Leaching and Biodegradation of Darocur 1173 used as a Photo-Initiator in the Production of Photocrosslinked Silicone Acrylates

Journal of Polymers and the Environment, Feb 2017

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.

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Leaching and Biodegradation of Darocur 1173 used as a Photo-Initiator in the Production of Photocrosslinked Silicone Acrylates

Leaching and Biodegradation of Darocur 1173 used as a Photo- Initiator in the Production of Photocrosslinked Silicone Acrylates Salma Ouali 0 1 Yoann Louis 0 1 Patrick Germain 0 1 Rémy Gourdon 0 1 Valérie Desjardin 0 1 0 CNRS UMR5240, MAP , Univ Lyon, INSA-Lyon, Université Lyon 1, 11 Av J. Capelle, F-69621 Villeurbanne , France 1 DEEP Laboratory , Univ Lyon, INSA-Lyon, Bld. S. Carnot, F-69621 Villeurbanne , France 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. Silicone acrylates; Photoinitiator; Leaching; Biodegradation; End-of-life - 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. One of the application fields for UV curing is silicone release coatings. These ones are commonly obtained by photopolymerization of silicone acrylate monomers in the presence of a radical photoinitiator such as Darocur 1173 (2-hydroxy-2-methyl-1-phenylpropan-1-one) [4–7]. 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). Consequently only part of the photoinitiator is actually consumed in the reactional process [7, 8]. In the case of Darocur 1173, it is considered that only about 10% of the amounts applied are converted. The coated products therefore retain most of the amounts of Darocur initially added [8–10]. Due to the small size and molecular weight (164.2 g mol−1) of the molecule and its hydrosolubility, its migration within the coatings and transfer from the film surface into an aqueous phase seems quite possible. Green (2010) has reported that Darocur 1173 can be readily extracted from cured coatings with various solvents in Soxhlet extraction [8]. Unless the coated products are liberally washed, the residual amounts of Darocur remaining within the cured coatings are therefore available for potential release into environmental media if the products are contacted with water during their use and/or at their end-of-life stages. Regarding the products’ end-of-life, little is known on the fate and behavior of solid polymers, and especially silicone coatings in the different waste treatment processes like wastewater treatment plants or landfills [11]. The fate of silicone in the environment has been extensively studied in the 1990s until the early 2000s by Dow Corning Company. Indeed, following a very strong market development of these products, producers have widely communicated to reassure consumers about the non-toxicity of the degradation products for themselves and for the environment. Since those years, very few studies on their end-of-life have been published [11] and to our knowledge no work has been yet published on silicone acrylates or Darocur 1173. Thus, special care has to be paid to potential emissions of photoinitiator and acrylate monomers and the fate of these substances in the environment. Al (...truncated)


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Salma Ouali, Yoann Louis, Patrick Germain, Rémy Gourdon, Valérie Desjardin. Leaching and Biodegradation of Darocur 1173 used as a Photo-Initiator in the Production of Photocrosslinked Silicone Acrylates, Journal of Polymers and the Environment, 2017, pp. 1-10, DOI: 10.1007/s10924-017-0939-z