5 years ago



48 Nanotechnology for

48 Nanotechnology for packaging applications Nanotechnology is, by definition, the creation and subsequent utilization of structures with at least one dimension in the nanometre length scale that creates novel properties and phenomena otherwise not displayed by either isolated molecules or bulk materials. Since Toyota researchers in the late 1980s found that mechanical, thermal and barrier properties of nylon-nanoclay composite material improved dramatically by reinforcing with less than 5% of nanoclay, extensive research work has been performed in the study of nanocomposites for food packaging applications. The term nanocomposite refers to composite materials containing typically low additions of some kind of nanoparticles. Specifically in the food biopackaging sector, nanocomposites usually refer to materials containing nanofillers, typically 1 to 7 wt.-%. For reinforcing purposes, a good nanofiller-matrix interaction is highly desired, which is often one of the major challenges faced when developing new nanocomposite materials. It has been observed that the interactions matrix-filler significantly improve when reducing the size of the reinforcing agent. Macroscopic reinforcing components usually contain defects, which become less important as the particles of the reinforcing component are smaller. Therefore, shifting from micro- to nanosized particles incorporated into the polymeric matrices leads to better performance of the composite materials. Current nanotechnologies of value in the food packaging area are nanoclays, cellulosic nanomaterials, electrospun nanofibers and nanocapsules, carbon based nanomaterials, nanoparticles of metal and metal oxides, and nanoparticle containing carriers. These nanomaterials are used as an efficient gas, UV light and vapour barrier, to enhance mechanical and thermal properties, to reduce migration issues, and to provide controlled release, and active or bioactive functionalities to packaging. The high surface-to-volume ratio of many nanoscale structures which favours this improved performance of packaging materials, also becomes ideal for applications that involve chemical reactions, drug delivery, controlled and immediate release of substances in active an functional food packaging technologies and energy storage in, for instance, intelligent food packaging.

Risk assessment of migration Regarding inherent nanoparticle hazard assessment, due to their small size, nanoparticles are generally much more reactive than their corresponding macrocounterparts. On the other hand, as a result of this, much smaller filler loadings are required, and hence added to the matrix, to achieve the desired properties. The large surface area of nanoparticles allows a greater contact with cellular membranes, as well as greater capacity for absorption and migration. Therefore, assessment of the effects of nanoparticles in food packaging materials such as migration to foods and potential bioaccumulation, needs to be considered in the expected dosages. Currently, data on toxicity and oral exposure of nanoparticles are extremely limited and controversial when it comes to the studied dosages. In addition, the small size of many nanoparticles causes them to take on unique chemical and physical properties that are different from their macroscale chemical counterparts. This implies that their toxicokinetic and toxicity profiles cannot be extrapolated from data on their equivalent non-nanoforms. Thus, the risk assessment of nanoparticles should be performed on a case-by-case basis. However, it is also very important to differentiate between three-dimensional nanoparticles (spherical or otherwise 3D nanoparticles such as nanometals), bidimensional nanoparticles (nanofibers, with only nanodimensions in the 2D cross-section) and the least concerned, one dimensional nanoparticles (nanoclays with only one nanodimension in the thickness direction). Nanoclays should be considered aside because in essence they are heat stable microparticles, which remain such all along the process of production and commercialization and to a significant extent also as two-dimensional microparticles within the biopolymer matrix during service. In any case, the general risk assessment of migration products resulting from packaging materials has posed and continues to pose a difficult challenge. As a general rule, nanocomposites within the European Union must currently comply with the EFSA total migration limit of 10 mg/dm 2 , with the functional barrier stringent migration level of 0.01 mg/kg of food or food simulant and/or with the specific migration levels for their constituents in case they comprise food contact components (Commission Directive 2007/19/CE that modifies Directive 2002/72/CE). The existing information about actual migration to food or food simulants is very scarce but suggests that no specific relevant issues are to be 49

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