writer：Jingjing Yang, Huagao Fang, Yaqiong Zhang, Wentao Shi, Peng Chen and Zhigang Wang*
keywords：Polypropylene, Carbon nanotubes, Networks, Rheology, Die shrinkage
source：期刊
specific source：Acta Polymerica Sinica, 2013,10, 1325-1333
Issue time：2013年

摘 要: 通过动态流变学方法研究了两种不同黏弹性的聚丙烯(iPP-1和iPP-2)及其与碳纳米管(CNTs)的复合材料（CNTs/iPP）的熔体动态黏弹性，并进一步以毛细管流变仪研究了熔体黏弹性对iPP及CNTs/iPP复合材料在高速挤出流场中挤出特性的影响.研究表明,200 oC下 iPP-1的黏度和储能模量明显低于iPP-2；CNTs/iPP复合材料的储能模量在低频区域均显示出与频率无关的类固体平台区，说明CNTs含量为5 wt%的复合材料体系中均形成了稳定的CNT网络结构. iPP及CNTs/iPP复合材料在高剪切速率下均表现出强烈的剪切变稀行为，CNT网络结构存在导致复合材料的黏度和剪切应力同iPP基体相比则明显提高.CNTs/iPP复合材料的挤出物螺旋畸变和挤出胀大比同iPP相比显著减弱.以黏弹性较强的聚丙烯(iPP-2)为基体的复合材料熔体在较高挤出速率下仍然表现出挤出胀大行为，然而在较低剪切速率下甚至可以出现挤出收缩特性，更为显著的是以黏弹性较弱的聚丙烯(iPP-1)为基体的复合材料熔体在全部挤出速率下均表现出挤出收缩特性，这是因为在高剪切速率下CNT网络结构不足以抑制黏弹性较强的iPP链弹性形变和回复，而在低剪切速率下CNT网络结构足以抑制黏弹性iPP链的弹性形变和回复，导致了这种奇特的复合材料熔体挤出收缩特性.

关键词:  聚丙烯；碳纳米管；网络结构；流变学；挤出收缩

Abstract: Studies on viscoelastic properties of two types of isotactic polypropylene (iPP-1 and iPP-2) and their composites filled with carbon nanotube (CNTs) (CNTs/iPP composites) were carried out by using rheometer. The influences of viscoelastic properties on the melt extrusion behaviors of iPPs and CNTs/iPP composites were further investigated by using capillary rheometer. The rheological results demonstrate that at 200 oC the viscosity and storage modulus, G? for iPP-1 are obviously lower than that for iPP-2. The appearance of frequency-independent plateau of G? at low frequencies and solid-like elastic behaviors for the CNTs/iPP composites containing CNT mass fraction of 5 wt% indicate the formation of entangled CNT networks in the composites. Both iPPs and CNTs/iPP composites exhibit prominent shear-thinning behaviors and the composites exhibit relatively higher viscosities and shear stresses than their iPP counterparts. The extrudate distortion and die swell for CNTs/iPP composite melts decrease compared with iPPs due to the formation of CNT networks in the composites. Although the die swell can still be observed at the high applied shear rates for the CNTs/iPP composite with the relatively high viscoelastic iPP-2 as the matrix, an appreciable phenomenon of “die shrinkage” rather than the common “die swell” at the low applied shear rates is observed for this CNTs/iPP composite. More interesting, the particular “die shrinkage” phenomenon is observed at all the applied shear rates for the CNTs/iPP composite with the relatively low viscoelastic iPP-1 as the matrix. The above results can be explained by that the CNT networks in the composites under shear might be able to restrict the deformation and elastic relaxation of iPP chains, which have the relatively low viscoelastic properties.

Keywords: Polypropylene; Carbon nanotubes; Networks; Rheology; Die shrinkage