The degradation and weathering of modern polymer coatings: assessment and monitoring of the chemical signature

聚合物涂料在我们的环境中非常常见，用于表面和物体的保护、装饰甚至卫生。因此，了解它们的结构-性能关系、流变学、表面化学和降解对于工业(例如控制生产、耐久性和性能)以及其他相关领域非常重要，例如艺术和保护科学(例如修复、识别假冒油画)和刑事调查(例如比较入室盗窃(工具涂料、家用涂料)、故意破坏(喷漆)或车祸(汽车涂料)时可疑涂料和参考涂料的成分)。这些领域中的每一个，虽然面临着不同的问题，但都有一个共同的分析挑战：正在分析的涂层在其使用寿命内可能会受到风化和降解的影响。通过暴露在外部环境中，聚合物涂层会老化、降解并获得改变的化学特征。科学界面临的挑战是了解这些变化，以便预测聚合物涂层的长期老化。然而，油漆的老化和降解是一项很难理解的任务，因为基质是一种动态的介质。降解是多种因素综合作用的结果，包括成分的迁移或蒸发，以及结构的某些物理化学修饰(氧化、交联化)。热、水(湿气)、紫外线辐射或生物/化学污染物可进一步催化所有这些效应。此外，最常见的涂料材料(如丙烯酸、醇酸、聚氨酯、聚酯)具有不同的流变性和表面化学特性，并且含有紫外线防护(受阻胺光稳定剂，HALS)、热稳定剂、机械改性剂或抗微生物添加剂，这些都有助于它们的化学特征，并进一步增加了综合评价其降解的复杂性。对文献的调查表明，关于聚合物涂层降解的知识严重缺乏，这一问题一直通过案例研究或具体应用来解决，但在更一般的层面上仍未完全了解。在我的发现号研究计划中，我打算回答以下目标：1)彻底评估导致降解的影响因素及其物理化学结果，2)通过自然和加速风化对影响因素的协同方法评估测年潜力，3)建立一个按涂料成分、分析方法和降解条件组织的综合化学特征数据库。这项研究将与业界合作，为聚合物的降解建立新的分析标准。此外，通过数据库收集和分享结果将对科学界产生直接和持久的影响。

Polymer coatings are extremely common in our environment and used for protection, decoration or even sanitation of surfaces and objects. Understanding their structure-property relationship, rheology, surface chemistry, and degradation is therefore important for industry (e.g. control of production, durability, and performance), and other related fields such as art and conservation science (e.g. restoration, identification of counterfeited paintings) and criminal investigations (e.g. comparing the composition of suspected and reference paints in case of burglaries (tool paint, domestic paint), vandalism (spray paint), or car accidents (automotive paint)). Each of these fields, although facing distinct problematics, have one common analytical challenge: the coatings under analysis will potentially be subject to weathering and degradation over their lifetime. Through being exposed to the exterior environment, polymer coatings age, degrade, and acquire an altered chemical signature. The challenge for the scientific community is to understand these variations in order to predict the long-term weathering of polymer coatings. The weathering and degradation of paints is nonetheless a difficult task to apprehend, as the matrix is a dynamic medium. The degradation is a combination of many factors, including the migration or evaporation of components, and some physico-chemical modifications of the structure (oxidation, cross-linking). All these effects can further be catalyzed by heat, water (moisture), UV radiation, or biological/chemical contaminants. Additionally, the most common paint materials (i.e. acrylic, alkyd, polyurethane, polyester) have different rheologic properties and surface chemistry, and contain UV protection (hindered amines light stabilizers, HALS), heat stabilizers, mechanical modifiers, or anti-microbial additives that all contribute to their chemical signature and further increase the complexity of comprehensively evaluate their degradation. A survey of the literature shows that there is an important lack of knowledge on the degradation of polymer coatings, which has always been approached by case studies or specific applications, but remains incompletely understood at a more general level. In my Discovery research program, I intend to answer the following objectives: 1) Thorough evaluation of the influencing factors that contribute to degradation and their physical and chemical outcomes, 2) Assessment of the dating potential by a synergistic approach of the influencing factors using natural and accelerated weathering, 3) Creation of a comprehensive database of chemical signatures organized by paint compositions, analytical methods, and degradation conditions. This research will establish new analytical standards for the degradation of polymers in collaboration with the industry. Additionally, collecting and sharing the results through a database will have a direct and lasting impact on the scientific community.