Experiment 3: Brominated fire retardants in Plastics by XRF

Transcription

1 Chemistry 461: Advanced Analytical Laboratory Lab Experiment Descriptions Experiment 3: Brominated fire retardants in Plastics by XRF 1.0 Introduction: The addition of brominated fire retardants to plastics helps prevent combustion in plastic materials that experience high heat, such as those used in electronics. In Europe there are new regulations that regulate plastics that contain these materials. A description is provided in the attached article. You will be required to develop a screening protocol for plastics using the XRF instrumentation available in the teaching laboratory. 2.0 Brief Procedure Summary: In XRF matrix effects are significant. However, absorption of X-Rays is dependent on the density of materials and the types of atoms present. Once this is matched the chemical properties of the materials are not that significant. As a result of this many solid organic materials can be matrix matched by using PVA as a binding agent and then pressing the material of interest under pressure to generate standards and samples with similar densities. With this in mind you will make a series of brominated standards by pressing PVA pellets containing different amounts of brominated organic compounds. In order to have some plastic materials to test you will need to identify appropriate materials by a literature search and then arrange to have some of these available in the lab. You are required to determine the limit of detection and limit of quantization for the XRF technique you develop. You will test a range of different plastic materials and determine the advantage, if any, of a direct detection vs a standard addition approach. How can you determine if your approach produced accurate determination of real samples? Propose an alternate technique for determining total bromide content in the plastic samples. If time and resources permit run proof of concept analysis in this secondary method and test it against your XRF method. 3.0 Report Requirements: Develop a rapid screening approach to sort plastic computer components. Determine detection limits and other figures of merit for your technique. Propose a viable alternate method for the analysis. If time permits run this method and compare results.

2 The EU RoHS Directive and its implications for the plastics industry The European Union Restriction of Hazardous Substances Directive will prohibit the use of certain substances in electrical and electronic equipment from 1 July Paul Cusack and Tom Perrett of Tin Technology Limited explain what this means and discuss some of the implications for the plastics industry. The European Union (EU) Restriction of Hazardous Substances (RoHS) Directive (2002/95/EC) will prohibit the use of certain substances in electrical and electronic equipment from 1 July The substances restricted under RoHS are lead, cadmium, mercury, hexavalent chromium and two specific families of brominated flame retardants - polybrominated biphenyls (PBBs) and Testing underway at Tin Technology s UK facilities polybrominated diphenyl ethers (PBDEs), although one member of the latter family, decabromodiphenyl ether (deca-bde) has recently been granted an exemption from the restriction. The maximum permitted concentration of these substances will be 0.1% by weight of homogeneous material, except in the case of cadmium, where the limit will be 0.01%. Products placed on the market after 1 July 2006 will be presumed to comply with RoHS and the authorities in each Member State will introduce their own surveillance regime and conduct checks where appropriate. Manufacturers and importers of electrical and electronic equipment are likely to be the first line of enforcement. As part of their compliance programmes, many manufacturers are asking their suppliers to confirm component compliance to ensure that the finished product is in turn compliant. If compliance is in doubt, it is recommended that random analysis of 'high risk' components and materials is undertaken, and many electronics companies are now adopting this approach as a means of demonstrating 'due diligence' in ensuring that their products are RoHS compliant. RoHS clearly has significant implications for the plastics industry as the restricted substances may be found in a wide range of applications that use polymeric materials (see Table 1). Although there are a number of exemptions that have been proposed (and some which have already been granted), the main justification for an exemption is the lack of a technically viable alternative, and it is expected that many of the current exemptions will be reviewed at a future date. Suppliers of polymeric materials to the electrical and electronic manufacturing industry will be asked to show that their 46 ISSN X/ Elsevier Ltd.All rights reserved.

