical reactions by DSC is given in
1.5. Besides, the use of the DSC for a specific non-standard
application is described in 1.6.
1.1.2 DSC calibration and stability
The DSC measurements reported in this book are performed with
the p o w e r - c o m p e n s a t i n g DSC-2 and DSC-7 systems from Perkin
Elmer. The block surrounding the DSC sample holders is kept at
-150~ • I~ with the aid of a controlled liquid nitrogen
supply, both cells are purged with helium (60 ml/minute).
The standard temperature calibration is performed at a heating
rate of 20~
using the melting effects of cyclohexane
~ICTA,
International
Committee for Thermal Analysis
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Ii
(-87.06~ and 6.3~
indium (156.60~
and tin (231.88~
The computer controlled two point calibration p r o c e d u r e is
performed using the cyclohexane -87.06~ value and the indium
156.60~ value. The heat of fusion of indium (Hf-value = 28.45
J/g) is introduced to p e r f o r m the energy calibration. A tin
sample fusion measurement is, subsequently, p e r f o r m e d to check
the possible deviation in the u p p e r part of the temperature
region. This deviation proved always to be less than 0.5~
If the temperature region of interest is ranging from about
100~ up to 350~
the two-point calibration p r o c e d u r e is
performed using indium and tin. The m e l t i n g effect of lead
(327.4~
is used in that case as the high temperature check.
The temperature and energy calibrations of the DSC-2 and DSC-7
are surprisingly stable as shown by a series of fusion
measurements on the same indium sample placed in the F~_~_~DSC7 apparatus, see Table I.I. The average indium T(onset) value
proved to be 156.6~ • 0.1~
whereas the average Hf-value
proved to be 28.5 J/g • 0.3 J/g measured over a p e r i o d of
about three month while the system was in use five days a
week.
Table i.I Results of a temperature calibration stability test
of a Perkin Elmer DSC-7
,, ~,J
time,
days
,,~
deviation,
~
Hf-value,
J/g
deviation
28.10
-0.35
28.63
+0.18
28.86
+0.41
,.
.
.
.
.
0
156.59
9
156.54
17
156.75
+0.15
3O
156.47
-0.13
28.40
91
156.47
156.53
-0.13
-0.07
28.40
28.40
,
a.
b.
c.
d.
,j,,
T (onset),
oc
-0.01
.
.
.
.
.
.
.
.
-0.06
.
.
.
.
.
.
,
:,,,,
, t,,
~
.
.
.
.
.
. . . .
,
.
,
,
.
.
.
.
.
.
I',I,
,
.
....
,', . . . .
,
,,
......
-0.O5
,
-0.05
-O.O5
........ ~ , ,
,~
~
,
I
.......
DSC cell base at -150~
Helium purge gas, 60 ml/minute,
Indium sample 5.81 mg.
Indium T(onset) and Hf-values m e a s u r e d at 20~
second heating scan values after a first heating/
cooling scan between 120oc and 160~
1.1.3 T u , v a l u e d e t e r m i n a t i o n
The DSC is widely used to measure the g l a s s - r u b b e r t r a n s i t i o n
temperature (Tg-value), which is an important p a r a m e t e r for
polymer characterisation. The T g - v a l u e represents the
temperature region at w h i c h the (amorphous phase) of a p o l y m e r
is transformed from a brittle, glassy material into a tough
rubberlike liquid. This effect is accompanied by a 'step-wise'
increase of the DSC heat flow/temperature or specific heat/
temperature curve. Enthalpy relaxation effects can hamper the
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12
( ) = COOLING RATE, ~
THROUGH Tg AFTER PREHEATING AT 150~
[ ] = AGEING TIME, DAYS
AGEING AT ROOM TEMPERATURE
FOLLOWING QUICK COOLING (320~
FROM 150~
HEAT FLUX
OLAS'~'
(3ZO)
[03
I
(40)
Sl
/
(10)
51
1:23
. ~~s t
(2.5)
I
u
I!
