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Diffusion of Methanol Ethanol and Toluene in Nylon 12 and Poly(butyleneterephthalate).

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Dev. Chem. Eng. Mineral Process. 12(1/2), pp. 159-168, 2004.
Diffusion of Methanol, Ethanol and Toluene
in Nylon 12 and Poly(butyleneterephtha1ate)
M.P. McCourt, G.M. McNally, A.C. Ruddy
and W.R. Murphy
Polymer Processing Research Centre, Queen 's University of Belfast,
Stranmillis Road, Belfast BT9 5AH, Northern Ireland, UK
This work investigates the difision of methanol, ethanol and toluene in
polybutyleneterephthalate (PBr) and nylon 12 over a range of temperatures from 8°C
to 60°C. The results show that substantial solvent uptake was noted for nylon in
methanol and ethanol. Solvent uptake in PBT occurred only at the higher
temperatures in toluene. Dynamic mechanical thermal analysis (DMTA) also showed
progressive decrease in the glass transition temperature (T, ) and storage modulus
(E with increase in solvent uptake.
Introduction
Advances made in the processing of high performance polymers continue to trigger
improvements in their performance and critical applications. This is particularly true
in the automotive industry where temperature resistant, lightweight materials are
being developed for under-bonnet applications. Although there are many hlgh
temperature polymers commercially available for use in engineering applications,
there is currently little information available with regard to the resistance and the
mechanical performance of these materials in automotive fluids. Many of the reported
studies have investigated the diffusion of fuels and fuel components on the
mechanical performance and changes in polymer microstructure of first generation
polymer materials, as used in multilayer tube extrusions for automotive fuel lines [I].
Recently PBT has tended to replace polyamides in precision engineering applications
on account of its dimensional stability, particularly in water.
M.P. McCourt, G.M.
McNally, A.C. Ruddy and W.R. Murphy
In the automotive sector PBT compounds are now used for small interior
mouldings and bumpers. However this polymer is now being considered for use in
automotive fuel line application. Recently absorption and diffusion of organic
solvents in polymers has been a topic of great relevance from the theoretical and
technological point of view, and the transport properties of various engineering
polymers have been reported [2-71. However the transport properties of fuels in
engineering polymers are rarely found in the literature, even though they are widely
used in many applications. The aim of this present work was to compare the diffusion
of fuel components in a conventional nylon 12, currently used in automotive fuel line
systems, and PBT. As a result of improved efficiencies, the temperature around the
engine compartment has increased significantly over recent years. Therefore this work
investigated the effect of temperature (8°C to 60°C) on the transport properties of the
he1 components, methanol, ethanol and toluene, in both polymers, both below and
above their glass transition temperatures (T,J.
Experimental Details
(a) Materials
All the materials were supplied in pellet form and were dried prior to the manufacture
of test pieces, which were produced using a 50 tonne Arburg injection moulding
machine. The recommended processing conditions from the manufacturer were
followed. All the samples were carefully labelled and stored for subsequent analysis.
(6) Immersion Procedure
Prior to the analysis, all of the test specimens were placed in a drying oven at 80-C.
When the specimens reached their equilibrium weight, individual samples of each
polymer were then immersed in sealed vessels containing methanol, ethanol or
toluene at 8"C, 20"C, 40°C and 60°C. The vessels containing the specimens were
maintained at these temperatures throughout the duration of this investigation.
Specimens were removed at regular time intervals and the change in weight with
immersion time was recorded using a balance, accurate to 4 decimal places. An
average of 10 readings were recorded for each sample tested.
