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FR Applications of Plastic Nanocomposites

by
Tie Lan, Guoqiang Qian, Ying Liang and Jae Whan Cho
Nanocor, Inc.
1500 West Shure Drive
Arlington Heights, IL 60004


ABSTRACT
Quick jump to:
Introduction and Background
Nanomer and Polyolefin-Nanomer
Concentrate Products

Study Materials Preparation
Synergistic Effect with Mg(OH)2
Synergistic Effect with
Halogenated FR Systems

Commercial Example
Conclusion
References

Nanometer scale layered silicates have been incorporated into plastics to form fire retardant nanocomposite compounds in commercial scale. In particular, nanocomposites have been formulated with traditional fire retardants to provide certified fire retardation and enhanced mechanical properties.



INTRODUCTION
Nanomers
® are surface surface modified montmorillonite minerals available for a range of polymer resins from commodity polyolefins to specialty polyamides. Nano-effects have been demonstrated for resins in which Nanomers are added either during polymerization or by melt compounding. Montmorillonite’s unique morphology contributes to improved strength and toughness, heat/dimensional stability, gas barrier and flame retardancy. Recently, Nanomer product lines have been expanded to polyolefin-Nanomer concentrates. These concentrates feature easy handling, improved dispersion and other benefits.

Nanomers® have been used commercially to make plastic nanocomposites. Because Nanomers are used at low addition levels, significant property improvement is achieved with lighter part weight. Due to Nanomers platey morphology and propensity to accelerate polymer crystallization, gas barrier enhancement is a common feature. Nanocomposite plastics are also potent char formers, making them a valuable tool in creating improved fire retardant materials. FR applications of nanocomposites attract a great attention of academic and industrial researchers. A number of mechanistic theories have been proposed, such as char formation, fuel/exhaust transport or diffusion, and free radical capture. This presentation will be focused on Nanomer products, and their usage in FR-nanocomposite formulations. Particular attention is focused on the use of Nanomers with traditional FR agents in polyolefin matrices and the synergy created by these combinations.



Nanomer and Polyolefin-Nanomer Concentrate Products

Nanomers® I.30P, and I.44PA are Nanocor’s commercial products. Each is an onium ion modified montmorillonite, designed for maximum compatibility and dispersion in a polyolefin matrix. Available as free-flowing powders with a mean dry particle size of 15-25 microns, they are capable of dispersing to nanoscale in twin screw compounders. I.30P is required for film grade nanocomposite while I.44PA is used for engineering grade applications.

A typical Nanomer-Polyolefin concentrate contains 40~60 wt% Nanomer with the balance a combination of compatibilizer and standard polyolefin. Concentrate product pre-disperses Nanomers, promoting full nanocomposite formation while minimizing heat history during letdown. Currently, Nanocor is actively marketing C.30P4 and C.44PA concentrates. These concentrates contain 40wt% I.30P and 50 wt% I.44PA, respectively.



Study Materials Preparation

For this study concentrates were first prepared, they were letdown with combinations of traditional FR agents to create the final nanocomposite.

A Lestritz co-rotating twin screw extruder was used to produce both the concentrates products and nanocomposites. The extruder has a diameter of 27 mm and a L/D ratio of 36:1. There are three shear-mixing zones in the extruder set-up to maximize dispersive energy. Screw speeds ranged from 300-500 rpm and extrusion temperatures ranged from 170~190 ºC. A detailed screw configuration is shown in Figure 1.

Figure 1. Extruder screw design for Polyolefin nanocomposite and Nanomer-polyolefin concentrates





Synergistic Effect with Mg(OH)2

Nanomer synthergy effect with Mg(OH)2 was studied in an EVA (UE-635-000, Equistar) system. Nanomer I.30P and standard grade Magnifin® H10 Mg(OH) 2 were used as received. The incorporation of Nanomer can also be achieved through a Nanomer-EVA concentrate, which is very similar to C.30P4 product. Various EVA/Mg (OH)2/Nanomer formulations were listed in Table 1. Materials were injection-molded and tested following UL94 vertical burning testing method.

Table 1. EVA/Mg(OH)2/Nanomer Compositions and UL-94 1/8” FR Rating

Components
EVA (wt%) 40 45 42 39 50 47
Mg(OH)2 (wt%) 60 55 55 55 50 50
Nanomer (wt%) 0 0 3 6 0 3
UL94 rating V-0 Fail V-0 V-0 Fail V-0

Nanocomposite formulations burn at a noticeably reduced burning rate and a hard char forms on the surface. They also exhibit minimum dripping and fire sparkling. The UL-94 test results indicate that 60wt% addition of Mg(OH) 2 is required to maintain FR rating for this EVA system. Inclusion of Nanomer at 3 wt% maintains the V0 rating, while lowering the Mg(OH) 2 to only 50wt%. With lowering the amount of Mg(OH) 2, the formulations containing Nanomer I.30P provide comparable FR rating, but improved processing and mechanical properties.



