Impact of processing methods on molecular structure of raw natural rubber: New insights on differences between ribbed smoked sheet and technically specified rubber

To elucidate the effect of processing methods on the molecular structure of raw natural rubber (NR), this study systematically compared ribbed smoked sheet (RSS) and technically specified rubber (TSR). To eliminate the effects of rubber tree clones and storage hardening, both RSS and TSR were derived from two distinct rubber tree clones: IAN873 (unimodal molecular weight distribution, MWD) and Reyan73397 (bimodal MWD), and also subjected to hydroxylamine neutral sulphate (HNS) treatment to prepare CV rubbers (RSSCV and TSRCV). Results revealed that RSS exhibited significantly higher protein content, molecular weight, Mooney viscosity, initial plasticity, plastic retention index, macrogel content and microgel <1μm content than TSR, while TSR showed higher total fatty acid contents than RSS. Rheological analyses further indicated that RSS possesses more crosslinking density and entanglement compared to TSR. Therefore, the differences in molecular structure between RSS and TSR were not only evident in structural parameters but also in entanglement. It was critical that HNS treatment did not substantially modify the structural disparities between the two. Strikingly, across different rubber tree clones, RSS and TSR from IAN873 clone outperformed RSS from Reyan73397 clone in non-rubber composition, structural characteristics, and rheological performance. This highlighted that clonal variations not only influenced the structure of NR produced via the same process but also modulated the structure of NR prepared by different processing methods. • Differences between RSS and TSR in macro-, meso-, and microstructure were elucidated. • Entanglement critically distinguished molecular structures of RSS and TSR. • HNS treatment had no effect on the structural difference between RSS and TSR. • Ensure RSS and TSR were from the same rubber tree clone when compared.