Study on Degradation of Natural Rubber Latex Using Hydrogen Peroxide and Sodium Nitrite in the Presence of Formic Acid.

Abstract

Liquid natural rubber (LNR), a depolymerized natural rubber (NR) consisting of shorter chains, was prepared via oxidative degradation using NaNO2 and H2O2 degrading agents in the presence of HCOOH. The influence of reagent concentrations, temperature, and reaction time on the number-average molecular weight (Mn) was studied. Results showed the higher concentration of H2O2 and HCOOH employed faster degradative rates. However, a higher concentration of NaNO2 decreased the Mn reduction. Prolonged reaction time and high temperature resulted in a product with low Mn. FTIR spectra indicated the synthesized LNR contained hydroxyl end groups resulting from the breaking of the NR chains at an acidic pH, whereas a carboxyl terminated LNR was formed at an alkaline pH. SEM micrographs showed the latex particles of LNR were spherical and smaller compared to NR. The experimental results showed the reaction orders of [H2O2], [HCOOH], and [NaNO2] were 1.58, 0.79, and -0.65, respectively. In addition, the pre-exponential factor and activation energy were 1.04 × 109 M-1.72 t-1 and 78.66 kJ/mol, respectively. Based on TGA analysis, the thermal stability of the rubber depended on its Mn. The LNR containing functional end groups exhibited thermal instability and could be a starting material for many applications.