Characterization of liquid deproteinized natural rubber prepared via oxidative degradation

Abstract

In the present work, liquid deproteinized natural rubber (LDPNR) was prepared by oxidative depolymerization of deprotcinized natural rubber using hydrogen peroxide (H₂O₂) and sodium nitrite (NaNO₂) as oxidizing reagents. Structural characterization of LDPNRs was performed using FT-IR, ¹H-NMR, ¹³C-NMR, and Heteronuclear Multiple Quantum Coherence (HMQC) spectroscopy. After degradation, the intensity of vibration mode at 1660 cm⁻¹ (Vc=c) decreased, indicating the decrease in the number of C=C bonds in the NR Chain. ¹H-NMR signals at 1.6 ppm and ¹³C-NMR signals at 40.0 ppm appeared in the NMR spectra of LDPNR prepared in acidic condition suggesting the occurrence of isomerization from cis-1,4-isoprene units to trans-1,4-isoprene units. Epoxidation also occurred during degradation of DPNR as a side reaction. End groups of LDPNRs were found to depend on pH of reacted latex. LDPNR prepared in pH 5-6 contains aldehyde end group, while LDPNR prepared at pH 8-9 has a hydroxyl end group. The gel content of LDPNRs was found to reduce compared to that of DPNR, significantly. GPC was employed to determine molecular weight of LDPNRs. The results show that the degradation in acidic medium behaves more effectively in comparison to in alkaline medium.