A study of emission of nanoparticles during physical processing of aged polymer-matrix nanocomposites

Nanotechnology research and its commercial applications have experienced an exponential rise in the recent decades. Although there are a lot of studies with regards to toxicity of nanoparticles, the exposure to nanoparticles, both in terms of quality and quantity, during the life cycle of nanocomposites is very much an unknown quantity and an active area of research. Unsurprisingly, the regulations governing the use and disposal of nanomaterials during its life cycle are behind the curve. This work aims to assess the quantity of nanoparticles released along the life cycle of nanocomposites. Machining operations such as milling and drilling were chosen to simulate the manufacturing of nanocomposites parts, and impact testing to recreate the end-of-life of the materials. Several studies have tried to simulate different release scenarios, however these experiments had many variables and in general were not done in controlled environments. In this study, a reliable method was developed to assess the release of nanoparticles during machining and low velocity impact of nanocomposites. The development and validation of a new prototype used for measurement and monitoring of nanoparticles in a controlled environment is presented, as along with release experiments on different nanocomposites. Every sample tested was found to release nanoparticles irrespective of the mechanical process used or the type of material tested. Even neat polymers released nanoparticles when subjected to mechanical forces. The type of matrix was identified to play a major role on the quantity of nanoparticles release during different process. Thermoset polymers (and especially polyester) were found to release a higher number concentration of particles, mainly due to their brittle properties. A polyester sample was found to release up to 48 times more particles than a polypropylene one during drilling. The nanofiller type and percentage used to reinforce the polymer is also a key point. For example, the addition of 2 wt.% of nano-alumina into polyester increases the number concentration of particles by 106 % following an impact. The nanofiller chosen and its quantity affect the mechanical properties and machinability of the composites and therefore its nanoparticles release potential. The mechanical process and the process parameters chosen were also found to be crucial with regards to the nanoparticles released with different trends observed during drilling and impact of similar materials. Finally, thermal ageing of nanocomposites increases the number concentration of nanoparticles released (by 8 to 17 times after 6 weeks)

Mechanical properties of three-phase polyamide 6 nanocomposites

This work focus on the mechanical properties of three-phase nanocomposites using multiscale reinforcements. The influence of the nano-fillers content, as well as the temperature were studied. Polyamide-6 reinforced with short glass fibre 30 wt.% and with an addition of nanoclay (montmorillonite) and/or nanosilica (SiO2) were tested in order to characterise their tensile properties at room temperature and at 65oC just above the polyamide 6 glass transition temperature. SEM analysis were conducted on the fracture surface of the tensile bars. SEM investigations showed the importance of the interaction matrix/filler for the material behaviour. Our study also shows that the increase of OMMT percentage in polyamide-6/glass fibre composite made the material more brittle and had a negative effect on the tensile properties. Further, for the silica-based nanocomposites, an optimum was found for a nanofillers content of 1wt.%

Measurement of Nanoparticles Release during Drilling of Polymer Nanocomposites

Nanomaterials are one of the promising technologies of this century. The Project on Emerging Nanotechnologies [1] reports more than 1600 consumer products based on nanotechnology that are currently on the market and advantages link to the reinforcement of polymeric materials using nano-fillers are not to demonstrate anymore. However, the concerns about safety and its consumer perception can slow down the acceptance of nanocomposites. Indeed, during its life-cycle, a nanotechnology-based product can release nano-sized particles exposing workers, consumers and environment and the risk involved in the use and disposal of such particles is not well known. The current legislation concerning chemicals and environment protection doesn’t explicitly cover nanomaterials and changes undergone by nanoparticles during the products’ life cycle. Also, the possible physio-chemical changes that the nanoparticles may undergo during its life cycle are unknown. Industries need a standard method to evaluate nanoparticles release during products’ life cycle in order to improve the knowledge in nanomaterials risk assessment and the legislation, and to inform customers about the safety of nanomaterials and nanoproducts. This work aims to propose a replicable method in order to assess the release of nanoparticles during the machining of nanocomposites in a controlled environment. For this purpose, a new experimental set-up was implemented and issues observed in previous methods (background noise due to uncontrolled ambient environment and the process itself, unrepeatable machining parameters) were solved. A characterisation and validation of the chamber used is presented in this paper. Also, preliminary testing on drilling of polymer-based nanocomposites (Polyamide-6/Glass Fibre reinforced with nano-SiO2) manufactured by extrusion and injection moulding were achieved

Mechanical and impact performance of three-phase polyamide 6 nanocomposites.

