Film formation kinetics of small rubber particles from Hevea latex in their hydrated state at the air-liquid interface

Latex obtained by tapping the Hevea brasiliensis tree is a colloidal suspension of various micrometricobjects, mainly composed of rubber particles (RP) which contain cis-1,4-polyisoprene chains. Hevea latexis the only commercial source of natural rubber (NR), a strategic raw material used for automotive,medical and consumer applications. RP composed of a hydrophobic cis-1,4-polyisoprene coresurrounded by a lipoprotein monolayer membrane exhibit a bimodal size distribution, small rubberparticles (SRP, diameter ~ 0.05-0.4 μm) and large rubber particles (LRP, diameter ~ 0.4-3.0 μm). Thebiochemical composition vary according to their size [1]. The size of ammonia-stabilized RP has alsobeen shown to influence various properties of NR samples, such as RP film formation or mechanicalproperties of NR [2]. However, drying of the RP film leads to rearrangement and deformation of theparticles.In this study, we propose a new approach where SRP are characterized in their hydrated state by formingRP thin films at the air-liquid interface. In this way, they remain as close as possible in their native state,i.e. when latex exudes from the tree. The adsorption kinetics of the ammonia-free SRP is monitored bysurface pressure and ellipsometric angle measurements, and completed by a visualization of the film byatomic force microscopy (AFM)[3]. The results highlight a destructuration of the SRP during theiradsorption, which is reflected by a spreading of the membrane and polymer chains at the air-liquidinterface. This work provides a new insight into the behavior of hydrated ammonia-free SRP films