This paper reports on the thermal properties of reduced graphite oxide (RGO) flakes, studied by means of scanning thermal microscopy (SThM). This technique was demonstrated to allow thermal characterization of the flakes with a spatial resolution of the order of a few tens of nanometers, while recording nanoscale topography at the same time. Several individual RGO flakes were analyzed by SThM, both as obtained after conventional thermal reduction and after a subsequent annealing at 1700°C. Significant differences in the thermal maps were observed between pristine and annealed flakes, reflecting higher heat dissipation on annealed RGO flakes compared with pristine ones. This result was correlated with the reduction of RGO structure defectiveness. In particular, a substantial reduction of oxidized groups and sp 3 carbons upon annealing was proven by X-ray photoelectron and Raman spectroscopies, while the increase of crystalline order was demonstrated by X-ray diffraction, in terms of higher correlation lengths both along and perpendicular to the graphene planes. Results presented in this paper provide experimental evidence for the qualitative correlation between the defectiveness of graphene-related materials and their thermal conductivity, which is clearly crucial for the exploitation of these materials into thermally conductive nanocomposites.©2016. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

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.

Poly(lactic acid) (PLA) represents one of the most promising and attractive bio-based polymer for the industrial development of environmentally sustainable packaging. However, oxygen and water barrier properties of PLA based films cannot compete with those of commercially available composite multilayers. To fill this gap, we used the Layer-by-Layer deposition technique on commercially used PLA thin films (30 µm thick) in order to increase their barrier properties to oxygen and water vapor. Nanometric films were grown by alternating branched poly(ethylene imine) (BPEI), hydrophobic fluorinated polymer (Nafion) and montmorillonite clay (MMT) layers with the aim of obtaining low gas permeability in both dry and moist conditions as well as low water vapor permeability. Two different kinds of architectures were designed and successfully prepared, based on a 4 layer repeating-unit (BPEI/MMT/BPEI/Nafion), represented here as quadlayer (QL), and on a 6 layer repeating-unit ((BPEI/Nafion)2/ BPEI/MMT), hexalayer (HL). Reduction in oxygen and water permeabilities is observed for films based on both types of repeat units. The reduction of the permeabilities increases with the number of quad and hexalayers achieving reductions in terms of oxygen permeability in both dry and humid conditions up to 98% and 97% respectively for 10 HL and QL. Furthermore, a reduction of 78% of water vapor transmission rate through the functionalized film was obtained for these films. As far as oxygen permeability is concerned, HL films are more efficient than QL films for smaller numbers of deposition units. These properties are shown to result from the complementarity between the presence of BPEI/Nafion and MMT layers.

Successful preparation of polymer nanocomposites, exploiting graphene-related materials, via melt mixing technology requires precise design, optimization and control of processing. In the present work, the effect of different processing parameters during the preparation of poly (butylene terephthalate) nanocomposites, through ring-opening polymerization of cyclic butylene terephthalate in presence of graphite nanoplatelets (GNP), was thoroughly addressed. Processing temperature (240°C or 260°C), extrusion time (5 or 10 minutes) and shear rate (50 or 100 rpm) were varied by means of a full factorial design of experiment approach, leading to the preparation of polybutylene terephthalate/GNP nanocomposite in 8 different processing conditions. Morphology and quality of GNP were investigated by means of electron microscopy, X-ray photoelectron spectroscopy, thermogravimetry and Raman spectroscopy. Molecular weight of the polymer matrix in nanocomposites and nanoflake dispersion were experimentally determined as a function of the different processing conditions. The effect of transformation parameters on electrical and thermal properties was studied by means of electrical and thermal conductivity measurement. Heat and charge transport performance evidenced a clear correlation with the dispersion and fragmentation of the GNP nanoflakes; in particular, gentle processing conditions (low shear rate, short mixing time) turned out to be the most favourable condition to obtain high conductivity values. . This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ ©2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ higher thermal conductivity [28,29]. In a recent paper, we demonstrated that the addition of hightemperature-annealed rGO in a polymer matrix leads to a thermal conductivity which is about 2-fold those of poly (butylene terephthalate) containing pristine rGO (higher defectiveness) or GNP [30], further confirming the need of high quality nanoflakes for the preparation of highly thermally conductive polymer nanocomposites. On the other hand, the control of GRM organization into a polymer matrix remains crucial in terms of nanoparticle distribution and quality of contacts between particles. Attempts in precisely controlling orientation and contacts between nanoparticles indeed resulted in an improvement of thermal transfer [31-33] but the methods adopted for the preparation of these nanocomposites are hardly up-scalable or requires very high filler concentrations. Finally, the reduction of interfacial thermal resistance was also pursued by nanoparticle functionalization [34][35][36], despite the effectiveness of this strategy may be also related to the lateral size of the nanoflakes [37]. Recently, the preparation of polymer nanocomposites was obtained by in-situ ring-opening polymerization of cyclic butylene terephthalate (CBT) oligomers into poly (butylene terephthalate), ...

The ring-opening polymerization of cyclic butylene terephthalate into poly(butylene terephthalate) (pCBT) in the presence of reduced graphene oxide (RGO) is an effective method for the preparation of polymer nanocomposites. The inclusion of RGO nanoflakes dramatically affects the crystallization of pCBT, shifting crystallization peak temperature to higher temperatures and, overall, increasing the crystallization rate. This was due to a supernucleating effect caused by RGO, which is maximized by highly reduced graphene oxide. Furthermore, combined analyses by differential scanning calorimetry (DSC) experiments and wide-angle X-ray diffraction (WAXS) showed the formation of a thick α-crystalline form pCBT lamellae with a melting point of ∼250 °C, close to the equilibrium melting temperature of pCBT. WAXS also demonstrated the pair orientation of pCBT crystals with RGO nanoflakes, indicating a strong interfacial interaction between the aromatic rings of pCBT and RGO planes, especially with highly reduced graphene oxide.