## 1 Introduction  
This article is the first in a series of two dealing with the investigation of the potential release of Nanomaterials (NMs) from nanocomposites under intense material stress conditions. NMs offer new or improved properties when used in food packaging materials, but to date there is no broad agreement whether the use of NMs in such products could lead to higher risk for consumers [1; 2; 3; 4]. Risk is the product of hazard (toxicological properties) and exposure [5], thus the risk of NMs that are used in nanocomposites can be assessed by determining whether the NMs are able to be released from packaging into foodstuff at all, and if yes, to which degree. The number of studies dealing with the potential diffusion based migration of NMs has significantly increased in the last ten years. An overview of the published literature can be found in the reviews by [PERSON] et al., [PERSON] et al. and [PERSON] et al. [6; 7; 8]. Results from these migration studies are often inconsistent and in some cases even contradictory. Positive migration results were typically found either when direct contact of the food (simulant) with the NM was possible e.g., at cutting edges of the test specimen or when the surrounding matrix caused severe interactions with the nanocomposite e.g., due to the swelling or even degradation of the polymer. The investigation of nanocomposites in contact with complex matrices like food or food simulants is still a new analytical field that certainly requires a different analytical approach than for the investigation of classical polymer compounds. The occurrence of experimental errors or artefacts due to inadequate experimental designs might also play a non-negligible role. This issue finds, however, insufficient consideration in the reported studies so far. A comprehensive experimental design (i.e., sample preparation, storage conditions of the samples, matrix interactions, and the choice of analytical method for the detection of NMs) should respect the particulate nature and the stability of the investigated NM at any time during the whole migration experiment, including sample preparation steps and analytical methods. The inherent complexity of the migration studies on nanocomposites is one reason why risk assessment of NMs still has to be performed on a case-by-case basis [9]. When considering the potential migration of NMs from polymers, it is generally accepted though that NMs are too large to have a significant mobility within a polymer matrix and thus do not have the potential to migrate due to diffusion in the polymer [10; 11]. In these studies, supported by migration modelling, a \"cut-off diameter\" for diffusion of 3-4 nm was derived for NMs incorporated into polyolefins and 1-2 nm in polyethylene terephthalate (PET) or similar polymers. In practice, these small NM sizes are not encountered in nanocomposites that are used as food contact material (FCM). Thus, exposure for consumers will not take place, especially when the NM is fully embedded within the polymer (i.e., fully dispersed and incorporated in the matrix) when mechanical release can also be excluded. The above mentioned modelling of NM migration considered carbon black (CB) as a worst-case model substance that overestimates the migration of any other NM, due to the low molecular weight of carbon. CB, with its aciniform structure, whereby primary particles are fused together to form aggregates, presents diameters that are well above the mentioned cut-off diameters. Besides theoretical considerations, the non-migration of CB from plastic food packaging materials was experimentally demonstrated in a static migration test [12]. Migration scenarios other than diffusion-based are conceivable: (i) dissolution of the NMs by the contact medium (e.g., acidic food or simulant) either in the polymer matrix or after release and (ii) the desorption of NMs that are not fully embedded in the polymeric matrix (e.g., located at the surface of the nanocomposite) or release of NMs after degradation of the polymeric matrix [6; 13; 14].