(c) Dynamic Mechanical Thermal Analysis (DMTA)
Changes in viscoelastic characteristics, i.e. glass transition temperature (TJ and
storage modulus (E') of the materials with immersion time in the various fluids were
measured using a Dynamic Mechanical Thermal Analyser (Polymer Laboratories
Mark 11). Specimens of dimensions 45 mm x 10 mm x 4 mm for analysis were cut
from the test specimens, and the analysis was carried out using dual cantilever mode
over a temperature range of -130°C to +150°C, using a frequency of 1 Hz. Glass
transition temperatures (TJ were recorded as being the temperature at which Tan 6
max. occurred,
I60
Diffiion of Methanol, Ethanol and Toluene in Nylon 12 and PBT
Results and Discussion
(i) Nylon Weight Gain and Swelling
The effect of immersion time in methanol on the weight gain in Nylon 12 is shown in
Figure 1
j
0
5
10
2c
15
Tlmr (hrs)"
Figure 1. The efect of immersion time in methanol on the weight gain in nylon.
There was an initial increase in weight with immersion time and progressive
increase with temperature, the highest weight gain being recorded at an immersion
temperature of 60°C. A higher equilibrium weight gain occurred over shorter periods
at higher temperatures, as shown in Table 1.
Temperature
Max.wt. gain I
Max.wt. gain 2
f"C)
(!A)
PA) a f 300 hours.
60
40
20
8
6.0 (9 hours)
(16hours)
5
(140 hours)
1.8 (50hours)
5.2
3
1.5
-----
I
After the initial increase in weight had been achieved, there was a net decrease in
weight for all the nylon samples at each immersion temperature, as observed in
previous studies [8]. It is due to both ingress of the alcohol into the polymer matrix
simultaneously accompanied by solvation and extraction of the plasticiser by the
alcohol. With progressive increase in immersion time the samples reached new
equilibrium weight gain values, also shown in Table 1. These new equilibrium weight
gain values were much smaller than the initial values. Figure 2 shows the effect of
immersion time in methanol on the cross sectional area (swelling) of nylon 12.
161
M.P.McCourt, G.M. McNally, A.C. Ruddy and W.R. Murphy
l
o
5
10
lime (hrrl"
2c
15
Figure 2. The effect of immersion time in methanol on the swelling of nylon.
The percentage change in cross sectional area was approximately proportional to
the percentage weight increase at the various temperatures. The effect of immersion
time in ethanol on the weight gain of nylon 12 is shown in Figure 3.
l o
5
10
15
2c
l l m s (hrr)"
Figure 3. The effect of immersion time in ethanol on the weight gain of nylon.
There was an initial increase in weight with immersion time and the progressive
increase in temperature. A higher equilibrium weight gain occurred over shorter
periods at the higher temperatures, as shown in Table 2.
Temperature
Max. wt, gain 1
Max.wt. gain 2
("C)
(96)
7.3 (25 hours)
6.2 (75 hours)
5.5 (140 hours)
1.0 (180 hours)
(%)
4
2.2
60
40
20
8
162
.
I
-
-..-
Difision of Methanol, Ethanol and Toluene in Nylon 12 and PBT
With progressive increase in immersion time, the samples reached new
equilibrium weight gain values as shown in Table 2. Much higher equilibrium gains
were recorded at progressively higher temperatures. In Figure 4 the increase in the
swelling was similar to the weight gain. The effect of immersion time in toluene on
the weight gain in nylon 12 is shown in Figure 5 . There was a higher equilibrium
weight gain which was achieved over shorter periods with progressive increase in
temperature as shown in Table 3. With progressive increase in immersion time the
samples reached new equilibrium weight gain values, which were lower than the
initial equilibrium weight gains. Figure 6 shows the swelling of the nylon samples in
toluene, again the increases in weight are reflected by the increases in swelling.
5
0
10
2c
15
Tlms (hrr)'
Figure 4. The eflect of immersion time in ethanol on the swelling of nylon.
c.
S 7"
-8 6 :
ii:
32-
li
0
0
5
10
15
20
25
30
Time (hrr)'
L
Figure 5. The effect of immersion time in toluene on the weight gain of nylon
Table 3. The effect of dwell time and temperature on equilibrium weight gain I and 2
in toluene.
