The result is a successful combination of fundamentals for newcomers to the field and the latest results for experienced scientists, engineers, and industry researchers. Guo's Integrated Composites Laboratory focuses on multifunctional nanocomposites for energy, environmental and electronic devices applications. He received his PhD in chemical engineering from Yale University. His research focuses on carbon nanomaterials for sustainable energy and environmental applications.
Fundamentally, her group studies electron, phonon, and photon transport mechanisms for a given materials system, and designs the transport properties to meet the targeted performance. Her research work has been featured in national and regional media. Li et al. The hierarchical structure in the micro- and nanoscale consists of more than one layer of protrusions on the surface, with the bigger particles at the bottom and the smaller particles on the surface. One alternative is the use of nanoparticle-assisted lithographic techniques, which rely on masks to create geometric patterns on surfaces, adjusting the roughness by changing the etching duration and the lattice space of nanoparticles with different sizes.
Chemical [ ] or reactive-ion etching [ ] processes have been studied to remove the polymer matrix. Layer by layer LBL deposition is a process of constructing multilayered films based on alternating the charge of a substrate, with no need of a special environmental chamber to control the reaction conditions unlike plasma treatment or chemical vapour deposition CVD. To create the roughness structures for desired surface wettability nanoparticles are often added into the solutions. Cao and Gao [ ] fabricated transparent superhydrophobic and highly oleophobic coatings through LBL assembly of 20 nm silica nanoparticles and sacrificial 60 nm polystyrene nanoparticles, that were removed afterwards by calcination.
Self-assembly processes, in which the interactions among the components in solutions spontaneously form an organized distribution, have also been used. Particularly, to organize nanoparticles in a molecular way, self-assembled monolayers SAMs designed to have a specific and favourable interaction with the solid substrate of interest are used [ ]. Lassiaz et al. Electrospinning can produce fibres with various diameters and a low fibre diameter introduces one degree of roughness to the electrospun materials.
By tuning the electrospinning parameters, post-treatments steps or using some additives in the polymer solution, the second scale of roughness needed for superhydrophobicity is created. Polystyrene PS and their copolymers are the most frequently used due to their low surface energy, low cost and easiness of use for electrospinning. Nanoparticles like polytetrafluoroethylene [ ], titania or graphene [ ] can also be added to increase PS roughness.
Other non-fluorinated [ ] and fluorinated [ ] polymers have also been used to fabricate superhydrophobic surfaces. Hydrophilic polymers can also be coated by annealed electrospun nanostructured fibres of hydrophobic silanes to achieve a hydrophobic surface and reduce moisture sensitivity [ ].
However, the challenge of achieving such electrosprayed superhydrophobic and especially superamphiphobic surfaces with strong adhesion to the substrate and with non-intended migration, using application complying materials remains a challenge; this challenge is even greater when it comes to food packaging applications. Other non-conventional approaches have been used to create this type of surfaces. Deng et al. The resulting soot consisted of carbon particles with a typical diameter of 30 to 40 nm, forming a loose, fractal like network.
This layer exhibited superamphiphobic behaviour but was extremely fragile. It had to be coated by a silica shell using CVD techniques. In a latter study, a paraffin wax was used to fix the candle soot, creating a paraffin wax-fixed candle soot PFCS coating [ ]. This PFCS coating method has been tested on various surfaces, such as metal, ceramic, wood, plastic and paper. Some of these processes and materials have already been patented. Huang developed a hydrophobic and lipophobic coating material comprising nanoparticles with a determined molecule for easy clean touch screens [ ].
Johnson and Son, Inc. Cas Guangzhou Chemistry Co. Ashland Licensing and Intellectual Property Llc patented a coating composition and process for generating transparent, near-transparent, and semi-transparent super-hydrophobic coatings whose composition comprises hydrophobic nanoparticles of silsesquioxanes containing adhesion promoter and low surface energy groups [ ]. For example, Eka Nobel patented a paperboard packaging with hydrophobic zeolite that enhances their water-repellent capacity [ ] and Bostik Findley Sa patented a system for gluing hydrophobic and oleophobic substrates that are intended for packaging [ ].
