The effects of sonication time and frequencies on degradation, crystallization behavior, and mechanical properties of polypropylene

Abstract

The effects of ultrasound with different frequencies on the degradation, crystallization behavior, and mechanical properties of polypropylene were investigated by means of intrinsic viscosity, gel permeation chromatography, dynamic rheological measurements, X-ray diffraction, differential scanning calorimetry, polarized optical microscopy, and tensile and impact measurements. The results demonstrated that the degradation extent of polypropylene (PP) increased with increasing sonication time, especially for the samples treated in more than 5 min. Meanwhile, PP treated at 20 KHz was more easily degraded than other two frequencies. On the other hand, b-form PP could be induced by ultrasonic irradiation, its amount increased as the sonication time increased to 3 min and then decreased as the time further increased due to the degradation of PP. Likewise, b-phase was more easily formed when PP was treated at 20 KHz. The results of mechanical properties showed that the toughness of PP could be enhanced by the formation of b2phase, while the mechanical properties would be weakened by the substantial degradation under ultrasonic irradiation with higher intensity. Therefore, it was believed that the effects of both sonication time and frequency should account for the balance between toughening and degradation of PP. POLYM. ENG. SCI., 55:2566-2575

Studies on ultrasonic disintegration kinetics of SEBS in PP melts and the influencing factors

“…Moreover, the average particle diameter of SEBS in the blends treated at 20 kHz was smaller than those in the systems treated at the other two frequencies. As our previous article 31 reported, in case of the higher frequency the amplitude is lower at the same ultrasonic power. Therefore, the disintegration of SEBS drops treated at a low frequency with high amplitude is more effective than that of the ones treated at a high frequency with low amplitude.…”

“…The increase in complex viscosity is attributed to better dispersion of SEBS in the PP matrix with enhanced PP-SEBS interaction, while the latter decrease in the viscosity is apparently due to the degradation of polymer under ultrasonic treatment with high intensity, which was reported in our previous study. 31 The ultrasonic degradation caused by random scission of polymer chains was also reported by the early studies. 19,[34][35][36] Figure 13(b) shows the complex viscosity of the blends ultrasonically treated at different ultrasonic frequencies.…”

“…The increase and decrease of the viscosity are also attributed to the enhanced dispersion of SEBS and the degradation of the blends respectively. Moreover, the complex viscosity of the blends remained almost unchanged as the sonication time increased to 20 min, showing that the blends would not undergo any degradation as the time continued to increase, which agrees well with our previous study . Figure (d) shows the complex viscosity of the blends ultrasonically treated at different heating temperatures.…”

“…The power of ultrasound ranges from 0 to 630 W. The frequency of ultrasound is 20 kHz, 25 kHz, and 30 kHz, respectively. The apparatus was also described in our previous study …”

“…The apparatus was also described in our previous study. 31 PP and SEBS with the mass ratio of 90/10 were first mixed in a high-speed mixer for 10 min. The mixtures were then preblended and pelletized by a twin screw extruder.…”