Abstract
Photocrosslinked silicone acrylates are used for a wide variety of applications, such as photocurable coatings, printing inks and adhesives. Their production requires the use of a photoinitiator (PI), such as Darocur 1173 (2-hydroxy-2-methyl-1-phenyl-propan-1-one). Even if PI represents a minor part of the formulation, residual amounts may remain in the polymerized products and possibly migrate into the environment during the use of the end products and/or at their end-of-life stage. To assess its possible fate under different environmental conditions, the release of Darocur 1173 from photocrosslinked silicone acrylates and its biodegradation were investigated. Leaching tests in water were conducted on thick coating and thin coated plastic films. Results showed that approximately 90% of the amount of Darocur 1173 used to synthesize thick coatings was released within 8 days of experiment. Biodegration assays were also done to assess the biodegradation of silicone coatings and PI under experimental conditions simulating the products’ end-of-life in sewage treatment plants (aerobic conditions) or in domestic waste landfills (anaerobic conditions). Results showed no biodegradation of thick coatings and PI under anaerobic conditions. An inhibitory effect was even observed on the biodegradation of glucose used as a reference biodegradable molecule. Under aerobic conditions however, PI was totally biodegraded and used as a carbon source, unlike the silicone coating which was not biodegraded.
Highlights
National and European regulations such as REACH (Registration, Evaluation and Autorisation of Chemicals) encourage industries to progressively replace potentially hazardous substances they might use by environmentally friendly substances
In scenarios where coated materials would be contacted with water, eitheir during their use or at their end-of-life stages, PI may migrate within the coating and be released into water and transported to environmental targets with potential impacts
When the coatings, silicon oil or Darocur were used as sole carbon sources, almost no biogas production was observed, indicating that these substrates were almost not biodegraded under anaerobic conditions
Summary
National and European regulations such as REACH (Registration, Evaluation and Autorisation of Chemicals) encourage industries to progressively replace potentially hazardous substances they might use by environmentally friendly substances. In coatings and ink industries, photo-induced crosslinking has become a mainstream technology for many applications because it provides products with better properties, sush as glossness, durability and abrasion resistance [1]. This technology is considered as a “green” one [2, 3] because it allows instant curing with low energy consumption and low emissions of volatile organic compounds. During the UV curing process at industrial scale in this field application, photoinitiator is generally applied in excess in order to favour its reactivity, usually at concentrations ranging from 2 to 10% (by weight of the total photocured formulation).
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