Nanomaterials have already invaded the market and research and development centres thanks to their many advantages. However, the Health and Safety aspects and potential risks of this new technology still need to be studied in depth to ensure their continued success.
Concluding this literature review, it is safe to say that the risks of nanomaterials are defined according to two factors: toxicity and exposure. Toxicity of nanomaterials was found to be dependant of different parameters: shape, size, chemical composition, surface modification and charge, and solubility and persistence. This is not in line with the classical chemical substances for which the toxicity is defined by mass. However, current legislations and regulations classify toxicity of nanomaterials in proportion of the toxicity of their bulk substances, then in term of mass. Change of regulations specific to nanomaterials is the first step to be taken.
Route of exposure and behaviour of nanomaterials with regards to human health and environment are also a crucial point to understand. ENMs are different from
nanoparticles released during ageing or mechanical stress situations handle by a nano-product. The assessment of toxicity and exposure need to be done throughout the life cycle of products, and a complete analysis of all the possible exposure scenarios is necessary. Also, standard methods need to be developed in order to have comparable results.
Standards and regulations are actually the heart of the problem. Currently, only one standard explains how to choose the measurement device and the sampling procedure to follow, but it is specific to nanopowders. Standards related to different nano-product forms need to be developed. Also, standardized methods and reference tests should be produced in order to create a reference database to compare results from experiments with new materials and applications.
The general conclusion for this literature review is that considerable efforts and work is needed by both research institutions and government agencies in order to ensure a successful future for nanomaterials.
2.8.1 Gap in the Knowledge
The current work published in the area of exposure to nanoparticles is not able to provide a quantitative assessment of exposure to nanoparticles [117]. Some challenges still need to be tackled:
- A complete analysis of all the possible exposure scenarios is necessary;
- No standardised method exists to measure and characterize nanoparticles released during mechanical stress situations;
- The equipment used in order to estimate the quantity of nanoparticles released in the air can be a source of error for an accurate measurement;
- Background noises were often reported as a source of variability. One solution is to work in a perfectly clean room or chamber where only the particles induced by the process can be measured but again the perfect or standard method or equipment does not exist yet.
- The lack of standard methods for the measurement and collection of released nanoparticles makes the comparison between the results of different studies difficult, and the risk assessment of nano-products by the industry impossible. Also, the guides mentioning exposure to nanomaterials define occupational exposure limits in term of mass.
This is not relevant as it is known that toxicity is linked to size and surface area of nanoparticles. Thus, it is necessary to undertake a study to define not only the quantity (mass) but also the quality (shape, size, chemistry, etc.) of nanoparticles released.
- The release of nanoparticles and the evolution of nanofillers after ageing of the nanocomposites have not been studied so far, and it is an important factor to simulate the end-of-life implications of a nanotechnology-based product. Also, even though the ageing of polymers has been studied for a long time, the ageing of polymeric-matrix nanocomposites is still not well known.
The gap in the knowledge graph is presented in Figure 8.
Figure 8: Gap in the Knowledge
2.8.2 Methodology
In order to fill the gap in the knowledge and reach the aim and objectives previously explained, a methodology was defined. The different tasks for the methodology are presented Figure 9.
A literature review was conducted in order to select the polymer matrices and nanofiller additive combinations to test. The materials and samples selected were manufactured and then tested to assess the improvement in term of mechanical or electrical properties of nanocomposites materials compared to neat polymers.
Temperature ageing was also performed on a set of nanocomposites.
In parallel, the literature review helped to select potential exposure scenario to test and existing protocol currently used. Three types of experiments viz. drilling, milling and impact were selected to simulate different potential release scenarios along the life cycle of a nanocomposite component. Drilling and milling are common procedures in different stages of product’s usage phase, and impact Figure 9: Methodology
recreates accidental or intended fractures. After an assessment of the protocols used in the literature, a new method overcoming the deficiencies observed in the previous ones (high background noise in the measurement, high effect of the process on the measurement…) was set-up, improved and validated.
With a suitable protocol, all types of materials selected were exposed to physical degradation (either drilling, milling or/and impact) in order to generate particles.
Deposited and airborne particles collected were characterised taking into account shape, size, chemical composition, number concentration, and size distribution.
Following the experimental work, an analysis of the effect was conducted regarding the effect of the materials parameters: matrix type, filler type and percentage, ageing, and the effect of the processes studied.
The following chapters will first present the implementation of a standard method to assess the release of nanoparticles during physical processing of nanocomposites parts (the experimental design). Then, the three next chapters will focus on the three types of experiments conducted: drilling, milling and impact. Each chapter will include the manufacturing process for the materials and samples, as well as their electrical or mechanical properties. This will be followed by characterisation of the particles emitted during physical processing and a discussion about the effect of matrix materials, nanofiller type and percentage, process parameters and ageing on the nanoparticles emitted.