Repeatability and reproducibility of thermal field-flow fractionation in molecular weight determination of processed natural rubber

The purpose of this study is (1) to determine the repeatability and reproducibility of thermal field-flow fractionation (ThFFF) in measuring the molecular weight of compounded natural rubber, and (2) to examine the correlation between the molecular weights obtained from ThFFF and the rheological data. 8 batches of compounded natural rubber were obtained from a thermomechanical mastication process, and were analyzed by ThFFF in a designed testing sequence. ThFFF analysis showed the compounded natural rubbers range in weight-average molecular weight (M_w) from 143 000 to 360 000. By taking into account both the short term variability (repeatability) as well as the long term variability (reproducibility) of the instrument, ThFFF was shown to be able to distinguish between samples differing by as little as 21 000 in M_w and 15 600 in number-average molecular weight, M_n (based on cis-polyisoprene calibration); and thus is a useful tool for the molecular weight analysis of natural rubber-related materials. It was also found that the rheological data (G′ and tan δ) measured on both the virgin and the compounded natural rubber correlated well with the molecular weights obtained from ThFFF when normalized.