|
Colloidal
Antimony Pentoxide in Flame Retarded ABS
Fire Retardant Chemicals
Association
Renaissance Stanford Court
Hotel
San Francisco, California
March 16-19, 1997
Jeffrey Bartlett
Nyacol Nano Technologies,
Incorporated
Megunko Road
P.O. Box 349
Ashland, MA 01721
ABSTRACT
In flame retarding thermoplastics,
the synergistic action between halogenated flame retardants and
antimony trioxide is well known in the plastic industry (1). For the
terpolymer acrylonitrile-butadiene-styrene (ABS), formulating an
efficient flame retardant (FR) system constantly challenges the end
user. The Izod impact strength and translucency are two key properties
that are diminished because of the particle size and pigmentation
strength of antimony trioxide. The loss in translucency limits the
range of available color choices because of the high loading required
to offset the tinting effect of antimony trioxide.
This paper will demonstrate
the benefits of flame retarding ABS with the synergist BurnEx ADP494
colloidal antimony pentoxide. Most notably, higher Izod impact strength
and a minimal loss of translucency can be achieved. These advantages
are a result of the differences in physical properties between antimony
pentoxide (Sb2O5) and antimony trixoide (Sb2O3).
In addition, during
processing, BurnEx ADP494 disperses in the ABS matrix to a 0.03 micron
particle size, which not only reduces any tinting effects, but is less
detrimental to the Izod impact strength as well. Production of FR-ABS
with BurnEx ADP494 colloidal antimony pentoxide achieves higher impact
strength and the ability to use most color concentrates at a low
loading resulting in lower cost formulations for the end user.
INTRODUCTION
As the information
revolution evolves, personal computers and telecommunication equipment
are expanding from the office to the home and becoming part of our
everyday life. In some
cases, these devices require flame retardancy, which typically
diminishes the polymers physical properties(2). The end user is constantly
challenged to balance performance and cost-effectiveness when formulating
an efficient flame retardant package.
In flame retardant
formulations, the use of metal oxides as synergists in organohalogen
systems is well known throughout the industry. The three most important metal
oxides are antimony trioxide (ATO), antimony pentoxide (APO) and sodium
antimonate(1). Nyacol manufactures
and distributes antimony pentoxide as either colloidal sols or as a
spray-dried powder. The
typical physical properties of antimony trioxide and antimony pentoxide
are summarized in Table 1(3). Antimony pentoxide offers unique performance
advantages because of its lower refractive index and submicron particle
size. This paper will show
that by using BurnEx colloidal antimony pentoxide in flame retarding
ABS, the non-pigmenting submicron particles are less detrimental on the
polymers physical properties and preserves the translucency of the base
ABS.
Table 1 – Typical
Properties of Antimony Pentoxide and Antimony Trioxide
|
Property
|
Antimony Pentoxide
|
Antimony Trioxide
|
|
Chemical Formula
|
Sb2O5
|
Sb2O3
|
|
Molecular Weight
|
323.5
|
291.5
|
|
Refractive Index
|
1.7
|
2.1
|
|
Particle Size
|
0.03 microns
|
0.25-3.0 Micron
|
|
Specific Gravity
|
3.8
|
5.3
|
|
Acidity
|
Weakly acidic
|
Usually neutral
|
|
Solubility
|
Concentrated hot acids
|
Dilute acids and bases
|
|
Color
|
Off white
|
White
|
|
Form
|
Colloid or powder
|
Powder
|
|
Surface Area m2/gm
|
50
|
0.4-2.3
|
EXPERIMENTAL RAW MATERIALS
The ABS resin used was a general
purpose high-gloss grade from Dow Chemical. The melt flow rate (MFR)
was 6.0 g/10 min (3.8 kg, 230° C) and the Izod impact strength was 5.5 ft-lb/in.
The halogens that were
evaluated are commonly used to flame retard ABS. The three brominated compounds
were: tetrabromobisphenol-A (TBAA),
1,2-bis(2,4,6-tribromophenoxy)ethane (TBPE) and octabromodiphenyl oxide
(OBDPO).
