Toward sustainable protein-free natural rubber: Buoyancy-driven latex purification

Buoyancy-driven latex purification method was developed to prepare protein-free natural rubber (PFNR), due to the growing demand for allergy-safe natural rubber materials in medical and biomedical applications, including surgical gloves, catheters, balloons, and related devices. High-ammonia natural rubber (HANR) latex was treated with NaOH, SDS, and urea, followed by the buoyancy-driven latex purification using CO 2 bubbling. Nitrogen content, representing residual protein amounts, was determined by the Kjeldahl method, while fatty acid ester content was evaluated using FT-IR spectroscopy. The chemical structure was examined by 1 H NMR spectroscopy. Particle size distribution and zeta potential were measured to examine colloidal stability and flocculation behavior. Mechanical properties were assessed by tensile testing of unvulcanized rubber samples. Contents of nitrogen and fatty acid esters were reduced from 0.194 w/w% and 24.3 mmol/kg rubber for HANR to 0.000 w/w% and 15.6 mmol/kg rubber for PFNR, respectively. 1H NMR analysis showed that high stereoregularity was maintained after the buoyancydriven latex purification. Tensile strength of unvulcanized PFNR film was lower than that of HANR film due to the removal of proteins and lipids.