|
Jeffrey Bartlett
Product Development Chemist
Nyacol Products, Inc.
Megunko Road
P.O. Box 349
Ashland, MA 01721
"Colloidal
Antimony Pentoxide in Flame Retarded ABS"
Fire Retardant Chemicals Association
Renaissance Stanford Court Hotel
San Francisco, California
March 16-19, 1997
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 trioxide (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 polymer's 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 & 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 & 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
|
|
| 