1r
ILl
z
I,,o
K
W ~
-~0
52
(0.62)
-
=|
50
Figure 1.1
The Tg(onset)-value
go
10
50
go
10
50
TEMP[RATURE,
Figure 1.2
Effects of cooling rate and ageing
time
(heating rate 20~
gO
~
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13
DSC Tg-value determination. A s t a n d a r d i s e d procedure is
therefore necessary, to arrive at reproducible results.
In general two types of DSC thermograms can be obtained for
the glass transition of a rigid polymer. Figure I.I shows
these two types for a linear epoxy resin. The u p p e r t h e r m o g r a m
was obtained by scanning a sample of this resin at a rate of
20~
without pretreatment.
The lower thermogram was obtained on the same sample, which
was preheated at 150oc for one minute, then q u i c k l y cooled
(320~
to room temperature before scanning it under
the same conditions. In the lower curve the glass t r a n s i t i o n
is visible as the expected 'step-wise' heat flow shift. In the
upper curve, however, a strong endothermic effect is
superimposed on the heat flow shift. The temperature at the
intersection of the e x t r a p o l a t e d heat flow curve at the low
temperature end and the tangent of the ascending curve at the
inflection point is defined as Tg-value often indicated as DSC
Tg(onset)-value. It is evident from Figure i.I the this Tg
definition leads to different results for both thermograms.
This is caused by the different thermal histories of the
samples, which results in a d i f f e r e n c e in the extent of the
so-called enthalpy relaxation effect [2].
Figure 1.2 illustrates, u s i n g the same sample, how the rate of
cooling through Tg and storage at room temperature bring into
evidence the presence of the e n t h a l p h y relaxation effect as a
superposition on the heat flow curve shift. Figure 1.2 also
shows the extent of the T g ( o n s e t ) - v a l u e differences due to the
presence of these endothermic peaks. It will be clear that a
standardised Tg-value d e t e r m i n a t i o n procedure is n e c e s s a r y to
obtain reproducible resultsthe sample (I0 to 15 mg.) is p l a c e d in the DSC sample
holder,
- the sample is heated at a rate of 20~
through the
possible present enthalphy r e l a x a t i o n maximum,
the sample temperature is decreased, subsequently, at
m a x i m u m cooling speed to a temperature of at least 50~
below the measured Tg effect,
- the sample is heated a second time through its Tg region at
a rate of 20~
and this second scan result is used to
calculate the Tg(onset)-value,
the sample weight is checked to see if any weight loss
occurred due to the thermal treatment of the sample (for
instance due to loss of moisture).
-
-
-
The Tg-values reported in this book are m e a s u r e d a c c o r d i n g to
this procedure. A series of T g ( o n s e t ) - v a l u e d e t e r m i n a t i o n s on
rubber samples (i.e. 100% amorphous samples, p r o v i d i n g a good
sample/sample holder contact) resulted in a T g ( o n s e t ) - v a l u e
precision of • 0.5~ and a r e p e a t a b i l i t y of • l~
for this
method. The reproducibility of this method was d e t e r m i n e d as •
4~ during a round robin test with seven samples, m e a s u r e d in
twenty-three laboratories [5]. These values might increase,
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14
however, for Tg-value determinations on semi-crystalline and
crosslinked polymers. The sample/sample holder contact is less
good for the more brittle semi-crystalline polymers while
crosslinked polymers show a clearly smaller 'step-wise' heat
flow increase effect compared with rubbery samples.
The disadvantages of using the Tg(onset)-value as Tg-value are
discussed by Richardson [2]. Determination of the Tg-value
using the enthalpy/temperature curve results in a
theoretically better defined Tg-value. Software to follow this
procedure is commercially available at present. In the
(european) industry, however, the Tg(onset)-value method is
used almost exclusively because it is not only convenient, but
also yields an indication for the maximum application
temperature of a polymer.