Temperature
Max.wt. gain 1
Max.wt. gain 2
("C)
PA)
8 (40 hours)
7.3 (140 hours)
8 (480hours)
(2%)
5
3.2
2
60
40
20
8
_--
_--
I 63
M.P. McCourt, G.M. McNally, A.C. Ruddy and K R . Murphy
-
-
-+-
I
-
8 7 -
0
60%
--t 40%
--c 209:
5
10
15
Tlme (hrr)"
20
25
30
Figure 6. The effect of immersion time in toluene on the swelling of nylon.
(ii) PBT Weight Gain and Swelling
Figure 7 shows the effect of temperature and immersion time in methanol on the
weight gain of PBT. There was a progressive increase in weight gain with time and an
increase in temperature, with an equilibrium weight gain of 3.1% being recorded for
PBT at 60°C. Equilibrium weight gain had not been achieved for immersion at the
lower temperatures within the 900 hours of this study.
0
5
10
15
20
25
3[
Tlme (hrr)'
Figure 7. The effect of immersion time in methanol on the weight gain of PBT.
There was no observable decrease in weight over this time period, which would
indicate that the PBT did not contain any extractables. The effect of immersion time
and temperature in methanol on the swelling of PBT is shown in Figure 8. There was
a progressive increase in cross sectional area with a progressive increase in dwell time
and temperature, with the highest percentage swelling (2.2%) being recorded for PBT
at 60°C. Very little swelling (~0.2%)was recorded at the lower immersion
temperatures.
164
Diffusion of Methanol, Ethanol and Toluene in Nylon 12 and PBT
-
..
. _ _
Tlma ( h n ) '
Figure 8. The effect of immersion time in methanol on the swelling of PBT
Figure 9 shows much smaller percentage weight gains for PBT in ethanol.
However, the percentage weight gain was much greater at 60°C than at the lower
temperatures, with recorded weight gains of only 0.5% to 0.6%. Very little change in
cross sectional area was observed as shown in Figure 10. The weight gain of PBT in
toluene is given in Figure 11.
I
-
__]_.
-
-
-- -
---
---
60.c
8
0
5
10
15
Tlm. (hrs)'
20
20-
25
Figure 9. The effect of immersion time
in ethanol on the weight gain of PBT.
1s
.
30
Figure 10. The effect of immersion time
in ethanol on the swelling of PBT.
.
Figure 11. The effect of immersion time
in toluene on the weight gain of PBT.
Figure 12. The effect of immersion time
in toluene on the swelling of PBT.
The results indicate much higher weight gains for toluene than for methanol and
ethanol. The highest equilibrium weight gain occurred at 60°C immersion
temperature, with a percentage weight gain of 15%. Equilibrium weight gain had not
been achieved at the lower immersion temperature. However there was a progressive
increase in weight gain with time and temperature. The swelling of PBT in toluene
I65
M.P. McCourt, G.M. McNally, A. C. Ruddy and W.R. Murphy
(see Figure 12) also showed a progressive increase with time and temperature, the
highest swelling of 13% being recorded for 60°C immersion temperature. The
considerable increase in the rate of percentage weight gain and much higher
equilibrium weight gain recorded for the immersion temperature 60°Cis probably due
to the fact that ths temperature is in the region of the T, of this particular grade of
PBT (T,= 60°C).
(iii) Calculation of Diffusion CoefJicients
Diffusion coefficients for methanol, ethanol and toluene in each polymer, at the
various temperatures, were calculated fiom the weight gain data and are shown in
Figure 13 and 14. The diffusion coefficients of nylon in Figure 13 show that the
diffusion coefficients for methanol in nylon are greater than ethanol and toluene,
particularly at the higher temperatures. Diffusion coefficients of various solvents in
PBT (see Figure 14)highlights that the largest diffusion coefficients were observed to
occur for toluene. The PBT difhsion coefficients for methanol and ethanol were
much lower than those recorded for nylon, suggesting that PBT has an improved
barrier to these alcohols. It is interesting to note that much higher diffusion
coefficients were recorded at 60"C,which is approximately the T, of this particular
PBT grade.
