Download Heat Resistance, Water Resistance and Bin Storage Stability in

ELASTOMERE UND KUNSTSTOFFE
ELASTOMERS AND PLASTICS
Chlorosulfonated polyethylene Heat resistance Water resistance Bin stability
Achieving optimum heat and water
resistance in chlorosulfonated polyethylene (CSM) based compounds
has usually required the use of lead
containing materials as acid acceptors. Bin storage stability, or specifically poor or marginal bin stability,
can be an issue with some CSM
formulations under hot, humid storage conditions. This paper discusses results showing hydrotalcite
is a suitable replacement for lead in
heat and water-resistant CSM formulations. It also discusses ways to
compound CSM for improved bin
stability and the use of maleated
polybutadiene resins as mill release
agents having minimal impact on
bin stability.
Hitze-, WasserbestaÈndigkeit
und LagerstabilitaÈt bei
CSM-Compounds
Chlorsulfoniertes Polyethylen HitzebestaÈndigkeit WasserbestaÈndigkeit LagerstabilitaÈt
Um eine optimale Hitze- und WasserbestaÈndigkeit bei auf chlorsulfoniertem Polyethylen (CSM) basierenden Elastomermischungen zu erreichen, wurden uÈblicherweise bleihaltige Verbindungen eingesetzt, um
entstehende SaÈure zu binden. Unzureichende oder kritische LagerstabilitaÈt der Fertigmischung kann
fuÈr einige CSM-Mischungen bei
warmen, feuchten Lagerbedingungen zu Problemen fuÈhren. Die vorliegende Arbeit beschreibt den Einsatz von Hydrotalcit als eine geeignete Alternative fuÈr bleihaltige Verbindungen in waÈrme- und wasserbestaÈndigen CSM-Mischungen. Es
werden ebenfalls MoÈglichkeiten beschrieben, CSM fuÈr verbesserte LagerbestaÈndigkeit anzumischen, und
in wieweit maleinsaÈuremodifizierte
Polybutadienharze als Trennmittel
auf dem Walzwerk eingesetzt werden koÈnnen, ohne die LagerstabilitaÈt der Fertigmischung nennenswert
zu beeintraÈchtigen.
506
Heat Resistance, Water
Resistance and Bin Storage
Stability in CSM Hose
Compounds
R. E. Fuller and K. S. Macturk , Stow, OH USA
Chlorosulfonated Polyethylene (CSM),
available from DuPont Dow Elastomers
L.L.C. under the trade name Hypalonâ,
has been used in hose applications for
50 years because of its balance of properties including good resistance to heat,
oils and chemicals, ozone and weather.
Chlorosulfonated Polyethylene also possesses good mechanical toughness,
color stability and a degree of inherent
flame resistance. In addition, it adheres
well to metal and fabric reinforcement.
This unique balance of properties makes
CSM an ideal choice for many hose tube
and cover applications.
Properly compounded, CSM can be
used in hot environments up to 140 8C
or 150 8C. Achieving optimum heat and
water resistance, however, has usually required the use of lead compounds as the
acid acceptor. Lead improves heat aging
of CSM compounds by reacting with, and
thus trapping, chloride ions released as
hydrogen chloride (HCl) during curing
and subsequent exposure to heat. The
resulting lead chloride (PbCl2 ) is very
heat stable with low solubility in water.
In cases where the elimination of lead is
deemed advantageous due to environmental or health issues, there remains a
strong desire to eliminate lead wherever
possible from rubber formulations. Several grades of hydrotalcite were evaluated
as alternatives to lead in heat and waterresistant CSM formulations designed for
use in the hose industry.
Hydrotalcite (magnesium aluminum
hydroxy carbonate) has a crystalline
structure of magnesium, aluminum, hydroxyl and carbonate ions. Hydrotalcite
occurs naturally as a mineral and is
also produced synthetically. The chemi-
cal formula for naturally occurring hydrotalcite is Mg6 Al2 …OH†16 CO3 4 H2 O.
When hydrotalcite reacts with hydrogen
chloride upon exposure to heat, the
chloride ion is incorporated into the crystal structure rendering the resulting crystal structure heat stable with low solubility
in both water and oil.
