Multifaceted Flame Retardant Plastic Development Routes Accelerating Forward!

TAGS:  Flame Retardants 

1. Flame Retardants: Overview
2. Traditional FR Development Routes
3. Circular FR Development Routes
4. Radical FR Development Routes
5. Synergistic FR Development Routes
6. Recycling FR Development Routes

Flame Retardants: Overview

New Flame Retardant (FR) plastics trends are being driven by end-use customer needs for non-halogenated, low-smoke systems in demanding applications, and even recycling options with established halogenated FRs.

Established halogenated FR systems still hold the dominant market share position, but Halogen-free Flame Retardants or HFFR systems are emerging rapidly and are making the most noise in the marketplace about their developments.

More stringent environmental and health regulation on the horizon is also driving FR development towards more sustainable alternatives. Let’s take a look at various traditional, circular, radical, synergistic, and recycling FR development routes.

Traditional FR Development Routes

Momentive’s Silicon-based FRs as Replacements for Halogenated-based FRs

Starting off, Momentive is promoting their low toxicity silicone-based additives as replacements for halogenated-based flame retardants (FR). The core silicone oxygen bond is very safe in use from environmental, health, and safety perspectives in light of expected regulation to phase out halogenated FRs. Silicone oxygen bonds also promote:

• Very good mechanical property maintenance
• UltraViolet (UV) stability
• Flexibility range, and
• Electrical insulation capability important in key low smoke, wire and cable applications.

Momentive’s specific silicone-based flame retarded grade is SFR320 that at low 1% by weight loading levels can deliver an Underwriters Lab UL94-V-0 highest flammability resistance rating, and is very compatible with many different plastics.

No.	Composition (%)			FR Testing (1.6mm)	Transparency (1mm)	Izod Impact Notched (-30°C)
	PC	Anti-drip	SFR320	UL94	%	kJ/m2
1	100	0	0	V2	89	12
2	99.85	0.15	0	V2	88	17
3	99.85	0.15	1	V0	88	14

Huber’s FR Product Lines – Key Features and Applications

Next, Huber Engineered Materials is moving in multiple FR development directions with its Safire™ and Kemgard® product lines. Their new Safire™ 400 FR grade has:

• Reduced flame spread
• Low smoke suppression, and
• High char formation

It is based on a zinc phosphate melamine formulation and is very effective in wire and cable sheathing applications. Safire™ 400 also blends well with aluminum hydroxide producing a halogen-free, low smoke additive system with a high char surface layer that prevents plastic cable resin dripping.

Huber’s molybdate-based Kemgard® FRs are more specifically targeted at crosslinked PolyVinyl Chloride (PVC) to deliver high surface char formation in cable applications without any sacrifice to extrusion processability.

Overall a 10% Safire™ 400 FR additive by weight loading, when added to a traditional Huber's Hydral® 710 aluminum trihydrate clearly, demonstrates:

• Improved char formation
• Increased thermal insulation, and
• Reduced thermal conductivity

It is ideal in low smoke, low dripping wire and cable applications.

Byk’s Silicate Clay-based FR Additives Targeted at Nylon and Related Thermoplastics

Continuing, Byk has commercialized BYK-MAX CT 4260 FR additive, specifically targeted at nylon and related thermoplastics. This silicate clay-based additive finds strong use in non-halogen compounds where it enhances not only FR properties but adds low material dripping under a flame and high surface char formation.

Also, BYK-MAX CT 4260 offers reduced filler content translating into lower finished part weight and ease of processability. Additionally, improved oxygen and water barriers in concert with increased melt viscosity yield excellent dimensional stability, for example, in profile extrusion. As a further rule, nylon compound mechanical and electrical properties remain unchanged.

Kraiburg’s Non-halogenated FR ThermoPlastic Elastomers for E&E Applications

Delving further, Kraiburg is marketing non-halogenated FR ThermoPlastic Elastomers (TPE) compounds based on a variety of commercially available FR additives that readily bond to nylon that allow for soft TPE, hard nylon combinations for demanding electrical and electronic applications such as connectors, and small housings/enclosures.

Kraiburg’s primary focus is on developing Underwriters Lab UL94 lower V-2 to highest V-0 TPE ratings with a unique attention to compound temperature sensitivity. Under existing normal processing conditions 240°C is required to obtain TPE/nylon adhesion, whereas with Kraiburg’s newly developed proprietary FR TPE compounds only 190°C is needed for adhesion, thereby adding a key benefit in more energy-efficient, lower cycle time processing.

Polymer Resources’ Creating FR Compound Developments with UL94 V0 Ratings

Finally, specialty compounder Polymer Resources has taken a very traditional FR compound development approach by creating a range of Underwriter Labs UL94 V-0 across high-end engineering plastic blends, such as:

• Polycarbonate (PC)/PolyButylene Terephthalate (PBT) and
• PC/Acrylonitrile Styrene Acrylonitrile (ASA)

PC/PBT provides improved impact resistance, whereas PBT/ASA enhances Ultra Violet (UV) stability.

