Step 2. Profile Lifecycles Physical and Chemical Information

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1 Nanomaterial Risk Assessment Worksheet Incorporation of Single and Multi Walled Carbon Nano Tubes (CNTs) into Polymer Nanocomposites by Melt Processing Synopsis: In this case study, DuPont investigated the use of CNTs as nano fillers to improve mechanical and electrical properties of engineering thermoplastics. While this research project was terminated prior to commercialization for business reasons, this case study exemplifies how DuPont handles nanomaterials in the product research and evaluation phase of development. Utilization of the Framework allowed the company to further refine internal management procedures and to identify questions to be answered for such applications before they move to commercialization. Step 1. Describe Materials and Applications Carbon nanotubes exhibit extraordinary strength, unique electrical properties and are efficient conductors of heat. DuPont is testing the impact of these properties when blended in to a wide range of polymers for potential applications in electronics, optics, and other advanced polymer materials applications. Both single walled carbon nanotubes (SWCNTs) and multi walled carbon nanotubes (MWCNTs) are being tested. In this case study, DuPont investigated the use of CNTs as nano fillers to improve mechanical and electrical properties of engineering thermoplastics. Commercial sources of CNTs were evaluated that varied in type, purity and method of synthesis. Experiments and employee exposure air sample monitoring tests were conducted in 2005 and 2006, in parallel with the creation of the Framework document, and these data were used for this case study. While the research project was halted in late 2006 for business reasons, the CNT case study exemplifies how DuPont handles nanomaterials in the product research and evaluation phase by applying; 1) facilities and engineering controls designed to contain and capture ultra fine powders, 2) personal protective equipment (PPE) and 3) specific operating procedures governing sample preparation, equipment operation, cleanup and waste disposal. Step 2. Profile Lifecycles Physical and Chemical Information Many of the chemical and physical properties, along with the health and environmental fate and effects data, are unavailable or unknown for the CNTs evaluated by DuPont for this project. To the extent that such data exist, it usually resides with the CNT suppliers who are unwilling to divulge what they consider proprietary information. Some CNT suppliers will not allow analysis of their material, since it may reveal proprietary information about coatings, surface treatments, impurities, etc. Today, CNTs are available from a wide variety of sources, and are made using a range of manufacturing methods, that generate materials with widely varying compositions, structures and properties. CNTs are generally supplied as a black powder in the form of

2 2 highly agglomerated visible fibrils with less dusting potential than carbon black, or as pellets, which are CNT concentrates encapsulated in a polymer. DuPont is not currently synthesizing CNTs, except for limited research purposes for other projects, and has no current plans to manufacture CNTs for the commercial uses envisioned by this case study. DuPont is, however, purchasing CNTs from outside suppliers and investigating applications where they are incorporated into a polymer matrix by one of the following routes: a) CNT powder compounded into a polymer melt using conventional batch mixers or continuous extrusion equipment. Incorporation may be by direct addition of the CNT powder into the compounder at the final composition (typically 0.5 to 5% by weight), or at high concentrations (5% 50% by weight) to create a masterbatch. The composite product would normally be in a pellet form. b) Addition of a pre compounded CNT masterbatch pellet form into a melt compounding or shaping/forming process, commonly called a letdown step. c) Addition of CNT powders into monomers, solvents or other carrier liquids for addition to polymerization, compounding or shaping/forming processes. Presently CNTs in powder form are of a concentration approaching 100%, typically with 0% to 4% impurities. Masterbatch concentrations may range from 5 50 wt.%, with 10 25% being typical. Nanocomposite products may contain wt.% CNTs, with 1 5% being typical. Nanotube diameters range from ~0.4 to > 3 nm for single walled nanotubes (SWCNT) and from ~1.4 to at least 100 nm for multi walled nanotubes (MWCNT). Nanotube lengths vary from 100nm to several millimeters, depending on type and supplier. Planning for Human Health and Environmental Safety Toxicity, human safety hazard, and environmental fate and effects data available from potential suppliers are minimal and highly variable. In many cases, it is not clear whether the Environmental Health and Safety (EHS) data are based on the CNT or on larger sized graphite. Until an attractive project and a single candidate CNT (or a limited number of choices) emerges, there is very little opportunity or leverage to obtain EHS data. In the interim, DuPont operates its laboratory based on the very conservative assumption that all samples are potentially hazardous. Air monitoring was conducted to evaluate potential exposure to CNTs while performing extrusion and molding of a mixture o an example polymer and a CNT. DuPont Industrial Hygiene experts sampled the workplace air to determine if exposure potential is being adequately controlled. Air sampling monitoring was performed on laboratory nanocomposite sample preparation and CNT nanocomposite melt processing with research technicians performing the tasks. Area samples were collected from various positions in the room around a sample preparation enclosure and small scale batch mixing and injection molding systems. An air sampling device was worn by the research technician performing the nanocomposite synthesis experiments. Air monitoring and sample analysis was conducted in accordance with NIOSH method 0500 for Total Dust.

