## 4 Discussion and Conclusions  
Exposure to CB nano-particulates that were used in FCM is unlikely when the NM is fully incorporated into a polymer matrix [12; 17] because the mobility of CB nano-particulates is too low to cause migration based on Fickian diffusion. In practice, conditions of use could impact the integrity of the polymers and, as a consequence, could cause the NMs to not be fully embedded anymore within the host polymer matrix. There are thus legitimate concerns that intensive use of the food contact material under stress conditions might facilitate the release of CB nano-particulates. To date, the number of studies on the mechanical stress related release of NMs from nanocomposites is very limited. [PERSON] et al. [18] investigated the release of silicon dioxide and titanium dioxide nanoparticles from ceramic cookware after stress conditions that simulated intensive use. A linear abrader equipped with scrubbing pads, steel wool, or a tungsten carbide burr was used to abrade the surface of the ceramic coating. Single-particle inductively coupled plasma  
Figure 9: AF4 fractograms of abraded nanocomposites that were pre-stressed by heat (**a**), deep-freezing (**b**), solvent swelling (**c**), and stretching (**d**). The black curves are the fractograms of samples that were additionally fortified with carbon black (in this case PX 80 at 5 ng/mL). mass spectrometry (sp-ICP-MS) was used to determine the release of silicon dioxide and titanium dioxide particulates and to differentiate them from solubilized ionic species. Release of particles was only detected after abrasion of the surface with the tungsten carbide burr. As the authors stated, this condition obviously damaged the ceramic coating beyond reasonable use. Although the other abrasion conditions with scrubbing pad and steel wool can also be considered as severe, any release of nanomaterials was not detected. Clearly, an investigation of the potential release of NMs from nanocomposites requires suitable analytical techniques [19; 20; 21] and a suitable experimental design [5]. Due to the particulate nature of CB [22; 23; 24; 25], both requirements must be met. In a previous study we have demonstrated the non-migration of CB in a static migration experiment using AF4/MALLS [12]. In this new study, the focus was not on diffusion based migration of CB, but on release that is caused by mechanical abrasion of the surface and potentially triggered by various pre-stress treatments. To this end, a suitable abrasive dry substance was selected ensuring the stability of the CB dispersion for the AF4/MALLS measurements. The combination of quartz sand and 96% ethanol gave the best results. Verification that abrasion did occur effectively was achieved by microscopical images that demonstrated homogeneous matting of the nanocomposite's surface after abrasion. To simulate the intensive use of FCM and to draw worst case scenarios where the polymer integrity could be affected, the nanocomposites were subjected to thermal, chemical and mechanical stress prior to the abrasion test. Heating aimed at enhancing the flexibility of the polymer, deep-freezing at making the surface more brittle, the immersion in a solvent at swelling the LDPE, or increasing the stiffness and brittleness of the EPDM. Finally, stretching was to decrease the thickness of the polymer surrounding the CB nano-particulates. Under all of these conditions, both without and with pre-stressing, no release of CB was detected. The overall limit of detection (LOD) of the method, considering the LOD of the device, the recovery rates, the nanocomposite area in contact with the dry simulant, as well as the amount of abrasive sand and ethanol used were in relation to the food contact area 0.78 \(\upmu\)g/dm\({}^{2}\) for PX 80, 0.83 for PX 85, 0.78 for N550, and 0.74 for N772. Assuming a surface to volume ratio of 6 dm\({}^{2}\) per kg of food, according to the European Union (EU) cube model, this corresponds to a detection limit of approximately 5 \(\upmu\)g of CB per kg of food.