Bio-Based PA11/Graphene Nanocomposites Prepared by In Situ Polymerization.

Bio-based polyamide 11 (PA11)-graphene nanocomposites with different filler concentrations (0.25, 0.5, 0.75, 1.5 and 3 wt%) were prepared by In Situ polymerization starting from a water dispersed suspension of graphene nanoplatelets. The effects of the incorporation of the filler were studied in terms of molecular, morphological, thermal and dynamic mechanical properties of the final materials. During the crystallization process from the melt, the filler induces a notable nucleating effect even if the crystal growth rate tends to decrease. The glass transition temperature tends to shift to higher temperatures indicating a decrement of the molecular mobility. Thermal stability is enhanced confirming a good filler dispersion into the matrix. Mechanical reinforcement, investigated by means of a dynamic mechanical thermal analyzer was also highlighted. It was observed that a graphene concentration of 0.75 wt% induces the highest final performances.

Ready-to-use graphene-related material-added multi-grade oils: characterization and performance in car engine working conditions.

The need for energy efficiency is leading to the growing use of additives to enhance the performance of oil in automotive engines. Great interest is focused on nano-additives even if to date there is still no practical use in commercial liquid lubricants. Herein, the potential of industrially scalable and low-cost graphene-related materials (GRMs) as additives to enhance the performance of oil in automotive engines is explored. The use of polyalkylmethacrylate dispersants, the most common key additives to formulate "green technology" lubricant oils liquid-processed GRM, is explored, investigating the role of the lateral size and the chemical analysis in the stability of the lubricant GRM dispersions. Showing the maximum duration of stability and a production method that avoids the use of strong oxidants, rheological tests were then focused on multilayered graphene flakes with sub-micrometre lateral size mixed in two commercial oil grades (5W-30 and 5W-40) under conditions similar to those of engine operation. The addition of such a filler increases the viscosity without affecting the Newtonian fluid behavior, while four-ball tests show a reduction in wear, indicating improved lubrication performance. Finally, preliminary bench-test on a commercial car engine showed increased power output corresponding to enhanced engine efficiency. The results clearly indicate the effective improvement in lubricating commercial oils due to GRM additives.

Bio-Based Furan-Polyesters/Graphene Nanocomposites Prepared by In Situ Polymerization.

In situ intercalative polymerization has been investigated as a strategic way to obtain poly(propylene 2,5-furandicarboxylate) (PPF) and poly(hexamethylene 2,5-furandicarboxylate) (PHF) nanocomposites with different graphene types and amounts. Graphene (G) has been dispersed in surfactant stabilized water suspensions. The loading range in composites was 0.25-0.75 wt %. For the highest composition, a different type of graphene (XT500) dispersed in 1,3 propanediol, containing a 6% of oxidized graphene and without surfactant has been also tested. The results showed that the amorphous PPF is able to crystallize during heating scan in DSC and graphene seems to affect such capability: G hinders the polymer chains in reaching an ordered state, showing even more depressed cold crystallization and melting. On the contrary, such hindering effect is absent with XT500, which rather induces the opposite. Concerning the thermal stability, no improvement has been induced by graphene, even if the onset degradation temperatures remain high for all the materials. A moderate enhancement in mechanical properties is observed in PPF composite with XT500, and especially in PHF composite, where a significative increase of 10-20% in storage modulus E' is maintained in almost all the temperature range. Such an increase is also reflected in a slightly higher heat distortion temperature. These preliminary results can be useful in order to further address the field of application of furan-based polyesters; in particular, they could be promising as packaging materials.

Polyvinylamine Membranes Containing Graphene-Based Nanofillers for Carbon Capture Applications.

