Polyvinylpyrrolidone and Xanthan Gum Co-Stabilized Cuprous Oxide Submicron Suspension for Effective Preservation of Natural Rubber Latex

Abstract

Fresh natural rubber latex (NRL) is rich in nutrients such as proteins and sugars, making it highly susceptible to microbial growth and deterioration. Traditional ammonia-based preservatives generate irritating gases, posing hazards to worker health and the environment. Therefore, developing an effective, ammonia-free, and eco-friendly preservative for NRL is urgently needed. Herein, we report a facile one-pot synthesis of a polyvinylpyrrolidone (PVP)/xanthan gum (XG)/Cu2O (PX/Cu2O) submicron suspension as an efficient ammonia-free preservative for NRL. In this process, PVP regulates the particle size distribution of Cu2O through steric hindrance, while XG provides long-term stability via its steric hindrance and weak gel network, resolving the problems of agglomeration and sedimentation of submicron particles at high concentrations. The resulting PX/Cu2O preservative exhibits excellent long-term stability, with a ζ-potential of −32.85 mV and no obvious sedimentation for 7 days. It also demonstrates excellent broad-spectrum antibacterial activity, with inhibition zone diameters of 18.35 mm against Staphylococcus aureus (S. aureus) and 19.26 mm against Escherichia coli (E. coli), and a minimum inhibitory concentration of 1.28 g/L. In NRL preservation tests, an addition of only 0.4% (w/w) of PX/Cu2O extended the shelf life of fresh NRL to over 7 days, outperforming traditional ammonia preservation. Moreover, at this dosage, PX/Cu2O also improved the mechanical properties of both raw and vulcanized NRL sheets without adversely affecting their processing properties. This method is cost-effective and scalable, offering a practical strategy for the ammonia-free preservation of fresh NRL and holding great promise for industrial application.