3 product conforms to the RoHS Directive or be prepared to lose customers. Electrical and electronic equipment suppliers can be fined or have their product withdrawn from the European market if they do not comply with this legislation. In general terms, lead and cadmium have both found widespread use as stabilizers (particularly in PVC) and pigments for plastics, whereas chromium and mercury are rarely found. Brominated flame retardants Of the estimated 430,000 tonnes of flame retardants used annually in the EU, brominated compounds represent some 52,000 tonnes, with the electrical/electronics industry being the largest consuming sector (see Figure 1). Hence, approximately 29,000 tonnes per annum of bromine-based flame retardants find use in Europe's electronics industry, key applications being equipment casings (usually ABS, HIPS or blends with polycarbonate), epoxy resin laminates for printed circuit boards, and a range of thermoplastics for connectors, relays and other components (see Figure 2). With regard to brominated flame retardants, it is important to stress that the RoHS Directive only restricts the use of certain specific additives. In any case, an earlier Directive (2003/11/EC), relating to marketing and use of dangerous substances, effectively banned the use of two PBDEs, octa-bde and penta-bde, from 15 August These compounds are no longer manufactured or used in the EU or the US. The fate of a third member of the PBDE family, decabromodiphenyl ether (deca-bde), is still uncertain. The EU Commission has argued that the Risk Assessment on Deca-BDE has been concluded and that there was no evidence of any risks that needed to be managed by legislative restrictions. On this basis, the Technical Adaptation Committee (TAC) has voted to amend the RoHS Annex to include an exemption for Deca-BDE in polymeric applications. However, some Member States consider that there are continuing doubts about the environmental and human health impacts of Deca-BDE and have argued that any exemption should be postponed until further data was available. A neurotoxicity study on Deca-BDE has yet to be undertaken. Similarly, the only member of the PBB family which found extensive use as a flame retardant - decabromobiphenyl - was withdrawn some years ago. Substance Lead Cadmium Mercury Hexavalent chromium PBBs and PBDEs A summary of the key generic brominated flame retardants that have found use in the electronics industry is given in Table 2. While only PBB and PBDE type flame retardants are restricted, screening equipment is unlikely to be capable of distinguishing between these 'banned' Table 1:Applications of RoHS substances Application areas Solders, termination coatings, paints (pigment, drier), plastics (PVC stabilizer),batteries,glass (cathode ray tubes,seals,lamps),ceramic components (piezoelectric devices, dielectric materials) Plastics (pigment, PVC stabilizer), electrical contacts, semiconductors (light sensors, solar cells), batteries, solders Fluorescent lamps, batteries, sensors, relays Corrosion-resistant coatings and paints,etchants in plastic metallization processes Flame retardants in plastics,foams,elastomers,textiles and paints Figure 1: EU brominated flame retardant use by industry sector. Figure 2: EU brominated flame retardant use in the electronics sector. 47

4 Table 2: Brominated flame retardants in electronics applications A wide range of proprietary brominated flame retardants has also been developed for use in electronics applications; none of these additives is banned under the RoHS Directive. Compound Bromine Key uses Banned under content RoHS? Decabromobiphenyl (deca-bb) 84% Casings, resistors, capacitors Yes Pentabromodiphenyl ether (penta-bde) 71% PU foams,elastomers,printed circuit boards, fuse boxes, panels Yes Octabromodiphenyl ether (octa-bde) 79% Casings, electrical components Yes Decabromodiphenyl ether (deca-bde) 83% Casings, connectors, switches, capacitors, wire and cable Tetrabromobisphenol-A (TBBPA) 59% Printed circuit boards,encapsulating resins, casings No No Hexabromocyclododecane (HBCD) 75% EPS insulation foams, casings No substances and permitted brominated flame retardants. This subtle point needs to be understood before more expensive chemical analysis is undertaken. Compliance testing The RoHS Directive specifies maximum permissible concentration values of hazardous substances in homogeneous materials, i.e: materials that cannot be mechanically disjointed into different materials and which are of uniform composition throughout. For this reason, there is no simple test for RoHS compliance - testing has to be conducted on each of these materials individually. A draft IEC standard (111/24/CD) has recently been issued and this details a twotier approach comprising an initial screening procedure followed by a more quantitative verification procedure, where appropriate (see Table 3). X-ray fluorescence (XRF) is probably the most cost effective and convenient technique for the preliminary screening stage. Low cost portable hand-held devices are being used for 'in the field' analysis, although these are usually limited with regard to detection limits and focus on small areas. Higher cost bench-top instruments give better accuracy and can analyze components whole or those that have been dismantled or sectioned. The use of XRF enables rapid determination of lead, cadmium, mercury, chromium and bromine, although speciation (required in the case of hexavalent chromium, PBBs and PBDEs) is not possible. If levels of these elements are close to the RoHS critical limits, then there is a requirement for more accurate analysis using an appropriate verification technique (see Table 4). Speciation of PBBs and PBDEs XRF analysis of a polymer. PBBs and PBDEs are only two specific families of the many brominated flame retardants that have found use in polymeric substrates, so analysis of total bromine alone is not sufficient to determine whether a product or component is RoHS compliant or not. If XRF does not detect any bromine at levels approaching 0.1%, then it is safe to assume that PBBs and PBDEs are not present at >0.1%. However, if bromine is detected by XRF, then further techniques 48