In this work, three-phase nanocomposites using multiscale reinforcements were studied to evaluate the influence of nanofillers on static and dynamic mechanical properties at varying temperature conditions. In particular, short-fibres reinforced polyamide 6 (30wt.%) composites with various weight fractions of montmorillonite (OMMT) and nanosilica (SiO2), manufactured and investigated. Quasi-static tensile properties were investigated at room temperature and also at 65°C just above the polyamide 6 (PA6) glass transition temperature. The low velocity impact tests were conducted on the manufactured cone-shaped structures to evaluate the crash behaviour and energy absorption capability. The study results shows that the increase of the weight percentage level of OMMT in PA6/glass fibre (30wt.%) composite made the nanocomposites more brittle and simultaneously deteriorated the tensile properties. SiO2 nanofiller at 1wt.% was found to be the optimum ratio for improving tensile properties in silica-based nanocomposites studied. It was further noted that for both types of nanofillers, the crashing behaviour and energy absorption in dynamic properties were improved with increase in nanofillers weight percentage in the composites. The study also shows that the brittleness behaviour of the nanocomposites investigated is associated to the fibre/matrix interaction which is dependent on the nanofiller type and has significant effect on crash modes observed

EFFECT OF MULTIFILLER REINFORCEMENT ONTO ENERGY ABSORPTION PERFORMANCE OF LIGHTWEIGHT THERMOPLASTIC NANOCOMPOSITES FOR AUTOMOTIVE APPLICATIONS

Abstract Modern vehicle structures must be able to withstand severe impact loads at the same time providing safety of the occupants. For the same reasons, structural materials used for crashworthy applications must be characterized by good energy absorption capability. In order to ensure survivability of an accident, structure has to dissipate energy in a controlled manner. This is limited by two factors i.e. induced decelerations and maintenance of a survival space for occupants during a crash. In case of nano-fillers the stress concentrations are significantly reduced therefore, composite ductility can be maintained at a constant level or even improved, in relation to the neat polymer. Moreover, it has been proved that the addition of nano-sized fillers, rather than micro-sized fillers, can significantly enhance the mechanical properties of the polymeric materials at low filler content. If the filler is in the nano-metric size, an important enhancement can be obtained at content in the range of 0.5-5%, whereas in case of micro-fillers the reinforcing effect is observed at loadings typically higher than 20%. These unique properties of nanocomposites come from the large number of interfacial effects, existing due to the high surface-area-to-volume ratio of the nano-filler. For spherical nanoparticles and nano-fibres this ratio is irreversibly proportional to their radius, and its value can be even up to 1000 m2/g. This work focuses on the improvement of the mechanical properties of polymer composites reinforced with glass-fibres and nano-fillers, and better understanding of the energy absorption mechanism in these materials. In this study mechanical and morphological properties of PP and PA6 composites filled with different nano and micro materials, were investigated. The effect of matrix and filler material, as well as testing speed, on the mechanical properties of injection moulded composites will be discussed in details

Development of CNC prototype for the characterization of the nanoparticle release during physical manipulation of nanocomposites

This work focuses on the release of nanoparticles from commercially used nanocomposites during machining operations. A reliable and repeatable method was developed to assess the intentionally exposure to nanoparticles, in particular during drilling. This article presents the description and validation of results obtained from a new prototype used for the measurement and monitoring of nanoparticles in a controlled environment. This methodology was compared with the methodologies applied in other studies. Also, some preliminary experiments on drilling nanocomposites are included. Size, shape and chemical composition of the released nanoparticles were investigated in order to understand their hazard potential. No significant differences were found in the amount of nanoparticles released between samples with and without nanoadditives. Also, no chemical alteration was observed between the dust generated and the bulk material. Finally, further developments of the prototype are proposed