FR PC/PBT compounds are aimed at molded electrical and fiber optic sockets and plugs in medical electronic devices, and residential/outdoor uses. PC/ASA FR compounds are effective for medical/dental equipment molded electronic fixtures subjected to indoor UV light. Polymer Resources currently has seventy-five UL94 V-0 rated and approved compounds.

Circular FR Development Routes

Clariant’s Environmentally Friendly FR Versus Brominated FRs

First, let’s review Clariant’s environmentally friendly FR additive development approach. To this end, Clariant has internally developed a thirty-six standard Ecotain label keyed to emphasizing circular economy goals. For example, Clariant’s Exolit® OP 1400 FR additive for nylon use highlights sustainability in combination with a UL94 V-0 flame spread rating and a 600-volt comparative tracking index, ideal for use in the emerging electric vehicle market.

Similarly, Clariant’s Exolit® OP 1260 (TP) FR additive carries an Ecotain label for thermoplastic polyester like PolyButylene Terephthalate (PBT) use due to very good recycling capability in glass reinforced compounds averaging 30% regrind in a range of 10-50% regrind levels. Clariant’s Exolit® OP 1260 (TP):

• Has the highest UL 94 V-0 flame resistance in thin 0.4-millimeter wall thicknesses 
• Maintains excellent color fastness
• Has a 600-volt tracking index, and
• Holds a good mechanical property balance targeted at demanding connector applications in electric vehicles, where it can replace traditional brominated flame retardants, or BFRs.

George H. Luh’s Graphite-based FR for Nylon Compounds

Moving further, the George H. Luh company has developed a smoke-free, nonhalogenated, graphite-based FR additive for nylon compounds. Normally graphite has an upper 230°C temperature limit, rendering it useless in higher melting point nylons.

George H. Luh successfully introduced here their new expandable graphite GHL PX 95 HT 270 FR additive grade with its 270°C temperature capability that makes it useful in the 260°C nylon compound processing temperature range.

Work continues at George H. Luh on higher melting point expandable graphite grades. Temperature improvements center around blending different Magnesium DiHydroxide (MDH) and Ammonium PolyPhosphate (APP) combinations into expandable graphite to enhance its heat shield performance.

NeoGraf Solutions’ Expandable Graphite Flake Additives for Aerospace and Automotive Paneling

Ending with NeoGraf Solutions’ synthetic graphite sheets and powders, here is another non-halogenated, low-smoke FR additive development approach. NeoGraf’s GrafGuard® 280-50N expandable graphite flake additive is aimed at plastic molded and thermoformed applications.

GrafGuard® 280-50N has a current market high 280°C temperature resistance. It is used in plastic compounds based on:

• PolyStyrene (PS)
• PolyPropylene (PP)
• Acrylonitrile Butadiene Styrene (ABS)
• PolyEthylene Terephthalate (PET), and
• PolyAmide (PA, Nylon)

It can be blended with Magnesium Hydroxide (MgOH) for improved heat resistance and possesses a 300-micron particle size for ease of compound dispersion. It finds specialty application use in an extruded and thermoformed aerospace cabin and automotive FR heat shield paneling.

Radical FR Development Routes

Fraunhofer LBF’s Novel Free Radical Oxyimide FR Additive Technology Used in Plastic Compounds & Polyolefins

Let’s begin with a novel free radical oxyimide FR additive technology being developed by the Fraunhofer LBF. Oxyimide materials are non-halogenated FRs by themselves with 380°C upper melting temperature and are blendable with traditional phosphonate FRs. Their increased melt degradation temperature makes them useful in UL94 V-0 highest flame-retardant-rated engineering plastic compounds, for example at 3% loading levels in PolyAmide 6 (PA, Nylon).

Also, oxyimide is a very effective replacement for antimony trioxide in halogenated FR systems. Further, in polyolefin formulations such as PolyPropylene (PP) at low 2% blends of oxyimide with phosphonate show reduced burning profiles due to the formation of a novel glassy, intumescent barrier layer.

Fraunhofer LBF’s Bio-based FR Additives for Compounded in PLA

Concluding, let’s look at the Fraunhofer LBF’s work in flame retarding bioplastics. FR research focused on blending renewably sourced, phosphorous based lignins, cellulose, and pentaerythritol that created 5% and 10% based LBF-Polymer FR additives and when compounded into PolyLactic Acid (PLA) result in UL V-0 rated materials versus traditional polyester FR additives in PLA that only attain lower UL94 V-2 flame ratings due to polyester dripping upon burning ignition.

PLA Grade	Flame Retardant	UL-94 V
Low viscosity	no	V-2
Low viscosity	15% Polyester	V-2
Low viscosity	5% LBF-Polymer	V-0
High viscosity	no	Not classified
High viscosity	15% Polyester	V-2
High viscosity	5% LBF-Polymer	V-0

Fraunhofer LBF’s UL 94 Performance of Bio-based FRs in PLA

Synergistic FR Development Routes

MCA Technologies’ Triazine-based FR Showing Flammability & Thermal Stability

To begin with, flame retardant additive suppliers have put major development effort into synergistic FR systems. MCA Technologies has established a proprietary market lead here. Their technology is centered on triazine-based chemistry called piperazinyl-morpholinyl-triazine.

