Assessment of nanoparticle emission of polypropylene, polyester and epoxy nanocomposites during automated drilling process.

Polymer nanocomposites are becoming established widely across the industry due to (among other reasons) their lightweight performance advantages, and ability to meticulously target material properties with great control and precision. Despite the beneficial properties, certain nanofillers have shown potential health risks and toxicity, to both humans and the environment. The use and introduction of these materials into the workplace may therefore be hazardous if it involves human exposure. Research has yet to evaluate or quantify either the risk, the process of potential exposure, or the impact of embedded nanoparticles in commercial composites when they are released during machining processes. In this thesis, four groups of nanocomposites are identified as being used within industry and having potentially-harmful nanoparticles - the nanocomposites incorporate seven different nanoparticles of relevance, at different weight concentrations. This study involved the manufacture of the materials and an investigation into their effect on mechanical properties, through various methods: tensile tests, three-point bend flexural tests, SEM, EDX and FT-IR. The study employed a process approach for the assessment of nanoparticle emissions, using an automated drilling methodology in which the background noise was eliminated from the measurements. The investigation used real-time measurements with a combination of a condensation particle counter (CPC), a scanning mobility particle sizer spectrometer (SMPS), a real-time fast-mobility particle spectrometer (DMSSO) and post-test analytical methods. The research investigated the influence of a variety of nanofillers on nanoparticle release during drilling, from three different polymers: polyester (PE), polypropylene (PP) and epoxy (EP). Suitable fillers were tested for each polymer and demonstrated modifications to the material properties. The four sets of nanocomposites included PP-based, PE-based, EP-based and a hybrid EP/carbon fibre-based (EP/CF). PP-based samples were reinforced with talcum (Talc), montmorillonite (MMT) and wollastonite (WO). PE-based samples were reinforced with two weight concentrations of nano-silica (Si02) and nanoalumina (Al203). EP-based samples were reinforced with carbon nanotubes (CNT) and carbon nanofibres (CNF). EP/CF-based samples were reinforced with three weight concentrations of graphene oxide (GO). The fillers utilised within the PP-based samples were observed to decrease the material density, without significantly affecting the tensile and/or flexural properties. The fillers in the PE-based samples had minimal effect on the tensile properties; however, all of the reinforcing fillers improved both the flexural modulus and flexural strength. The incorporation of CNFs and CNTs in EP displayed both positive and negative effects on the tensile and flexural properties in comparison to the EP sample. The use of GO within EP/CF demonstrated minimal effect on both the tensile and flexural properties in comparison to the sample without nanoparticle reinforcement. The study on the PP-based nanocomposites is the first such study to explore and demonstrate the nanoparticle release from WO and Talc-reinforced composites. The nano-filled samples exhibited a 33% decrease (PP/MMT) or a 30% increase (PP/WO) on average released particle number concentration in comparison to the virgin PP sample. Size distribution analysis found a substantial percentage of the particles released from the PP, PP/WO and PP/MMT samples to be between 5 nm to 20 nm, whereas the PP/Talc sample produced larger particle diameters. The results from the PE-based nanocomposites show that the nano-reinforced samples displayed an increase in nanoparticle number concentration by up to 228% compared to virgin PE. This suggests that the nanofillers adhered to the PE matrix, showing a higher released concentration of larger particles (20 nm to 100 nm). The correlation between nanoparticle weight concentration and nanoparticle release varied considerably between the Si02 and Al203 samples. In comparison to the virgin EP, the results revealed that the EP/CNF and EP/CNT samples returned statistically significant differences for all samples, and produced an increase of 93% and 211% respectively in average particle number concentration. The particle mass concentration released from EP/CNT and EP/CNF samples demonstrates that a new perspective is needed for occupational exposure assessment of CNTs and CNFs embedded within nanocomposite materials. The incorporation of GO within the EP/CF-based samples displayed a statistically significant increase in nanoparticle release at the three different weight concentrations. However, the study did not find any relationship between filler weight concentration and nanoparticle release. Also, although a statistically significant increase was observed, the independent fillers appeared to have no effect in the characterisation and particle size distribution. Overall, 83% of the investigated samples demonstrated that the introduction of nanoparticles within the material had a statistically significant influence on the average particle number concentration: 67% of the nanocomposites displayed a statistically significant increase in the particle number concentration, while 17% displayed a statistically significant decrease. The study found no clear correlation between mechanical properties and particle number concentration; however, it was revealed to be highly dependent on polymer brittleness and ductility. The results demonstrated that the incorporation of most nanofillers can have a significant influence on particle number concentration and therefore may have a detrimental effect on nanoparticle release. On several occasions during the drilling, it was observed that the concentrations emitted by some samples were so high as to surpass the limits of the CPC instrument. The evidence presented by this research contributes a substantial amount of data for the assessment of nanoparticle release from polymer nanocomposites during drilling

The influence of graphene oxide on nanoparticle emissions during drilling of graphene/epoxy carbon-fiber reinforced engineered nanomaterials.

Graphene oxide (GO) nanoparticles are increasingly being used to tailor industrial composites. However, despite the advantages, GO has shown conceivable health risks and toxicity to humans and the environment if released. This study investigates the influence that GO concentrations have on nanoparticle emissions from epoxy-reinforced carbon fiber hybrid composites (EP/CF) during a lifecycle scenario, that is, a drilling process. The mechanical properties are investigated and an automated drilling methodology in which the background noise is eliminated is used for the nanoparticle emissions measurements. Real-time measurements are collected using a condensation particle counter (CPC), a scanning mobility particle sizer spectrometer (SMPS), a real-time fast mobility particle spectrometer (DMS50) and post-test analytical methods. The results observe that all three nanoparticle reinforced samples demonstrated a statistically significant difference of up to a 243% increase in mean peak particle number concentration in comparison to the EP/CF sample. The results offer a novel set of data comparing the nanoparticle release of GO with varying filler weight concentration and correlating it the mechanical influence of the fillers. The results show that the release characteristics and the influence in particle number concentration are primarily dependent on the matrix brittleness and not necessarily the filler weight concentration within the nanocomposite

A review on the effect of mechanical drilling on polymer nanocomposites.