To avoid the adherence of liquids, in addition to the lotus effect that nanocoatings can provide, they can also promote other self-cleaning mechanisms by, e. TiO 2 , the most thoroughly semiconductor investigated in the literature, seems to be the most promising compound for this purpose. As photocatalysis is an interfacial phenomenon, nanostructured TiO 2 surfaces exhibit superior photocatalytic activity due to a high surface area-to-volume ratio.
There are common ways of applying coating with photocatalytic TiO 2. Among these various deposition systems, ESD Electrostatic Dissipative Coating is attractive because it produces extremely fine sub-micron , selfdispersive non-agglomerating , highly wettable electrowetting , adhesive droplets that yield a uniform coating on the substrate.
The pigmentary properties are no longer relevant for nanostructured particles, giving therefore almost transparent composite. TiO 2 semiconductor provides the best compromise between catalytic performance and stability in aqueous media [ , ]. Among the different phases, TiO 2 anatase is one of the most promising photocatalyst because of its high oxidative power, abundance and chemical stability.
Under UV-illumination, it generates electron-hole pairs able to degradate organic matter or even microorganisms. As a consequence, efforts have been devoted to extending the light absorption of TiO 2 to the visible region. Tudor et al. Further benefiting from its antimicrobial capacity, self-cleaning active textiles could be manufactured applying by electrospray this specifically doped nano-TiO 2 on fabrics [ ]. Another recently studied application using the photocatalytic effect of such nanocomposites is the incorporation of active TiO 2 nanostrucures in poly methyl methacrylate PMMA for the removal of dyes, phenols and bacteria from water [ ].
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This approach benefits from the lack of need for a recovery of the active nanoparticles after water treatment due to their immobilization. As indicated above in Section 3. Two main types of layered nanomaterials have been studied as nanofillers to decrease the permeability to gases of polymers: layered silicates such as nanoclays and graphene based materials graphene and graphene oxide. Nanoclays have been extensively investigated over the last decades because of their excellent barrier properties, low price and food contact compatibility [ ].
The use of graphene in nanocomposites is much more recent, but several examples in literature have shown that it can be a strong candidate for gas-barrier materials [ ]. A description of the most representative polymeric nanomaterials for packaging based on these two types of layered materials is shown in the following paragraphs. By far the most studied nanoscale fillers for polymeric nanocomposites destined to packaging are nanoplatelets composed of clays or other silicate materials.
Montmorillonite [ Na,Ca 0. Each platelet contains a layer of magnesium or aluminium hydroxide octahedra sandwiched between two layers of silicon oxide tetrahedra. Structure of montmorillonite phyllosilicate clay. These structural characteristics contribute to the excellent utility of montmorillonite as nanofiller in composites, significantly increasing the mechanical and barrier properties of the polymer with a few percent addition into the matrix.
Montmorillonite is not the only layered silicate used in polymeric nanocomposites. Related clays such as saponite, hectrite and kaolinite have also been used and have shown properties improvements [ ]. During the last two decades, hundreds of polymer-clay nanocomposites have been described, and nanoclays have been incorporated into every important class of polymer, both synthetic and natural. Some representative examples of clay nanocomposites whose polymeric matrices are typically used in packaging are provided in Table 3 , along with selected moisture and oxygen permeability data.
This table shows just some examples that have been studied. A more comprehensive list can be found in the literature, consulting any of the numerous specific reviews on the subject [ 12 , ]. Examples of polymer-clay nanocomposites and their barrier improvements. Permeabilities are expressed as improvement ratios: the ratio of the gas permeability or transmission rate of the virgin polymer to the gas permeability or transmission rate of the polymer-clay composite, measured at the same conditions [ ].
