127. Studies on influences of viscoelastic properties on melt extrusion of carbon nanotubes-filled isotactic polypropylene composites
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: 通過動態(tài)流變學(xué)方法研究了兩種不同黏彈性的聚丙烯(iPP-1和iPP-2)及其與碳納米管(CNTs)的復(fù)合材料（CNTs/iPP）的熔體動態(tài)黏彈性，并進一步以毛細管流變儀研究了熔體黏彈性對iPP及CNTs/iPP復(fù)合材料在高速擠出流場中擠出特性的影響.研究表明,200 oC下 iPP-1的黏度和儲能模量明顯低于iPP-2；CNTs/iPP復(fù)合材料的儲能模量在低頻區(qū)域均顯示出與頻率無關(guān)的類固體平臺區(qū)，說明CNTs含量為5 wt%的復(fù)合材料體系中均形成了穩(wěn)定的CNT網(wǎng)絡(luò)結(jié)構(gòu). iPP及CNTs/iPP復(fù)合材料在高剪切速率下均表現(xiàn)出強烈的剪切變稀行為，CNT網(wǎng)絡(luò)結(jié)構(gòu)存在導(dǎo)致復(fù)合材料的黏度和剪切應(yīng)力同iPP基體相比則明顯提高.CNTs/iPP復(fù)合材料的擠出物螺旋畸變和擠出脹大比同iPP相比顯著減弱.以黏彈性較強的聚丙烯(iPP-2)為基體的復(fù)合材料熔體在較高擠出速率下仍然表現(xiàn)出擠出脹大行為，然而在較低剪切速率下甚至可以出現(xiàn)擠出收縮特性，更為顯著的是以黏彈性較弱的聚丙烯(iPP-1)為基體的復(fù)合材料熔體在全部擠出速率下均表現(xiàn)出擠出收縮特性，這是因為在高剪切速率下CNT網(wǎng)絡(luò)結(jié)構(gòu)不足以抑制黏彈性較強的iPP鏈彈性形變和回復(fù)，而在低剪切速率下CNT網(wǎng)絡(luò)結(jié)構(gòu)足以抑制黏彈性iPP鏈的彈性形變和回復(fù)，導(dǎo)致了這種奇特的復(fù)合材料熔體擠出收縮特性.
關(guān)鍵詞: 聚丙烯；碳納米管；網(wǎng)絡(luò)結(jié)構(gòu)；流變學(xué)；擠出收縮
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