Parameters Governing Void Formation and Expansion of Hollow Natural Rubber Latex Particles for Their Use as Bio-based Nanocapsules

This work reports the hollow latex (HL) particles developed from natural rubber latex particles (NRPs), known for their broad size distribution and non-spherical shape. HL-NRPs, prepared via the seeded emulsion polymerization in one pot, are studied as potential bio-based nanocapsules for the first time. Effects of types of crosslinking agents and swelling agents, the addition of sodium dodecyl sulfate (SDS), and monomer compositions on the void formation and expansion are systematically investigated. The combined effects of phase separation between NR core swelled with divinyl benzene (DVB) and hydrophilic poly(methyl methacrylate/acrylic acid) P(MMA/AA) shell, the entanglement of rubber chains copolymerized with MMA/DVB/AA monomers, and the osmosis from external aqueous medium promoted the void formation. While crosslinking agents affected the void formation and shell strength, SDS and type of monomers governed colloidal stability and polymerization loci as well as morphology, respectively. The ability of HL-NRPs as nanocapsules is explored by encapsulating fluorescent dyes, i.e., hydrophilic fluorescein isothiocyanate (FITC) and lipophilic Nile red (NiR), as model cargo. From the dye release test after 24 h, the cumulative concentrations of FITC in methanol and of NiR in tetrahydrofuran are 0.17 and 0.11 µg mL⁻¹, respectively. The results suggested that FITC is released from HL-NRPs easier than NiR possibly due to the different encapsulation location.