Recently, graphene has received significant attention and has become one of the most studied materials due to its superior properties. Graphene, a monolayer of graphite, has not only excellent mechanical, electronic and optical properties [ ], but also is considered an ultrathin, perfect two-dimensional 2D barrier against gas diffusion [ ], since the electron density of aromatic rings in graphene is high enough to repel the penetration of atoms or molecules [ ]. When compared with clays, graphene nanoplatelets can have some advantages as two-dimensional nanofillers for polymer nanocomposites.
Polymers incorporating graphene show not only enhanced gas barrier properties but also reinforced mechanical strength and improved thermal properties and electrical conductivity when properly dispersed in the polymer matrix [ ]. As compared with other nanocarbon forms, such as fullerenes or carbon nanotubes, graphene has a higher surface-to-volume ratio aspect ratio and so will be able to achieve the longest gas-diffusion pathway, even at low loadings.
The main drawback when using this promising material is that the synthesis of defect-free, large-area, monocrystalline graphene at large scale is still challenging and too expensive for packaging application [ ]. One alternative for the use of the gas-barrier properties of graphene in mass production is to use graphene oxide GO or its reduced form, reduced graphene oxide rGO. GO, which consist of oxygen-containing functional groups on the basal plane [ ], can be produced at large scale in polar solvents and can be well-dispersed with high aspect ratio in hydrophilic polymers [ ].
Some representative examples of graphene-based nanocomposites targeting to improve gas barrier properties for food packaging are presented in Table 4. Polymer nanocomposites are mainly produced by solution mixing and melt processing. Representative examples of graphene-based nanocomposites targeting to improve gas barrier properties [ ]. For graphene-nanocomposites the platelet size, stacking orientation and degree of graphene exfoliation in the polymer matrix are important factors influencing the gas transport [ ]. In addition, the high mechanical strength, thermal stability and electrical conductivity allow excellent applications.
However, the aggregation of graphene derivatives at high loadings, the local defects of nanocomposites during preparation and the good dispersability in the matrix are significant obstacles to overcome when preparing graphene-polymer nanocomposites. As a further very positive perspective in terms of the use of graphene in packaging applications, graphene deposits were shown to have sufficient resilience to withstand thermoforming [ ].
It was also demonstrated to extend the shelf life of beer packed in PET bottles by a factor of 2 to 5 [ ]. In this study, diamond-like carbon DLC was deposited using a microwave plasma reactor to reach nanocoatings in the range of 50 nm thickness leading to over fold decrease in the oxygen permeation. The optical properties of the coating were reported to vary from semi-transparent to fully transparent depending on the technology used.
This is a consequence of its platy nature, having micron-sized dimensions on length and width, with nanometric thicknesses. Layer charge is zero or very small, as there are not ions present between layers. The effects of talc on synthetic polymers have been large studied.
It was demonstrated that talc improves mechanical properties and macromolecular orientation of polypropylene [ ]. Moreover, an induced crystalline structure has been reported, suggesting that talc particles act as a nucleating agent for polymer crystallization.
Also, high aspect ratio platelets have been used to improve gas barrier properties. Furthermore, even though this is not a primary goal, other nanoparticles such as pyrogenic silica have also been reported to improve the barrier properties of the matrices where they are dispersed [ ].
Although non-platelet like nanoparticles lead to lower increase of tortuosity effect, their high specific surface area may lead to gas adsorption and above all, as here when dispersed in PP, they may act as nucleating agent increasing the crystallization degree of the matrix which is well known to increase barrier properties.
Carbon and materials for energy applications
Electrospraying is an efficient technique to develop nanostructured surfaces and incorporate nanofillers into the package polymer matrix, as shown in several published studies [ 83 , , ]. The use of EHDP is also very interesting for the incorporation of active substances e. The adherence of liquids and other viscous products result in residues in packages, which leads to needless waste at the consumer end and difficulties in the packaging recycling.