I$ :::
II
f
1.0
1.0
IS
00
Y.lh.n.1
Clh.n.1
1.IY.W
Figure 13. Drffusion coefficients
for various solvents in nylon.
I I
Y.lhmnd
Ichnnd
T.IY..
Figure 14. Difision coefficients
for various solvents in PBT.
The introduction of organic molecules into glassy polymers gives rise to a
depression of the glass transition temperature, which influences solvent solubility,
diffusivity and permeability. This behavior is usually attributed to plasticisation,
which changes the polymer configuration by increasing the free volume. Recent
research [9] has shown that plasticisation results in much wider pore size distribution.
In particular, the effect of solvent plasticisation causes a change in polymer
configuration and mobility, resulting in a decrease in Tg with increasing solvent
concentration .
(iv) Dynamic Mechanical Analysis
A typical DMTA trace is given in Figure 15 for the nylon 12 material. The Tan 6
maximum (TJ was 17'C for the dry sample, and there was a large (T3 at -24'C for
the sample after immersion in methanol for 850 hours. Also there was a large
decrease in E' from 8.91 Pa to 8.36Pa with immersion in methanol.
166
Difusion of Methanol, Ethanol and Toluene in Nylon 12 and PBT
Delta 850 hrs
-Tan
Log F Dry
Log F 850 t t s
020
5
.' .
0.15
c
8
0
7.5
0.05
0.034
-70
m
' 7
-20
30
Bo
Temperature ("C)
Figure 15. Chart showing decrease in T, and storage modulus of
nylon upon immersion in methanol at 60°C.
Table 4. Comparison of Tan 6 may. and storage
modulus values for nylon and PBT at 40°C.
Table 4 lists the T, and E' values at 25°C for the polymers at an immersion
temperature of 40°C in the various solvents. The T, of nylon was lowered
significantly by the ingress of the polar ethanol and methanol by up to 37 C.The
depression of T, with ingress of the non-polar toluene was only 22 degrees C.In PBT,
depression in the T, value was recorded as being 35 and 32 degrees C in methanol
and ethanol respectively. The recorded decreases in T,, and the associated weight
increases with immersion times in the various solvents, is confinnation that
plasticisation of the polymer matrix has occurred. The depression in glass transition
ultimately led to a deterioration in mechanical properties as shown by the reduction in
the recorded storage moduli at 25°C.
167
M.P. McCourt, G.M. McNaIly, A.C. Ruddy and K R . Murphy
Summary and Conclusions
This work investigated the effect of immersion in methanol, ethanol and toluene at
temperatures of 20"C, 40°C and 60°Con the weight gain and swelling of nylon 12 and
PBT.Absorption studies showed that a relatively high absorption of methanol and
ethanol occurred for the nylon materials, but this effect was much less pronounced for
immersion in toluene. The PBT material showed good resistance to methanol and
ethanol in terms of swelling and weight gain but the material was susceptible to the
ingress of toluene. DMTA studies on the materials showed a significant decrease in
T, for nylon in the three solvents. In general, the depression in T, was found to be
related to the extent of fluid uptake, thus indicating that these fluids had a plasticising
effect on the supramolecular structure and the mechanical performance of the
materials. In addition, due to the increased fiee volume, the diffusion of solvents was
higher above the glass transition temperature of the material.
References
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4.
5.
McCourt, M., and McNally, G. 2000. High temperature polymers in automotive applications. J. Reinf:
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Plasiics Composiies,
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Nulman, M., and Rossi, G. 1998. Diffusion in glassy polymers. SAE Pnper No. 981360.
Vergnaud, J.M. 1991. Liquid Transport Processes in Polymeric Materials Modelling and Industrial
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Vesely, D. 2001. Molecular sorption mechanism of solvent diffusion in polymers. Polymer, 42,4417-
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Kobuchi, S., and Yasuhiko, A. 2002. Prediction of mutual diffusion coefficients for acrylic polymer
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a,
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