The antimony pentoxide was
BurnEx ADP494 formulated at mole ratios of 3:1 and 4:1, bromine to antimony
metal respectively, for each system.
Antimony trioxide was
formulated with each halogen for comparison purposes at either a 3:1 or
4:1 mole ratio.
Table 2 is a list of all the
raw materials used in this evaluation.
Table 2 – Raw Materials
|
Compound
|
Type
|
%
Br
|
MP
°
C
|
Manufacturer
|
|
ABS
|
|
|
|
Dow
|
|
Tetrabromobisphenol-A
(TBBA)
|
Soluble
|
58.8
|
179-181
|
Albemarle
|
|
Bis(tribromophenoxy)ethane
(TBPE)
|
Soluble
|
70.0
|
223-228
|
Great Lakes
|
|
Octabromodiphenyoxide
(OBDPO)
|
Soluble
|
79.8
|
70-140
|
Great Lakes
|
|
Antimony Pentoxide
BurnEx ADP494
|
|
|
|
Nyacol
|
|
Antimony Trioxide
|
|
|
|
Campine
|
|
Reed OmniColor
Color Concentrates
|
|
|
|
Reed Spectrum
|
|
Chlorinated
polyethylene (CPE)
|
|
36% Cl
|
|
Dow/Dupont
|
PROCESSING
The synergist, either APO or
ATO, was blended with the halogen in a V-blender prior to compounding. All the formulations were
processed on a ZSE-27 mm Leistritz intermeshing twin-screw extruder
with a length to diameter ratio of 36 to 1. The gear box was set up for counter-rotation and the
screw configuration was a "general mixing" design used to
compound fillers. The ABS
resin and the flame retardants were fed into the feed throat of the
extruder and one barrel section was vented for devolatization of the
melt stream. The extrudate
strands were cooled in a water trough and chopped into pellets. Process conditions were kept the
same for all formulations.
After extrusion, the pelletized
samples were injection molded on a 33-Ton Cincinnati-Milacron injection
molding machine using a standard ASTM test specimen mold cavity. Zone temperatures, injection
pressures and mold temperature were kept the same for all samples. All the specimens were
conditioned and tested according to ASTM test protocols. Table 3 is a summation of the
process conditions.
Table 3 – Process
Conditions
|
Extrusion Conditions
|
|
Melt Temperature
|
225-250° C
|
|
Screw Configuration
|
Counter-rotation
|
|
RPM
|
100
|
|
Molding Conditions
|
|
|
Mold Temperature
|
130° F
|
|
Melt Temperature
|
420° F
|
|
Total Cycle Time
(sec)
|
30
|
|
Back Pressure (psi)
|
50
|
TESTING
All the materials were tested
according to ASTM standards for plastics. Tensile properties were determined using ASTM D638.
Izod impact testing and instrumented impact testing were carried out
according to ASTM D256 and D3763. Melt flow rate was performed according to ASTM D1238
and the heat deflection temperature used ASTM D648.
RESULTS AND DISCUSSION
FR-ABS TBBA BLENDS
The melt-blendable flame
retardant TBBA is widely used for formulations requiring good
processability and cost-effectiveness. This halogen provides excellent flow
characteristics but sacrifices Izod impact strength. Summarized in Table 4 are the
results of the physical properties for all the formulations based on
TBBA. Formulation #1 is
the base ABS and formulation #2 contains only the halogen TBBA.
From this data, the Izod
impact strength for the formulations using antimony pentoxide were
higher than the Izod values for antimony trioxide, 2.0 to 2.2 ft-lb/in
versus 1.0 to 1.5 ft-lb/in respectively. This compares to the Izod impact strength of 5.5
ft-lb/in for the neat ABS and 1.7 ft-lb/in for formulation #2, which
contained only the halogen TBBA.
