Cyclization of natural rubber (NR) latex: Synthesis, characterization and application in NR compounds and as a compatibilizer in NR/acrylonitrile butadiene rubber (NBR) blends
Azizon Kaesaman
, Tassaneeya Khunrang, Charoen Nakason
, Tassaneeya Khunrang, Charoen NakasonVol. 19., No.8., Pages 753-772, 2025
DOI: 10.3144/expresspolymlett.2025.58
DOI: 10.3144/expresspolymlett.2025.58
Corresponding author: Charoen Nakason 
GRAPHICAL ABSTRACT
ABSTRACT
Cyclized natural rubber (CNR) was synthesized through the acid-catalyzed reaction of natural rubber (NR) latex using sulfuric acid as a catalyst and stabilized with a non-ionic surfactant. Cyclization was evaluated by iodine numbers under varying reaction times, temperatures, and NR-to-acid ratios. Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance spectroscopy (1H-NMR) confirmed the formation of cyclic structures in CNR molecules. Differential scanning calorimetry (DSC) showed that the glass transition temperature (Tg) of CNR increased with cyclization, indicating greater rigidity and less chain flexibility. CNR was then blended with NR and used as a compatibilizer in NR/acrylonitrile butadiene rubber (NBR)blends. It increased blend viscosity, hardness, and dimensional stability but reduced tensile strength and elongation due to its rigid cyclic domains. In NR/NBR blends, CNR outperformed a commercial homogenizer in enhancing interfacial interactions, leading to superior shear flow properties, curing behavior, and mechanical performance. This is attributed to the polar groups in CNR, which enhance intermolecular interactions and phase compatibility, resulting in finer phase morphology. This study highlights the potential of CNR as a versatile material for enhancing the performance of rubber compounds, with promising applications in advanced industrial formulations.
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