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Physical & Chemical properties

Particle size distribution (Granulometry)

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Description of key information

NaOH is mainly commercialised as a solution in water at different concentrations (lye), or as solid (cast, flakes, pearls). Solid NaOH was produced at 27% of the production sites, but covers only a small percentage (4%) of the total market; the remaining amount (96%) is NaOH in solution.

The data of the EU Assessment Report confirm that solid NaOH is manufactured although not at all NaOH production sites. However, the particle size of pearls, flakes and cast is very large and therefore there will be virtually no particles < 100 μm. Based on Figure R.7.1-7 (page 144) of the REACH Guidance document R.7a. (Endpoint specific guidance) there is no need to do further testing if there are virtually no particles < 100 μm. Furthermore it is technically not possible to do further testing because sodium hydroxide is very hygroscopic and therefore the small particles agglutinate. This results in the formation of small droplets.

Additional information

Sodium hydroxide is mainly manufactured as a solution but solid NaOH is also placed on the market. According to section 2.1.1 of the EU Risk Assessment Report (European Commission, 2007): "NaOH is mainly commercialised as a solution in water at different concentrations (lye), or as solid (cast, flakes, pearls). Solid NaOH was produced at 27% of the production sites, but covers only a small percentage (4%) of the total market; the remaining amount (96%) is NaOH in solution". The data of the EU Assessment Report confirm that solid NaOH is manufactured although not at all NaOH production sites. However, the particle size of pearls, flakes and cast is very large and therefore will be virtually no particles