Effect of morphology and defectiveness of graphene-related materials on the electrical and thermal conductivity of their polymer nanocomposites

Abstract

In this work, electrically and thermally conductive poly (butylene terephthalate) nanocomposites were prepared by in-situ ring-opening polymerization of cyclic butylene terephthalate (CBT) in presence of a tin-based catalyst. One type of graphite nanoplatelets (GNP) and two different grades of reduced graphene oxide (rGO) were used. Furthermore, high temperature annealing treatment under vacuum at 1700°C was carried out on both RGO to reduce their defectiveness and study the correlation between the electrical/thermal properties of the nanocomposites and the nanoflakes structure/defectiveness. The morphology and quality of the nanomaterials were investigated by means of electron microscopy, x-ray photoelectron spectroscopy, thermogravimetry and Raman spectroscopy. Thermal, mechanical and electrical properties of the nanocomposites were investigated by means of rheology, dynamic mechanical thermal analysis, volumetric resistivity and thermal conductivity measurements. Physical properties of nanocomposites were correlated with the structure and defectiveness of nanoflakes, evidencing a strong dependence of properties on nanoflakes structure and defectiveness. In particular, a significant enhancement of both thermal and electrical conductivities was demonstrated upon the reduction of nanoflakes defectiveness.

Effect of processing conditions on the thermal and electrical conductivity of poly (butylene terephthalate) nanocomposites prepared via ring-opening polymerization

“…Instead, in pure pCBT the presence of an additional endothermic peak at lower temperatures was related to melting/recrystallization of imperfect crystals [55,56]. The presence of carbon nanoflakes usually affects the crystallization behavior of the polymer matrix [30]: in fact, while pure pCBT has a crystallization temperature of 192.2°C, values ranging between 195.2°C and 204.6°C were measured for pCBT + GNP nanocomposites, the highest for pCBT_GNP/240/10/100, thus indicating a pronounced nucleating effect of GNP. Crystallinity degree (Table S1) of pure pCBT was estimated equal to 49.2%, while for nanocomposites values ranging between 45.9% and 53.6% were calculated.…”

“…Recently, the preparation of polymer nanocomposites was obtained by in-situ ring-opening polymerization of cyclic butylene terephthalate (CBT) oligomers into poly (butylene terephthalate), pCBT [38], taking advantage of both the extremely low viscosity of CBT and of the viscosity increase occuring during polymerization, to disperse nanoparticles, including organoclays [39], carbon nanotubes [40], silica [41] and graphenerelated materials [30, 42]. The presence of GRM was reported to affect the polymerization kinetic of CBT, with increase of the polymerization time [43] and decrease of the average molecular weight [44].Furthermore, the exploitation of GRM was described to improve mechanical, electrical and thermal properties [30,42,43,45]. Indeed, in a previous paper we reported a 12-fold increase in the thermal conductivity when 30 wt.% of GNP is added to pCBT, while the addition of 5 wt.% of rGO annealed at 1700°C led up to a 4-fold increase [30].In this work, the optimization of different processing paremeters in the preparation of pCBT nanocomposites through ring-opening polymerization of CBT is addressed.…”

“…The presence of GRM was reported to affect the polymerization kinetic of CBT, with increase of the polymerization time [43] and decrease of the average molecular weight [44].Furthermore, the exploitation of GRM was described to improve mechanical, electrical and thermal properties [30,42,43,45]. Indeed, in a previous paper we reported a 12-fold increase in the thermal conductivity when 30 wt.% of GNP is added to pCBT, while the addition of 5 wt.% of rGO annealed at 1700°C led up to a 4-fold increase [30].In this work, the optimization of different processing paremeters in the preparation of pCBT nanocomposites through ring-opening polymerization of CBT is addressed. In particular, the effect of processing temperature, mixing time and shear rate on electrical and thermal conductivity of nanocomposites are described in this work, aiming at a systematic study of processing conditions vs. material properties, which is still lacking in the field of polymer nanocomposites containing graphenerelated materials ©2017.…”

Molecular junctions for thermal transport between graphene nanoribbons: Covalent bonding vs. interdigitated chains

“…However, graphene properties are only partially reflected in nanocomposites 10 , where thermal transport is not limited by the thermal conduction of graphene itself but rather by the high thermal resistance at the contact between nanoplatelets [11][12][13] . In fact, the reach of a percolation threshold, a value over which the particles inside a composite material get physically in contact, is not enough to improve radically the overall thermal conductivity 14 . Indeed, for every single contact, physical limitations in phonon transfer have to be taken into account, leading to a highly inefficient heat transfer across the nanoparticles network that characterize nanocomposites materials 15 .…”

Decoupled trends for electrical and thermal conductivity in phase-confined CNT co-continuous blends

“…the transition from non-conducting to conducting material, occurring at CNT content as low as 0.002 wt.%, depending on the nanotube aspect ratio, degree of alignment, state of aggregation, as well as mixing condition and the type of polymer matrix [16,17,18,19,20,21]. On the other hand, the improvement of thermal conductivity with the inclusion of CNT or other nanoparticles is significantly less sharp and strongly dependent on many factors, including nanoparticles type, quality, dispersion, alignment, contact between nanoparticles and interfacial interaction with the polymer matrix [2,15,17,22,23,24,25]. A possible route to enhance the effectiveness of a percolative network is the confinement of conductive particles in well-defined continuous regions [2,26,27,28].…”