In the present study, the separation performance of new self-standing polyvinylamine (PVAm) membranes loaded with few-layer graphene (G) and graphene oxide (GO) was evaluated, in view of their use in carbon capture applications. PVAm, provided by BASF as commercial product named LupaminTM, was purified obtaining PVAm films with two degrees of purification: Low Grade (PVAm-LG) and High Grade (PVAm-HG). These two-grade purified PVAm were loaded with 3 wt% of graphene and graphene oxide to improve mechanical stability: indeed, pristine tested materials proved to be brittle when dry, while highly susceptible to swelling in humid conditions. Purification performances were assessed through FTIR-ATR spectroscopy, DSC and TGA analysis, which were carried out to characterize the pristine polymer and its nanocomposites. In addition, the membranes' fracture surfaces were observed through SEM analysis to evaluate the degree of dispersion. Water sorption and gas permeation tests were performed at 35 °C at different relative humidity (RH), ranging from 50% to 95%. Overall, composite membranes showed improved mechanical stability at high humidity, and higher glass transition temperature (Tg) with respect to neat PVAm. Ideal CO2/N2 selectivity up to 80 was measured, paired with a CO2 permeability of 70 Barrer. The membranes' increased mechanical stability against swelling, even at high RH, without the need of any crosslinking, represents an interesting result in view of possible further development of new types of facilitated transport composite membranes.

Permeability and Selectivity of PPO/Graphene Composites as Mixed Matrix Membranes for CO2 Capture and Gas Separation.

We fabricated novel composite (mixed matrix) membranes based on a permeable glassy polymer, Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), and variable loadings of few-layer graphene, to test their potential in gas separation and CO2 capture applications. The permeability, selectivity and diffusivity of different gases as a function of graphene loading, from 0.3 to 15 wt %, was measured at 35 and 65 °C. Samples with small loadings of graphene show a higher permeability and He/CO2 selectivity than pure PPO, due to a favorable effect of the nanofillers on the polymer morphology. Higher amounts of graphene lower the permeability of the polymer, due to the prevailing effect of increased tortuosity of the gas molecules in the membrane. Graphene also allows dramatically reducing the increase of permeability with temperature, acting as a "stabilizer" for the polymer matrix. Such effect reduces the temperature-induced loss of size-selectivity for He/N2 and CO2/N2, and enhances the temperature-induced increase of selectivity for He/CO2. The study confirms that, as observed in the case of other graphene-based mixed matrix glassy membranes, the optimal concentration of graphene in the polymer is below 1 wt %. Below such threshold, the morphology of the nanoscopic filler added in solution affects positively the glassy chains packing, enhancing permeability and selectivity, and improving the selectivity of the membrane at increasing temperatures. These results suggest that small additions of graphene to polymers can enhance their permselectivity and stabilize their properties.

Selective Gas Permeation in Graphene Oxide-Polymer Self-Assembled Multilayers.

The performance of polymer-based membranes for gas separation is currently limited by the Robeson limit, stating that it is impossible to have high gas permeability and high gas selectivity at the same time. We describe the production of membranes based on the ability of graphene oxide (GO) and poly(ethyleneimine) (PEI) multilayers to overcome such a limit. The PEI chains act as molecular spacers in between the GO sheets, yielding a highly reproducible, periodic multilayered structure with a constant spacing of 3.7 nm, giving a record combination of gas permeability and selectivity. The membranes feature a remarkable gas selectivity (up to 500 for He/CO2), allowing to overcome the Robeson limit. The permeability of these membranes to different gases depends exponentially on the diameter of the gas molecule, with a sieving mechanism never obtained in pure GO membranes, in which a size cutoff and a complex dependence on the chemical nature of the permeant is typically observed. The tunable permeability, the high selectivity, and the possibility to produce coatings on a wide range of polymers represent a new approach to produce gas separation membranes for large-scale applications.

Nanoscale Mechanics of Graphene and Graphene Oxide in Composites: A Scientific and Technological Perspective.

Graphene shows considerable promise in structural composite applications thanks to its unique combination of high tensile strength, Young's modulus and structural flexibility which arise due to its maximal chemical bond strength and minimal atomic thickness. However, the ultimate performance of graphene composites will depend, in addition to the properties of the matrix and interface, on the morphology of the graphene used, including the size and shape of the sheets and the number of chemical defects present. For example, whilst oxidized sp(3) carbon atoms and vacancies in a graphene sheet can degrade its mechanical strength, they can also increase its interaction with other materials such as the polymer matrix of a composite, thus maximizing stress transfer and leading to more efficient mechanical reinforcement. Herein, we present an overview of some recently published work on graphene mechanical properties and discuss a list of challenges that need to be overcome (notwithstanding the strong hype existing on this material) for the development of graphene-based materials into a successful technology.