New Generation of Inorganic Colloids

for Flame Retardancy

and UV Stabilization of Polymers

Edward A. Myszak, Jr. and Michael T. Sobus

PQ Corporation

P.O. Box 840,

Valley Forge, PA 19482 USA

Contact:

Nyacol Nano Technologies, Inc.

P.O. Box 349

Ashland, MA 01721

ABSTRACT

Flame retardants composed of solid inorganic particles generally have an adverse effect on the physical and aesthetic properties of polymers and synthetic fibers. This paper will discuss the advantages offered by colloid-sized particles for flame retardancy and UV stabilization of polypropylene materials as well as several other polymers. Particular attention will be given to the importance of choosing a comprehensive flame retardant system, halogen and antimony oxide, and their affect on flame retardancy, aesthetics and the polymer processing system.

INTRODUCTION

Flame retardants have typically been used in polymeric formulations with only marginal concern for the physical properties/aesthetics of the polymer produced. Most of the applications have been in colored formulations of reasonably thick parts. However, when you need to flame retard an end product which must be translucent and/or must have good strength in a film, fiber or thin-walled application, considerations of physical properties and aesthetics become paramount.

In this paper, we will consider the effects of flame retardant ingredients on the physical properties/aesthetics of polymers (primarily polypropylene) with the goal of achieving good FR efficiency while maintaining good physical properties and/or good aesthetics, defined as translucency. In this area of interest, we will consider only halogenated systems since they offer the advantage of lower loadings to achieve flame retardancy versus non-halogenated systems. Every non-halogenated system we are aware of results in an opaque final product with poor physical properties due to the high loading levels of flame retardant ingredients (generally 40% or more by weight).

FLAME RETARDANT SYSTEMS

Since we will only consider halogenated systems and ancillary ingredients, we must look at both the halogen and the antimony synergists separately and together. The one exception is for wire and cable applications where we looked briefly at magnesium hydroxide.

ANTIMONY SYNERGIST

There are two antimony synergist products to consider in this evaluation, antimony pentoxide and antimony trioxide. A detailed comparison of colloid-sized antimony pentoxide versus antimony trioxide is give in Table 1. As you can see from this table, pentoxide has a significant particle size advantage in that its small particle size should render itself invisible in normal usage quantities in an FR formulation. Whereas trioxide, at 0.8-1 micron particle size, will behave as a white pigment and turn a PP polymer opaque.

Also, pentoxide is insoluble in most waste streams which represents another advantage of this unique synergist. We also considered particle size modifications in our testing of pentoxide and trioxide synergist (see Table 2).

HALOGEN

In contrast to the synergist materials, there are many halogen materials to consider for use with polyolefins. We considered a number of materials such as BN451, BT93, FB-72, GPP39, Pyro-Chek 68PB and C6OPB, Pyronil 63, Clorez 760, FR1034 and others (see Table 3). In general, however, the problems with all the tested halogens but one was that the materials were 1) not melt blendable at normal processing temperatures resulting in large particulates in the material, 2) had too low a bromine/chlorine content requiring high dosage levels resulting in poor physical properties/translucency, or 3) the efficiency of the halogen was poor relative to the other candidates resulting in higher dosage levels. The one halogen which performed exceptionally well was a brominated aromatic compound. Alone it was unexceptional in its performance but with an antimony synergist (as all the other halogens were tested), it performed even better than expected from the normal synergistic effects of the halogen:antimony relationship.

OTHER FLAME RETARDANTS

Colloidal-sized magnesium hydroxide was investigated in combination with commercially available materials. Colloid-sized smoke suppressants were also investigated. Table 4 details the materials considered in these areas.

POLYMERS

Table 5 details the polymers we investigated. We conducted most of our research using polypropylene where we achieved excellent results indicating more research in this area was justified. Two other areas also showed significant promise. They were flexible PVC and colloid-sized magnesium hydroxide for wire and cable applications. This is not to say that the antimony pentoxide or trioxide is functional only in PP, PVC, etc. It does say, however, that the halogen system needs to be studied in greater detail for each polymer separately. One FR system does not fit all applications.