For reducing the residues in packages, the main objective consists of minimizing the interaction forces between the filled good and the food contact material of the packaging [ ]. In Section 3. It has been shown that the wettability of a solid surface is governed by its surface energy determined by chemistry and texture [ ]. A typical commercial example for anti-adhesive materials is Polytetrafluoroethylene PTFE well-known under the tradename Teflon , usually used in non-stick cookware.
The incorporating of fluorine atoms, which have a small atomic radius and high electronegativity, provide a low surface energy [ ]. However, the use of Teflon in packaging is hindered due to its high cost, high processing temperatures and low acceptability because of its fluorinated content. Alternatively, low temperature surface modification processes have been described, since generally the polymers currently used in the packaging industry PP, PE, PET … are not heat-resistant.
For example, ultra-water-repellent poly- ethylene terephthalate PET substrates have been fabricated by a two-step dry process. First, PET substrates were treated with oxygen plasma in order to provide a proper nanotexture, and subsequently a hydrophobic layer was coated on the nanotextured PET surfaces by means of either low-temperature chemical vapour deposition CVD using fluoroalkylsilane or plasma enhanced CVD using tetramethylsilane [ ]. Recently, the Massachusetts Institute of Technology developed the first permanently wet slippery surface that can be used for easy-to-empty packaging LiquiGlide.
This solution is durable and makes viscous liquids slide easily [ ]. For determination and comparison of the emptying behaviour, depletion or tack test methods can be applied for evaluation [ ]. Although the development of non-wetting surfaces has been studied for a long time, easy emptying packaging is not a widely used option nowadays, due to the higher costs of the packages compared to traditional materials.
However, the last improvements made in the nanomaterials field and the focus on high added value goods will pull the market for easy-to empty packaging solutions. Organic photovoltaic films have several advantages over conventional silicon cells. Photoactive organic materials are printed in extremely thin layers on transparent plastic film. The patented special inks used in printing consist of formulated blends of materials which after coating create electricity when exposed to light. This technology allows lightweight and flexible semi-transparent modules.
As a result, they can be used on all kinds of surfaces.
Multifunctional Nanocomposites for Energy and Environmental Applications
A further key advantage is that the modules generate relatively constant output, for instance even if it is cloudy or artificial light is being used. In addition, they can be produced in different colours and thus adapted to the surroundings. This is a property that creates new possibilities, particularly for building design.
The cost-effective production of the OPV modules is also advantageous. Since these polymer materials can be processed as liquid solutions, they are suitable for multiple printing processes: spin coating, ink-jet printing or roll-to-roll processing such as gravure and flexographic printing [ ]. In addition, semi-transparency and tunable colours as well as freedom of design in shape and form are attractive and often even essential features for BIPV applications. The achievement of the legally binding NZEB objectives will require active building envelopes since passive materials are reaching their own limits.
Gray OPV-based active building elements are an important step forward to combine energy generation and the aesthetic needs of architects [ ]. Nanostructures on the front of the PV can guide light into the absorbing layer, or reduce reflection. Nanostructures on the back of a PV could be used as high performance reflectors, bouncing otherwise lost light back into the PV. The light-absorbing layer itself can benefit from a sculpted nanostructure, which could change its ability to absorb light of different wavelengths, for instance.
Besides lower material costs, thin-film photovoltaics tfPV also are flexible because they only use very thin silicon, whereas current non-thin-film PVs are rigid. This could make tfPVs easier to install; like paper, they could be spooled off a roll [ , ].
Carbon and materials for energy applications | EMRS
Fullerenes are used as electron acceptor and electron transporting material [ 29 ]. As inorganic n-type contacts, TiO x and ZnO can be used. Also indium-doped zinc oxide IZO is possible [ 29 ]. An additional incorporation of metal nanoparticles such as gold or silver showed efficiency enhancement of polymeric solar cells, mainly ascribed to improved photocurrent density resulting from an excited localized surface plasmon resonance [ , , ]. During their usage, OPV cells are exposed to several atmospheric degradation agents and thus they need to be protected by coatings and encapsulants.
