Chen Jinyao, Chen Yingzi, Li Huilin, Lai Shih-Yaw, Jow Jinder
The State Key Laboratory of Polymer Materials Engineering, Polymer Research Institute of Sichuan University, Chengdu 610065, China.
Ultrason Sonochem. 2010 Jan;17(1):66-71. doi: 10.1016/j.ultsonch.2009.05.005. Epub 2009 May 18.
The physical and chemical effects of ultrasound on polypropylene (PP) melts in extrusion were investigated. By applying ultrasound vibration to the entrance of the die, apparent pressure and viscosity of PP can be obviously decreased under the appropriate ultrasound power. Ultrasound has both physical and chemical effects on the polymer melt. In our study with specific polymer and ultrasound system, we determined that the chemical effect makes up 35-40% of the total effect of ultrasound on the apparent viscosity reduction of PP melts at most of the studied intensities. The physical effect plays a more important role in the ultrasound-applied extrusion than the chemical effect. This chemical effect is an irreversible and permanent change in molecule weight and the molecular-weight distribution due to ultrasound. As the ultrasound intensity increases, the molecular weight of PP reduces and its molecular-weight distribution becomes narrower; the orientation of PP molecules along the flow direction reduces (in melt state) and the crystallinity of PP samples (in solid state) decreases by applying the ultrasound vibration. Ultrasound vibration increases the motion of molecular chains and makes them more disorder; it also affects the relaxation process of polymer melts by shortening the relaxation time of chain segments, leading to weakening the elastic effect and decreasing the extruding swell ratios. All the factors discussed above reduce the non-Newtonian flow characteristics of the polymer melt and result in the viscosity drop of the polymer melt in extrusion.
研究了超声对挤出过程中聚丙烯（PP）熔体的物理和化学作用。通过在模头入口施加超声振动，在适当的超声功率下，PP的表观压力和粘度可明显降低。超声对聚合物熔体既有物理作用又有化学作用。在我们针对特定聚合物和超声系统的研究中，我们确定在大多数研究强度下，化学作用在超声对PP熔体表观粘度降低的总作用中最多占35 - 40%。在施加超声的挤出过程中，物理作用比化学作用发挥更重要的作用。这种化学作用是由于超声导致的分子量和分子量分布的不可逆且永久性的变化。随着超声强度增加，PP的分子量降低且其分子量分布变窄；通过施加超声振动，PP分子沿流动方向的取向降低（在熔体状态下），PP样品（在固态下）的结晶度降低。超声振动增加了分子链的运动并使其更加无序；它还通过缩短链段的松弛时间来影响聚合物熔体的松弛过程，导致弹性效应减弱并降低挤出胀大比。上述所有因素均降低了聚合物熔体的非牛顿流动特性，并导致挤出过程中聚合物熔体的粘度下降。
