Nanopolymers and Nanofillers
There are many technological advances in the development of complex biocomposites and nanopolymers that are relevant for consideration here. Nanocomposites are complex macromolecular materials containing small quantities of nanoscale additives, or nanofillers. The most commonly employed nanofillers for food packaging (the most common type of plastic litter) are nanoclays. Other common nanofillers include nanocellulose fibres, carbon nanotubes, metals and oxides. Nanofillers are intended to enhance or improve the inherent properties of the polymer, including factors such as mechanical strength, thermal and ultraviolet stability, and gas and vapour barrier properties (Lagaron and LopezRubio 2011). The high surface-to-volume ratio of nanofillers enhances their inherent chemical and mechanical properties compared with larger-scale versions of the same material, whilst allowing them to disperse within polymers without introducing structural defects. For example, addition of nanoclays can enhance the oxygen barrier properties of plastics, which makes them particularly attractive for keeping food from spoiling (Lagaron and Lopez-Rubio 2011).
The addition of nanomaterials into polymers can also cut down on the need for large amounts of additives, for example by acting as antioxidants or antimicrobial agents themselves (De Azedero 2013). In relation to plastic discarded to the environment, a major added benefi of nanofi is that they may also be able to reduce the unintended migration of additives out of polymers (de Abreu et al. 2010).
Table 13.5 Indicators of potential toxicity for nanoparticles contained within food packaging
Adapted from EFSA (2011)
The migration of various polymer additives, including triclosan and diphenyl butadiene from polyamide into food stimulants was found to be up to six times lower when nanoclays were added to the polyamide. The nanoclay particles were thought to slow down the rate of migration of the additives due to their layering within the polymer matrix, creating a tortuosity effect (Fig. 13.3) (de Abreu et al. 2010). Thus, new advances in nanotechnology may bring unintended benefi in terms of the reduced leaching of their additives and hence the environmental safety of the polymers that contain them.
Fig. 13.3 Tortuosity effect of nanoclay in limiting the diffusion of permeants through polymers (adapted from Ray and Okamato 2003)
Conclusions and Future Work
This short account has identified some of the most widely encountered plastics in everyday use and illustrated some of the attempts that have been made to assess their potential hazards to human health. Different routes of exposure to human populations, both of plastic additives, microand nanoplastics from food items and from discarded debris are discussed in relation to the existing literature for nanomedicines and nanocomposite packaging materials, for which an increasing body of knowledge exists. It is clear that our understanding of the potential contamination of the human population by microor nanoplastics sourced from the environment is in its infancy, leaving many questions unanswered:
• Does significant bioaccumulation and trophic transfer for microand nanoplastics occur in the environment? If so, what species are most at risk?
• How does ageing of plastics affect their physico-chemical properties and subse-
• Following ingestion, does uptake of microand nanoplastics occur? Do proteins bind to the surface of the particles to form a protein corona? How does this vary for different plastic litter types and what cell types are most vulnerable to toxicity?
• What methods should we be using for locating, identifying and quantify-
ing microand nanoplastics in complex matrices including biological tissues? Techniques mentioned in this chapter include field flow fractionation, multiangled light scattering (MALS), inductively coupled plasma mass spectrometry (ICP-MS) and non-linear optical bioimaging. Further development of suitable methods for extracting microand nanoplastics from biological materials and for studying them in situ remains a compelling research gap for the future.
Acknowledgements TG gratefully acknowledges financial support from grants EU FP7 Cleansea Grant Agreement 308370 and NERC NE/L007010/1 during the preparation of this chapter.