RESULTS AND DISCUSSIONS

In the testing process many combinations of ingredients were evaluated which would be too numerous to review here. Therefore, we will review the data by analyzing antimony pentoxide versus antimony trioxide versus modified versions of both. The ideal versions of the synergist will then be analyzed with the various halogens (keeping in mind that to identify the ideal antimony synergist, we had to identify the ideal halogen for polypropylene polymer). The other polymers will then be considered followed by the smoke suppressants.

The ideal synergist, based on our goal of obtaining good FR characteristics, good physical properties, and good aesthetics (translucency), was identified as antimony pentoxide. The data supporting this claim is detailed in Table 6. This table clearly shows that standard grade antimony pentoxide is superior to antimony trioxide when you consider the three primary objectives, flame retardancy, physical properties (notched Izods), and aesthetics (translucency). Only pentoxide permits translucency and essentially no degradation of the physical characteristics of the polymer. From a flame retardancy standpoint, both antimony pentoxide and trioxide yield V-2 results. However, at 1.0% FR loading, the trioxide fails UL-94 whereas pentoxide yields a V-2 result. At larger average particles sizes of antimony pentoxide, up to 0.150 micron, the flame retardancy, physical property and aesthetics are unaffected. Interestingly, as the trioxide particle size was reduced to 0.138 micron, the physical and aesthetic aspects improved but the flame retardancy decreased at 2.5% FR loading and still failed at 1.0% FR loading. Figure 1 graphically details the physical property (notched Izod) results of antimony pentoxide versus trioxide. Notched Izod results are particle size dependent. If the particle size is 0.150 micron or smaller, the ingredient does not detract from the virgin polymer results, at least in this case in polypropylene. Translucency may sound like an arbitrary characteristic. However, in those situations where a translucent appearance is not required and pigments are added, this translucency benefit results in less pigment being required with pentoxide since you do not have to overcome the whitening (opacity) effect of the trioxide. This can result in substantial pigment cost savings.

The next area considered is the ideal halogen to be used with the antimony pentoxide synergist. Again, we are following the same goal criteria, i.e., good flame retardancy, good physicals, and good aesthetics. Table 7 details the results achieved in this halogen study. As is shown clearly from this table, the brominated aromatic compound performed the best from a flame retardancy and translucency standpoint. The ideal flame retardant (BAC) was also melt blendable at normal processing temperatures of the polymer. Required addition levels to achieve UL V-2 results were very low.

The area considered next was smoke suppression and other flame retardant systems, namely non-halogenated, and how colloid sized particles could benefit these systems. Table 8 details the preliminary study of smoke suppression systems, i.e., zinc borate and molydenum-based materials. Apparently, there is no advantage to a colloid-sized zinc borate. However, a colloid-sized molydendum oxide gives slightly better results than a regular grade of molydendum oxide. This area will be studied further in future work.

Table 9 details the work completed with magnesium hydroxide in polypropylene (no other FR material was used in conjunction with this material). Even though most of the data shows UL-94 failures, there is a significant amount of data to be gleaned from the % LOI and notched Izod results. Kyowa material is considered the best magnesium hydroxide for wire and cable applications. As you can see in Table 8, a modified magnesium hydroxide, 0.225 micron particle size, yields a better % LOI but poorer notched Izod. At the same FR loading level, a standard, commercially available grade of magnesium hydroxide blended with our modified magnesium hydroxide yields both a better % LOI and notched Izod results. At the normal loading levels of 62% FR, the modified magnesium hydroxide improves the FR efficiency of the system. The processability of this system, with the modified magnesium hydroxide, was significantly improved. The extrusion rates were higher and the processing easier.

Of the polymers tested, only the polyolefins, flexible PVC and nylon showed interesting results with the halogen/antimony synergist identified. Additional testing would be required to test other halogen systems to identify the ideal combination for flame retardancy and physical characteristics. The flexible PVC area is worth noting, however. Table 10 details the results of this study. Only antimony synergist was added to the flexible PVC. The result was astounding: Flexible PVC with no FR additive burns, while with antimony pentoxide it has a V-O rating and is as transparent as the virgin PVC. Trioxide also will flame retard the flexible PVC, but it causes the PVC to become opaque.

