Brominated Flame Retardants

7. Materials and Products with Alternative Flame Retardants

7.1 General Aspects
7.2 Electronic and Electrical Appliances
7.2.1 Printed Circuit Boards
7.2.2 Electronic Component Encapsulates
7.2.3 Housing of Electronic and Electric Appliances
7.2.4 Switches, Sockets, etc.
7.2.5 Other EE Equipment Parts
7.3 Lighting
7.4 Wiring
7.4.1 Wires and Cables
7.4.2 Wall Sockets and Mounting Boxes
7.4.3 Relays, Contactors, Starters, etc.
7.5 Textiles
7.5.1 Furniture
7.5.2 Carpets
7.5.3 Clothing
7.6 Building Materials
7.6.1 Expanded Polystyrene and Extruded Polystyrene Foam
7.6.2 Rigid Polyurethanes
7.6.3 Foils
7.7 Paint
7.8 Transportation
7.9 New Flame Retardant Concepts

In the following section, products containing halogen-free flame retardants substituting for the main applications of brominated flame retardants are reviewed.

A description of the main alternatives to brominated flame retardants is included in section 8.

The exposition of alternatives should not be interpreted as a recommendation from the authors or the Danish EPA to use specific flame retardants or specific products.

7.1  General Aspects

Flame retardants safe lives. A recently published assessment from the University of Surrey of the risks and benefits in the use of flame retardants in consumer products concludes that: 'Information available suggests that the benefits of many flame retardants in reducing the risk from fire outweigh the risks to human health' /100/. The assessment proposes that continued reduction in fire losses can be achieved by reducing the inherent fire risk of consumer products by product modification (e.g. using flame retardants or low flammability materials) particularly for higher risk items like furniture and TV-sets.

When replacement of brominated flame retardants is discussed, it is thus essential that the alternatives do not increase the risks to human health, but on the other hand the goal must be a situation where - with reference to the quotation above - the benefits of all used flame retardants outweigh the risks to human health and the environment.

Previous reviews

Alternatives to brominated and other halogenated flame retardants in EE equipment have previously been reviewed by the German Electrotechnical and Electronic Association, ZVEI (1992) /34/ and OECD (1994) /11/.

Alternatives

Brominated flame retardants only account for about 15% of the global flame retardant consumption. Consequently a large number of compounds may be considered as alternatives to BFRs. The Index of Flame Retardants (1997) /13/, an international guide to more than 1000 products by trade name, chemical, application, and manufacturer, contains more than 200 commercial flame retardant chemicals.

The alternatives in question here, however, are compounds that can be used as substitutes for BFRs for applications where BFRs are in use today. The review will focus on alternatives that are commercially available or upcoming. In section 7.9 some new halogen-free flame retardants still at the experimental stage will shortly be mentioned.

Subjects to be considered

Alternatives will most often on the face of it have some disadvantages in comparison with the currently used material. For the selection of alternatives for a specific application the following subjects have to be considered:

In principle there will be alternatives to halogen-containing flame retardants for almost all applications - it depends on the costs and/or technical disadvantages the user is willing to accept.

Changes in machinery

The expenses of changes in tools and machinery may be a very significant restriction to the introduction of alternative plastic materials, and this parameter is very sensitive to the time factor of substitution. If substitution can take place within the frame of the periodical renewal of machinery, the extra expenses will often be very limited. The expenses, however, will be dependent on the actual machinery of the individual manufacturer and it is not possible to give a general estimate on these expenses. Consequently these expenses will not be included here.

In a discussion of the feasibility of substitution of brominated flame retardants it is necessary to discuss to what extent the alternatives fulfil the same function as the current used material. With a term applied from the field of life cycle assessment (LCA) it is necessary to define the ‘functional units’. The functional units will here be defined as some physical/chemical requirements to the end product containing the flame retarded plastic part.

Three levels

The substitution of brominated flame retardants can then take place at three levels:

1. The brominated flame retardant can be replaced by another flame retardant without changing the base-polymer.
2. The plastic material, i.e. the base polymer with flame retardants and other additives, can be replaced by another plastic material.
3. The product can be replaced by a different product, or the function can be fulfilled by the use of a totally different solution.

An example of the latter can be a solution where a reduction of the risk of flame spread in electronics is achieved by a metal sheet covering the plastic in contacts with current-carrying parts.

Fire safety requirements

In Denmark fire safety standards for electric appliances do not set up material specific requirements. The object of the tests is the whole appliance. It is convenient, however, when discussing substitutes for BFR-containing plastics to refer to properties of the plastics tested with material specific test methods.

Flammability parameters

Two parameters often used are the limiting oxygen index and the UL94 flammability rating. The UL94 tests have been described in section 6.2.1.

Limiting oxygen index

The limiting oxygen index expresses the minimum percentage of oxygen required to sustain ignition and combustion. If the limiting oxygen index is 20% (atmospheric concentration) or lower, the plastic will continue burning when ignited in atmospheric air.

There is no simple relation between UL94 rating and oxygen index, but the oxygen index gives a broad indication of the flammability performance of the material.

