Pressure exerted by the consumers is demanding flame retardant goods. Manufacturers need to
supply products that are not only flame retardant, but also maintain their physical and
aesthetic properties. Advances in fine denier polypropylene fiber processing have opened
the carpet face and wall covering markets to this versatile polymer. Aesthetically pleasing
polypropylene structural products, such as lamp housings and other containers, have found a
niche in the marketplace.
There are currently two systems that effectively flame retard polymers: halogenated systems and
non-halogenated systems. Many manufacturers would prefer a non-halogenated system, such as
magnesium hydroxide, aluminum trihydrate, ammonium phosphate, etc., principally because
halogenated systems have received negative publicity. Non-halogenated systems, however, require
loadings of upto 60% of flame retardant, and physical and aesthetic properties of the base
polymers are negatively affected as a result.
In the case of fine-denier fibers, a usable fiber could not be produced with these high flame retardant loadings. Halogenated systems offer the advantage of lower loadings due to the synergistic effect between the halogenated organic compound and antimony oxide, to achieve the desired levels of flame retardancy. In fact, several fiber manufacturers have dictated that no more than 8% active FR ingredients can be used in a finished fine denier fiber. Most halogenated FR compounds and all non-halogenated systems, however, cannot meet these criteria.
An ideal flame retardant system would be easily processed and would safeguard the physical and aesthetic properties of a polymer. It would incorporate a melt-blendable halogenated additive with a sub-micron antimony oxide particle. This combination should yield an acceptably flame-retarded product with good tensile strength, impact resistance and elongation. The finished product should also be untinted / translucent.
An antimony pentoxide powder that disperses to colloidal size (0.03 micron) particles is the only FR additive that meets all these criteria. A detailed comparison of colloidal-sized antimony pentoxide versus antimony trioxide (the smallest particle size commercially available) is given below.
| Property |
Antimony Trioxide |
Antimony Pentoxide |
| Formula |
Formula Sb2O3 |
Sb2O5 |
| Solubility |
Dilute acids & bases |
Only concentrated, hot acids |
| Particle Size |
0.8 - 1.0 microns |
0.03 microns |
| Surface Area m2/gm |
2 |
50 |
| Specific Gravity |
5.3 |
4.0 |
| Refractive Index |
2.1 |
1.7 |
| Surface Activity |
Usually neutral |
Weakly acidic |
Antimony pentoxide particle occupies only 0.2% of the cross-sectional area of fiber vs. 7% for antimony trioxide.
Several blends of antimony oxide/halogenated additive systems for PP fiber and translucent products have been evaluated
Table given below summarizes the flame tests results of the initial screening of FR compounds. Only one halogen/antimony oxide compound exhibited flame retardancy according to the UL-94 vertical flame test. That one system is antimony pentoxide or trioxide with a brominated aromatic compound.
Flame Test Summary of Polypropylene
| Additive Material |
Percent7Additive |
LOI8 Percent |
UL-949 Test |
After Flame Rating Time (Sec) |
| Virgin PP |
NA |
17.3 |
Fail |
NA |
| BAE 1 |
12.0 |
22.7 |
Fail |
NA |
| BP-60 2 |
12.0 |
19.3 |
Fail |
NA |
| BAC4 |
8.06 |
23.1 |
Fail |
NA |
| ADP48010 /BAE |
could not extrude |
| Trioxide BAE |
12.0 |
22.9 |
Fail |
NA |
| ADP480/BP-60 |
12.0 |
18.5 |
Fail |
NA |
| Trioxide/BP-60 |
12.0 |
20.3 |
Fail |
NA |
| ADP480/BP-66 3 |
12.0 |
18.5 |
Fail |
NA |
| Trioxide/BP-66 |
12.0 |
20.5 |
Fail |
NA |
| ADP480/C5 |
2.5 |
19.6 |
Fail |
NA |
| BurnEx 2000 /BAC |
12.0 |
23.6 |
V-2 |
0.0 |
| ADP480/BAC |
8.0 |
28.6 |
V-2 |
0.3 |
| |
4.0 |
26.9 |
V-2 |
9.4 |
| |
2.5 |
25.0 |
V-2 |
2.9 |
| |
1.0 |
20.1 |
V-2 |
3.8 |
| Trioxide/BAC |
12.0 |
32.3 |
V-0 |
0.0 |
| |
8.0 |
32.9 |
V-0 |
0.0 |
| |
4.0 |
28.9 |
V-2 |
0.0 |
| |
2.5 |
24.6 |
V-2 |
0.2 |
| |
1.0 |
21.6 |
Fail |
NA |
| 1 Brominated Aromatic Ester (63% Br) |
| 2 Brominated Polystyrene (60% Br) |
| 3 Brominated Polystyrene (66% Br) |
| 4 Brominated Aromatic Compound (66% Br) |
| 5 Chlorinated Paraffin (74% Br) |
| 6 Could not extrude at 12% loading |
| 7 Data for % Additive less than 12 not reported if sample failed UL-94 |
| 8 Limiting Oxygen Index (ASTM D2860) |
| 9 Vertical Burn Test |
| 10 ADP480 is a colloidal sized antimony pentoxide |
The antimony pentoxide compounds were all rated V-2 according to UL-94 with after flame times ranging from
0 to 3.8 seconds, depending on FR concentration. The trioxide compounds were rated V-O through FAIL depending
on FR concentration. The V-O ratings achieved by trioxide at high loading levels (8 and 12%) were probably due
to the rheology of the polymer being changed as a result of the trioxides’ larger particle size, which reduced
the quantity of drips as well as their flaming characteristics.
