Creaming kinetics and aggregation of concentrated natural Hevea latex

Abstract Natural rubber latex (NRL), extracted from the Hevea brasiliensis tree, plays a pivotal role in many industrial sectors due to its unique physical properties. This study investigates the colloidal properties and creaming behavior of concentrated NRL, up to a volumetric fraction of Φ = 0.54. First, using a set of experimental techniques such as dynamic light scattering, electrophoretic mobility experiments and environmental scanning electron microscopy, we characterize both Small Rubber Particles (SRPs) and Large Rubber Particles (LRPs) within NRL. Then, using light scattering, we monitor across a wide range of volume fractions the creaming fronts of concentrated NRL. The creaming behavior of both SRPs and LRPs is modeled using the Richardson-Zaki (R-Z) equation for both low (unscreened surface charges) and high (screened surface charges) ionic strengths, identifying creaming speeds under laminar flow conditions with an R-Z parameter close to 𝑛 = 4.65. In contrast to diluted suspensions, high particle volume fraction in concentrated NRL restricts diffusion and allows the development of slow moving creaming fronts with speeds in the range of nm.s −1 . Findings also reveal that higher ionic strengths, notably when calcium ions are involved, enhance particle aggregation, transitioning the suspension from bimodal to monomodal size distribution. Results point to the subtlety of studying latex aggregation in concentrated media to observe the onset of particle aggregation. This research provides insights into the physicochemical interactions in concentrated latex suspensions, offering implications for improved processing techniques in the rubber industry. Graphical Abstract