Improvement of the ISO 16564:2004 Standard Method for Molar Mass Determination of Natural Rubber to Enhance Measurement Accuracy

The molar mass of natural rubber (NR) is a critical structural parameter that strongly influences its processing behavior and final mechanical properties. However, owing to its complex molecular architecture and inherent natural network structure, accurate molar mass characterization of NR remains challenging using conventional methods. In this study, the limitations of the ISO 16564:2004 standard method for the SEC-based molar mass determination of NR are systematically analyzed, and corresponding optimization strategies were proposed. NR samples were prepared and analyzed according to the ISO 16564:2004 procedure. The losses of insoluble gel and microgel during dissolution and filtration were quantitatively evaluated, and sample recovery during chromatographic analysis was determined. In addition, size-exclusion chromatography coupled with multi-angle light scattering (SEC-MALS) was employed to investigate adsorption interactions between NR components and the chromatographic column. The results showed that substantial sample loss occurred when the ISO standard method was applied, with the cumulative loss reaching approximately 35.0 wt%. By systematically optimizing the sampling strategy, dissolution conditions, filter pore size, and the introduction of tetrabutylammonium bromide (TBABr) as a desorption agent, the total sample loss was reduced from 35.0 wt% to 26.9 wt%. The optimized method effectively minimizes sample loss arising from dissolution, filtration, and column adsorption, thereby improving the representativeness and reliability of molar mass and molar mass distribution (MMD) characterization under the present THF-based SEC conditions. • Severe sample loss of natural rubber occurs in SEC analysis following ISO 16564:2004 • Tetrabutylammonium bromide effectively suppresses polymer adsorption • TBABr-modified THF significantly improves sample recovery and reproducibility • The proposed approach contributes to optimization of ISO 16564:2004 testing protocols