A bin stable rubber compound is one
that will process, cure and yield consistent physical properties independent of
the time between when it is mixed and
when it is processed. A bin stable compound should also show no changes in
viscosity or scorch behavior when stored
after mixing and prior to use. Bin stability
issues with CSM stocks are manifested
by an increase in stock viscosity over
time. Scorch times, i. e. time to a 5 or
10 point rise during a Mooney Scorch
test, are not a reliable measure of, or control tool for, bin stability in CSM. Increases
in the Mooney Scorch (MS @ 121 8C)
initial and minimum viscosities are a
much more reliable predictor of processing problems resulting from bin aging.
It is postulated that water accelerates
crosslinking by hydrolyzing the sulfonyl
chloride groups making them reactive
with metal oxides and curing agents.
Water may also play a part in forming reversible ionomeric bonds between the
sulfonyl chloride groups and the metal
oxides. In any event, storage of CSM
stocks under warm, moist conditions
can lead to significant increases in stock
viscosity and subsequent processing difficulties.
The best strategy for minimizing bin
stability issues with CSM stocks is to
practice good stock control and management. Stocks should be used within a
KGK Kautschuk Gummi Kunststoffe 53. Jahrgang, Nr. 9/2000
Heat Resistance . . .
Table 1. Synthetic Hydrotalcite Grades Used in This Study
Table 2. Formulation for Hydrotalcite
Study
Tradename
Chemical Formula
Particle Size (lm)
Heat Treatment
DHT-4A
DHT-4A2
DHT-4C
KW2200
KW2100
Mg4:5 Al2 …OH†13 CO3 3:5 H2 O
Mg4:5 Al2 …OH†13 CO3
Mg4 Al2 …OH†12 O0:2 …CO3 †0:8
4:5 MgO Al2 O3
4:5 MgO Al2 O3
0.5
0.5
0.5
0.5
6±7
No
Yes
Partially Calcined
Fully Calcined
Fully Calcined
week or two after being mixed and exposure to hot humid conditions should be
minimized. Since this may not always
be possible or practical, it is also important to formulate the compound to
achieve the best balance of bin stability,
processing and desired cured properties.
There are certain materials that should
be avoided or eliminated from CSM
stocks when formulating for the best
bin stability. Acidic materials can contribute to ionomeric bond formation which
causes a viscosity increase. Hygroscopic
materials can increase the water absorption of the stock. Neither of these types of
materials should be used where bin stability is likely to be an issue. The effect of
several compounding ingredients on bin
stability is discussed in the results and
discussion section of this paper. The impact of hydrotalcite and other compounding ingredients on CSM bin storage stability is also discussed.
Experimental
Several grades of synthetic hydrotalcite,
differing primarily in particle size and
heat history during production, were
used in this study. DHT-4A is a standard
grade that has a small particle size, ap-
phr
proximately 0.5 lm average, and has
not been heat-treated. DHT-4A2 has
been heat-treated to remove the water
of hydration. DHT-4C has been further
heat-treated, in fact partially calcined,
to remove not only the water of hydration
but also about 20 % of the carbonate.
KW2200 has been fully calcined to remove all of the water and carbonate.
KW2100 is also fully calcined but with a
much larger particle size, on the order
of 6 to 7 lm. A summary of the hydrotalcites used in this study is provided in Table 1.
In this study, all of the above grades of
hydrotalcite were evaluated in a high
quality, black CSM hose formulation.
This allows for separation of the effects
of heat treatment and particle size on
the performance of the hydrotalcite. Huber's Hysafe 510 synthetic hydrotalcite
was included for comparison. Magnesium oxide, litharge (lead oxide, PbO)
and a litharge-magnesium oxide compound were included as controls. Twenty
parts of the acid acceptor was used in all
formulations with the exception of the
magnesium oxide control, where only
10 parts of magnesium oxide was
used. The formulations are shown in Table 2. Compounds used in the bin stability
HYPALON 4085
HYPALON HPG-6525
ST2320 CARBON BLACK
DOS
TOTM
CARBOWAX 3350
PE 617A
HVA 2
MBTS
NBC
TETRONE A
PE 200
ACID ACCEPTOR
HYDROTALCITE
or
90% LITHARGE (PbO) in PIB
or
MAGNESIUM OXIDE
or
90% LITHARGE (PbO) in PIB
MAGNESIUM OXIDE
75
25
70
5
25
3
3
1.25
1
2
1
3
20
25
10
12
8
and maleated polybutadiene studies are
shown in Tables 3, 4 and 5.