Nowadays, the following main properties are basically required for solar cells coating materials to ensure devices durability: UV, oxygen and water barrier; thermal stability, transparency, anti-reflectance, anti-soiling, flexibility, affordable cost, electrical isolation. The fouling due to dust, rains, bird faeces, etc. Surface-bound fog similarly scatters light and reduces optical transmission for transparent materials which is detrimental to their function [ ]. The application of nanocoatings is also an interesting prospect for solar panels leading, in an easier way than the creation of organized nanostructured surfaces, to tailored repellence of liquid and other unwanted substances that deposit on the panel with time.
Indeed, typical fouling dust, dirt, rain, etc. Therefore, a number of initiatives related to their self-cleaning are already on the market [ , ]. They employ coatings based on nanoparticles or texturation to get a lotus effect [ ], or alternatively apply small electrical field to prevent dust from adhering on the surface. Nonetheless, this later coating is applied manually post production, whereas electrospray seems an optimum route for the application of tailored coatings both on the point of view of reducing the amount needed to get a required effect therefore saving cost and of its easy integration within the existing process.
Zhao and others described the electrospray deposition as a thin film deposition method that is uniquely suited for manufacturing organic photovoltaic cells with the desired characteristics of atmospheric pressure fabrication, roll-to-roll compatibility, less material loss, and possible self-organized nanostructures [ ]. The main functionalities developed in the last reported studies focus on increasing the conductivity [ , ], and providing self-cleaning and anti-reflective properties [ ] which contribute to extending the photovoltaic cells lifespan. Although a significant number of patents regarding self-cleaning solar panels in general none for flexible OPVs though were returned in representation of some of the above listed technologies, none of them employed electrospray as a deposition technique.
Furthermore, based on nanostructured surfaces, researchers recently developed solar cells that can harvest light from any angle, and lead to self-cleaning panels at the same time [ 30 ]. Finally, inorganic nanocoatings and nanocomposites are well known to be transparent in the visible range of the spectra to allow harvesting useful light while filtering UV-light [ ] potentially resulting in increasing the lifetime of the OPVs by preventing UV weathering.
All in all, the prospects of nano in solar energy are countless, and it has been one of the key drivers contributing to huge energy efficiency enhancement of the solar panels since their creation over 50 years ago.
The automotive sector can benefit from the utilization of nanomaterials. In this sense, the polymer nanocomposites can improve the performance of existing technologies in applications such as engines and powertrains, exhaust systems and catalytic converters, paints and coatings, tires, lighter but stronger materials, suspension and breaking systems, electric and electronic equipment, or frames and body parts [ ].
On the one hand, the traditional fillers used in automotive parts talc, mica and calcium carbonate provide a higher stiffness, increasing melt viscosity and weight, and decrease the toughness and optical clarity. The glass fibre reinforcements introduce higher stiffness, but increased costs and difficulty of fabrication. Both glass fibre reinforcement and traditional fillers must be used at high loading to enhance the properties such as high modulus, or improve the dimensional stability, and the weight, toughness and surface quality are affected.
An improvement in modulus, fire retardancy, dimensional and thermal stability has been reported [ ]. Nanoclays are the dominant commercial nanomaterials. Nanoclay replaces the traditional fillers at a ratio. There is currently a growing interest to reduce the weight of the components in a car to reduce the fuel consumption. Another example with the same nanofiller was shown again for General Motors in to diminish the weight. Maserati engine bay covers were made with a nanocomposite of nylon 6 and nanoclays, reducing the weight, and increasing mechanical properties.
Nowadays, Mucell Microcellular foaming technology for injection moulding industry is another process to reduce the weight in not structural components parts. It injects supercritical fluid in molten polymer to form microstructured foam with a solid skin layer and closed cells. As opposed to the use of nanofillers for reinforcement, this process leads to significant loss of mechanical properties and therefore of structural function.