3 3 Samples were analyzed by an American Industrial Hygiene Association (AIHA) accredited laboratory. Also a P Trak Ultrafine particle counter was used to a measure increases in airborne particle levels in order to assess containment and control. Following DuPont standards for fitted respirator use, the research technicians participate in a respiratory health monitoring program. Some dust generation was observed, contained within ventilated enclosures, during operations involving handling of the powder. A condensation particle counter was used to measure concentrations of particles, in the range of 20 to 1000 nanometers, emitted from processes in close proximity to the point where material was handled during sample preparation (decanting CNTs from a jar or bag and weighing) and insertion into the mixing equipment. Particle count readings quickly rose when material was added and quickly fell to background levels, indicating that engineering controls were effectively collecting airborne particulate matter. Particle count readings were taken at the HEPA vacuum cleaner filter exhaust (filtered air). Levels dropped to below background levels, indicating that HEPA filter was removing airborne particles. The results show that the samples were below the established OSHA permissible exposure guidelines (PEL) for Total Dust, PEL 15mg/m 3 for 8 hour TWA, and Respirable Dust, PEL 5 mg/m 3 for 8 hour TWA. Currently, exposure limits have not been established for carbon nanotubes. Also, there are no established exposure guidelines for particles in the nano sized range (less than 100 nm or 0.1 µm). Since an arbitrary PEL could not be set for CNTs, the engineering controls developed, PPE used and operating procedures adopted were designed to reduce exposure to as low a level as reasonably achievable. The air monitoring tests showed that exposure potential near the equipment ranged between the non detection limit of the measurement and a maximum of 0.65 mg/m 3. Current work practices and controls appear to be adequately controlling the exposures. DuPont will continue to use current PPE, including respiratory protection, which includes: PPE worn: N100 HEPA filtering respirator lab coat and Tyvek disposable gauntlets (or rear tied disposable gown) Nitrile and leather gloves Safety glasses with side shields Engineering Controls: Portable HEPA filtered Vacuum Cleaner Ventilated enclosure for weighing /mixing Local exhaust trunk Local exhaust canopy All laboratory areas will conduct a full Laboratory Process Hazards Review, or the equivalent, working with DuPont experts. Similarly, procedures and controls used in manufacturing area workplaces will be reviewed as appropriate to the particular situation as any specific project becomes successful and the volume increases, with particular attention to the drying, trimming and packaging areas. Similar programs with other nanomaterials (e.g., TiO 2, SiO 2, nanoclays) have included monitoring of the workplace air

4 4 during continuous melt compounding and post processing operations (grinding and cutting). The grinding and cutting tests of such composites have not thus far indicated any detectable regeneration of any nanoparticles. Toxicity As noted earlier, CNTs can be produced using a variety of methods, including arc discharge, laser ablation, high pressure carbon monoxide (HiPco), and chemical vapor deposition (CVD). Each method uses different starting materials and conditions, thus producing different CNT samples that vary with respect to their electro chemical and physico chemical properties. Because of this variation, it is logical to hypothesize that the toxicity of each CNT sample could also be different. Therefore, the toxicological assessment of CNT systems is a complicated issue. Toxicity is expected to be CNTspecific and generalizations likely cannot be made. A few peer reviewed toxicity studies on CNTs have been published (see review by Helland et al., EHP, 2007), including studies by David Warheit (DuPont Haskell Laboratory, Newark, DE. USA), Anna Shvedova (NIOSH, Morgantown, WV, USA), Andrew Maynard (NIOSH, Cincinnati, Ohio, USA), and Chiu Wing Lam (Johnson Space Center, NASA, Houston, TX) involving pulmonary instillation in rats. 1 The very low volumes being used by DuPont currently solely for R&D purposes, lack of clarity surrounding how users would be exposed to the material/product, and uncertainty of project success do not justify development of further toxicity data at this time. As any specific project becomes successful and the volume increases, DuPont will develop relevant toxicology data, appropriate to the specific exposure scenarios. Potential Exposure Pathways All work is presently at the research and development stage, with less than 5 researchers and technicians handing and using CNTs in sub kilogram quantities. Typically, grams of CNTs are consumed, per set of experiments, to make nanocomposites by direct compounding, masterbatch letdown or in situ polymerization approaches. These research activities occur under written Standard Operating Procedures (SOPs) covering all ultrafine powder handing and clean up, with risk mitigation safeguards developed through many years of experience with highly hazardous materials. In this stage, worker safety is the primary concern, and these safeguards are expected to minimize exposure risk. At 1 Warheit DB, Laurence BR, Reed KL, Roach DH, Reynolds GA, Webb TR Comparative pulmonary toxicity assessment of single wall carbon nanotubes in rats. Toxicol Sci 77: Shvedova AA, Kisin ER, Mercer R, Murray AR, Johnson VJ, Potapovich Alla I, et al Unusual inflammatory and fibrogenic pulmonary responses to single walled carbon nanotubes in mice. Am J Physiol Lung C 289(5):L698. Maynard AD, Baron PA, Foley M, Shvedova AA, Kisin ER, Castranova V Exposure to carbon nanotube Material: aerosol release during the handling of unrefined single walled carbon nanotube material. J Toxicol Env Heal A 67(1): Lam C W, James JT, McCluskey R, Hunter RL Pulmonary toxicity of single wall carbon nanotubes in mice 7 and 90 days after intratracheal instillation. Toxicol Sci 77(1):