The compounds were mixed in a OOC
laboratory Banbury mixer in a single pass,
up-side-down mix with the accelerators
and curatives added at the sweep. The
compounds were dumped at an indicated temperature of 190 8C. The
dump temperature of the stocks as
measured with a pyrometer ranged
from 220 8C to 255 8C. The stocks were
cooled on a sheet off mill. Test slabs
were compression molded and cured
for 30 minutes at 162 8C. Compression
set pellets were cured for 35 minutes at
162 8C. Testing was performed according
to the applicable ASTM test procedure.
Table 3. Formulation for Non±Black Bin Stability Study
Description
Carbo wax
PE
3MA20
5MA20
3MA8
5MA8
HYPALON HPG±6525
TACKTENE 1203
ATOMITE
SUPREX CLAY
TIPURE R960
CALSOL 8240
BLUE ULTRAMARINE
TMTD
MAGLITE D
PE 200
SULFUR
CARBOWAX 3350
PE 1702
PE 617A
RICON 131 MA20
RICON 130 MA 8
100
3
150
50
20
40
0.25
2
5
3
1
3
±
3
±
±
100
3
150
50
20
40
0.25
2
5
3
1
±
3
3
±
±
100
3
150
50
20
40
0.25
2
5
3
1
±
±
2
3
±
100
3
150
50
20
40
0.25
2
5
3
1
±
±
2
5
±
100
3
150
50
20
40
0.25
2
5
3
1
±
±
2
±
3
100
3
150
50
20
40
0.25
2
5
3
1
±
±
2
±
5
TOTAL
380.25
380.25
379.25
381.25
379.25
381.25
KGK Kautschuk Gummi Kunststoffe 53. Jahrgang, Nr. 9/2000
507
Heat Resistance . . .
Table 4. Formulation for Black Bin Stability Study
Description
Carbowax
PE
None
3MA20
5MA20
3MA8
5MA8
HYPALON 4085
N762
ATOMITE
DOS
KENFLEX A1
TOTM
HVA 2
MBTS
NBC
TETRONE A
MAGLITE D
PE 200
CARBOWAX 3350
PE 1702
PE 617A
RICON 131 MA20
RICON 130 MA 8
100
75
100
15
5
20
1
1
0.5
1
5
5
3
±
3
±
±
100
75
100
15
5
20
1
1
0.5
1
5
5
±
2
2
±
±
100
75
100
15
5
20
1
1
0.5
1
5
5
±
±
±
±
±
100
75
100
15
5
20
1
1
0.5
1
5
5
±
±
±
3
±
100
75
100
15
5
20
1
1
0.5
1
5
5
±
±
±
5
±
100
75
100
15
5
20
1
1
0.5
1
5
5
±
±
±
±
3
100
75
100
15
5
20
1
1
0.5
1
5
5
±
±
±
±
5
TOTAL
334.5
332.5
328.5
331.5
333.5
331.5
333.5
Table 5. Formulation for Plasticizer Bin Stability Study
Description
DOS/ Sundex
TOTM
Drapex/TOTM
Hypalon 4085
N762
N990
Atomite
DOS
Drapex 409
Kenflex A1
SUNDEX 790
TOTM
CARBOWAX 3350
PE 617A
HVA 2
MBTS
NBC
Tetrone A
Maglite D
PE 200
100
60
±
90
7.5
±
5
22.5
±
3
3
1
1
2
1
5
3
100
60
±
90
±
±
5
±
30
3
3
1
1
2
1
5
3
100
60
±
90
±
15
5
±
20
3
3
1
1
2
1
5
3
Total phr lab
304
304
309
Results and discussion
The effect of hydrotalcite heat history
and particle size on several key properties
will now be discussed. Unless otherwise
stated the results are given in Table 6. The
compound viscosity (ML(1 ‡ 4) @ 100 8C)
of the hydrotalcite formulations is comparable to that of the lead-magnesium
oxide and magnesium oxide controls
and somewhat higher than that of the
lead oxide formulation. The heat history
of the hydrotalcite does not appear to
affect viscosity but hydrotalcite particle
size has a large effect. The larger particle size KW2100 gives a significant increase in compound viscosity compared
Table 6. Variations in Properties with Acid Acceptor Type
Hysafe
DHT-4A
DHT-4A2
Mooney Viscosity, ML @ 100 8C
ML(1+4) [MU]
57.9
62.1
59.0
Mooney Scorch, MS @ 121 8C
T5 [min]
15.0
11.4
17.0