1.1.4 Meltina/recrvstallisation temperature determinations
Semi-crystalline polymers generally-melt over a wide
temperature range. This behaviour is related to imperfections
in the crystallites and non-uniformity in their size- the
smaller and/or less perfectly formed crystallites will melt at
lower temperatures. The endothermic fusion effect as measured
by the DSC is in many cases indicated by the temperature of
the maximum heat flow (the Tm-value) and by the total heat
involved in the fusion process (the Hf-value). Often reported
is also the Te-value i.e. the temperature at which the last
crystallite has fused.
Figure 1.3 illustrates the sensitivity of the measured Tmvalue for the sample weight. The maximum sample weights
possible to measure a sample weight independent Tm-value are,
of course, heating rate dependent.
20 ~
sample weight & 4 mg.,
i0 ~
sample weight & 6 mg.,
5 ~
sample weight & 8 mg.,
(Perkin Elmer DSC-2/DSC-7, standard aluminum sample pans).
The Tm-values reported in this book have been measured on 4
mg. samples at a heating rate of 20~
unless other
conditions are mentioned.
A fused sample is often subsequently cooled, to follow the
recrystallisation from the melt. The resulting exothermic
recrystallisation effect is usually described by the
temperature of the minimum heat flow (the Tc-value) and by the
total heat effect involved (Hc-value). Some advance knowledge
is necessary, however, to arrive at reproducible data.
Incompletely fused crystal residues remain present when the
temperature of the fused sample has been too low. These
residues cause the nucleation process to start at higher
temperatures than would normally be the case, resulting in
higher Tc-values.
Samples of a commercial polypropylene (PP) grade were heated
at a rate of 20~
up to a temperature Tmax.
Subsequently, the samples were cooled and reheated again. The
resulting melting/recrystallisation/melting values are listed
www.pdfgrip.com
6.0
6.0
3.1 mg
5.5
5.2
4.2 mg
s. o fl
!11
4.5"~ 4.0-
5.5
I~ \ e . l
mo
5.0
\'t 12.4 mg
4.5
/
o~ 3.5-
/
.,,.,,.
LL
~ 3.o~
mg
/Z
2.5-
4,0
,
1
i
i
2.5
2.0
2.0
1.5
1.5
1.0
1.0
0.5
o.
o t~~--------r---------r-------T-------
200. 0
210. 0
Figure 1.3
220. 0
2~0. 0
240. 0
250. 0
260. 0
270. 0
Temperature (~
The influence of the sample size on the Tm-value of a linear polymeric system during
heating in the DSC at a rate of 20~
0.0
www.pdfgrip.com
16
in Table 1.2. These data show that heating up to at least
210~
is necessary to avoid the so-called self-seeding effect.
Therefore, PP samples are heated up to 220~ as a standard
procedure, before recrystallisation measurements are
performed.
Table 1.2 Melting/recrystallisation data of PP samples after
heating the samples up to different temperatures
,,
',"l
i, heating
Tml,
Hfl,
~
J/g
'
,
2, cool ing
Tc,
Hc,
~
J/g
"l~ax.
oc
3, heating
Tm2,
Hf2,
~
J/g
162.5
I00
230
108.6
i01
160.9
95
162.1
102
220
108.7
99
160.5
96
162.5
97
210
108.7
96
161.0
95
162.5
99
2OO
109.2
102
161.0
90
162.4
88
190
109.3
98
161.0
95
99
180
9
110.0
98
161.2
162.2
I
. . . .
........
,,,
98
a. 4 mg. powder samples
b. heating/cooling rates 20~
A series of heating, cooling and heating scans is the general
approach to get an impression of the melting/recrystallisation
behaviour of a semi-crystalline polymer. The Tml/Hfl-values
are influenced by the thermal history of the sample. The
Tc/Hc-values are characteristic for the recrystallisation of
the polymer under standard (thermal) conditions. Finally, the
Tm2/Hf2-values can be used to compare different samples
recrystallised under identical conditions.
