Barrier Properties of GnP–PA-Extruded Films

Abstract

It is generally known that significant improvements in the properties of nanocomposites can be achieved with graphene types currently commercially available. However, so far this is only possible on a laboratory scale. Thus, the aim of this study was to transfer results from laboratory scale experiments to industrial processes. Therefore, nanocomposites based on polyamide (PA) and graphene nanoplatelets (GnP) were prepared in order to produce membranes with improved gas barrier properties, which are characterized by reduced permeation rates of helium. First, nanocomposites were prepared with different amounts of commercial availably graphene nanoplatelets using a semi-industrial-scale compounder. Subsequently, films were produced by compression molding at different temperatures, as well as by flat film extrusion. The extruded films were annealed at different temperatures and durations. In order to investigate the effect of thermal treatment on barrier properties in correlation to thermal, structural, and morphological properties, the films were characterized by differential scanning calorimetry (DSC), wide angle X-ray scattering (WAXS), optical microscopy (OM), transmission electron microscopy (TEM), melt rheology measurements, and permeation measurements. In addition to structural characterization, mechanical properties were investigated. The results demonstrate that the permeation rate is strongly influenced by the processing conditions and the filler content. If the filler content is increased, the permeation rate is reduced. The annealing process can further enhance this effect.Polymers 2020, 12, 669 2 of 13 in a level up to 31%, indicating a behavior [17] comparable to classical fillers like talc [18], showing an increase of more than 300% at a comparable filler content of 35%. A study by Edelmann and coworkers [19] came to the conclusion that the processing of graphene-like materials on industrial like machinery does not lead to comparable results found on a lab scale. Our earlier studies emphasize these results [20]. Thus, the greatest challenge is still to obtain well dispersed graphene nanoplatelets. A typical method for the preparation of nanocomposites is melt compounding with highly shearing equipment twin screw extruders. In this way, GnPs are mixed directly with the polymer in the molten state and no solvents are required, making it an economical and environmentally friendly method for the mass production of nanocomposites. Another challenge is the bulk density of graphene nanoplatelets as a powder. The low apparent density of commercially available GnP powders leads to complications in extruder feeding [19].The incorporation of nano additives has a significant effect on crystallization behavior. In particular, reports of GnP showing enhanced crystallinity can be found for polypropylene [21] and polyamide-6 [22]. Furthermore, it is known that crystallinity has beneficial effects on the permeation rate, where two aspects of crystallinity have to be considered: degree of crystallization and crystallin...

Molecular Dynamics Investigation of the Effect of Shear during Extrusion on the Permeation Behavior of CH4 in High-Density Polyethylene

“…A decrease in chain spacing leads to an increase in intermolecular interaction strength and a higher degree of material compaction. It can be obtained by wide-angle X-ray diffraction (WAXD) [42]. The D-spacing is inversely proportional to the diffraction angle corresponding to the prominent diffraction peak.…”

“…ray diffraction (WAXD) [42]. The D-spacing is inversely proportional to the diffr angle corresponding to the prominent diffraction peak.…”

Graphene/graphene nanoplatelets reinforced polyamide nanocomposites: A review

“…The compaction process allowed loading up to 20 wt% of GNPs in PA6 and showed that the compaction process did not hinder dispersion of GNPs or their thermal properties. Boldt et al 84 developed PA/GNP nanocomposites at a laboratory scale and a semi-industrial level using flat film extrusion. The nanocomposites were applied to make membranes with better-quality gas barrier properties at laboratory scale.…”

Effects of an industrial graphene grade and surface finishing on water and oxygen permeability, electrical conductivity, and mechanical properties of high-density polyethylene (HDPE) multilayered cast films

“…polyamide [10] and polycarbonate [11], compounded by means of extrusion, have been reported. However, in order to ensure lower cost and processability, as low as possible filler concentrations are usually recommended.…”

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