Mooney Scorch, MS @ 121 8C, Aged 14 days 95 % RH/40 8C
Change ML [MU]
5.4
6.3
4.8
MDR2000 30 min @ 162 8C
t95 [min]
10.3
7.2
10.6
Original Physical properties
Cure 30 min @ 162 8C
M100 [MPa]
4.1
4.8
5.3
Average Change After Heat Aging
Change M50 [%]
179
172
110
Change Eb [%]
51
50
46
Oil Aging, IRM 903 Oil
Aged 70 hr @ 150 8C
Volume Change [%]
57
47
46
Compression Set Pellet (B)
CS 70 hr @ 125 8C [%]
60
52
50
Water Aging
Aged 70 hr @ 100 8C
Volume Change [%]
21
17
19
508
DHT-4C
KW2100
KW2200
Pb
Mag
Pb-Mag
59.4
83.3
61.5
52.9
59.9
61.5
19.8
13.2
20.9
13.1
16.0
10.5
3.1
3.5
3.2
19.6
15.2
17.8
11.1
11.2
14.0
14.5
14.3
13.6
5.9
5.0
4.9
5.7
3.9
5.4
113
46
222
53
110
40
175
60
157
54
126
45
46
73
54
45
62
47
52
67
60
39
63
47
17
10
8
2
50
20
KGK Kautschuk Gummi Kunststoffe 53. Jahrgang, Nr. 9/2000
Heat Resistance . . .
to KW2200 and the other hydrotalcite
grades.
Processing safety can be measured
by time to a five-point rise of Mooney
Scorch at 121 8C (T5). The processing
safety of the hydrotalcite stocks is comparable to, or better than, that of the
controls. In this case, there is a significant
effect of the heat history of the hydrotalcite. Scorch safety increases as the
amount of heat treatment increases as
evidenced by the larger T5 times. The
T5 for the fully calcined KW2200 is nearly
twice that of the untreated DHT-4A
(21 min. v. 11.5 min.).
The poorer scorch safety of the stock
with the larger particle size hydrotalcite
(KW2100) has at least two possible explanations. The first is increased chemical
reactivity. The second is an increased
tendency to build heat due to the higher
compound viscosity. In any event, the
scorch safety of the KW2100 stock is
equivalent to that of the litharge control.
The effect on cure rate parallels that of
Mooney Scorch. The T95 times measured by an MDR2000 at 162 8C increase
with increasing hydrotalcite heat history
and decrease somewhat as the particle
size increases from KW2200 to
KW2100. Note that the cure times of
the hydrotalcite stocks, except for the
KW2200 sample, are all shorter than
the controls. In some cases these shorter
cure times may translate into an economic advantage in the factory if the curing
cycle is a limiting factor in production.
The use of hydrotalcite results in compounds with cured physical properties
comparable to those obtained with other
acid acceptor systems. There does not
appear to be a significant impact of hydrotalcite heat history or particle size on
the original physical properties. One possible exception is that room temperature
modulus may be increasing as the hydrotalcite heat history increases, at least up
to the partially calcined DHT-4C grade.
Any effect is probably due to ionomeric
interactions influenced by surface area
effects. This hypothesis is supported by
the fact this effect is not seen in the
100 8C properties where the ionomeric interactions are destroyed by the higher
temperatures.
The heat aging performance of the hydrotalcite stocks compared favorably
with the lead-magnesium oxide control.