Oxygen indexes of a number of base polymers and V-0 grade plastics based on the same polymers are shown in table 7.1. The oxygen index of the polymers and plastics will vary somewhat and slightly different values can be found in different references.

The flammability of the plastics will be dependent on the thickness of the materials, and in the specification of the flammability of the materials the necessary thickness for the rating will often be mentioned.

The oxygen index is also dependent on addition of reinforcement material. The addition of for instance glass fibres will lower the oxygen index of the plastic material.

Selfextinguishing polymers

Polymers with a limiting oxygen index of more than about 30% are selfextinguishing, i.e. they can be used as flame retardant grades without addition of flame retardants. The three plastics, polysulfone, polyaryletherketone and polyethersulfone in table 7.1 have so high oxygen index that flame retardant grades are obtained without addition of flame retardants.

Table 7.1
Limiting oxygen index of base polymers and V-0 grades of some plastics

Flame retardants

Flame retardants are added to inhibit or suppress the combustion process. The necessary load of flame retardants required to obtain a certain flammability rating of a plastic material will depend on the flammability of the base polymer. As an example, the red phosphorus concentration required for UL94 V-0 rating for a number of polymers is shown in table 7.2. The required concentration is broadly inversely proportional to the oxygen index of the polymer ranging from 15% in polystyrene (LOI ~ 18) to 1.2% in polycarbonate (LOI ~ 29).

The results show that the required flame retardancy of the polymers can be obtained with red phosphorus. Similar results may be shown for other non-halogen flame retardants as magnesium hydroxide, melamine derivatives, organophosphorus compounds and zinc borate (may be in combination). There are a number of non-halogen flame retardants available to make the polymers flame resistant - the main question is to what extent the addition of the flame retardants has some adverse effect on other technical properties of the polymers and increase the total costs.

Table 7.2
Red phosphorus concentration required forUL94 V-0 rating (applied from /11/)

Relative price of alternatives

The price of some of the alternatives and most used brominated flame retardants are shown in table 7.3. Prices for more flame retardants can be found in IAL Consultants 1999 /18/. The prices of the alternatives are in general not higher than the BFRs but higher loading is often necessary. This is in particular true with respect to the inorganic compounds aluminium trihydroxide and magnesium hydroxide. Due to the low price of aluminium trihydroxide alternative materials may not be more expensive than BFR containing materials, but magnesium containing materials will usually be significantly more expensive.

Table 7.3
Prices of flame retardants on the W. European market 1998 (after /18/).

In the following halogen-free commercially available raw materials and end products that fulfil the requirements of the market will be presented. Prices of the alternative materials in comparison to BFR containing materials will be included in the presentation.

7.2  Electronic and Electrical Appliances

Possible substitutes of brominated flame retardants in electronics were in 1992 reviewed by the German Electrotechnical and Electronic Association, ZVEI /34/.

In the report a number of substitution initiatives in the German industry was discussed - initiatives that meanwhile have led to introduction of a number of commercially available halogen-free flame retarded plastics. A 1992 review of possible halogen-free flame retardants by base polymers from the report is shown in table 7.4.

Table 7.4
Halogen-free flame retardants for polymers used in EE-equipment, 1992 (Based on /34/)

For some of the main applications in electronics, substitution is, however, still on the experimental stage. At the Swedish Institute for Production Engineering Research (IVF), Göteborg, an international research project on flame retardancy in electronics, including demonstration of halogen-free alternatives for printed circuit boards, is presently going on /102 /. The project is planned to completed during the spring of 1999.

7.2.1 Printed Circuit Boards

In order to meet international standards (UL 94 V-0, see section 6) printed circuit board base materials have to be flame retarded. At present this is predominantly achieved by using TBBPA retarded epoxy-laminates or paper/phenolic laminates with TBBPA or PBDEs.

Epoxy laminates

Alternatives

A printed circuit board with a halogen-free epoxy resin has been presented by Gentzkow et al. (1997) /103/. A detailed description of the material and investigation of products formed during combustion of the material can be found in /104/.

The alternative epoxies contain tailor-made nitrogen and phosphorus constituents, that form flame retardant structures during processing and curing of the material.

The alternative material is more expensive than traditional printed circuit board base material but has, according to Gentzkow et al. /103/, higher dimensional stability at elevated temperatures that should result in reduced waste and repair during processing.

Price of alternative

The alternative is available from a major German producer of laminates for printed circuit boards. The price of the alternative is at present 2-4 times the price of a traditional FR4 printed circuit board laminate.

It is estimated by Gentzkow et al. /103/ that the price of the alternative printed circuit board base material in full-scale industrial production will be 20 to 30% higher than current bromine-based materials.

According to the producer of laminates, a new halogen-free epoxy-based laminate should be on the market in spring 1999 at an expected price of about 30% higher than current bromine-based materials.

Japanese produced halogen-free FR4 laminate should be available on the world market, but it has not been possible to obtain specific information on the laminates.

Products with alternatives

The halogen-free FR4 laminates are only used in a limited number of products, among them a programmable logic control for control and monitoring of industrial processes. Computers with halogen-free epoxy laminates are not available (Dec. 1998).

