The recycling and re-use of polymers has grown in importance. Recyclability of industrial production waste is a longstanding practice and an economical need.
This implies several challenges for the materials used, including flame retardants.
Similarly, mechanical recycling and re-use of plastics from post-consumer electrical and electronic devices is today expected by regulators and society.
Post-consumer plastic parts have been exposed during service life to humidity from the air and in most cases to UV light. They have also been extensively exposed to water and other solvents during the washing and plastic sorting operations. Hydrolytic stability of flame retardants is therefore a key issue.
Extensive tests have been performed on various fire retardant polymers and showed contrasting results. Most brominated and certain phosphorous formulations showed good hydrolytic stability and could be properly recycled, while other phosphorous formulations faced challenges in terms of the quality of the recycled plastics.
Recycling and Waste Management
Materials containing flame retardants can be safely disposed of in municipal waste incinerators for energy recovery. As flame retardants delay and inhibit the burning process, but do not make materials incombustible, then waste incineration is no problem.
When domestic waste is sent to landfill sites, the flame retardants will mostly remain within the discarded treated materials, because they are chemically or physically bound, therefore the loss of significant levels into the environment is very unlikely.
State of the art incinerators will remove any pollutants formed during combustion to the required levels: e.g. acids like hydrogen bromide or hydrochloric acid from halogenated flame retardants will be scrubbed from the flue gasses and phosphorus compounds will primarily remain in the bottom ash as inorganic phosphates together with aluminium oxides from aluminium hydroxide.
Flame retardants in plastic wastes are also compatible with valorisation in metal smelters and recovery of the precious metal and copper contents of mixed wastes via this route. The plastics content partly substitutes coke as a reducing agent, and partly provides smelter feed energy. [Source : PlasticEurope]
EFRA and E&E - End of Life Forum
EFRA has an active forum which includes workshops and meetings to follow the end of life situation for plastics containing flame retardants.
Working in cooperation with branch organisations, plastics manufacturers, the re-cycling industry and standardisation bodies holds a high priority under EFRAs product stewardship programme.
European legislation fixes obligations for end of life management of waste electrical and
electronic equipment (WEEE), with ambitious targets for both equipment re-use or materials recycling and for energy recovery.
Economic and environmentally appropriate valorisation routes for WEEE materials with high plastics contents therefore have to be identified. These must be adapted to plastics with and without containing flame retardants, which are used in many electrical and electronic products to improve fire safety, either to meet mandatory safety standards or because of manufacturers’ voluntary product safety objectives.
Integrated metal smelters represent one recycling route for such WEEE materials: metals can be recovered and recycled, and the plastics content can serve as an energy source and reducing agent.
EFRA, together with the plastics producing industry federation- PlasticsEurope and Umicore Precious Metals Refining, carried out a full scale trial to assess the technical feasibility of including mixed WEEE materials with high plastics contents in the feed to an integrated metals smelter. The trial ran for a total of 8 days, using a sample of 217 tonnes of household WEEE. Impacts on plant performance, metals recovery, emissions and energy balance were assessed.
Results show :
Chemical recycling of plastics containing flame retardants has been done :
exemplified in polyurethane foams containing ammonium polyphosphate (APP).
Glycolysis breaks down the material into a polyol which can be used as a polyol component. With the exception of a slightly enhanced acid number, no disadvantages occur during glycolysis in the presence of APP.
A study carried out at ECN Holland showed that E&E plastics can be treated in a pyrolysis/ gasification process safely and the bromine can be recovered as HBr.
Another pilot trial carried out in Japan by PWMI showed the same results including the bromine recovery option.
Bromine recovery from waste electrical and electronic equipment incinerated in a pilot plant for waste combustion is possible, by quenching the flue gases in water, collecting the hydrogen bromide (HBr) with the option of transforming it into elemental bromine as a basis for producing brominated flame retardants.
Flame retardants have been shown to be fully compatible with recovery of waste electronic and electrical plastics (WEEE) in metal smelters, enabling recycling of precious metals and copper in circuitry, of antimony in flame retardants, and valorisation of the plastics content as a reducing agent, replacing use of coke and as an energy source. (Umicore Hoboken PlasticsEurope EFRA trials, 2005)
Mechanical recycling is simpler where the origin and composition of the plastics is known by the owner of the plastic used, so that sorting of substances is facilitated.
Where TV and household E&E equipment are returned from the market, mechanical recycling is difficult because of the diverse mixture of historical plastic materials.
It is a demanding task to sort plastics into individual polymer types like PVC, PP, ABS etc. but what makes it really challenging, are further differences in the pigments and additives used - not only flame retardants but also light stabilizers, compounding aides etc.
All plastics containing Penta-, Octa-BDE and PBB's must be separated according to the WEEE directive.
It is, therefore, extremely difficult to reach a quality comparable to virgin material. Further, the economics are under pressure due to the scale of the process :
- where mechanical recycling is done in installations up to 15 000 tons per year
- plastics are produced in processes of up to 300 000 tons per year.
Most recycling in the EU is carried out at licensed facilities complying with stringent health and environmental standards.
There is, however, sufficient evidence of electrical and electronic waste being illegally exported to developping countries for disposal.
While certain recycling facilities in these countries are operating to standard, some hazardous practices have also been recorded. Regardless of the composition of the materials, the burning in open fires of cable plastic insulation or printed wiring boards for metal recovery is particularly dangerous for the health of the local populations and the environment.