A summary of the physical property test results of the UL-94 acceptable materials is given in the two tables below.
The results show the antimony pentoxide and trioxide to be reasonably comparable from the perspectives of elongation
and tensile strength. It would be expected that the larger trioxide particles would have a negative effect on these
characteristics as the thickness of the test piece decreased.
|
Additive Material |
Percent Additive |
Notched 2 Izod Impact
(ft-lb/in) |
| Virgin PP |
NA |
0.64 |
| BurnEx 2000 |
12.0 |
0.62 |
| ADP480/BAC 1 |
8.0 |
0.63 |
| |
4.0 |
0.58 |
| |
2.5 |
0.64 |
| |
1.0 |
0.65 |
| Trioxide/BAC |
12.0 |
0.44 |
| |
8.0 |
0.36 |
| |
4.0 |
0.35 |
| |
2.5 |
0.37 |
| |
1.0 |
0.37 |
| 1 Brominated Aromatic Compound (66% Br) |
| 2 ASTM D256 |
|
Additive
Material |
Percent
Additive |
Elongation 3
at Yield
Percent |
Tensile 1
Strength
at Yield
PSI |
Elongation 2
at Break
Percent |
Tensile 2
Strength
at Break
PSI |
| Virgin PP |
NA |
16.8 |
4937 |
204.0 |
3055 |
| BurnEx 2000 |
12.0 |
8.0 |
5168 |
29.4 |
3453 |
| ADP480/BAC 1 |
8.0 |
9.9 |
5087 |
29.5 |
3643 |
| |
4.0 |
11.4 |
5173 |
30.3 |
3862 |
| |
2.5 |
15.9 |
5144 |
29.9 |
3564 |
| |
1.0 |
16.1 |
5068 |
49.6 |
3045 |
| Trioxide/BAC |
12.0 |
9.9 |
5040 |
32.5 |
3083 |
| |
8.0 |
11.5 |
4863 |
37.4 |
2841 |
| |
4.0 |
13.8 |
4892 |
31.9 |
2931 |
| |
2.5 |
13.7 |
5141 |
33.1 |
3265 |
| |
1.0 |
14.8 |
5122 |
30.9 |
3365 |
| 1 Brominated Aromatic Compound (66% Br) |
2 ASTM states that tensile strength and elongation at break value for unreinforced polypropylene plastics generally are highly variable due to inconsistencies in necking of the center section of the test bar. Tensile strength and elongation at yield are more reproducible. |
| 3 ASTM D638 |
The Izod impact data, however, show that the material with pentoxide has a significant advantage at all loading levels. In fact, the Izod data for polypropylene processed with antimony pentoxide-based flame retardants are comparable to the Izod result for virgin PP.
The antimony pentoxide- and trioxide-based flame retardant compounds processed equally well at all loading levels except at 12%, where the trioxide-based flame retardant compounds processed more easily. The larger trioxide particles may have absorbed the halogen material and thereby prevented slippage in the throat of the extruder. Ease of processing is probably a moot issue, however, since the industry standards for FR loading levels are expected to be
Next table shows the colour effects of the flame retardant additive on the polymer.
Colour Effect of Additive on Polymer - Unpigmented
Additive Material |
Percent Additive |
L'a'b' Total Color Difference |
Translucency (Visual) |
| Virgin PP |
NA |
0.0 |
Translucent |
| BAC |
4.0 |
41.2 |
Opaque |
| ADP480 |
4.0 |
34.2 |
Slightly Translucent |
| Trioxide |
4.0 |
58.7 |
Opaque |
| BurnEx 2000 |
12.0 |
51.1 |
Opaque |
| ADP480/BAC |
8.0 |
50.1 |
Opaque |
| |
4.0 |
43.7 |
V Slightly Translucent |
| |
2.5 |
37.2 |
Slightly Translucent |
| |
1.0 |
19.4 |
Translucent |
| Trioxide/BAC |
12.0 |
54.4 |
Opaque |
| |
8.0 |
53.4 |
Opaque |
| |
4.0 |
52.1 |
Opaque |
| |
2.5 |
47.1 |
Opaque |
| |
1.0 |
35.7 |
V Slightly Translucent |
Source Courtsey: Nyacol Nanotechnologies Inc.