Traditionally, the lead-magnesium oxide
acid acceptor system has given the
best heat aging performance in CSM
stocks. Here we have presented the average modulus change over four aging periods (3 and 7 days at 150 8C and 7 and 14
days at 135 8C) and the average elongation change over the same periods. This
averaging method was chosen in order
not to give undue weight to any one
set of conditions. The conclusion that
heat-treated hydrotalcites, with the exception of the small particle size, fully calcined version (KW2200), give heat aging
performance as good as or better than
lead-magnesium oxide system is consistent for all of the aging periods.
The poorer performance of the small
particle size, fully calcined grade of hydrotalcite appears to be real since this effect was seen for different aging periods
and for multiple batches of this hose
compound. However, this poorer relative
performance was not seen in another formulation tested. In that case, both calcined versions were equivalent. Further
work is needed to verify that the effect
is compound dependent.
Compression set (Method B) of the hydrotalcite compounds, measured after
conditioning for 70 hours at 125 8C, is
not quite as low as the lead oxide system.
The standard hydrotalcite grades give set
values approximately equal to those of
the lead-magnesium oxide system and
somewhat better than those of magnesium oxide control. There is an effect of
hydrotalcite heat history on compression
set as is evidenced by the differences between the compression set values for the
calcined versus the non-calcined grades.
The fully calcined hydrotalcites yield com-
pounds with higher compression set. Increasing the hydrotalcite particle size appears to be deleterious to set.
Use of hydrotalcite, especially the fully
calcined versions, yields water swells
(70 hr and 100 8C) approaching those
of the lead oxide system. While the use
of hydrotalcite does not yield the extremely low water swells of a straight lead
oxide system, it offers significant improvement over the standard magnesium
oxide system and does so without the
health and environmental issues associated with lead. Standard hydrotalcite
grades give water swells similar to those
achieved in a lead-magnesium oxide system. The fully calcined hydrotalcites reduce water swell by an additional factor
of two and yield swells approaching those
of a lead oxide system. There appears to
be little or no effect of hydrotalcite particle
size on water swell.
Oil swell in IRM903 oil (70 hr and
150 8C) with the non-calcined hydrotalcites is approximately equal to that of
the lead and lead-magnesium oxide
compounds and significantly better
than that of the magnesium oxide system. Stocks made with the calcined hydrotalcites are poorer in oil swell than
those made with the non-calcined
grades. The larger particle size gives
stocks that have significantly worse oil
swell.
Before addressing the impact of hydrotalcite on CSM bin stability, the influence
of several types of compounding ingredients on bin stability will be discussed. Bin
stability can be influenced by the plasticizer choice. Fig. 1 shows the change in
Mooney Scorch minimum viscosity after
Fig. 1. Effect of
Plasticizer Type on
CSM Bin Stability
KGK Kautschuk Gummi Kunststoffe 53. Jahrgang, Nr. 9/2000
509
Heat Resistance . . .
humid aging (14 days at 40 8C and 95 %
relative humidity) for a typical CSM hose
compound containing 60 parts carbon
black, 90 parts whiting and 30 parts of
plasticizer. The compound with trioctyl trimellitate (TOTM) shows less viscosity increase than one with a blend of aromatic
oil (Sundex 790) and dioctyl sebacate
(DOS). However, both show smaller viscosity increases than the compound with a
blend of TOTM and an adipic acid polyester plasticizer (Drapex 409). Polyethylene glycol based plasticizers such as
polyethylene glycol 400-di-2-ethylhexoate (TegMeR 809) are particularly poor
for bin stability. One stock tested with
this plasticizer had experienced such a
large viscosity increase during bin storage that it was not possible to measure
the Mooney Scorch viscosity after 14
days aging at 40 8C and 95 % relative humidity. While no data exists for other plasticizers with polyether backbones, these
also may lead to poor bin stability and
should be evaluated prior to use.
The choice of cure system components can also affect bin stability.
TMTD, for example, can yield stocks
that are more prone to bin stability problems. MBTS, in contrast, usually produces stocks that show good bin stability.
Nickel dithiocarbamate (NBC) is used in
CSM to give the optimum in heat resistance. NBC can contribute not only to
short original scorch times but also to
poor bin stability. It should be used at
the minimum level necessary to impart
the degree of heat stabilization required
for the particular application.