According to an article in Environmental Data Services (1997) /105/, the halogen-free epoxy circuit board will not be used widespread until electronic components with halogen-free coatings are available on the market. As long as the component encapsulates contain BFRs, it will no be possible to make a complete halogen-free assembled printed circuit board and the products cannot be marketed as 'halogen-free'.

This ascertainment is only right in so far as the prices of halogen-free products are significantly higher than the brominated.

Epoxy laminates with nitrogen/phosphorus constituents

Halogen-free flame retardants for thermosets (e.g epoxy and unsaturated polyester) have been described by Hörold and Hürth-Knapsack (1988) /106/. By a combination of ammonium polyphosphate and aluminium trihydroxide FR formulations for polyurethanes, polyester (UP) and epoxy laminates can be made. For epoxy laminates UL94 V-0 rating can be passed with a filler rate of about 60 parts powdered flame retardants to 100 parts resin. Similar flame retardancy can be obtained by a combination of aluminium trihydroxide and red phosphorus. The flame retardants may be used for technical laminates in electronic/electrical applications or laminates used in trains and aircraft (see also section 0).

As to the knowledge of the author of this report, the use of the formulation for electronic/electrical applications is still at the experimental stage.

Phenolic laminates

In paper/phenolic laminates for printed circuit boards TBBPA or PBDEs are typically applied as additive flame retardants.

Several types of halogen-free FR2 laminates are traded on the Danish market. The laminates are flame retarded with nitrogen and phosphorus constituents. The specific compounds and concentrations are considered confidential.

Price of alternative

Halogen-free FR2 laminates are according to the producers of the same price as European produced bromine based FR2 laminates.

Products with alternatives

TV-sets and other home-electronics with halogen-free FR2 laminates are available on the market.

Alternative materials

Ceramic laminates are available today for specific applications, but they are expensive compared to the epoxy based laminates. According to experts within the line of business, the application of ceramic laminates is not expected to be widespread within the years to come.

7.2.2  Electronic Component Encapsulates

Encapsulates for semiconductors and other electronic components have traditionally been made of epoxy based thermosets containing brominated flame retardants.

Epoxy based

An epoxy based halogen-free moulding compound for electronic component encapsulations of same the structure as described for FR4 laminates /103/ has been developed together with the laminates. The compound is at present not commercially available and electronic component encapsulates based on the resin are not available. Commercialisation of the material in 1999 is planned in a co-operation of Japanese and German companies.

Casting resins of epoxy and unsaturated polyester flame retarded with red phosphorus should be available for encapsulation of electronic devices, but it has not been possible to obtain specific information on the current application of the resins.

Polyphenylene sulphide

Low fluidity and susceptibility to humidity have been the main drawback to the use of thermoplastics in electronics encapsulates. Recent experiments with polyphenylene sulphide (PPS) have shown that the polymer can be improved for encapsulate application. The improved polymer has lower viscosity required for damage-free moulding, is unaffected by the heat generated in soldering, and remains viable in highly humid conditions /107/. The polyphenylene sulphide is selfextinguishing and does not need flame retardant additives. The new encapsulates have initially been applied to power transistors, and mass production is planned to start in January 1999.

The production cost of the PPS encapsulates is according to the producer not higher than the cost of traditional encapsulates.

7.2.3  Housing of Electronic and Electric Appliances

Traditionally BFRs have been applied for housing of business electronics and TV-sets made from HIPS, PC or ABS among other polymers /11/.

According to /11/ the consumption of DeBDE with HIPS and PC made up 30% and 5%, respectively, of the total consumption of DeBDE. In Denmark BFR-containing ABS rather than HIPS, however, has been used for production of housing for consumer electronics and electromedical appliances.

In 1997 only bromine-free FR-grades of PC was used for Danish production, and the consumption of BFR containing ABS was only a few percentages of the former consumption.

Alternatives

Presently, no halogen-free ABS is commercially available.

There are several halogen-free alternatives for housings on the market:

For most of the compounds the specific organic phosphorus compounds used are considered confidential, but according to a review of phosphorus-containing flame retardants, triaryl phosphates and resorcinol bis(diphenylphosphate) are used as flame retardants for polyphenylene ethers and PC/ABS /109 /.

Triphenyl phosphates have been used (and may still be used) for PC/ABS blends. According to /109/, the triaryl phosphates vaporise at the high temperatures required for processing engineering plastics and resorcinol bis(diphenylphosphate) that is less volatile has to a large extent substituted for the triaryl phosphates in modified PPE and PC/ABS.

'The Index of Flame Retardants' /13/ specifically mentions the following triaryl phosphates as used in thermoplastics: Tricresyl phosphate, triphenyl phosphate, and triisopropylphenyl phosphate. Tricresyl phosphate and triphenyl phosphates are described in section 8.1 and 8.1.2.

Price of alternatives

The price of halogen-free alternatives to BFR-containing ABS e.g. ABS/PC blends is comparable to the price of PBDE free ABS on the market, but some 20-30 % higher than the cheapest PBDE containing ABS compounds.

Products with alternatives

Most TV-set backplates and PC-monitor housings on the North European market are today halogen-free. It should be noted, that the fire safety requirements for TV backplates and PC monitor housing in Europe can be met using materials of lowest fire safety performance, the HB rating, whereas V-0 rating is required for TV-set enclosures in the USA. The fire safety requirements for TV backplates in Europe will presumably be V-1 rating from year 2002.