5 capable of speciating brominated compounds should be employed. Although it is possible to differentiate between specific brominated flame retardants in polymers using Fourier Transform - Infrared (FT-IR) Spectroscopy, the method is generally regarded as being of low sensitivity and 'several percent' (probably 3-5%) of the species is required to be above the detection limit. Rather more success has been achieved using High Performance Liquid Chromatography (HPLC) with detection by UV absorption, and it is claimed that PBBs and PBDEs can be determined at the critical 0.1% level using this method. However, probably the most successful method used to date has been Gas Chromatography - Mass Spectrometry (GC-MS). GC is a versatile means for the separation and identification of complex mixtures of volatile organic compounds, such as brominated flame retardants. To analyze for these compounds in a polymeric sample, the sample must first be dissolved in a suitable solvent or the analyte must be completely extracted. For certain polymers, including those that are highly filled, accelerated extraction procedures, such as microwave digestion, may be required. Following injection into the GC column, the individual brominated species are detected by MS, which provides unequivocal identification of the eluted peaks. Standards containing known mixtures of PBB and PBDE isomers are commercially available and are required to positively identify the peaks. Using GC-MS, PBBs and PBDEs can be determined at the critical 0.1% level and good chromatographic resolution allows easy distinction between deca-bde (which is exempt from the RoHS ban) and the partially brominated diphenyl ethers (which are banned). RoHS compliance analysis and testing services Tin Technology's Soldertec Global Division has recently launched its RoHS Table 3: RoHS analytical procedure overview Stage Process Details 1 Initial screening Non-destructive surface analysis X-ray fluorescence (ED-XRF or WD-XRF) 2a Pre-treatment Dissolution of sample For example,acid digestion,alkali fusion,microwave-assisted methods and organic solvent extraction. 2b Verification tests Various techniques For example, ICP-AES, AAS, UV-Vis, GC-MS, HPLC-UV and FT-IR. Compliance screening service, which provides the electronics industry with an independent analytical facility for determining levels of the prohibited substances in components, boards, cables, screws, casings and electronic assemblies, in order to help them comply with the RoHS Directive. Tin Technology also offers a comprehensive range of polymer compounding, physical characterization and fire testing facilities within its Fireproof Division for undertaking re-formulation and development work. In summary, the plastics and rubber supply chain is now beginning to wake up to the need for RoHS compliance. The use of alternatives to lead stabilizers for PVC, such as calcium/zinc stearates, is growing. Organic pigments are now widely available as replacements for cadmium in low temperature applications, including many plastics. Even the continued use of brominated flame retardants is being questioned as halogenfree systems are introduced into the market from a number of suppliers. These advances will enable the electrical and electronic manufacturing industry to ensure that its products fully comply with the RoHS Directive thereby making a positive contribution to the protection of the environment and human health. Contact: Tin Technology Limited Tel: tom.perrett@tintechnology.com Website: Table 4: RoHS analytical techniques Substance RoHS level Screening technique Typical verification techniques Lead 0.1% ED-XRF ICP-AES,AAS Cadmium 0.01% ED-XRF ICP-AES,AAS Mercury 0.1% ED-XRF ICP-AES, cold vapour-aas Hexavalent chromium 0.1% ED-XRF (total Cr) ICP-AES (total Cr),diphenylcarbazide complexation/uv-visible spectrometry (Cr6+), ion chromatography (Cr6+) PBBs and PBDEs 0.1% ED-XRF (total Br) Schoniger Oxygen Flask (total Br), GC- MS, HPLC-UV (speciation techniques) 49