Multifunctional role of calcium chloride in improving the chemical, mechanical, and physical properties of natural and synthetic rubber latex for gloves and transdermal patch films

Abstract

Synthetic and natural rubber latex gloves and transdermal patch films were prepared using a dipping process with unglazed porcelain molds. Calcium chloride (CaCl₂) was added to the rubber latex formulations at concentrations of 0, 0.2, 0.4, and 0.8 wt% to enhance their chemical, mechanical, and physical properties. The formation and characteristics of the rubber gloves and transdermal patch films were evaluated using standard testing methods. Calcium chloride, an inorganic compound composed of calcium ions (Ca^2 +) and chloride ions (Cl^-) with a pH of 2–3, proved highly effective in influencing the isoelectric point of the rubber latex compounds. It reduced the isoelectric point from −68.1 mV to −45 mV, maintaining it within the range conductive to stable film formation. Furthermore, it adjusted the pH of the rubber latex compounds from 10.5 to a range of 5.89–6.29 on the surface of the rubber film. Additionally, it facilitated ionic crosslinking between calcium ions and carboxylate groups on the particulate surface of natural rubber latex. These adjustments led to gradual improvements in tensile strength, elongation at break, and maximum stress of the dipped films, while simultaneously reducing water-extractable proteins. To further optimize the process, a small amount of Terric 16 A-16 was incorporated into the inorganic solution. This addition shortened coagulation time, particularly for synthetic rubber latex compound, and improved the physical properties of natural rubber latex. The resulting films were smooth, thin, and free of surface porosity. A key advantage of this study is the elimination of the need for a coagulant coating on the ceramic mold surface, achieved through a one-step dipping process. This innovation significantly reduces costs, processing time, and waste.