Therefore, nanofillers are still in development to reduce the weight with an improvement of other properties and a low cost. The cost-performance ratio is the main objective for nanocomposites, due to the manufacturing cost of the nanoparticles. Besides, it is important to consider the change of design in the weight reduction with nanocomposites, as well as the improvement of material properties. The growth in research activity in terms of nanocomposites for the automotive sector continues to expand their applications. As is evident in this review, there are many applications of nanotechnology that involve the use of nanoparticles in a variety of applications and products.
This was one of the first reports to highlight the potential risks to health and the environment that may arise from exposure to nanomaterials. Since then, innumerable national and international reviews have provided a consistent view about the nature and the potential risks of nanoparticles, which may be summarised as follows:. There are potential hazards to human health and the environment from certain types and forms of nanoparticles, but not all, and this is largely influenced by their composition and morphology;.
There is a paucity of knowledge about whether and how these potential hazards manifest as actual risks to human and environmental health, through exposure, and their significance;. The absence of data makes it challenging for manufacturers, suppliers and users to have well-informed and effective risk management processes in compliance with their regulatory obligations.
Over the past decade, there has been a significant increase in research activity internationally, intended to fill these gaps. Several frameworks are available for assessing and managing risks from particulate nanomaterials, all of which are based on a common risk assessment approach. For example, the International Organization for Standardization ISO has proposed a step-by-step approach for nanomaterial risk evaluation and management [ ]. Risk assessment is an integrative approach that considers the effects that potential hazards can have should exposure occur.
Undertaking a risk assessment relies on having:. Exposure is characterized by measuring concentration and duration of exposure and this exposure analysis is important for risk assessment and subsequent risk management involving exposure control plans. In an occupational setting, exposure to nanomaterials can occur for workers at all phases of the material life cycle. During the development of a new material or process, it is likely that the material will be produced under controlled conditions, typically in small quantities, and although accidental releases, for example due to spills, are a possibility although in general, relatively few people are likely to be exposed at this stage.
Once the material moves through pilot-scale into commercial production, more widespread exposures can potentially occur following the manufacture of the material or in downstream activities such as recovery, packaging, transport, and storage. Some materials may be subsequently incorporated into a range of other products or may be used in other processes as a feed-stock material.
In these circumstances, the quantities of materials being handled can be expected to be much larger. Exposure to nanoparticles depends upon the formulation of nanoparticles during production, their use in products, and their potential release at during service life and at the point of recycling or disposal. Nanoparticles may be attached to surfaces e. Suspensions of nanomaterials may represent a risk in terms of dermal exposure see Poland et al. Suspensions of the materials are generally considered safer in terms of inhalation. However, care should be taken if physical processes such as centrifugation, ultra-sonication, heating and milling are applied to these suspensions which may release aerosols or dry material after solvent evaporation.
In case of nanocomposites, the nanomaterial is fully embedded within a polymer matrix. Exposure to the nanomaterial would only be possible by migration of the nanomaterial out of the polymer based on the Fickian law of diffusion or by degradation of the polymer. In the first case it is believed that, once the nanomaterial is incorporated into a polymer matrix, it is immobilized wherefore migration cannot take place.
This was examined for a variety of nanocomposites intended to be used as food packaging plastics. However, detection of possibly migrated nanomaterials in complex matrices, like food or food simulants, is quite challenging, wherefore the results of migration studies are often not consistent and sometimes even contradictory. A comprehensive overview on this topic can be found elsewhere [ , , ]. Nevertheless, they provide a first indication of the potential for nanoparticle release during the use of such methods, which could potentially be used during the finishing of nanocomposite articles.
In order to obtain some preliminary information on potential release, researchers from the US National Institute for Occupational Safety and Health NIOSH undertook monitoring during the cutting of a nanocomposite paper containing graphene platelets, carbon nanotubes and other ingredients, using an unventilated band saw [ ]. Real-time monitoring showed a very large increase in both particle number and mass concentrations when the composite was cut, with particles detected in the size range 7— nm.
