Polymer nanocomposites are candidates to exploit the excellent electrical, thermal and mechanical properties of graphene and other related nanomaterials. Using thermoplastic polymers to this aim - e.g. by melt compound extrusion - is especially useful due to their versatility and reusability. The low apparent density of some graphene nanoparticle (GNP) powders (in the order of a few grams per liter) makes the melt compounding extrusion of GNP/polymer composites problematic, especially at high GNP concentrations. The high GNP/polymer volume ratio makes the premixture in the extruder hopper quite irregular and results in composites with badly distributed GNPs. In this project, we consider different pretreatments, namely compaction of very low apparent density GNP and functionalization processes, of Avanzare’s GNP1 to increase the maximal load that can be melt compounded with polyamide 6 (PA6) using a twin-screw extruder. GNP1 are partially oxidized graphene nanoplatelets (4% oxygen by XPS) with a lateral size of 84 μm (D50) and 6 nm of thickness. A physical process of agglomeration was conducted, which increased more than ten times the apparent density of the GNP1 powder. Moreover, the functionalization of GNP1 with (3-aminopropyl)triethoxysilane (APTES) was investigated to improve its dispersion in the polymer. The higher apparent density allowed higher loadings in a one-step extrusion: from around 2 wt% with untreated GNP1, to 10 wt% with compacted GNP1. Loadings up to 20% were achieved with two consecutive extrusions. The thermal conductivity of the composites with agglomerated GNP1 did not decrease compared to the composites with untreated GNP1 at the same concentrations, suggesting that the physical treatment did not damage GNP1 or hinder its dispersion.