Rheology, Processing, Tensile Properties, and Crystallization of Polyethylene/Carbon Nanotube Nanocomposites

Abstract

A nanocomposite sample was prepared by melt mixing a high density polyethylene (HDPE) with an in situ polymerized HDPE/multi wall carbon nanotube (MWNT) masterbatch. The nanocomposite had an approximate content of 0.52 wt % MWNT. Rheological, thermal, and mechanical properties were investigated for both neat HDPE and nanocomposite. The nanocomposite, when compared to the neat polymer, exhibits lower values of viscosity, shear modulus and shear stress in extrusion and a concurrent delay of the distortion regimes to higher shear stresses and rates. The nanocomposite presents also improved dimensional stability after processing, and lower values of the melt strength, draw ratio and viscosity in elongational flow. This behavior has been observed in composites in which an adsorption of a fraction (that with the highest molecular weight or relaxation time) of the polymer chains is considered. Furthermore, the enhancement in the crystallization kinetics, probed by rheometry and DSC, suggests that the carbon nanotubes act as nucleating agents for the polymeric chains. Additionally, the presence of adsorbed chains does not only influence the molten state but also induces interesting effects in the mechanical properties of the polymer. As a result, an increase of up to 100% in elastic modulus was observed in the HDPE/MWNT nanocomposite without losing the ductility present in neat HDPE.

Influence of mixing methods on the properties of high density polyethylene nanocomposites with different carbon nanoparticles

“…In Table 4, we see an increase in Young´s modulus with increasing mass fraction of carbon nanotubes, regardless of the process used. This behavior was also observed by different authors [14,17,21]. Different behavior was observed with graphene addition.…”

“…It can be observed that melt and crystallization temperature showed no significant change regardless of the nanoparticle and the preparation process. This behavior was also observed by different authors [14,[21][22][23]. The preparation methods interfere in the crystallinity index of neat HDPE (P00S and P00M).…”

Effects of carbon nanotubes on polymer physics

“…However, two authors found rheological measures such as melt strength and storage modulus decrease with the introduction of nanotubes at very low nanotube concentrations consistent with the selective adsorption of high molecular weight species. 8,9 Such decreases are not unique to nanocomposites made with carbon nanotubes; nanocomposites with polystyrene spheres 10 also show this effect. In fact, using a more narrow molecular weight distribution polymer eliminated the decrease in storage modulus.…”

Influence of carbon nanotube–polymeric compatibilizer masterbatches on morphological, thermal, mechanical, and tribological properties of polyethylene

“…Increase in Young's modulus [8,[11][12][13][14][15][16][17][18] and decrease in elongation at break [8,12,14,[18][19][20] have frequently been reported for CNT-polyethylene nanocomposites.…”

“…Thermal properties such as melting and crystallization temperatures and crystallinity are reported to change slightly or not at all upon CNT addition [8,[15][16][17][18][19]21]. Besides mechanical properties, thermal expansion and tribological behavior of composites are critical factors in many applications.…”