Investigation of Structure-Property Relationships in Thermoplastic Polyurethane/Multiwalled Carbon Nanotube Composites

Abstract

In this study, the structure-property relationships in thermoplastic polyurethane (TPU) filled with multi-walled carbon nanotubes (MWCNTs) were investigated. Firstly, the contribution of MWCNTs to the melt shear viscosity and the pressure-volume-temperature (pVT) behavior was investigated. Secondly, injection-molded samples and 2 mm diameter filaments of TPU/MWCNT composites were fabricated and their mechanical and electrical properties analyzed. It was found that the melt processability of TPU/MWCNT composites is not affected by the addition of a small amount (1–5 wt.%) of MWCNTs, all composites displaying shear-thinning at high shear rates. The mechanical and electrical properties of the TPU/MWCNT composites were substantially enhanced with the addition of MWCNTs. However, the conductivity values of composites processed by injection molding were two and three orders of magnitude lower than those of composites processed by extrusion, highlighting the role of melt shear viscosity on the dispersion and agglomeration of nanotubes.

Experimental Investigation of the Melt Shear Viscosity, Specific Volume and Thermal Conductivity of Low-Density Polyethylene/Multi-Walled Carbon Nanotube Composites Using Capillary Flow

“…Owing to their electrical, thermal, mechanical and chemical properties, complemented by a high surface area [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ], carbon nanotubes (CNTs) are ideal fillers for a multitude of applications, particularly for structural aerospace, defense and automotive components [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ]; conducting components in the field of electronics; sensors and biosensors [ 2 , 3 , 4 , 5 , 6 , 9 , 10 , 11 , 12 , 13 , 15 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]; and coatings and paints [ 33 ].…”

“…Melt viscosity is one of the most important thermo-physical properties for the polymer processing industry as it is required for product development, tooling design, process optimization, quality control and troubleshooting [ 34 , 35 , 36 , 37 , 38 ]. Specifically, for polymer/CNT composites, melt rheology can be used to assess, in a systematic way, the state of CNTs in polymers (e.g., dispersion, agglomeration and adhesion) after melt processing, which links to the mechanical and electrical properties of the final products [ 1 , 3 , 5 , 9 , 10 , 11 , 13 , 15 , 18 , 21 , 22 , 24 , 25 , 39 ]. Moreover, melt rheology is an important tool for understanding how CNTs affect the processing behavior of polymer/CNT composites [ 3 , 5 , 11 , 14 , 15 , 18 , 39 , 40 , 41 ].…”

“…Although considerable research has been conducted regarding the material properties of polymer/CNT composites, including mechanical, thermal and electrical properties, only a few investigations have focused on the high shear rate rheological behavior [ 10 , 11 , 13 , 15 , 18 , 25 , 39 , 40 , 41 , 42 , 43 ]. Usually, the rheological properties have been measured by parallel plates or con-plates using dynamic oscillation frequency sweeps under linear viscoelastic conditions and shear rates in the range of 0.01 to 100 s −1 [ 1 , 9 , 14 , 19 , 21 , 22 , 24 , 26 , 44 ].…”

“…Usually, the rheological properties have been measured by parallel plates or con-plates using dynamic oscillation frequency sweeps under linear viscoelastic conditions and shear rates in the range of 0.01 to 100 s −1 [ 1 , 9 , 14 , 19 , 21 , 22 , 24 , 26 , 44 ]. However, in practice, polymer/CNT composites are processed at higher shear rates, such as 10 3 –10 4 s −1 for injection molding [ 3 , 5 , 15 , 18 , 36 ].…”

“…Rheological studies on polymer/CNT composites have revealed that the incorporation of CNTs into a polymer matrix brings significant changes in the melt viscosity, which in addition to the temperature and shear rate is affected by the CNT features (type, aspect ratio, loading, and state of dispersion) [ 1 , 3 , 10 , 11 , 13 , 15 , 18 , 24 , 25 , 39 , 40 , 41 , 42 , 43 ]. Specifically, it was reported that the viscosity of polymer/CNT composites usually increases with increasing CNT loading and, at high shear rates, exhibits shear thinning behavior [ 11 , 13 , 15 , 18 , 25 , 40 , 41 , 42 , 43 ].…”