Thermal and electrical conductivity of melt mixed polycarbonate hybrid composites co-filled with multi-walled carbon nanotubes and graphene nanoplatelets

Influence of Polyvinylpyrrolidone on Thermoelectric Properties of Melt-Mixed Polymer/Carbon Nanotube Composites

For thermoelectric applications, both p- and n-type semi-conductive materials are combined. In melt-mixed composites based on thermoplastic polymers and carbon nanotubes, usually the p-type with a positive Seebeck coefficient (S) is present. One way to produce composites with a negative Seebeck coefficient is to add further additives. In the present study, for the first time, the combination of single-walled carbon nanotubes (SWCNTs) with polyvinylpyrrolidone (PVP) in melt-mixed composites is investigated. Polycarbonate (PC), poly(butylene terephthalate) (PBT), and poly(ether ether ketone) (PEEK) filled with SWCNTs and PVP were melt-mixed in small scales and thermoelectric properties of compression moulded plates were studied. It could be shown that a switch in the S-value from positive to negative values was only possible for PC composites. The addition of 5 wt% PVP shifted the S-value from 37.8 µV/K to -31.5 µV/K (2 wt% SWCNT). For PBT as a matrix, a decrease in the Seebeck coefficient from 59.4 µV/K to 8.0 µV/K (8 wt% PVP, 2 wt% SWCNT) could be found. In PEEK-based composites, the S-value increased slightly with the PVP content from 48.0 µV/K up to 54.3 µV/K (3 wt% PVP, 1 wt% SWCNT). In addition, the long-term stability of the composites was studied. Unfortunately, the achieved properties were not stable over a storage time of 6 or 18 months. Thus, in summary, PVP is not suitable for producing long-term stable, melt-mixed n-type SWCNT composites.

An Industrial Case for Polypropylene Nanocomposite Foams: Lightweight, Soundproof Exterior Automotive Parts

Lightweighting is a challenge for the automotive industry, and foaming is a key technology used to address this problem. A new practical approach is studied to regulate the cell formation of copolymer polypropylene (co-PP) by utilizing graphene nanoplatelets (xGnP) as a process aid during foam injection molding. The approach was designed to enable process freedom to tune part performance by adjusting the amount of xGnP masterbatch. Two different levels of 1-2 wt % xGnP and 0.25-0.35 wt % supercritical fluid (SCF) were investigated. Prepared samples were compared with samples prepared by the traditional method (twin-screw extrusion followed by foam injection molding). The nanocomposite with 2 wt % xGnP comparatively showed about twofold reduction in cell size magnitude. Although the increment in SCF amount resulted in a 47% and 122% enhancement in flexural modulus and strength, respectively, and a 45% loss in Izod unnotched impact strength, the cell size was prone to increasing with regard to low melt strength as compared to neat foams. In conclusion, a 12% weight reduction fulfilled the desired performance parameters in terms of mechanical and sound insulation by utilizing 2 wt % xGnP as a process aid.

Size effect of hybrid carbon nanofillers on the synergetic enhancement of the properties of HDPE-based nanocomposites

High-density polyethylene (HDPE)-based hybrid nanocomposites containing graphene nanoplatelets (GnPs) and multiwall carbon nanotubes (MWCNTs) were fabricated using melt mixing followed by compression molding. The influences of size and weight ratio of both carbon-based nanofillers on the electrical, thermal, and mechanical properties of hybrid nanocomposites were evaluated. This study proves that the size and weight ratio of carbon-based nanofillers play a critical role in determining these properties. The optimum size and weight ratio of GnPs and MWCNTs are determined at the maximum achieved enhancement for each property. The HDPE-based nanocomposites containing GnPs with larger surface area and MWCNTs with higher aspect ratio display the highest electrical conductivity at GnPs/MWCNTs weight ratio of 2/3. The combination of GnPs with larger surface area and MWCNTs with lower aspect ratio provides the maximum Young's modulus enhancement of hybrid nanocomposites at 1/4 weight ratio of GnPs and MWCNTs. The nanocomposite containing GnPs with the largest lateral size and MWCNTs with a higher aspect ratio at a 3/2 weight ratio exhibits the highest thermal conductivity. Also, at around the percolation threshold of GnPs, the incorporation of MWCNTs with larger aspect ratio into the HDPE-based nanocomposites containing GnPs with the largest lateral size shows a distinct synergic effect on the thermal conductivity and Young's modulus, while an additive effect on the electrical conductivity and thermal stability.