Effects of Frequency and Sonication Time on Ultrasonic Degradation of Natural Rubber Latex

Ultrasonic degradation of fresh latex was investigated at frequencies of 20 and 25 kHz, at a constant temperature of 25 o C (±1 o C) to avoid temperature-related effects. The time-dependent evolution of the molecular weight of the natural rubber latex was determined using gel permeation chromatography, and its structure by means of the fourier transform infrared (FTIR) technique. A 10 minute period of sonication resulted in reduction in the molecular weight of both the 20 and 25 kHz treated samples, the lowest average molecular weight () being obtained in the case of the 25 kHz sample. The of the 25 kHz sample also decreased with increasing latex concentration. However, after 30 minutes, fluctuations had occurred in both samples with respect to the and and also the molecular weight distributions, an effect possibly explained by the competing processes of chain scission and radically-induced cross-linking of the polymer chains. The FTIR results also suggest that the structure of polyisoprene is unaltered by ultrasonic wave treatment at these frequencies.