Particle emission measurements in three scenarios of mechanical degradation of polypropylene-nanoclay nanocomposites

Researchers and legislators have both claimed the necessity to standardize the exposure assessment of polymer nanocomposites throughout their life cycle. In the present study we have developed and compared three different and independent operational protocols to investigate changes in particle emission behavior of mechanically degraded polypropylene (PP) samples containing different fillers, including talc and two types of nanoclays (wollastonite-WO- and montmorillonite-MMT-) relative to not reinforced PP. Our results have shown that the mechanical degradation of PP, PP-Talc, PP-WO and PP-MMT samples causes the release of nano-sized particles. However, the three protocols investigated, simulating industrial milling and drilling and household drilling, have produced different figures for particles generated. Results suggest that it is not possible to describe the effects of adding nano-sized modifiers to PP by a single trend that applies consistently across all different protocols. Differences observed might be attributed to a variety of causes, including the specific operational parameters selected for sample degradation and the instrumentation used for airborne particle release characterization. In particular, a streamlined approach for future assessments providing a measure for released particles as a function of the quantity of removed material would seem useful, which can provide a reference benchmark for the variations in the number of particles emitted across a wider range of different mechanical processes

THE RATE OF BINARY BLACK HOLE MERGERS INFERRED FROM ADVANCED LIGO OBSERVATIONS SURROUNDING GW150914

A transient gravitational-wave signal, GW150914, was identi fi ed in the twin Advanced LIGO detectors on 2015 September 2015 at 09:50:45 UTC. To asse ss the implications of this discovery, the detectors remained in operation with unchanged con fi gurations over a period of 39 days around the time of t he signal. At the detection statistic threshold corresponding to that observed for GW150914, our search of the 16 days of simultaneous two-detector observational data is estimated to have a false-alarm rate ( FAR ) of < ́ -- 4.9 10 yr 61 , yielding a p -value for GW150914 of < ́ - 210 7 . Parameter estimation follo w-up on this trigger identi fi es its source as a binary black hole ( BBH ) merger with component masses ( )( ) = - + - + mm M ,36,29 12 4 5 4 4 at redshift = - + z 0.09 0.04 0.03 ( median and 90% credible range ) . Here, we report on the constraints these observations place on the rate of BBH coalescences. Considering only GW150914, assuming that all BBHs in the universe have the same masses and spins as this event, imposing a search FAR threshold of 1 per 100 years, and assuming that the BBH merger rate is constant in the comoving frame, we infer a 90% credible range of merger rates between – -- 2 53 Gpc yr 31 ( comoving frame ) . Incorporating all search triggers that pass a much lower threshold while accounting for the uncerta inty in the astrophysical origin of each trigger, we estimate a higher rate, ranging from – -- 13 600 Gpc yr 31 depending on assumptions about the BBH mass distribution. All together, our various rate estimat es fall in the conservative range – -- 2 600 Gpc yr 31

Nanomaterials Life Cycle Analysis: Health and Safety Practices, Standards and Regulations – Past, Present and Future Perspective

A new technology always raises new issues with its introduction on the market. Nanotechnology is not an exception. The advantages of nanomaterials use are not to demonstrate anymore and so, the commercialization of consumer products based on nanotechnology doesn’t stop increasing. The introduction on the market of nanoproducts also involves some uncertainties. Risks regarding the environment and human health are not well known by the scientist, and the legislation doesn’t cover health and safety aspects related to nanomaterials. Especially, fate of nanoparticles during the life-cycle of nanoproducts is not fully experienced due the large variety of nanomaterials existing and their diverse applications. It is safe to say that, given the explosive R&D and commercial uptake of nanomaterials unsurprisingly, the regulations governing the use and disposal of nanomaterials during its life cycle is behind the curve. The wide acceptance of nanotechnology by the consumers depends on alleviating the perceived safety related concerns. This paper aims to review the state of the art about exposure to nano-sized particles during life-cycle of nanomaterials. Also, future challenges and necessary work to ensure the success of nanotechnologies will be reviewed in this paper