High impact strength polypropylene containing carbon nanotubes

Abstract

Abstract Polypropylene (PP)/carbon nanotube (CNT) nanocomposite studies have been extensively reported in the literature. Most of this previous work has been carried out by dispersing CNTs in PP matrix via melt processing, while only limited studies have been carried out where CNT dispersion in PP was achieved by solution processing. Here we report the melt processing of PP/multiwall carbon nanotubes (MWNT) nanocomposites after achieving functionalized MWNT (f-MWNT) dispersion in PP, and in maleic anhydride-g-PP (MA-g-PP) master batches using a butanol/xylene solvent mixture. For comparison, melt mixing of PP with pristine MWNTs (p-MWNTs) without functionalization was also carried out. The three types of nanocomposites (from PP/f-MWNT and MA-g-PP/f-MWNT master batches and from p-MWNT) were prepared using micro-compounding, followed by injection molding. In each case, the weight percent of MWNTs in the injection molded samples was 0.001, 0.005, 0.01, 0.1, 0.3, 0.5, and 1 wt%. Tensile properties, impact strength, and heat deflection temperatures of the composites have been studied. Mechanical property improvements were observed at concentrations as low as 0.001 wt% CNT loading. For example, at 0.001 wt% CNT, a statistically significant increase in modulus was observed using PP/f-MWNT master batch. At 1 wt% CNT loading, impact strength increased by 152% in samples prepared from PP/f-MWNT master batch, as compared to the control PP containing no CNTs. This is the highest percentage increase in impact strength reported to date for the homopolymer PP/CNT or for any other thermoplastic/CNT system, at 1 wt% CNT. This increase has been achieved while maintaining excellent ductility and high strain to failure of 113%. By comparison, the strain to failure at the same CNT concentration of 1 wt% was 12.5% and 19.9% for p-MWNT based and MA-g-PP/f-MWNT based nanocomposites, respectively. The changes in mechanical properties have been discussed in terms of crystallization behavior, structure, and morphology of the nanocomposites.