Controlling the characteristics of raw natural rubber by partial degradation in the latex stage using a water-soluble de
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ORIGINAL PAPER
Controlling the characteristics of raw natural rubber by partial degradation in the latex stage using a water‑soluble degrading agent Nurul Hayati Yusof1 · Krishna Veni Baratha Nesan1 · Fatimah Rubaizah Mohd Rasdi1 Received: 13 April 2020 / Accepted: 16 September 2020 © The Malaysian Rubber Board 2020
Abstract Partial degradation of high ammonia natural rubber (HANR) in the latex stage was successfully carried out in the presence of periodic acid as a water-soluble degrading agent at ambient temperatures, i.e. 30 °C. The number average molecular weight (Mn), weight average of molecular weight (Mw), gel content and Mooney viscosity were decreased as the periodic acid concentrations increased. The polydispersity was slightly increased with increasing periodic acid concentrations. The relationship between Mw, gel content and Mooney viscosity was established. Mw in the range of 8.0 × 105 g/mol to 1.2 × 106 g/mol, and gel content between 30 and 45 wt% successfully achieved the Mooney viscosity of raw natural rubber ranging from 60 to 85 MU. To obtain such properties, periodic acid concentration between 17 and 19 phr was used to partially degrade the natural rubber in the latex stage. The structural characterisations determined by Fourier transform infra-red (FTIR) and nuclear magnetic resonance (NMR) spectroscopies confirmed the occurrence of chain scission to form carbonyl terminal groups as a result of partial degradation. In summary, the Mooney viscosity of raw natural rubber can be controlled by partial degradation of natural rubber in the latex stage, contributed by a controlled decrease in molecular weight and gel content. Hence, this work may be useful in altering the properties of raw natural rubber that are suitable for processing of dry rubber products. Keywords HANR latex · Periodic acid · Partial degradation · Molecular weight · Gel content · Mooney viscosity
Introduction Partial degradation of natural rubber in the latex stage may significantly contribute to achieving the ideal characteristics of raw natural rubber since the characteristics are governed by its properties. Partial degradation is notably distinguished from full degradation, in which partial degradation of natural rubber in the latex stage is a controlled reaction that undergoes a certain degree of chain scission to obtain solid raw natural rubber with suitable properties, for instance molecular weight. The molecular weight can be controlled by partial degradation, in which the changes in polymer chain length may associate with other properties such as gel content and viscosity of raw natural rubber. According to previous work [1, 2], the molecular weight of natural rubber latex from Hevea Brasiliensis species was measured to be about 106 g/ mol. The very high molecular weight of natural rubber * Nurul Hayati Yusof [email protected] 1
Engineering and Technology Division, Malaysian Rubber Board, 47000 Sungai Buloh, Selangor, Malaysia
which reflects the abundance of polymer chain entanglements, as well as branching poi
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