Brominated Flame Retardants

9. Summary of Alternatives

Substitutes for brominated flame retardants are available for most applications, but the substitutes are in general more expensive.

Substitution has mainly taken place for:

Besides brominated flame retardants have been replaced in the aim of substitution of antimony trioxide used in combination with the BFRs.

For applications in textiles, carpets and furniture products with alternative flame retardants have been on the market concurrently with BFR containing products, and regional differences by tradition have to some extent determined the flame retardant system actually used.

Levels of substitution

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

The available information on halogen-free flame retardants for materials where brominated flame retardants are in use today is summarised in table 9.1.

Materials where alternatives are not available

Halogen-free alternative materials are at the moment not available for PBT/PET, ABS and expanded polystyrene.

For ABS - traditionally used for housing of electronic equipment - halogen-free flame retarded grades of PC/ABS blends and PPS/PS blends are widely used as substitutes.

For PBT/PET, experiments have been carried out by several producers of compounds and end products, and preliminary data sheets on alternatives exist. The results have until now not been satisfactory. For some applications polyamide, polyketone or other polymers may substitute for PBT, but a substitution may involve costly changes in tools and machinery.

In Denmark the use of flame retardants in expanded polystyrene is not required as plastic based insulation is normally only allowed when it is encapsulated in non-combustible and approved materials.

Table 9.1
Halogen-free flame retardants in commercial materials

An initial measure of the feasibility of substitution is to assess to what extent halogen-free end products are available on the market and at what price.

Practically no products containing electronics will be totally free of brominated flame retardants. It means that practically all electronic appliances, vehicles, and a significant part of all electric equipment contain brominated flame retardants. This is reflected in the fact that the ecolabels do not require that electronic products are totally free of brominated flame retardants. At present the ecolabels only have requirements of total absence of BFRs for building materials.

Halogen-free products

Hence, at this moment it is necessary to make the assessment at the component level. The availability of commercial halogen-free materials and products, for products covering about 90% of the total consumption of BFRs are summarised in table 9.2.

Halogen-free alternatives are available for both epoxy and phenolic/paper laminates for printed circuit boards, but until now electronic components encapsulated in halogen-free plastics have not been available. Halogen-free alternatives for electronic component encapsulates were developed several years ago, but the driving force for large scale production of halogen-free components on a very competitive market has until now not been strong enough.

Until all components for producing a complete halogen-free assembled printed circuit board are available producers of electronics avoid increased costs. And the increased costs have until now been noticeable; at least for the epoxy based laminates. According to a leading producer halogen-free alternatives at a price of 20-30% extra should be on the market in 1999.

The price depends on the demand. For many applications the price of the alternatives may be inherently somewhat higher due to higher loading of flame retardants or the use of more expensive base polymers, but the very high price differences seen for some products are expected to be reduced along with growing demand for alternatives.

For two major applications, electronic component encapsulates, and switches, relays, circuit breakers, etc. of PBT/PET alternatives are still at the experimental stage, and halogen-free end-products are not marketed (a few exceptions).

Substitution of PBDEs and PBBs

The aim of the present study has not been to discuss the possible substitution of one brominated flame retardant by another. It should, however, be noted that TBBPA and other brominated flame retardants can substitute for PBDEs and PBBs for all applications without significantly changing the properties of the materials. For all plastic materials, grades without PBDEs or PBBs are available on the market. Higher loading is often necessary, when other BFRs are used and in general PBDE containing grades are cheaper (10-20%) than grades with other BFRs.

Table 9.2
Availability of commercial halogen-free materials and products

Fire safety regulation

The addition of flame retardants increases the costs of the plastics and flame retardants are in general only used where fire safety requirements demand lower flammability of products/materials. The standards do not explicitly require the use of brominated flame retardants. For electric and electronic products the use of flame retardants is totally determined by the international standards, and the same standards are used in Denmark, UK and Germany. For building materials and furniture other fire safety requirements exist in Germany and UK. The use of brominated flame retardants with building materials and furniture in Denmark is to a large extent a spin-off of requirements in Germany (building materials) and UK (furniture).

Changed design

For a few applications the use of flame retardants may be omitted, and the fire safety requirements fulfilled by changes in the design of the products. Constructive solutions are possible (and actually used in Denmark) for some of the applications within the building sector. In electric and electronic products the use of flame retardants may be reduced by increased material thickness, increased distance to heat generating parts, or protective metal shields around heat generating parts of the appliances.

One example of a design where flame retardants in a PC-monitor are omitted is described in section 7.2.3. In electric and electronic products these solutions are in general significantly more expensive, and for most applications the use of halogen-free flame retardants is more economic.

Halogen-free flame retardants

There is a large number of commercially available halogen-free flame retardants. They are often used in combination, and the specific compounds and mixtures are often considered confidential. Eleven of the compounds used in alternative products, have shortly been described in the previous sections.

The flame retardants can be arranged into three groups: Organophosphorus, inorganic and nitrogen containing.

Comprehensive risk analyses like the EU risk assessments have not been carried out for any of the alternatives in question, but human and environmental hazard assessments are available for some of the flame retardants (see table 9.3).

Table 9.3
Available toxicity assessments of alternatives

Ideal demands

In the aim of product development the following ideal demands on the flame retardants can be put forward:

From a consumer point of view it is of high priority that the flame retardants are not released to the indoor environment during use and do not have adverse effects on human health.

The available information indicates that the organophosphorus compounds can be released from the products in significant amounts. The emission may not be of significance as to human health effects, but the issue claims attention. The attention on the issue is today reflected in the fact that halogen-free products are often marketed as 'free of halogenated and organophosphorus flame retardants'.

The inorganic flame retardants are on the contrary immobilised in the plastics.

Aluminium trihydroxide, the best described of the inorganic flame retardants in question, has the advantage of not being released during use, has minimum human and environmental toxicity, suppresses formation of hazardous fumes and decomposes into non hazardous substances. Similar properties are assumed for magnesium hydroxide, but no assessment have been available.

The major disadvantage of the compounds is that they are not very efficient, and high loading is necessary. If the flame retardants are used in polymers with a higher oxygen index, the loading can be reduced, and the adverse effects of the compounds on the processability of the plastic can be reduced. Such solutions are, however, often significantly more expensive than current brominated flame retardant containing plastics. In spite of these disadvantages the hydroxide flame retardants have been applied in halogen-free compounds of polyamide, polyketone, polystyrene, phenolic resins, and epoxy.

Inorganic phosphorous compounds are widely used as flame retardants. Apart from some handling problems with red phosphorous that can be overcome, they presumably have a more positive score with respect to the demands above than the organophosphorus compounds. An assessment of the possible human and environmental risks of the compounds are, however, necessary for a proper appraisal.

The same is the fact with respect to zinc borate and melamine.

Summary

Substitution is today possible for most applications at a relatively low extra cost, but more information on health and environmental properties of some of the alternatives - including their influence on fire atmospheres - would be of advantage for the choice of alternatives and marketing of products with alternative flame retardants.