Evaluation of structural change during fast transformation process of cross-linked NR into liquid NR by light pyrolysis

The presence of cross-linked networks in rubber creates a tremendous problem for recycling and reusing of waste rubber. Fast transformation of cross-linked natural rubber (NR) into liquid natural rubber was carried out by light pyrolysis in temperature range from 240 to 300 °C in variable time (in range: 1-30 min). The transformation efficiency was evaluated by measuring the sol fraction and the cross-link density of the gel fraction. Over 80 wt% sol fraction was obtained at 280 °C in 15 min and 100 wt% sol fraction was obtained at 300 °C in 3 min. The chemical structure of sol fraction was characterized by gel permeation chromatography, nuclear magnetic resonance and infrared spectroscopy. The molecular weight of sol fraction in cross-linked NR processed at 280 °C and 300 °C decreased when gel fraction is over 50%. The nuclear magnetic resonance results showed that mono-sulfidic linkages occurred mainly in the sol fraction of liquid NR obtained at 300 °C. Isomerization from cis to trans form of isoprene unit in NR increased with extending pyrolysis time.