Their MCA® PPM Triazine HF grade acts as a smoke/toxic gas suppressant. Also, this PPMT grade is an effective heat stabilizer, and synergistically retards degradation particularly during FR compound recycling where heavily loaded, heat sensitive, insoluble phosphorus, inorganic and nitrogen FRs, the so-called PINFRs are used. These triazine-based systems have a non-blooming, non-bleeding feature during the plastic compounds’ useful product life.

Finally, triazine-based FRs go beyond normal plastics recycling permitting energy extraction via pyrolysis without toxic gas release. MCA PPM Triazine improves thermal stability (TGA, Thermal Gravimetric Analysis) has been shown to enhance the fire retardancy of 35% glass-reinforced PolyAmide 66 (PA66, nylon) specifically a Durethan® AKV35CXH2.0 by Lanxess.

Quarzwerke’s Kaolin Clay-filled Nylon 6 Compounds with UL 94 Ratings

To end with, antimony trioxide has been identified as a cancer-causing carcinogen in humans. Enter Quarzwerke’s Kaolin clays as partial synergistic alternatives for antimony-based FRs in, for example, glass-reinforced nylon compounds.

Kaolin clay is good temperature resistance wise to 400°C and can thus act as a successful flame retardant. Normally 20% minimum phosphinate FR additive levels by weight are required to attain UL94 V-0 flame ratings in thin wall, 0.8 millimeter or less thicknesses. It was also found that traditional amounts of antimony-based FRs could be reduced with Kaolin clay addition while retaining key mechanical properties.

FR Content	FR Concentration	Burning Time After first flame	Burning Time After second flame	Flame Dripping	UL-94 Rating
Kaolin TEC 110 AST with Phosphinate1	30% Kaolin, 20% FR	7.06	9.87	0/51	V-0
	30% Kaolin, 18% FR	16.19	10.4	0/51	V-0
	30% Kaolin, 16% FR	16.67	14.8	0/51	V-0
	30% Kaolin, 14% FR	19.2	3.0	0/51	V-0
	30% Kaolin, 12% FR	68.4	5.7	0/52	V-2
Kaolin TEC 110 AST with Phosphinate2	30% Kaolin, 20% FR	9.32	-	0/51	V-0
	30% Kaolin, 18% FR	16.42	8.43	0/51	V-0
	30% Kaolin, 16% FR	11.51	24.73	0/51	V-0
	30% Kaolin, 12% FR	20.7	6.7	0/51	V-0
Note: 1 – None of 5 samples tested exhibited flame dripping; 2 – All samples exhibited flame dripping

Quarzwerke’s Kaolin Clay Filled Nylon 6 Compounds with UL 94 Ratings

Recycling FR Development Routes

Albemarle’s SAYTEX® BFR Product Lines Compared to Virgin Resins

The still globally dominant, halogenated, Brominated Flame Retardant (BFR) suppliers have not been standing idly by in the emerging era of halogen-free additive alternatives. For example, major specialty chemical and market-leading bromine chemistry supplier Albemarle is promoting their SAYTEX® FR additives product line.

This product line including grades SAYTEX® 8010 and SAYTEX® BT-93W is composed of large bromine molecules with very good toxicology profiles. These large molecules do not accumulate waste products as they are insoluble in water and organic substances like oils. Further in repeated recycle studies of up to six iterations they demonstrate superior retention of flame retarded, mechanical, and thermal properties, outdoing virgin resin property maintenance after three recycles going forward.

More specifically Albemarle has commercialized a newer Saytex Alero polymeric BFR targeted directly at maintaining impact and heat resistance in intermediate resins like High Impact PolyStyrene (HIPS) and Acrylonitrile Butadiene Styrene (ABS).

ICL’s Brominated FR Blended Additives for Electronic Applications  

Finally, ICL another major global BFR supplier has focused its FR recycle development on specific electronic TV display applications. ICL used three specific blended additives namely:

• An F-2400 epoxy BFR plus Antimony Tin Oxide (ATO),
• An F-2400/F-2016 epoxy BFR plus ATO—with both preceding FR additive systems compounded into Acrylonitrile Butadiene Styrene (ABS), and
• A Fyrolflex® Resorcinol bis DiphenylPhosphate (RDP) FR compounded into PolyCarbonate (PC)/ABS.

After the first recycle, 50/50 mixes of the preceding cycle were blended with the original virgin compound. The ABS compounds maintained their original UL94 V-0 ratings through five cycles, whereas the PC/ABS formulation maintained a UL94 V-1. Notched Izod impact dropped off 15% through five recycles for the ABS compounds, and fell off 30% for PC/ABS.

ICL also measured GreenHouse Gas (GHG) emissions in CO₂ equivalents and found that ABS as well as High Impact PolyStyrene (HIPS) TV cabinets had lower carbon footprints by a third versus PC/ABS.

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