Data for instrumented impact
testing was also generated for formulations #8 and #4. Testing was conducted on a GRC
Dynatup Instrumented Impact Tester. Formulation #8 based on antimony pentoxide had an
Average Total Energy of 3.33 joules as compared to 1.20 joules for
formulation #4 based on antimony trioxide. These results show that the resistance to break was
more than double for the FR-ABS formulated with antimony pentoxide as
compared to antimony trioxide.
The tensile strength was
slightly higher for the APO blends and flammability was the same for
all samples, a UL-O4 V-2 rating. The burning drip was not unexpected because the
melt-blendable TBBA is known to cause a reduction in viscosity.
The appearance of the
TBBA/APO samples was translucent as compared to the opaque TBBA/ATO
compounds.
Table 4 – TBBA
Formulations
|
Formulation wt.%
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
|
ABS
|
100
|
77.0
|
77.5
|
79.5
|
75.9
|
77.9
|
77.0
|
75.6
|
|
TBBA
|
|
23.0
|
17.6
|
16.0
|
17.1
|
14.9
|
15.5
|
16.4
|
|
BurnEx ADP494
|
|
|
|
|
7.0
|
7.2
|
7.5
|
8.0
|
|
ATO
|
|
|
4.9
|
4.5
|
|
|
|
|
|
MR (Br/Sb)
|
|
|
4
|
4
|
4
|
3
|
3
|
3
|
|
% Br
|
|
13.5
|
10.4
|
9.4
|
10.0
|
8.7
|
9.1
|
9.6
|
|
% Sb
|
|
|
4.1
|
3.7
|
4.0
|
4.1
|
4.3
|
4.5
|
|
Physical
Properties
|
|
MFR (g/10
min)
3.8 kg 230° C
|
5.8
|
|
10.5
|
11.6
|
15.8
|
16.0
|
18.2
|
17.5
|
|
HDT @ 264 psi, ° C
|
|
|
72.8
|
|
|
|
|
67.8
|
|
Instrumented Impact
(joules)
|
|
|
|
1.20
|
|
|
|
3.33
|
|
Izod (ft-lb/in)
|
5.5
|
1.7
|
1.0
|
1.5
|
2.0
|
2.2
|
2.2
|
2.1
|
|
Tensile Strength
(psi)
|
6870
|
6082
|
5766
|
5802
|
6138
|
6180
|
6285
|
7256
|
|
Elong @ Break (%)
|
16.0
|
12.0
|
14.0
|
15.0
|
16.5
|
14.6
|
16.1
|
13.9
|
|
UL-94 1.6 mm
|
Burn
|
Burn
|
V-2
|
V-2
|
V-2
|
V-2
|
V-2
|
V-2
|
|
Appearance:
Translucent (T)
Opaque (O)
|
T
|
T
|
O
|
O
|
T
|
T
|
T
|
T
|
TBBA/APO CPE EVAULATION
A preliminary study was done
to evaluate the effectiveness of chlorinated polyethylene (CPE) as an
impact modifier for antimony pentoxide based formulations (2,4). The weight percent of CPE was
2,4 and 7% and was combined with the flame retardants and blended
together. Table 5 lists
the formulations that were processed and tested.
At a little under 2% CPE,
the average Izod impact for formulations #1 and 2 increased by 1
ft-lb/in as compared to the unmodified TBBA/APO blends, 3.2 versus 2.2
ft-lb/in. At 7% CPE, the
impact was 4.4 ft-lb/in. In
Figure 1, the Izod impact results are plotted against the concentration
of CPE.
A side benefit to using CPE
is that it apparently behaves as a drip suppressant. The flammability rating for the
1.6 mm test specimen is now a V-O standard as compared to V-2 for the
unmodified blends. The failed flammability results for formulations #4
and 5 were probably because of the low halogen/antimony content. The overall results show that
antimony pentoxide FR formulations can be successfully modified with
CPE not only to increase the Izod impact, but also to achieve a UL94
V-O rating for a 1.6 mm test specimen.
