Zhang Mengmeng, Arunachalam Abinaya, Perrin Hugo, Polat Sevgi, Groenewold Jan, Mendes Eduardo, Eral Hüseyin Burak
Process & Energy Department, Delft University of Technology, Leeghwaterstraat 39, 2628 CB Delft, The Netherlands.
Polymer Science, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, Groningen 9747 AG, The Netherlands.
ACS Appl Polym Mater. 2023 Jun 5;5(7):4780-4788. doi: 10.1021/acsapm.3c00344. eCollection 2023 Jul 14.
Elevated humidity levels in medical, food, and pharmaceutical products may reduce the products' shelf life, trigger bacterial growth, and even lead to complete spoilage. In this study, we report a humidity indicator that mechanically bends and rolls itself irreversibly upon exposure to high humidity conditions. The indicator is made of two food-grade polymer films with distinct ratios of a milk protein, casein, and a plasticizer, glycerol, that are physically attached to each other. Based on the thermogravimetric analysis and microstructural characterization, we hypothesize that the bending mechanism is a result of hygroscopic swelling and consequent counter diffusion of water and glycerol. Guided by this mechanism, we demonstrate that the rolling behavior, including response time and final curvature, can be tuned by the geometric dimensions of the indicator. As the proposed indicator is made of food-grade ingredients, it can be placed directly in contact with perishable products to report exposure to undesirable humidity inside the package, without the risk of contaminating the product or causing oral toxicity in case of accidental digestion, features that commercial inedible electronic and chemo-chromatic sensors cannot provide presently.
医疗、食品和药品中的湿度升高可能会缩短产品的保质期，引发细菌生长，甚至导致产品完全变质。在本研究中，我们报告了一种湿度指示器，它在暴露于高湿度条件下时会不可逆地机械弯曲和卷曲。该指示器由两层食品级聚合物薄膜制成，这两层薄膜中乳蛋白酪蛋白和增塑剂甘油的比例不同，它们通过物理方式相互附着。基于热重分析和微观结构表征，我们推测弯曲机制是吸湿膨胀以及随之而来的水和甘油反向扩散的结果。在这一机制的指导下，我们证明了滚动行为，包括响应时间和最终曲率，可以通过指示器的几何尺寸进行调节。由于所提出的指示器由食品级成分制成，它可以直接与易腐产品接触，以报告包装内是否暴露于不良湿度环境，而不会有污染产品的风险，也不会在意外摄入时导致口腔中毒，这些是目前商业上不可食用的电子和化学变色传感器所无法提供的特性。