Bin stability is also influenced by process aids. Stearic acid, while very effective as a process aid in CSM, should be
not be used if bin stability is an issue.
CSM stocks with as little as 0.5 or
1 phr of stearic acid can become unprocessable in a relatively short time when
stored in hot, humid environments.
Polyethylene glycol process aids, such
as Carbowax, also are very effective in
CSM and are often used to impart
good mill and Banbury release. However,
these contribute to poor bin stability and
should be avoided where bin stability is
likely to be an issue.
Process aids that have minimal effect
on bin stability are combinations of low
molecular weight polyethylenes (e. g. a
blend of PE617A and PE1702), high cis
content polybutadiene, and maleated
polybutadiene resins. Maleated polybutadiene resins are particularly effective release aids in CSM stocks. Our lab evaluations and limited factory experience show
that maleated polybutadienes are at least
as effective, and in some cases more effective, than polyethylene glycol for imparting good mill and mixer release to
CSM.
Two versions of maleated polybutadiene from Ricon Resins were evaluated
at the 3 and 5 part level in both a black
and a non-black hose compound. The
grades differed primarily in their anhydride content with one containing 20 %
anhydride (Ricon 131MA20) and one
containing 8 % anhydride (Ricon
130MA8). In general, we found that higher levels of these resins produced better
Fig. 2. Release Aid Bin Stability in a Carbon Black Filled CSM Stock
510
release properties. In addition, higher anhydride contents also gave better release
properties. These materials tend to increase the compound modulus and
thus the formulation chemist needs to
evaluate the impact on physical properties prior to selecting the grade and level.
The effect of these resins on bin stability is
shown in Fig. 2 and 3.
The effect of hydrotalcite on bin stability
(14 days @ 40 8C and 95 % relative
humidity) can be seen in Table 6. Note
that these stocks contain both NBC
and Carbowax and haven't otherwise
been optimized for bin stability. The viscosity increases with hydrotalcite are
significantly less than for the other acid
acceptor systems. The heat-treated hydrotalcites are somewhat more bin stable
than the standard grades. In this case,
there is no effect of hydrotalcite particle
size.
Summary
Chlorosulfonated Polyethylene (CSM) is
widely used in hose applications due to
good heat, oil, chemical, ozone and
weather resistance, good physical properties and ease of processing. This paper
shows that hydrotalcite is a viable alternative to lead and lead-magnesium oxide
acid acceptor systems in CSM compounds where excellent heat and/or
water resistance is required. These results are noteworthy since hydrotalcite offers a good balance of properties without
the health and environmental issues associated with lead containing stocks.
Fig. 3. Release Aid Bin Stability in a Mineral Filled CSM Stock
KGK Kautschuk Gummi Kunststoffe 53. Jahrgang, Nr. 9/2000
Heat Resistance . . .
Hydrotalcite also offers improvements
in bin stability, scorch safety and cure
rate while giving heat aging performance
that is as good as or better than that of a
lead-magnesium oxide system. Water
swells, while not as low as for a lead oxide
system, are very good, especially with the
calcined hydrotalcite grades.
Several grades of hydrotalcite are available and performance is dependent on
the degree of heat treatment of the hydrotalcite and its particle size. For example,
the best water resistance is achieved by
using a fully calcined grade of hydrotalcite
while the best heat resistance is achieved
by using a grade that has been heat-treated to a lesser extent. Since there are
likely to be cost differences among the
grades, the formulation chemist needs
to evaluate the available grades and strike
a balance between cost and desired performance.
Finally, several mechanisms responsible for poor bin stability were discussed.
Bin stability can be improved by the proper choice of compounding ingredients
KGK Kautschuk Gummi Kunststoffe 53. Jahrgang, Nr. 9/2000
such as plasticizers, cure system components and process aids. Acidic and hydrophilic materials should be avoided in
order to produce acceptable bin stability.
Results were presented which show the
beneficial aspects of the use of maleated
polybutadiene as a process aid that gives
good mill release and bin stability.
Corresponding author
Kenneth S. Macturk
Du Pont Dow Elastomers
4330 Allen Road
Stow, OH USA 44224
511