Although further research is needed to determine whether individual nanoparticles are being released, the authors recommend that if composites are routinely being cut by a band saw, dust control measures should be implemented. In a later study at the same workplace, Heitbrink, Lo et al. A ventilated enclosure was built to capture and mix the emissions.
The authors suggest that that high number concentration and emission rates may have been caused by the formation of nano-aerosols generated by frictional heating and did not appear to be elevated by the presence of carbon nanotubes. Sanding of a composite containing carbon nanotubes, generated fibre emission rates of 1. The authors recommend the use of either a local exhaust ventilation hood or a high velocity, low volume ventilation system during such tasks.
Numerous other studies have indicated the potential for significant particle release during the machining of carbon-based nanocomposites [ , ], most noticeably during dry surface grinding [ , ], dry cutting [ , ] or dry drilling [ ] with the level of release being highly dependent on the sample material, sample composition, how well the nanomaterial is bound in the polymer matrix and the energy applied to the process. Performing the same tasks under wet conditions has been shown to be an effective method for reducing the number of airborne particles [ , ].
This implies that, whilst degradation occurs during such tasks, nanomaterials often remain bound to the matrix. Manual sanding of carbon-based nanocomposites appears to result in lower particle emissions overall [ , ], with results indicating that particle release may be no higher than for sanding conventional composite materials. However, studies have indicated that micro-sized particles may be produced by abrasion, including with CNTs protruding from the main core [ ].
Most recently, Schlagenhauf and colleagues have published two studies investigating CNT containing epoxy-based nanocomposites [ , ]. Their first study took a novel approach to the detection of CNT by labelling them with lead ions based on surface absorption before incorporation into an epoxy resin which was then abraded using a Taber Abraser.
They found that in contrast to previous studies, the poorer dispersed CNT were released to a lesser extent than found with better dispersions. This was attributed to the relatively low energy of the abrasion process used which they surmised was not sufficient to break up CNT agglomerates. Given the potential for release, it has therefore been recommended that effective personal protection and engineering controls are used for all tasks involving the machining of nanocomposites, such as a ventilated enclosure equipped with HEPA filtration to prevent fugitive releases from contaminating the work area.
Further processing or simply aging of composites containing nanomaterials may lead to the release of particles and potential exposure. Organic polymers are particularly sensitive to UV radiation that can degrade them could lead to the release of particles. There are several studies which have evaluated the effect of sunlight as well as other forms of weathering on nanocomposites and one such study is that of Bernard et al. The results indicated that under UV irradiation, the polyurethane matrix showed signs of degradation.
In parallel, accumulation of GFN at the surface of the composite was also recorded. They showed that dry weathering in a progressive way led to revealing of CNT as the matrix degraded but the nanofillers did not, leading to an accumulation at the surface. These results indicate that the choice of the matrix and its ageing under sunlight may lead to accumulation of nanomaterials at the surface which could influence releases to the environment [ ].
An additional key issue within risk is the nature of hazards posed by nanocomposites and in particular, the nano-fillers used. There are relatively limited numbers of studies considering the toxicity of particles released from nano-composites and those which do exist tend to focus on carbon-based nanomaterials such as carbon nanotubes CNT. Whilst these materials do present a rather polarised view of the use of nanomaterials in composites, they can be used to inform us as to how the toxicity profile of a nanomaterial may be altered by incorporation and subsequent release. One such study is that of Wohlleben et al.
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The results showed that instillation of the matrix alone induced no clinical signs of toxicity or genotoxicity and minimal inflammation in the lung which was greater for the cement a known respiratory irritant yet instillation of the inhalable fraction of the nanocomposites did not lead to any differences in terms of toxicity compared to the matrix alone [ ]. This was in stark contrast to instillation of carbon nanotubes at a four-fold lower dose which led to prominent lung inflammation which was abrogated by its inclusion into a composite. Similar results have been noted in a range of in vitro studies addressing CNT-polyurethane nanocomposites [ ] as well as CNT containing epoxy-based nanocomposites [ , ].