The Tml/Hfl values listed in Table 1.2 are giving an
impression of the repeatability of these measurements:
Tml-value, 162.4~ • 0.2oc
Hfl-value,
97 J/g • 5 J/g
The base-line drawing procedure is the main reason for the
relative low repeatability of the Hf-value determination. The
self-seeding effect, clearly influencing the Tc-value, makes
calculation of an average Tc-value meaningless. The Hc-, Tm2and Hf2-values are hardly influenced, thusHc -value,
99 J/g • 2 J/g
Tm2-value, 160.9~ • 0.2~
Hf2-value,
95 J/g • 3 J/g
The slightly improved repeatability of the Hc- and Hf2-values
in comparison with that of the Hfl-value might be caused by
the improved thermal contact between sample and sample holder
after the fusion process. Nakamura [5] reports a
reproducibility of • 3~ for the Tm/Tc determination. The
difference between the repeatability and the reproducibility
values of the Tm/Tc determinations is thus considerably higher
than those found for the Tg(onset)-value determination.
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17
1.2 Tg-values of car-tyre rubber systems
1.2.1 Introduction
The Tg-value is an important p r o p e r t y for tyre tread rubbers
[6]. It determines to a large extent the a b r a s i o n resistance,
the road holding behaviour on wet roads (wet grip), the
rolling resistance and the low t e m p e r a t u r e performance. A
rubber with a relative high Tg-value (about -40~
generally
results in a high wet grip but also in a reduced abrasion
resistance and winter performance. Moreover, the rolling
resistance is high! A rubber with a relative low Tg-value
(about -90"C) is giving a high a b r a s i o n resistance, a good
winter performance and a low rolling r e s i s t a n c e but a reduced
wet grip. Hence, the tyre tread rubber used is often a b l e n d
of different rubbers (and sometimes oil) to obtain a
compromise between the properties m e n t i o n e d and, of course,
the cost of the tyre.
The synthetic rubbers most frequently used for car tyres are
emulsion and solution s t y r e e n / b u t a d i e n e r a n d o m copolymers
(ESBR and SSBR) and butadiene rubber (BR). Truck tyres,
however, often contain a certain amount of natural rubber (NR)
or its synthetic version isoprene rubber (IR). The Tg-value of
BR rubber as such can vary, d e p e n d i n g on its chemical
structure between -100~
and -20~
the T g - v a l u e of SBR can,
in principle, vary between -100~
and 100~
1.2.2 The Ta-value of BR and SSBR rubbers
B u t y l l i t h i u m - i n i t i a t e d h o m o p o l y m e r i s a t i o n of butadiene results
in a BR polymer containing random d i s t r i b u t e d cis-l,4, trans1,4 and 1,2-BR or vinyl-BR units. The c o n c e n t r a t i o n of the
catalyst m o d i f i e r and the p o l y m e r i s a t i o n temperature (between
40~
and 75~
determine the c o n c e n t r a t i o n s of the three
different components. Thus, BR rubber is in fact nearly always
a terpolymer and its Tg-value can be d e s c r i b e d by means of the
G o r d o n - T a y l o r relation [7]. This relation is w r i t t e n in its
general form as:
Wi.Ai. (Tg - Tg, i) - 0
where: Wi
Ai
Tg
Tg, i
=
=
=
(1.1)
the weight fraction of m o n o m e r i,
a constant c h a r a c t e r i s t i c for m o n o m e r i,
the Tg-value of the co- or terpolymer,
the Tg-value of the h o m o p o l y m e r of m o n o m e r
i; by convention Tg, i+l > Tg, i.
Constant Ai represents the difference in the specific thermal
expansivities, AEi, above and b e l o w the Tg of the h o m o p o l y m e r
of monomer i. This equation can be w r i t t e n for BR in the
following form which is explicit for TgTg(BR)
= Wc.Tg.c + W~.Ki,Tg.t + W v , K 2 . T g , v
Wc + Wt.KI + Wv.K2
(1.2)