For polypropylene to avoid the antagonistic interactions between HALS UV stabilizers and halogens, a nonreactive UV absorber, zinc oxide, in colloidal particle size was evaluated. A liquid version of colloidal zinc oxide, at a particle size of 0.020-0.050 micron, and a dry powder version, at a particle size of 0.11 micron, was evaluated. The UV absorption efficiency of this material is quite astounding as shown in Figure 2. As can be seen, the colloidal zinc oxide, called DP5370, is an excellent adsorpter of wavelengths in the UVA and UVB ranges (2000Å through 4000Å) and is invisible, i.e., does not adsorb wavelengths in the visible light range (4000Å through 8000Å).

Table 11 details the formulations tested using the powder version zinc oxide. To determine the adsorption efficiency of these materials, a Q-Panel Tester with UVB lamps was used. UVB lamps generate the shortest wavelengths found in sunlight at the earth’s surface and are responsible for most polymer damage.

Figure 3 shows the yellowness index of the additives on the polymer when exposed to UV radiation. This data was measured on a Minolta CR-200 chromameter with virgin polymer as the base standard. There is a dramatic improvement in the UV degradation as observed with the flame retarded material versus the zinc oxide treated material. This improvement is apparent with zinc oxide loading levels as low as 0.5%.



CONCLUSION

Our goal was to develop a flame retardant system which had good FR efficiency, good physical properties and was translucent. We achieved this with antimony pentoxide and a BAC halogen combination which we call BurnEx 2000. We also found that these results are particle size dependant in that the particles should be less than 0.150 micron in size. In addition, we achieved excellent UV protection of polymers, in general, and the FR system, in particular, with a new colloidal sized zinc oxide powder which we call DP5372. We also had limited success with colloidal sized smoke suppressants. We showed that colloidal sized molybdenum based materials exhibited some FR improvement and little, if any, benefit in smoke suppression. We showed that colloidal sized antimony pentoxide offered a significant translucency advantage in flexible PVC. Finally, we showed some encouraging data with a colloidal sized magnesium hydroxide. The data suggests improved FR and physical property results with this material. Improved processability was also noted.

Table 1

Physical Properties of Antimony Pentoxide vs. Trioxide

Property	Antimony Pentoxide	Antimony Trioxide
Formula	Sb2O5	Sb2O3
Solubility	Only concentrated, hot acids	Dilute acids and bases
Particle Size	0.03 microns	0.8-1 micron
Surface Area, m^2/gm	50	2
Specific Gravity	4.0	5.3
Refractive Index	1.7	2.1
Surface Activity	Weakly acidic	Usually neutral

Table 2

Antimony Synergists Tested

Antimony Product	Dispersed Particle Size
Nyacol ADP480	0.03 micron
Sb2O5 (MOD. 1)	0.05 micron
Sb2O5 (MOD. 2)	0.15 micron
Sb2O3 (Commercial Grade)	0.8-1.0 mciron
Sb2O3 (MOD. 1)	0.138 micron

Table 3

Halogens Tested

Halogen	Bromine Equivalent
Brominated Polystyrene	68%
Brominated Polystyrene	61%
Brominated Ethylene Carboximide	48%
Brominated Ethylene Phthalimide	67%
Brominated Aromatic Ester	63%
Chlorinated Paraffin	74% (Cl)
Proprietary Brominated Compound	72%
Brominated Dipentaerythritol	62%
Brominated Aromatic Compound	66%
Brominated Phosphate Ester	70%

Table 4

Other Flame Retardants Tested

Materials	Particle Size
Magnesium Hydroxide	5-15 micron
Colloidal Magnesium Hydroxide	0.225 micron
Zinc Borate	5-15 micron
Zinc Borate (MOD. 1)	0.25 micron
Ammonium Octamolybdate	5-15 micron
Molybdum Oxide	0.321 micron

Figure 1. Notched Izod Results

Table 5

Polymers Investigated

Polypropylene	Flexible PVC
Polyethylene	Nylon
Polyolefin Copolymers	PET
ABS	Polystyrene

