Novel approach to determine non-rubber content in Hevea brasiliensis: Influence of clone variation on properties of un-vulcanized natural rubber

The mesostructure and non-rubber content, including proteins and lipids, in natural rubber from three different Hevea brasiliensis clones, namely RRIT408, PB235 and RRIM600, were investigated by a new technique, temperature scanning stress relaxation (TSSR), along with other relevant methods It was found that the significant relaxation spectrum of TSSR was found as broad peaks in the temperature ranges of 58-60 degrees C which indicated level of interaction for proteins and lipids at the chain terminals. This directly relates to storage hardening phenomenon. Furthermore, we found that the molecular mass distribution is bimodal for RRIM600 clone while it is unimodal for RRIT408 and PB235. Furthermore, the RRIM600 clone contained high aggregates and non rubber components that enhanced the mechanical and rheological properties and caused strong storage hardening phenomenon. This might be attributed to the high fraction of short chains providing many chain ends, and to the total content of proteins and lipids. However, the unimodal rubber from PB235 clone exhibited poorer mechanical and physical properties and less storage hardening than those from RRIM600 and RRIT408. This might be attributed to lower content of proteins and lipids and longer molecular chains (low number of chain ends), causing less formation of aggregates or lower gel content.