The above mentioned alternatives are also available in V-0 grades /101/, but the price differences between brominated plastics and alternatives may be higher.

Alternative solutions

In at least one product the PC monitor casing does not contain flame retardants. Fire safety is obtained by a constructive solution, where the electronic parts are separated from the casing by an aluminium sheet. The price of the solution is higher that traditional solutions, but there is no information on the exact difference.

7.2.4 Switches, Sockets, etc.

The flame retarded plastics used for switches, sockets and other applications where the material is in direct contact with live parts of electronic and electrical appliances are chiefly FR grades of thermoplastic polyester (PBT and PET) and polyamides (PA).

PA and PBT have traditionally been flame retarded with brominated flame retardants. According to OECD (1994) /11/ PBT/PET and PA accounted for 20% and 15%, respectively, of the global consumption of DeBDE.

In Danish production TBBPA has substituted for DeBDE in PBT and PET. Brominated styrene is used in minor part of the flame retarded grades of polyamides.

For polyamides several halogen-free alternatives are available on the market, but it is still difficult to find substitutes for bromine containing PBT.

The characteristics of PBT that are most difficult to substitute are high dimensional stability and low water absorption. Beside these characteristics PBT has great stiffness and strength, high resistance to chemicals and heat distortion, good dielectric properties and high gloss and surface hardness.

Alternatives

By the early nineties experiments on halogen-free grades of engineering thermoplastics were initiated by several of the leading European producers of plastic materials (see e.g. /34/).

Today there is a number of halogen-free engineering thermoplastics on the market. The main question is to what extent they actually can be considered as substitutes for the BFR-containing engineering plastics.

Substitution is of cause most difficult where the high UL94 V-0 rating is required. In table 7.5, examples of commercial halogen-free V-0 rating grades of engineering thermoplastics are listed.

PBT and PET may be flame retarded with diarylphosphonate /34/, melamine cyanurate /11/ or red phosphorus /11/.

Tests of halogen-free grades of PBT have been performed by various companies and preliminary data sheets on the compounds are available, but at present there is, as to the knowledge of the authors, only one commercial halogen-free V-0 grade PBT available on the market. The halogen-free grades have evinced some technical drawbacks, e.g. insufficient thermal stability.

The halogen-free PBT has been tested and is planned to be mass-produced by the end of 1998 by a Japanese producer /110 /. It has not been possible to obtain information on the flame retardant used in the PBT or the price of the compound. As to the producer, the halogen-free PBT should maintain the same machine properties and flame resistancy as bromine containing PBT.

Table 7.5
Examples of commercial halogen-free V-0 rating grades of engineering thermoplastics 1)

Polyamide (nylon) is commercially available in a number of products with at least four different flame retardants, either red phosphorus, magnesium hydroxide, melamine cyanurate, or melamine polyphosphate (some are e.g. described in /111 /).

Red phosphorus has actually been used for many years in polyamide /11/. Red phosphorus can be used as a flame retardant additive for a wide variety of plastics. However, it is most efficient in oxygen-containing polymers. The red phosphorus concentration required in polyamide for UL-94 V-0 rating is according to /11/ about 7%. According to one producer of red phosphorus containing polyamide, the mechanical properties of the polyamide are hardly impaired by the small quantities of phosphorus. One disadvantage of the red phosphorus is that the polyamides due to the reddish colour can only be offered in the colours grey and black.

There are risk factors working with red phosphorus including flammability and autoignition, and disproportionation will give toxic phosphine. Suitable stabilisation and encapsulation in polymers have led to commercial concentrates with 50% red phosphorus /108/.

Where red phosphorus cannot be used for aesthetic or other reasons, magnesium hydroxide may be used as a halogen-free alternative. Effective flame retardancy is only possible, however, when around 50% (w/w) of magnesium hydroxide is added to the plastic (V-0 grade). The high loading of magnesium hydroxide has an adverse affect on mechanical and processing properties of the polyamide.

In un-reinforced polyamide where extreme toughness is crucial, flame retardancy can be achieved by melamine cyanurate. Reinforced melamine cyanurate containing polyamide is only provided in V-2 rating grades.

A newly introduced reinforced polyamide with melamine polyphosphate is available in grades that meet the V-0 requirements.

Halogen-free polyamides may for some applications be used as substitutes for PBT. The polyamide has significantly higher water absorption than PBT and less dimensional stability. It has not been possible to identify a case of substituting polyamide for PBT.

In Danish production halogen-free grades of polyamide have for several years substituted for bromine-containing grades. In the assessment from OECD /11/ polyamide accounted for 15% of the DeBDE consumption, nearly as much as the consumption with PBT/PET. The lack of BFR containing polyamides in Danish production is not due to a characteristic consumption pattern in the Danish industry, but the fact that halogen-free grades of polyamide are used for most applications.

Polyketones can be rendered flame retardant with the use of magnesium hydroxide /112 /. The aliphatic polyketone used is an alternating polymer comprised of ethylene, carbon monoxide, and a minor amount of propylene. With a loading of 30% (w/w) uncoated magnesium oxide, the limiting oxygen index of the compound rose from 20% to 33%. UL94 V-0 rating (at 1/16 inch) could be obtained with a magnesium oxide loading of 20-30%.

