Colloidal Antimony Pentoxide

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








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