Nonisothermal Crystallization Behaviors of Nanocomposites Prepared by In Situ Polymerization of High-Density Polyethylene on Multiwalled Carbon Nanotubes

Abstract

Thermal properties and nonisothermal crystallization kinetics of polyolefin nanocomposites (high-density polyethylene/multiwalled carbon nanotubes) were characterized by differential scanning calorimetry and thermogravimetric analysis. In situ metallocence polymerization was used to prepare nanocomposites of multiwalled carbon nanotubes (MWCNTs) and high-density polyethylene (HDPE). This polymerization method consists of attaching a metallocene catalyst complex onto the surface of the MWCNTs followed by surface-initiated polymerization to generate polymer brushes on the surface. A kinetic equation for the nonisothermal crystallization was employed to analyze the crystallization characteristics of the nanocomposites. The Avramic exponent, n, can be reasonably well determined from the nonisothermal crystallization exotherm. The polarized optical microscopy showed that neat polyethylene possessed a well-developed spherulite morphology, whereas the nanocomposites displayed elongated entities that subsequently developed as bundlelike entities. Nonisothermal analysis implicitly provides clues about the morphological development history and HDPE molecular ordering around the carbon nanotubes.

Effects of carbon nanotubes on polymer physics

“…The normal spherulitic morphology does not appear in polarized optical micrographs; instead the crystallites appear as elongated entities that are consistent with an entirely transcrystalline or NHSK structures. 129 However, another study, also with metallocene-grafted HDPE, found a significant increase in the crystallization rate while also finding a substantial decrease in the Avrami exponent n. This study also found significantly thicker crystals as measured by a successive self-nucleation and annealing thermal fractionation technique performed in a DSC. 260 Both studies found that the fractional crystallinity initially increased to $10% nanotube content, then decreased as the nanotube content increased above 10%.…”

Synthesis and thermal behavior of poly(ε-caprolactone) grafted on multiwalled carbon nanotubes with high grafting degrees

“…So far, most CNTs-grafted polymers are non-crystallizable. Several examples for CNTs-grafted crystallizable polymers include polyamide [31,32], poly(ε-caprolactone) (PCL) [33e37], poly(ethylene oxide) [38], poly(L-lactide) (PLLA) [39e45], polyethylene [46], poly(3-hexylthiophene) [47], poly(adipic acidhexamethylene diamine) [48], poly(ether ether ketone) [ [27]. The grafted catalyst was used to polymerize L-LA and ε-CL.…”

Non-isothermal Crystallization Behaviors of HDPE/MWCNT Nanocomposites

“…The calculated average value of the Avrami exponent, n, from Figure 4 is approximately 2.56 for HDPE/MWCNT (1.5 wt%) nanocomposite, 1.99 for HDPE/MWCNT (2.4 wt%) nancomposite and 1.78 for HDPE/MWCNT (7.3 wt% close to that of the percolation threshold 28 ) nancomposite ( Table 1). 10 At the beginning of the process, faster crystallization proceeds due to the nucleating action of the MWCNT surface. In the absence of MWCNT, HDPE forms large spherulites (20~50m) with slightly twisted lamellae ( Figure 3).…”