A range of V-0 rating grades of polyketone is available for applications in the automotive and electrical/electronic appliance markets. There are at present no examples in Scandinavia of production processes where polyketones have substituted for BFR containing plastics.

The price of the polyketone is about 50% higher than that of polyamide (nylon 6).

Self extinguishing high performance polymers

There are a number of high performance thermoplastics such as polysulfone, polyaryletherketone (PAEK) or polyethersulfone (PES) which are selfextinguishing, i.e. they do not need flame retardant additives. The polymers are used for applications where high temperature resistance is needed or low smoke densities in the event of a fire are important (e.g. aircraft, ships or tunnel constructions). The relatively high price makes these high performance polymers less attractive alternatives to e.g. brominated PBT. The high performance polymers have additionally some drawbacks as regards the isolating performance of the plastics.

Prices of alternatives

The price of halogen-free grades of polyamide is basically the same as bromine containing grades.

The restraint on replacing bromine containing PBT by halogen-free polyamide is not the price, but the technical properties of the plastics. The price of PBT and polyamide is quite the same.

Halogen-free polyketone is about 50% more expensive than polyamide, and the price difference gives some restraints on replacing e.g. PBT/PET by halogen-free polyketone.

The price of high performance thermoplastics such as polysulfone, polyaryletherketone (PAEK) or polyethersulfone (PES) is significantly higher than the price of PBT and PA. In general terms the price varies from 2x for polysulfone to significantly more for the most expensive.

Products with alternatives

Products with halogen-free polyamide are widespread.

Products with halogen-free PBT have not been identified.

Summary

Halogen-free grades of polyamide are available for most applications, and halogen-free end products are widespread. There may be some specific applications where substitution is difficult, but they have not been identified.

Bromine containing PBT/PET may be replaced by halogen-free polyamides, polyketones or other polymers.

For many applications the technical requirements of the end products may be reached by the alternatives, but a substitution will often require changes in machinery and design of the products. The cost of such changes will be very dependent on the time scale of the substitution. If replacement of the brominated polymer is to follow the frequency of replacements of tools and machinery a time horizon in the order of 10 years is needed.

7.2.5 Other EE Equipment Parts

Wires for electronics
Brominated flame retardants are used for wires within electronic equipment. No information on alternatives for wires for internal use in electronics has been obtained.

Totally halogen-free solutions for data-network based on halogen-free wires and components are available on the market

7.3 Lighting

Sockets

PBT with brominated flame retardants is used for sockets for both incandescent lamps and fluorescent tubes.

It has not been possible to identify halogen-free thermoplastic sockets, but sockets of porcelain and Bakelite - a phenol based thermoset - are available.

Prices of alternatives

Sockets of porcelain are widespread used in more expensive lamps. The porcelain sockets have the advantage that they last the whole life of the lamp, but they are in the order of magnitude 5 times more expensive that the plastic sockets.

Plastic cover parts

Brominated flame retardants may be used in plastic cover parts close to heating parts of the lamp. The covers may be made of many different plastics. An example of substituting halogen-free polyamides for all BFR containing plastics is known from a Danish producer.

The technical requirements of plastic cover parts of lighting are usually not very stringent, and it is estimated that all BFR containing parts can be replaced by halogen-free plastics or metal - possibly in combination with minor changes in the design.

7.4 Wiring

The driving force in development of bromine free products for wiring is to avoid the formation of toxic and corrosive gasses by fire and to increase the recyclability of the materials. In this respect the brominated flame retardants share the fate with PVC and chlorinated additives.

7.4.1 Wires and Cables

Flexible rubber cables containing brominated flame retardants are used for provisional wiring on construction sites.

For non flexible wires a large number of halogen-free alternatives with aluminium trioxide are marketed for most applications.

Alternative products

Cables containing chlorinated flame retardants are available on the market at the same price as bromine containing cables.

Halogen-free rubber cables are available on the market, but only for small cross sectional areas. The rubber contains aluminium trihydroxide and zinc borate as flame retardants, and the flame retardancy is additionally improved by addition of EVA (ethylene vinyl acetate). The halogen-free cables are available for a product range covering about 2/3 of the market volume.

The halogen-free rubber compound for cables is according to one producer about 15% more expensive than a BFR-containing compound for the same application.

For larger cross sectional areas, where higher flame retardancy is required, no halogen-free cables have been identified. According to a leading producer of cables, bromine-free rubber cables for the whole product range is planned to be on the market by the end of year 2000.

Halogen-free rubbers with flame retardancy based on the synergistic effect of aluminium hydroxide and vinyl acetate is also marketed for other applications, e.g. floor coverings.

Alternative solutions

Several halogen-free flexible cables, based on e.g. crosslinked polyethylene or EVA copolymers (ethylene vinyl acetate) with aluminium trihydroxide as flame retardant are available on the market. This type of cable has for many years been used in the offshore industry and is today widely used for switchboard cabling, coil and transformer wiring, etc. Although somewhat flexible, these cables cannot be considered alternatives to rubber cables used for construction sites where higher flexibility and wear resistance are required.