Table 5 – CPE Modified
Formulations
|
Formulation wt.%
|
1
|
2
|
3
|
4
|
5
|
|
ABS
|
79.90
|
78.40
|
78.40
|
77.50
|
79.00
|
|
TBBA
|
12.40
|
13.30
|
11.86
|
10.44
|
9.42
|
|
BurnEx ADP494
|
6.05
|
6.50
|
5.79
|
5.09
|
4.60
|
|
CPE
|
1.65
|
1.77
|
3.95
|
6.97
|
6.28
|
|
MR (Br/Sb)
|
3
|
3
|
3
|
3
|
3
|
|
Total FR (%)
|
20.1
|
21.6
|
21.6
|
22.5
|
21.0
|
|
% Br
|
7.29
|
7.82
|
6.97
|
6.14
|
5.54
|
|
% Cl
|
0.59
|
0.64
|
1.42
|
2.51
|
2.26
|
|
% Sb
|
3.41
|
3.67
|
3.27
|
2.88
|
2.60
|
|
Physical
Properties
|
|
Izod (ft lb/in)
|
2.8
|
3.5
|
3.3
|
4.4
|
4.4
|
|
UL-94 1.6 mm
|
V-O
|
V-O
|
V-O
|
Fail
|
Fail
|
|
Appearance:
Translucent (T)
Opaque (O)
|
T
|
T
|
T
|
T
|
T
|
FR-ABS TBPE BLENDS
Table 6 shows the
formulations containing the halogen 1,2-bis(2,4,6-tribromophenoxy) ethane
(TBPE). Formulation #5
used antimony trioxide for comparison purposes and was formulated at a
3 to 1 mole ratio (Br/Sb).
Izod impact results for the
TBPE/APO formulations based on a 4 to 1 mole ratio were 1 ft-lb/in
higher on average than the 3 to 1 mole ratio blends, 3.9 versus 2.9
ft-lb/in respectively. In
comparison to the trioxide blend, which was at a 3 to 1 mole ratio, the
TBPE/APO average impact value was 2.7 ft-lb/in versus 1.8 ft-lb/in for
the TBPE/ATO formulation. No
significant differences in tensile properties were noticed for the APO
and ATO blends.
The flammability testing for
the antimony pentoxide blends resulted in UL-94 ratings of either a V-2
or V-O. Higher levels of
TBPE are needed because of the amount of bromine contained in the
structure. As stated in
most literature, to achieve a V-O standard when flame retarding with
TBPE the bromine level should be in the range of 15 to 18% Br(2). Our
V-O formulation had a 13.1% Br level. The antimony trioxide formulation was a UL-94 V-2 standard
but had only 10.3% bromine.
Once again, all the samples
based on antimony pentoxide were translucent as compared to the opaque
trioxide sample.
Table 6 – TBPE
Formulations
|
Formulation wt.%
|
1
|
2
|
3
|
4
|
5
|
|
ABS
|
79.0
|
75.6
|
74.7
|
69.7
|
79.01
|
|
TBPE
|
14.3
|
16.6
|
15.6
|
18.7
|
14.78
|
|
BurnEx ADP494
|
6.7
|
7.8
|
9.7
|
11.6
|
|
|
ATO
|
|
|
|
|
6.21
|
|
MR (Br/Sb)
|
4
|
4
|
3
|
3
|
3
|
|
% Br
|
10.0
|
11.6
|
10.9
|
13.1
|
10.3
|
|
% Sb
|
3.8
|
4.4
|
5.5
|
6.6
|
5.2
|
|
Physical
Properties
|
|
MFR (g/10 min)
3.8 kg 230° C
|
|
|
15
|
19.4
|
7.9
|
|
HDT @ 264 psi, ° C
|
|
|
|
62.3
|
|
|
Izod (ft lb/in)
|
3.9
|
3.9
|
3.1
|
2.7
|
1.8
|
|
Tensile (psi)
|
6386
|
6438
|
6219
|
6223
|
6327
|
|
Elong @ Break (%)
|
22.8
|
8.96
|
22.3
|
| | 
