Thermal properties of polypropylene nanocomposites: Effects of carbon nanomaterials and processing

Abstract

Design of experiments was used to elucidate the complex interactions that determine nanocomposite properties and enable predictive models for optimization. The thermal properties of nanocomposites containingpolypropylene, single‐walled carbon nanotubes (SWNTs), dodecyl‐functionalized SWNTs, and vapor‐grown carbon fibers were investigated as a function of extrusion temperature, screw speed, and time. The effects of extruder processing conditions on thermal properties was dependent on the fraction of polymer chains stabilized in the interphase, the extent of polymer degradation, and the type of nanomaterial incorporated. Melting and crystallization temperatures were primarily affected by nanomaterial type. However, thermal decomposition temperature was affected significantly by processing conditions and the response wasdependent on the type of nanomaterial incorporated. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers

The Effect of Melt Extrusion Process Parameters on Rotary‐Evaporated Poly(propylene) Nanocomposites

“…Conversely, long extrusion time and high temperature reduced T d . This indicates that the effect of these conditions on polymer degradation32 had a greater influence on T d than the improvements in dispersion. Since PP undergoes free radical thermal decomposition, the more it is degraded during extrusion, the more readily it will degrade when exposed to heating during TGA.…”

“…First, they thermally stabilize the polymer chains in the interphase between the nanotube and bulk polymer. Second, the presence of a percolated network reduces transport of thermal decomposition products thereby slowing further decomposition 22, 32–34. The reduced predictive models for the thermal decomposition temperature are shown in Table 2.…”

“…Rheological characterization provides profound insight into nanotube dispersion and nanocomposite microstructure, in addition to evidence of polymer degradation 22, 32. As such, rheology is a key tool in understanding the effect of processing parameters on nanocomposite properties.…”

“…SWNTs were functionalized with dodecyl (C 12 H 25 ) groups using the reductive alkylation method 32. The presence of dodecyl groups on product was confirmed by Raman spectroscopy (Figure 1) and thermogravimetric analysis (TGA, Figure 2).…”

“…Two processes, rotary evaporation (RE) and melt extrusion, were used sequentially for the preparation of the PP nanocomposites. In the RE process22, 32 the SWNT or C12SWNT were dispersed in ≈99% isopropyl alcohol (IPA) at a concentration of 2 mg · mL −1 with the aid of sonication. For SWNT a sonication time of 6 h resulted in an average bundle diameter, as determined by atomic force microscopy (AFM), of 2.7 nm, while for C12SWNT 1 h sonication was sufficient to produce bundles of 2.0 nm.…”