Addition curing systems involve two-part silicones which require the mixture of a silicone polymer with a catalyst to initiate the cure. Platinum is the most commonly used metal catalyst for addition curing of silicones by hydrosilylation which involves the crosslinking by the addition reaction of silicon hydride species to unsaturated bonds, mainly CC, but also CO or CN double bonds. After crosslinking of the polymers, the platinum catalyst cannot be recovered but remains in the silicone materials throughout the entire product life. In the end, platinum is disposed of together with the silicones and is thus lost to the value chain. The overall objective of this work was to develop a recycling process for the recovery of platinum from addition-cured silicone elastomers. In the first step, this was achieved by efficient digestion methods and by optimizing the leaching processes for exemplary commercial silicone elastomer products. Two different silicone materials were investigated, both of which were crosslinked with a platinum catalyst. The initial Pt content in the tested samples was 12.6 ± 0.2 mg/kg for a commercial silicone impression material and 6.3 ± 0.5 mg/kg for a silicone baking mold, measured by graphite furnace atomic absorption spectrometry (GF-AAS). Samples were first frozen with liquid nitrogen to improve brittleness and then crushed with a simple food processor to obtain a silicone granule. Various acid mixtures, mainly based on sulfuric acid, were investigated as digestion methods in order to extract platinum from the silicone network. These had different effects on the dissolution behavior of silicone samples and the amount of platinum extracted in each case. The amount of platinum leached from the filtrate of the digested samples in each case was measured by ICP-OES to evaluate the efficiency of different leaching mixtures. In addition, the dissolved platinum species present in the solutions was identified by UV/VIS as tetrachloridoplatinate(II) complex. The best platinum leaching results so far were obtained with two methods, both of which used a leaching mixture based on sulfuric acid and hexamethyldisiloxane (M). In the presence of hydrochloric acid, 9.6 ± 1.6 mg platinum/kg was leached from the silicone impression material and 4.2 ± 0.8 mg platinum/kg from the silicone baking mold. With the additional use of instead of hydrochloric acid, 10.4 ± 2.8 mg platinum/kg was extracted from the silicone impression material and 4.8 ± 1.0 mg platinum/kg was extracted from the silicone baking mold. These methods were replicated with = 3. Using statistical evaluation methods (F-test, -test, and confidence interval), no significant difference was found between these two best methods. Recovery of platinum(0) from leach mixtures has not yet been achieved due to high dilution and very low platinum concentration in samples and will be part of another study.

中文翻译：

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从固化有机硅弹性体中浸出催化剂铂：比较试剂的初步研究

加成固化系统涉及两部分有机硅，需要有机硅聚合物与催化剂的混合物来引发固化。铂是通过氢化硅烷化对有机硅进行加成固化最常用的金属催化剂，氢化硅烷化涉及通过氢化硅物质与不饱和键（主要是 CC，但也有 CO 或 CN 双键）的加成反应进行交联。聚合物交联后，铂催化剂无法回收，而是在整个产品生命周期中保留在有机硅材料中。最终，铂与有机硅一起被处置，从而消失在价值链中。这项工作的总体目标是开发一种从加成固化有机硅弹性体中回收铂的回收工艺。第一步，这是通过有效的消化方法和优化示例性商业有机硅弹性体产品的浸出工艺来实现的。研究了两种不同的有机硅材料，这两种材料都是用铂催化剂交联的。通过石墨炉原子吸收光谱法 (GF-AAS) 测量，测试样品中的初始 Pt 含量对于商业硅胶印模材料为 12.6 ± 0.2 毫克/千克，对于硅胶烘焙模具为 6.3 ± 0.5 毫克/千克。首先用液氮冷冻样品以改善脆性，然后用简单的食品加工机粉碎以获得有机硅颗粒。研究了主要基于硫酸的各种酸混合物作为消化方法，以便从有机硅网络中提取铂。这些对有机硅样品的溶解行为和每种情况下提取的铂量有不同的影响。通过 ICP-OES 测量每种情况下从消化样品滤液中浸出的铂量，以评估不同浸出混合物的效率。此外，溶液中存在的溶解铂物质通过 UV/VIS 鉴定为四氯化铂 (II) 络合物。迄今为止最好的铂浸出结果是通过两种方法获得的，这两种方法都使用基于硫酸和六甲基二硅氧烷（M）的浸出混合物。在盐酸存在下，从硅胶印模材料中浸出 9.6 ± 1.6 mg 铂/kg，从硅胶烘焙模具中浸出 4.2 ± 0.8 mg 铂/kg。额外使用 代替盐酸，从硅胶印模材料中提取出 10.4 ± 2.8 mg 铂/kg，从硅胶烘焙模具中提取出 4.8 ± 1.0 mg 铂/kg。这些方法以 = 3 重复。使用统计评估方法（F 检验、β 检验和置信区间），在这两种最佳方法之间没有发现显着差异。由于样品中的高稀释度和极低的铂浓度，尚未实现从浸出混合物中回收铂(0)，这将成为另一项研究的一部分。