Plasticizer Effect and Ionic Cross-linking: the Impact of Incorporating Divalent Salts in Methylcellulose Films for Colorimetric Detection of Volatile Ammonia

The growing generation of petroleum-derived plastic waste has been boosting research in the development of biodegradable polymers, which can also be applied as eco-friendly polymeric matrices to colorimetric sensors. However, poor mechanical performance and the difficulty in controlling analyte detection sensitivity of these materials disadvantaged their use in this application. Therefore, this study aimed to evaluate the influence of MgCl 2 and CaCl 2 ionic strength (IS) and ionic radius (IR) on the physicochemical properties of methylcellulose-based films. This work also assessed the IS effect on ammonia vapor detection via eco-friendly colorimetric sensors made of methylcellulose-base. Films were characterized using ATR-FTIR, contact angle, SEM and profilometry, and mechanical, thermal, optical, and barrier properties were measured. Tensile strength and Young’s modulus of the control film were 47 and 1090 mPa while increasing the IS to 500 mM using MgCl 2 reduced the values to approximately 1.9 and 1.5 mPa, respectively. IS values below 50 mM caused crosslinking, while above that concentration the salts acted as a plasticizer. The salts’ addition into the polymeric matrices dispersed better the polymeric network and increased methylcellulose films’ flexibility. Also, changing the IS changed the intensity of the sensors’ colorimetric response. Therefore, IS can be used as a tool to improve sensor sensitivity and detection limits, upgrading their quantification capacity. This discovery could lead to major advances in the optimization of colorimetric sensors so that the modulation of the precise moment of colorimetric change can be carried out using IS.