Table 6

Antimony Synergist Analyses in Polypropylene

Material Tested	% FR	UL-94 Rating	After-flame Time (sec.)	Notched Izod (ft-lb/in)	Translucency
Virgin PP	0.0	Fail	-	0.64	Translucent
BAC/ADP480	4.0	V-2	0.4	0.61	V.Sl. Translucent
	2.5	V-2	2.9	0.64	Sl Translucent
	1.0	V-2	3.8	0.65	Translucent
BAC/Trioxide	4.0	V-2	0.0	0.35	Opague
	2.5	V-2	0.1	0.37	Opague
	1.0	Fail	-	0.37	V.Sl. Translucent
BAC/MOD 1 Pent	2.5	V-2	2.9	0.63	Sl. Translucent
BAC/MOD 2 Pent	2.5	V-2	2.4	0.62	Sl. Translucent
BAC/MOD 1 Triox.	2.5	V-2	7.0	0.60	V.Sl. Translucent
	1.0	Fail	-		Translucent
MOD 1 Pentoxide = 50nm avg. particle size
MOD 2 Pentoxide = 150nm avg. particle size
MOD1 Trioxide = 138nm avg. particle size
PP = Homopolymer/Polypropylene
BAC = Brominated Aromatic Compound

Table 7

Halogen Analyses in Polypropylene

		UL-94"
Material Tested	% FR	Rating		After-flame Time (sec)	Translucency
Virgin PP	0.0	Fail		-	Translucent
BP-68/ADP480^1	12.0	Fail		-	-
BP-60/ADP480^2	12.0	Fail		-	-
BEC/ADP480^3	8.0	Fail		-	-
BEP/ADP480^4	8.0	Fail		-	-
BAE/ADP480^5	12.0	Fail		-	-
CP/ADP480^6	12.0	Fail		-	-
PBC/ADP480^7	8.0	Fail		-	-
BD/ADP480^8	4.0	V2		41.0	V.Sl. Translucent
	1.0	Fail		-	Translucent
	1.0	Fail		-	V.Sl. Translucent
BPE/ADP480^9	4.0	Fail		-	-
BAC/ADP480^10	4.0	V-2		0.4	V.Sl. Translucent
	2.5	V-2		2.9	Sl. Translucent
	1.0	V-2		3.8	Translucent
1. Brominated polystyrene			7. Proprietary brominated compound
2. Brominated polystyrene			8. Brominated dipentaerythritol
3. Brominated ethylene carboximide			9. Brominated phosphate ester
4. Brominated ethylene phthalimide			10.Brominated aromatic compound
5. Brominated aromatic ester			11.Vertical Burn Test
6. Chlorinated paraffin			12.ADP480 is a colloidal-sized antimony pentoxide

Table 8

Smoke Suppression Additives

		UL-94
Material Tested^1	% Additive	Rating	Afterflame Time (sec.)	Optical Density Dm (Corr.)	Translucency
Zinc Borate (250nm)	0.5	V-2	29.0	161.3	Sl. Translucent
Zinc Borate (std.)	0.5	V-2	2.0	148.6	Sl. Translucent
MoO (321nm)	0.75	V-2	2.0	113.6	Opaque
AOM (std.)	0.75	V-2	38.0	125.1	Opaque
Control	0.0	V-2	2.9	103.3	Sl. Translucent
^1All samples incorporated BAC/ADP480 at a 2.5% FR loading.
^2ASTM E-662

Table 9

Magnesium Hydroxide FR System

			UL-94
Material Tested	% Additive	% LOI^2	Rating	After-flame Time (sec.)	Notched Izod (ft-lb/in)
Commercial Mg(OH)2	50	21.5	F	-	0.23
Kyowa (coated)^1	50	21.0	F	-	0.31
MOD Mg (OH)2 (225nm)	50	26.0	F	-	0.26
MOD Mg(OH)2 (coated)	50	23.0	F	-	0.26
COM + MOD Mg(OH)2 (40:10)	50	24.0	F	-	0.34
Commercial Mg(OH)2	62	25.0	V-1	48.0	0.29
COM + MOD Mg(OH)2 (50:12)	62	25.5	V-1	19.0	0.30
^1Coating - Stearic Acid
^2ASTM D2863

Table 10

Flexible PVC Results

		UL-94
Material Tested	% Additive	Rating	Afterflame Time (sec.)	Translucency
Virgin Flexible PVC	0.0	F	-