7.4.2 Wall Sockets and Mounting Boxes

Wall sockets, switchboxes and mounting boxes for wiring in houses are made from a number of plastics among others PET, PP, PS and PC.

The relatively cheap PS and PE are used for e.g. mounting boxes.

Alternatives to polyethylene and polystyrene

Halogen-free polymer blends for wall sockets and mounting boxes used in buildings are available on the market.

A high density polyethylene (HDPE) based masterbatch, flame retarded with magnesium hydroxide, is available for production of wall sockets, plugs, etc. For wall sockets the masterbatch is used in a concentration of approximately 15% to meet the fire safety requirements.

To meet the UL-94 V-2 class, the masterbatch has to be used in 100%. In comparison, the equal BFR-based masterbatch is only used in 10-15% to meet the V-2 class. The high load of the magnesium hydroxide will be a main disadvantage with respect to processing properties of the HDPE.

Price of alternative

The price difference between a brominated and halogen-free HDPE compound depends on the actual load of the masterbatch. According to one specific Swedish masterbatch-producer, the price of a halogen-free HDPE compound used for wall sockets will be about 20% higher than a BFR-containing HDPE compound. For a V-2 class HDPE compound, the price of the halogen-free compound is approximately 60% higher than that of the BFR-containing compound.

Products with alternatives

Magnesium oxide containing wall sockets, ceiling, junction and mounting boxes, etc. are available on the market.

Complete data networks with halogen-free cables, sockets, switches, etc., are available as well. It should be noted that data networks is low-voltage.

Other alternatives

Polypropylene, flame retarded with ammonium polyphosphate with a halogen-free synergist, is available for wiring materials, but it has not been possible to obtain specific information on applications.

7.4.3 Relays, Contactors, Starters, etc.

Contactors, relays, circuit breakers, etc. - widespread used in the power supply system and for industrial automation - are often made of flame retarded engineering thermoplastics like PBT/PET and polyamide. The considerations in section 7.2.4 also apply to these applications.

Contactors

Contactors without halogens and phosphorus have recently been introduced on the market. No information has been obtained on the used flame retardants.

There seems to have been no focus on brominated flame retardants for these applications and the halogen-free contactor is the only commercially available halogen-free end products, it has been possible to identify. The development of halogen-free contactors, however, illustrates a move in the direction of halogen-free products also within this product group.

7.5  Textiles

Types of textiles

Textiles comprise a wide range of products with the main categories: Furniture, clothing, interiors, and technical textiles including tents.

Textiles may be rendered flame retardant by chemical after-treatment of the otherwise flammable fibres, by use of fibres which have been flame retarded during production, by use of inherently flame retardant fibres or by a combination of these methods.

In general, a wide range of non-halogenated alternatives to brominated flame retardants for textiles exists. The textiles may be flame retarded with phosphorus and nitrogen based additive flame retardants, or may be based on synthetic and natural fibres with good inherent flame retardancy characteristics, e.g. wool, down and leather.

A wide range of textile-solutions, beside those mentioned here, exists.

FRs for wool

Wool is regarded as a naturally flame-resistant fibre for many applications. For certain applications, such as use in aircraft, it is necessary to meet more stringent requirements. The Zirpro process, one of the most used methods for this purpose, is based on the exhaustion of negatively charged zirconium and titanium complexes on wool fibre. Specific agents used for this purpose are potassium hexafluoro zirconate, K2ZrF6 and potassium hexafluoro titanate, K2TiF6. Various modifications of this process have been made to improve durability and compatibility with wool shrinkproof finishes /113 /.

These compounds are halogen containing salts. To the knowledge of the authors, in practise only alternatives to the Zirpro process involving organo-halogens exist.

FRs for cotton

The currently available flame retardants for cotton may be divided into three groups, described in the following table 7.6. All these after-treatments are characterised by not being permanent.

Table 7.6
Currently available flame retardants for cotton (Based on /114 /)

Modifications for polyester fibres

Polyester fibres may be flame retarded by incorporating a co-monomeric phosphinic acid unit into the PET polymeric chains. Various additives and co-monomeric modifications are available, see the following table 7.7.

Table 7.7
Flame retardant modifications for polyester fibres Based on /114/

Flame and heat resistant textiles

Advanced classes of heat and fire resistant textiles have been developed especially to fulfil military and aerospace requirements. The fibres are organic polymers typically containing aromatic structures. Examples are meta-aramides and para-aramides.

The fibres are characterised by a high limiting oxygen index, typically in the interval of 30-50. When subjected to temperatures typically above 400°C, they convert to protecting, aromatic char structures /114/.

Price

The comparison of the price of BFR-based and non-halogenated flame retardants is not straight forward, as the durability may differ to a great extent.

However, if an antimony-bromine system is compared to a system based on organo-halogens with equivalent capabilities, the latter costs about the double.

7.5.1  Furniture

The relative advantage of brominated flame retardants, and probably an explanation of the widespread use in the United Kingdom, is the applicability to almost all fibre types and fabric constructions, meeting the correct level of flame retardancy according to the British Standard, combined with a relatively low cost. These features enable the application to any product, even though the original design and choice of materials do not include considerations regarding fire retardancy.

