Nonisothermal crystallization of isotactic polypropylene in carbon nanotube networks

Abstract

Isotactic polypropylene (iPP) composites with carbon nanotube (CNT) networks at relatively high loadings could have various applications such as electromagnetic interference shielding and thermal conductivity. The crystallization behavior of iPP inside CNT networks could be very much related to the above properties, which was found to be quite different from that of neat iPP in this work. In CNT networks, CNTs not only act as effective heterogeneous nucleating agents to noticeably increase the onset temperature (more than 18°C) of iPP crystallization but also bring strong confinement on the mobility of iPP chains and then reduce the overall crystallization rate of iPP matrix. It is interesting to find that CNT networks, especially in the case of ultrahigh loading (90 wt%), have remarkable confinement effect on crystallization of iPP, overcoming the heterogeneous nucleation of CNTs, resulting in a decline of crystallization rate of iPP. The nonisothermal crystallization kinetics of iPP in the dense CNT network quite fits to the modified Avrami mode by Jeziorny, even more satisfactorily than the case of neat iPP. When confinement effect is dominated during crystallization, we found that the perfection and size of crystallites are extremely decreased at ultrahigh loading, leading to a very low melting point of iPP (approximately 140°C).

Nonisothermal crystallization behaviors of ethylene–acrylic acid copolymer and ethylene–acrylic acid copolymer/chloroprene rubber thermoplastic vulcanizate

“…For the pure EAA and the EAA/CR TPV, the Z t increased roughly while n decreased with increasing the cooling rates; moreover, this result was consistent with that of Eder and Wlochowicz’s work. 33 Usually, two factors would lead to the decrease values of n , the first factor is that the fast crystallization rate at lower temperatures prevented the crystals from their full development, and the second factor is that the growth site impingement, truncation of crystals, and secondary crystallization might change the crystallization mechanism. When the crystalline volume fraction was high, the effects of impingement, truncation of crystals, and secondary crystallization would become very important and decrease the overall crystallization rate obviously.…”

Hydrophobic Graphene Oxide as a Promising Barrier of Water Vapor for Regenerated Cellulose Nanocomposite Films

“…Both of the two peaks are sensitive to the bound water in the cellulose because of interruption of hydrogen bonding. Another dispersion peak appears at 1640 cm –1 because of hydrogen bonding absorption of the weak interaction of OH water ···OH water , corresponding to the free water of free volume in cellulose. − From Figure , the intensities of all FTIR peaks of RC and RC0.5 gradually increase as a function of time, indicating that the water vapor slowly passes through the film samples. Furthermore, 2D correlation analysis can distinguish the sequence of time-resolved FTIR changes, reflecting the microstructural variations affected by water vapor molecules in detail.…”

“…At higher loading, the perfect cellulose crystal is further inhibited by the space restriction due to the dense structure of GO-ODA (probably a network) with oriented lamellar arrangement in the RC matrix. 41,42…”

“…During the crystallization process of cellulose, the GO-ODA nanosheets act as a kind of nucleation inhibitor, which could reduce nuclei and confine the cellulose II crystal for perfection. At higher loading, the perfect cellulose crystal is further inhibited by the space restriction due to the dense structure of GO-ODA (probably a network) with oriented lamellar arrangement in the RC matrix. , …”

“…At higher loading, the perfect cellulose crystal is further inhibited by the space restriction due to the dense structure of GO-ODA (probably a network) with oriented lamellar arrangement in the RC matrix. 41,42 The interfacial interaction between RC and GO-ODA was detected by FTIR, as shown in Figure 4. Noteworthy, the wellknown −OH stretching band at 3600−3000 cm −1 is sensitive to hydrogen bonding, which shifts to higher wavenumber from 3318 to 3339 cm −1 with the loading of GO-ODA.…”