Physical properties of nanocomposites prepared by in situ polymerization of high-density polyethylene on multiwalled carbon nanotubes

Abstract

In situ metallocence polymerization was used to prepare nanocomposites of multiwalled carbon nanotubes (MWCNT) and high density polyethylene (HDPE). This polymerization method consists of attaching a metallocene catalyst complex onto the surface of MWCNT followed by surface-initiated polymerization to generate polymer brushes on the surface. All the procedures of polymerization made progress with one-pot process. The morphological observation of nanocomposites using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the nanotubes are uniformly dispersed throughout HDPE matrix. Physical properties of thermal and electrical conductivities and rheological response have been characterized. Since the carbon nanotubes are wrapped by PE molecules, the large interface provided by MWCNT's lead to strong phonon boundary scattering. Thus, the enhancement of thermal conductivity by the inclusion of nanotubes was quite restrictive. On the other hand, electrical conductivity and rheological properties show the property transition at the critical concentration of carbon nanotubes (percolation threshold). The DC conductivity increased with increasing weight fraction of MWCNT from 1.0 x 10(-13) S cm(-1) (neat HDPE) to 1.3 x 10(-2) S cm(-1) (HDPE/7.3 wt% of MWCNT) at room temperature and the electrical percolation threshold was ca. 7.3 wt%. The percolation threshold concentration of MWCNT for the rheological properties was ca. 8.7 wt%, similar to that of the electrical conductivity. Difference in the percolation behaviors between the MWCNT mixed nanocomposites and the PE-coated MWCNT nanocomposites is discussed in terms of the dispersion and the tube-tube distance of MWCNT.

Easy one-pot method to control the morphology of polyethylene/carbon nanotube nanocomposites using metallocene catalysts

“…For PE/CNT nanocomposites the expected peak at 2θ026°is not visible. This is because the amount of CNT that dispersed in the polymer sample is very small [36]. The types of crystals are same in both cases as shown in the Fig.…”

“…6b with CpZrCl 2 /MWCNT/MAO system. Such structure was recently reported for PE nanocomposites when modified MAO was used, employing a more tedious experimental procedure or different catalyst [10,30,36,37]. The morphology of this coating was dramatically influenced by the metal center.…”

“…The morphology of this coating was dramatically influenced by the metal center. When Zr catalysts are used, as discussed above the CNTs are in fact decorated with disc-shaped objects (arrows), corresponding to PE single crystal lamellae, resulting in a new nanohybrid morphology ("shishkebab"-like structures) [30,[36][37][38]. The central shish is the carbon nanotube while the kebabs are formed by PE chains as shown in Figs.…”

Heterogeneous Catalysis on Nanostructured Carbon Material Supported Catalysts

“…However, the homogeneous dispersion of CNTs is a difficult task mainly due to their poor solubility. Three different approaches have been adopted to produce polymer-functionalized CNTs: 345 (i) a non-covalent functionalization method by which polymers are produced by ring-opening metathesis polymerization (ROMP); 346,347 (ii) a covalent functionalization performed by first grafting polymerization initiators onto the tubes through covalent bonds and then exposing these CNT-based macroinitiators to the monomer, the polymer being obtained by anionic polymerization, 348 reversible addition and fragmentation chain transfer (RAFT) polymerization, 349 atom-transfer radical polymerization (ATRP) 350,351 or ROMP 352 and (iii) a functionalization performed by first grafting polymerization catalysts or co-catalysts (olefin polymerization via anchored metallocene catalysts [353][354][355][356] or ROMP 357,358 ). In this section, we will only discuss the latter approach.…”

“…The catalytic system consisting of dichloro[rac-ethylene-bis(indenyl)]zirconium(iv) [rac-Et(Ind) 2 ZrCl 2 ] and MAO was also effective for the in situ generation of high density polyethylene/ CNT composites. 356 Owing to the presence of surface hydroxyl groups on functionalized graphene nanosheets (FLG), single FLG/MAO nanosheets can be effectively dispersed in n-heptane, thus enabling immobilization of a MAO-activated chromium single-site catalyst on FLG. 379 In contrast to CB, CNT, graphite, and nanoboehmite, which failed to form stable dispersions, FLG/MAO/Cr afforded the highest catalyst activities and excellent morphological control for ethylene polymerization.…”