Nonisothermal Crystallization Kinetics and Microhardness of PP/CNT Composites

Abstract

The nonisothermal crystallization kinetics and microhardness of nanocomposites consisting of a polypropylene matrix (PP) and carbon nanotube filler (CNT) have been investigated. Three types of PP matrixes have been used: two of them are nonfunctionalized PP that differ slightly in their melt flow index, whereas the third is grafted with maleic anhydride (MA). Ozawa formalism has been used to study the nonisothermal crystallization kinetics. The results show that the CNT filler has a nucleation role in the nonisothermal crystallization of PP. For all nanocomposites, the nonisothermal crystallization rate increases up to 4% CNT and then decreases slightly or remains almost constant at the higher filler content. This fact has been interpreted in terms of an aggregation of the particles at high filler concentration, which leads to a decrease of the nucleation ability of the filler because the number of heterogeneous nuclei decreases. The crystallization mechanism of the PP matrixes almost does not change in the presence of the CNT filler. The microhardness of the two nonfunctionalized PP increases when the filler content increases and then remains constant above a certain filler content. The experimental microhardness values of the composites based on the functionalized PP are lower than those of the corresponding calculated additive values. The decrease of the creep constant with the filler addition is not significant, as should be expected when inorganic filler is added to a polymer matrix. This is due to the very fine dispersion of the fillers into the polymer matrix at the nanoscale level.

Nucleating Effect of Carbon Nanoparticles and Their Influence on the Thermal and Chemical Stability of Polypropylene

“…The crystallization temperature of PP, from the melt, increased approximately 20 • C above that of pure PP, using a concentration as low as 0.05 wt% of carbon nanoparticles. This excellent nucleating capacity of CNTs and CNFs has also been reported by other authors [9][10][11][12][13], though some authors have found that above 4 wt% this ability reaches a plateau and remains constant [14]. In addition to this nucleating effect, it has been found, via TGA, that these carbon nanoparticles increase the temperature for the onset of the PP decomposition [12,13,[15][16][17] by as much as 20 • C [18].…”

“…A series of PP compositions with 0.05 wt% of each of CNFs, CNTs, and LiBe were prepared via melt mixing for 10 min, at 170 • C and 50 rpm, in a Brabender torque rheometer mixing chamber. Very low nucleating agent concentrations (0.05 wt%) were in order to prevent the excess of nucleating particles from interfering with the spherulitic growth, as has been observed by other authors when using high CNTs or CNFs concentrations [9,14,19]. Plain PP was also passed through the mixer to produce blank samples.…”

Microstructure and Properties of Polypropylene/Carbon Nanotube Nanocomposites

“…CNTs cause also a serious effect on the crystallization rate of PP and this can affect most of its properties. For this reason a lot of researchers have studied extensively the effect of CNTs on PP crystallinity [ 30 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 ]. iPP has normally a slow crystallization rate, forming large spherulites.…”

“…It is also found that the sizes of spherulites and nucleation density of iPP/CNTs shows no obvious changes with increasing CNTs concentration from 0.2 wt % to 1.0 wt %, which infers that the nucleating effect of CNTs may saturate at least at CNTs concentration of 0.2 wt %. This implies that a further elevation of CNTs concentration does not further improve the nucleation effect [ 52 , 57 ].…”

Morphological, Thermal, and Electrical Characterization of Syndiotactic Polypropylene/Multiwalled Carbon Nanotube Composites

“…Despite the large number of available articles referred to iPP/CNT systems, [7][8][9][10][11][12] the influence of the addition of CNT on the physical properties of sPP matrix is not so well studied. In this article, the morphological and thermal properties of sPP/multiwalled carbon nanotubes (MWCNT) nanocomposites are investigated by employing various techniques (scanning electron microscopy, X-ray diffraction, Raman spectroscopy, differential scanning calorimetry).…”