Synergistic Effect with Halogenated FR Systems

The bromine containing FR agent DBDPO (Decabromodiphenyl oxide) is available from Albemarle Corp. and Great Lakes Chemical, under the trade names of Saytex® 102E and DE-83R, respectively. DBDPO was used to study the synergistic effects with Nanomer in a homo-PP system. Both Nanomer and Nanomer concentrate were incorporated using twin screw extruder shown in Figure 1. In addition, Nanomer concentrate C.44PA can be incorporated into the formulation through single screw extruder equipped with mixing screw such as the “Nano-Mixer™” co-developed by New Castle Industries and Nanocor, Inc.

Table 2. PP/DBDPO/Nanomer Compositions and UL94 FR 1/8” Rating

Components
Homo-PP (wt%) 73.3 80 77 74 74 68
DBDPO (wt%) 20 15 15 15 15 15
Sb203 (wt%) 6.7 5.0 5.0 5.0 5.0 5.0
Nanomer I.44PA (wt%) 0 0 3.0 6.0 (3.0) (6.0)
Nanomer C.44PA (wt%) 0 0 0 0 6 12
UL94 rating V-0 Fail V-2 V-0 V-2 V-0


The burn characteristics are quite similar to the EVA/Mg(OH)2 nanocomposites: namely reduced burning rate/minimal dripping and sparkling. UL-94 test results (Table 2) indicate good synergy between DBDPO/ Sb2O3 with Nanomer. 6wt% Nanomer I.44PA addition can reduce DBDPO/ Sb2O3 use by 7wt%. and maintain the same UL-94 rating. In addition, the incorporation of Nanomer in the DBDPO/ Sb2O3 system increases the mechanical properties and lowers the FR agent migration. This will enable formulator to tailor the system composition to meet different application requirements.



Commercial Example

Nanocor is supplying Nanomer® products to the market. Nanocomposites for FR uses are available from Gitto/Global Corporation, Lunenburg, MA. One example of the FR application is heavy-duty electrical enclosures. These enclosures, typically injection molded polypropylene, vary in size from a cubic foot to a cubic yard. Because they house electrical items, flamability is a central concern. But weight is also important since many enclosures must also be portable. Lastly, electrical components can themselves be quite heavy, making enclosure strength a key element. By switching to a nanocomposite, the level of the FR additive package is significantly reduced, taking the enclosure’s specific gravity from 1.35 down to 1.16 and reducing overall weight by 18%. Both flexural and tensile moduli increase 25% on average without loss of izod impact. The enclosures maintain their original UL-94 V-0 rating, yet they are both stronger and lighter.



Conclusion

Incorporation of Nanomer into plastics can provide synergistic effect with traditional FR agents. In a typical formulation, Nanomers readily promote the formation of tough char layers during burning. Char formation impedes the movement of volatilized polymer from the interior of a plastic matrix, denying fuel at the air/surface interface. Employed in conjunction with traditional flame retardants, nanocomposites can achieve equivalent fire ratings using significantly reduced FR additive packages. With less FR additive dilution and greater reinforcement via nanocompositing itself, mechanicals are largely restored to levels seen in neat resin and at lower cost. This combination of benefits will likely make fire retardancy the largest application area in the near future.


 

References

  1. Gilman, J.; Kashiwagi, T.; Morgan, A.; Harris, R.; Brassell, L; Vanlandingham, M.; Jackson, C.; FLAMMABILITY OF POLYMER CLAY NANOCOMPOSITES CONSORTUM: YEAR ONE ANNUAL REPORT, 2000. NIST.

  2. Porter, D.; Metcalfe, E.; Thomas, M.; NANOCOMPOSITE FIRE RETARDARTS-A REVIEW; FIRE AND MATERIALS, 24, 45-52, 2002.

  3. Lan, T.; Cho, J.; Liang, Y.; Qian, G.; Maul, P.; APPLICATIONS OF NANOMER IN NANOCOMPOSITES: FROM CONCEPT TO REALTY; Nanocomposites-2001, Chicago, June 25-27, 2001.

  4. Qian, G.; Cho, J.; Lan, T.; PREPARATION AND PROPERTIES OF POLYOLEFIN NANOCOMPOSITES; Polyolefins 2001, Houston, TX, February 25~28, 2001.

  5. Zhu, J.; Uhl, F.; Morgan, A.; Wilkie, C.; STUDIES ON THE MECHANISM BY WHICH THE FORMATION OF NANOCOMPOSITES ENHANCES THERMAL STABILITY, Chemistry of Materials; 0897-4756, 2001.


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