5 5 this stage of development, potential DuPont customers and downstream users for these applications are not candidates for exposure via materials obtained from DuPont. If such products were to enter later stages of development, exposure potential for the relevant applications and the associated activities would need to be appropriately assessed, depending on the nature of the application. Environmental Fate and Transport There are few peer reviewed studies on environmental fate and effects (EFE) of CNTs (see review by Helland et al., EHP, 2007; Hyung et al., ES&T, 2006). The very low volumes being used by DuPont currently solely for R&D purposes, the uncertainty about the specific nature of probable applications and their associated user exposure scenarios, and uncertainty of project success do not justify development of further EFE data at this time. As any specific project further develops and the production or use volume increases, DuPont will develop relevant EFE data, appropriate to the specific exposure scenarios. Working with Others in the Supply Chain CNT suppliers are usually small start up companies, frequently located overseas. At present, it is difficult to determine the degree to which suppliers of CNTs have collected EHS data, conducted exposure analyses or determined what engineering controls and personal protective equipment they should employ. Recently, adverse findings from isolated tests on the toxicity or environmental fate of CNTs have been reported. Thus far, it is difficult to draw general conclusions about CNTs from these studies, some of which are unclear as to what specific CNTs were tested and whether the protocols employed are valid and yield reproducible results. It remains to be seen whether the limited data available suggesting either safety or concern for any particular CNT product, either from the suppliers or from published, peer reviewed studies, are reliable. For now, DuPont is handling CNTs used for research purposes as potentially hazardous materials. Should valid tests indicating adverse effects emerge, these should be shared with the suppliers and potential customers. Appropriate controls should be recommended and used. Step 3. Assess Risks A systematic assessment of risk was not considered appropriate at this stage of development, because of the very low volumes of CNTs being used by DuPont currently solely for R&D purposes, the diverse range of materials being evaluated, the uncertainty about the specific nature of probable applications and their associated user exposure scenarios, and the uncertainty of project success at this time. As any specific future project enters later stages of development, program leaders will work with DuPont experts to assess risks appropriate to the materials of choice and the specific exposure scenarios.

6 6 Step 4. Risk Mitigation DuPont is handling CNTs as if they are potentially hazardous. DuPont will establish an acceptable exposure level as more monitoring data are collected in laboratories using CNTs for different applications. For example, should DuPont pursue the development of a nanocomposite product requiring a continuous compounding process incorporating CNTs, new engineering controls will be developed and PPE improved if needed, and air monitoring evaluations will be conducted to establish an exposure level. Step 5. Decide, Document and Act For nanocomposite synthesis at the research scale, a laboratory was designed to process small quantities (typically less than one kilogram) of ultra fine powders and nanoparticles in a manner that minimizes exposure to personnel and the environment during sample preparation, melt blending, cleanup and waste disposal. Engineering controls, PPE and special operating procedures were implemented as preventative measures. The air monitoring tests described in this case study documents and supports the effectiveness of the approach taken. As a result of these and other nanoparticle air monitoring tests, significant capital improvements were made in 2006 and A new nanocomposites process lab was constructed and a bag in/bag out HEPA exhaust filtration system was installed in the ventilation system to trap aerosolized powders. Disposable Tyvek reartied gowns are being evaluated as additional PPE. Step 6. Review and Update DuPont s use of CNTs is under continuous review as they are the subject of research and development efforts. 06/07