Upholstery

It is, however, possible to avoid the use of halogenated flame retardants including BFRs and still meet the requirements stipulated by the BS 5852:1990, required by the British Upholstered Furniture Safety Regulations, and that is the normal required standard within the contract market for textiles in Denmark (e.g. for use in offices, theatres, institutions).

As an example from a Danish textile industry, a producer of fabrics reports that it has been possible to replace the brominated flame retardants by flame retardants based on phosphorus, nitrogen and zirconium depending on the textile. The phase out has had no consequences for the fulfilment of various standards. The producer supplies to both transportation industries and the contract market, fulfilling the requirements of aircraft, car industry, contract products for institutions and offices.

Foam

During the latest decade, brominated flame retardants have been totally phased out of flexible foams produced in Denmark. The used alternatives are chlorinated phosphate esters, in some cases combined with melamine. Halogen-free additives, containing ammonium polyphosphates, and reactive phosphorus polyols are used or will be used in the near future for automotive seats and foam-lamination of textiles.

Also an increase of the density of the foams may be sufficient to meet mild requirements. Such foams are supplied in Denmark for exclusive furniture. The product is expensive compared to other fire retardant solutions based on halogens and phosphorous substances.

Both car and foam manufactures mention high density foams as a possible solution which meets the requirements for fire retardant foams (e.g. MDI based polyurethane foams replacing the normally used TDI based foam).

It has not been possible to obtain unambiguous information on the price differences of the alternatives. Seemingly the prices for the solutions based on phosphorous compounds are comparable to the halogen based products.

7.5.2  Carpets

In Denmark, the most used flame retardant is aluminium trihydroxide, and all known requirements can be fulfilled without the use of brominated flame retardants.

The solutions based on aluminium trihydroxide are also price competitive compared to solutions based on BFRs.

7.5.3 Clothing

Protective clothing

In general, the use of halogen antimony systems for protective clothing in Denmark has disappeared today. The prevalent systems are either based on cotton treated with an organo-phosphorus washable treatment, or inherently flame retardant synthetic fibres, such as modified polyesters. Often the textile must be both heat and flame resistant, and hence the above described char forming meta-aramides and para-aramides are often chosen.

Some heavy duty clothes, e.g. for use in welding may imply the use of flexible glass fibre, where the binder might be flame retarded with a brominated compound, but also phosphorus based flame retardants may be used.

Other clothing

The use of flame retardants for night dresses is discussed above in the substance flow analysis. There are no such requirements in Denmark. The most used system is probably cotton treated with a organo-phosphorus compound. As described in the substance flow analysis, it is most unlikely that other types of clothing than protective clothing are to be found on the Danish market.

No information on prices compared to clothing flame retarded with BFRs has been obtained.

7.6 Building Materials

7.6.1 Expanded Polystyrene and Extruded Polystyrene Foam

European produced EPS and XPS are flame retarded with HBCD. Other known alternatives are also brominated, and most often also aromatic (HBCD is a cyclo-aliphatic compound). Hence no alternative halogen-free additives exist.

In Denmark though, no requirements exist regarding the flammability of these types of insulation materials. EPS building insulation used in Denmark is predominantly domestically produced, and as a consequence of the lack of requirements for flame retardant insulation panels no flame retardants are added. Contrary to this, XPS is solely imported, and is - depending on the supplier - always flame retarded. For the greater part of the applications of XPS, the flame retardant quality is not required in Denmark.

Alternative materials

As the alternative materials have very different characteristics from the EPS and XPS products, a direct comparison is difficult. However, some of the basic characteristics of some possible solutions are sketched below.

Mineral wool is widely used in Denmark. The material is not flammable. The insulation power of the product is comparable to that of the EPS and XPS materials. The relative price is very dependent on the actual application, but costs roughly the double compared to EPS-solutions. Regarding working environment the EPS/XPS have some advantages compared to mineral wool, and the two products are not completely comparable.

An alternative material for some applications is foam glass. The material consists solely of glass and has good insulation power (a practical l at about 45 mW/m K).

The foam glass material has though a considerably higher density than the XPS and EPS products (about 120 kg/m3 vs. round 40 and 20 kg/m3 respectively).

The product costs roughly 4 times more than the XPS product and hence roughly 8 times more than the EPS product.

Summary

The major share of the consumption of brominated XPS/EPS materials may be substituted by alternative materials - or replaced by non retarded grades of the same products.

It is typically the actual application that will be guiding for both the technical applicability and the relative price of the different alternatives. However, if a general comparison is made, the price of mineral wool are comparable to that of XPS, and approximately the double of that of EPS. Foam glass products cost about fifty percent more than XPS, and about three hundred and fifty percent more than EPS.

According to /43/ expanded PUR is a slightly more expensive solution for façade insulation than mineral wool.

7.6.2 Rigid Polyurethanes

Alternative flame retardants

Flame retardants for rigid PUR foams may be based on ammonium polyphosphates or red phosphorus. These types of flame retardants are commercially produced for rigid polyurethane foams, and permit the fulfilment of strong requirements of railway and aircraft standards (e.g. DIN 5510, ABD 031). According to /115 /, ammonium polyphosphate and red phosphorus enable applications up to the level of the strict DIN 4102 Class B1.