Whilst these studies deal with a specific form of nanomaterial which is of course not representative of all nanomaterials not least due to their fibrous nature which may influence release characteristics , they do show that incorporation into a composite can have a significant effect on toxicity. CNT are known to present a respiratory hazard and can induce inflammation as well as granuloma formation in the lung [ , ] and one form not addressed within the studies above has been classified as a possible carcinogen [ ]. However, despite this intrinsic activity, the studies above show that incorporation into a variety of different composites is associated with a decrease in respiratory toxicity to the levels of the composite material alone meaning that the hazards associated with such nanocomposites may in fact be more akin to that of the base composite than the pure nanomaterial.
Such observations are, however, based on a limited number of studies and do not consider many types of nanomaterials but if the overall principle noted is transferable i. The release of nanomaterials from coatings has been assessed in only a few studies, mainly testing the release of nanomaterials from paints and other coatings. Koponen et al. The authors showed that although the geometric mean diameter of aerosol released during the sanding of paints was only slightly different with compared to without nanoparticles, the particle number concentration was increased during sanding of nanoparticle-containing paints [ ].
To conclude, the safe use of chemicals and responsible development of processes and products are recognized as fundamental to ensuring a safe working environment through easy to implement, affordable and fit-for-purpose measures to mitigate any hazards and control exposure to nanomaterials, protecting the health of workers, consumers and the environment and supporting the commercialisation of nanotechnology for societal benefit.
As seen during the last 20—30 years, significant progresses have been made in synthesis, processing, performances of polymer nanocomposites and nanocoatings. This article reviewed some key aspects on these fast-growing research areas in order to understand potential applications of polymer nanocomposites. These materials offer improved performance over bulk materials and microcomposites and hence can be used to overcome the limitations of many currently existing materials and devices. Nevertheless, a full control over their morphology nanostructure dispersion or even orientation is still desired to consistently reach optimal properties.
While polymer nanocomposite materials have unique behaviour such as improved mechanical and gas barrier properties, even upon small addition of nanofillers, nano-coatings can tailor the surface properties where they are applied for example in terms of affinity to liquids, but also of UV, gas or flame protection.
There are different processes for the preparation of polymer nanocomposite materials each of each has its own advantages and drawbacks; therefore, the suitable methods should be adjusted to the target application, composition, dispersion performance, etc. In terms of process improvements, ultrasonic-assisted dispersions have shown some encouraging results both in liquid media and melt plastic stream. This later also faces questioning related with the nano-safety of workers when handling nanoparticles, as well as with their use within consumer applications.
While for specific nanoparticles, the amount of research performed allows us to confirm the absence of hazards, the number of parameters involved is so high that generalization to others should be avoided. The authors also wish to thank Johannes Bott for discussions and inputs regarding the field of nanosafety.
National Center for Biotechnology Information , U. Journal List Nanomaterials Basel v. Nanomaterials Basel. Published online Mar Find articles by Marcos Latorre. Find articles by Maria Jorda. Find articles by Oliver Miesbauer. Find articles by Marius Jesdinszki. Find articles by Martina Lindner. Find articles by Zuzana Scheuerer. Thomas Nann, Academic Editor. Author information Article notes Copyright and License information Disclaimer. Received Nov 30; Accepted Mar This article has been cited by other articles in PMC. Abstract For the last decades, nanocomposites materials have been widely studied in the scientific literature as they provide substantial properties enhancements, even at low nanoparticles content.
Keywords: nanodeposit, nanocomposite, electrospraying, barrier improvement, self-cleaning surfaces, light-weight materials. Introduction For the last decades, nanocomposites materials have been widely reported in the scientific literature to provide substantial properties enhancements, even at low nanoparticles content.
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