These alternative halogen-free flame retardants are to the knowledge of the authors not used commercially in Scandinavia. On a European scale, production of insulation panels with halogen-free flame retardants does exist, but only on a small scale.

If a flammability level corresponding e.g. to the strict German DIN 4102 B1 is needed, however, no halogen-free alternative is apparently commercially available today; but. a combination of chlorinated phosphate esters and red phosphorus are commercially available. The B1 level is, however only needed in very few cases such as mining and prisons, and only a few manufacturers in Europe are supplying products of this grade. According to industry information, developments of halogen-free B1 rigid foams are in progress.

Alternative solutions - pre-insulated pipes

The requirements stipulated in the Scandinavian standards, may be met through encapsulation of the plain PUR material with steel tubes, spiro-tubes or PE-tubes (without FRs), depending on the required level of fire safety. This solution does, though, not live up to the German test, as this test focuses on the weakest material, and not at the functional unit in which the PUR insulation is encapsulated.

Façade insulation 

A normally used solution for façade insulation and after insulation are based on mineral wool.

According to /43/ PUR is a slightly more expensive solution for façade insulation than mineral wool.

7.6.3 Foils

Foils used for roofing are made of PVC or polyolefins (PE or PP). The polyolefins are predominantly made flame retarded with brominated flame retardants.

Alternatives

Halogen-free foils are produced commercially, and makes out a considerable part of the Danish market for flame retarded roofing foils. The used flame retardant is ammonium polyphosphate, and the product fulfils all requirements.

The price of the product is approximately 10% higher than the price for foils flame retarded with halogen-based chemicals.

7.7 Paint

Intumescent paints

Flame retardant paints do usually not contain brominated flame retardants. It has not been possible to identify applications where the requirements cannot be meet by halogen-free paints.

Flame retarded intumescent paints are typically based on epoxy polymers. The retardancy effect is obtained by the combination of a carbon source, a catalyst (e.g. ammonium polyphosphates), and a blowing agent (e.g. melamine). Many different systems exist, but they do in general contain phosphorus and nitrogen components.

No information for comparison of prices has been available.

7.8 Transportation

Most of the materials and components described above are used in transportation. Hence the transportation industries and especially the car producing industries, have a very central role as regards the use of flame retardants and the development of more health and environmentally friendly solutions.

In general the above described alternative solutions will be of relevance to the transportation industry. To the knowledge of the authors there are today no halogen-free vehicles. The tendency in the N. European automotive industry is to replace brominated flame retardants, but the use is still widespread in e.g. textiles, and is today present in electric and electronic components of all vehicles.

The solutions described in section 7.2 - 7.7, are to a varying degree implemented in the different means of transport.

Cars

Some manufacturers have phased out the use of BFRs in all components except electronic components. Several manufacturers have banned the use of two specific groups; PBDEs and PBBs.

Trains

The Danish State Railways (DSB) has at the latest purchase of trains, in co-operation with contractors and to the greatest extent possible, avoided the use of BFRs. It has though been reported from the suppliers/sub-suppliers that BFRs are presently some specific components, most probably in electrical/electronic components.

Also the German Railways (DB) aims at avoiding the use of BFRs in the rolling stock.

Unsaturated polyester resins are often used, and may be flame retarded up to the most rigorous requirements with ammonium polyphosphate or red phosphorous combined with varying amounts of aluminium trihydroxide.

Phenolic laminates are widespread used for means of transport. Brominated flame retardants and ammonium bromide are widely used for flame retardancy of the laminates.

Halogen-free alternatives flame retarded with aluminium trihydroxide are available on the market. No information on price differences has been obtained.

Other means of transport

Specific information on the use of alternatives in other means of transport not been obtained. As for cars and trains, the solutions described above in section 7.2 - 7.7 are relevant regarding aircraft, ships, etc.

7.9 New Flame Retardant Concepts

Most of the flame retardants used as alternatives to brominated flame retardants have been known for many years. The ultimate alternatives may be basically different flame retardants systems.

Preceramic polymers

In the aim of developing new halogen-free and more environmentally friendly flame retardant systems, research from the National Institute of Standards and Technology, Gaithersburg has developed flame retardants based on so-called ‘preceramic polymers’ /116/. The principle of the method is the use of oligomeric or polymeric material that converts into ceramic (inorganic char) when heated above its decomposition point.

One system based on a mixture of silica gel and potassium carbonate (K₂CO₃) has been described by Gilman et al. 1996 /117/. The mixture was tested on a range of polymers, and it was concluded that the mixture was an effective flame retardant (at 10% w/w) in polypropylene, polyamide, polymethylmethacrylate, poly (vinyl alcohol), cellulose, and to a lesser extent polystyrene and styrene-acrylonitrile. A similar approach has been taken by researchers from Institute of Biochemical Physics, Moscow using a polyvinyl alcohol char former and silicon-organic systems /118 /

The flame retardants are still at the experimental stage, but the results indicate that preceramic polymers may be useful future flame retardants.

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