Over the past decade, polymer nanocomposites have undergone intensive research and development ensued by its increasing implementation within commercial applications. Consequently, the full life-cycle performance and any health risks associated with these materials have become of major interest. Throughout its use, a nanocomposite will undergo industrial machining where drilling can lead to material damage and/or exposure to the potentially toxic nanoparticles. This study assesses the existing and perspective research on nanocomposite drilling. Currently, although considerable amount of studies have investigated machining on conventional composite materials, there is a lack in knowledge on the effect of drilling on nanocomposites. The data underlines the various drilling parameters that will affect and influence the damage to the material and nano-sized particles released. Importantly, previous studies have identified potential mechanical damage caused by drilling and the release-ability of toxic nanoparticles from nanocomposites. It is therefore crucial to develop a full understanding and characterization on the effect of drilling on polymer nanocomposites

The effect of nanosilica (SiO2) and nanoalumina (Al2O3) reinforced polyester nanocomposites on aerosol nanoparticle emissions into the environment during automated drilling

The aim of this study is to investigate the effect nanosilica and nanoalumina has on nanoparticle release from industrial nanocomposites due to drilling for hazard reduction whilst simultaneously obtaining the necessary mechanical performance. This study is therefore specifically designed such that all background noise is eliminated in the measurements range of 0.01 particles/cm3 and ±10% at 106 particles/cm3. The impact nano-sized SiO2 and Al2O3 reinforced polyester has on nanoparticle aerosols generated due to drilling is investigated. Real-time measurement was conducted within a specially designed controlled test chamber using a condensation particle counter (CPC) and a scanning mobility particle sizer spectrometer (SMPS). The results show that the polyester nanocomposite samples displayed statistically significant differences and an increase in nanoparticle number concentration by up to 228% compared to virgin polyester. It is shown that the nanofillers adhered to the polyester matrix showing a higher concentration of larger particles released (between 20 – 100 nm). The increase in nanoparticle reinforcement weight concentration and resulting nanoparticle release vary considerably between the nanosilica and nanoalumina samples due to the nanofillers presence. This study indicates a future opportunity to safer by design strategy that reduces number of particles released concentration and sizes without compromising desired mechanical properties for engineered polymers and composites.European Commission Life+ project named “Simulation of the release of nanomaterials from consumer products for environmental exposure assessment” (SIRENA, Pr. No. LIFE 11 ENV/ES/596). QualityNano Project through Transnational Access (TA Application VITO-TAF-382 and VITO-TAF-500) under the European Commission, Grant Agreement No: INFRA-2010-26216

Influence of reduced graphene oxide on epoxy/carbon fibre-reinforced hybrid composite: flexural and shear properties under varying temperature conditions.

This study investigated the effectiveness of reduced graphene oxide as nanofiller in enhancing epoxy/carbon fibre-reinforced composite at varying temperature conditions. The graphene oxide was synthesised using modified Hummer’s method and then chemically reduced to yield reduced graphene oxide (rGO). The rGO was dispersed in epoxy matrix system through combination of mechanical and sonication methods. The flexural and shear test samples were manufactured using resin infusion technique. These samples were then tested to determine their shear and flexural properties at varying temperatures (-10°C, 23°C, 40°C) and the results correlated to neat samples. It was found that the composites’ flexural strength and flexural modulus increased with rGO wt.% content up to 62% and 44% respectively. The shear testing results showed improvement on the shear strength and modulus at maximum of 6% and 40% respectively. The rGO improvements advantage was lost for flexural strength, shear strength and modulus at elevated temperatures while flexural modulus withheld at 40% improvements over virgin epoxy/carbon fibre-reinforced composite. An interesting observation is that all samples with rGO exhibite reduced damage characteristics superior to the neat samples under flexural and shear loading conditions. This study indicates that the addition of rGO significantly alter the flexural and shear properties, failure modes, damage characteristics and they are overall sensitive to elevated temperature conditions

Assessment of nanoparticles release into the environment during drilling of carbon nanotubes/epoxy and carbon nanofibres/epoxy nanocomposites

The risk assessment, exposure and understanding of the release of embedded carbon nanotubes (CNTs) and carbon nanofibers (CNFs) from commercial high performance composites during machining processes are yet to be fully evaluated and quantified. In this study, CNTs and CNFs were dispersed in epoxy matrix through calendaring process to form nanocomposites. The automated drilling was carried out in a specially designed drilling chamber that allowed elimination of background noise from the measurements. Emission measurements were taken using condensed particle counter (CPC), scanning mobility particle sizer (SMPS) and DMS50 Fast Particulate Size Spectrometer. In comparison to the neat epoxy, the study results revealed that the nano-filled samples produced an increase of 102% and 227% for the EP/CNF and EP/CNT sample respectively in average particle number concentration emission. The particle mass concentration indicated that the EP/CNT and EP/CNF samples released demands a vital new perspective on CNTs and CNFs embedded within nanocomposite materials to be considered and evaluated for occupational exposure assessment. Importantly, the increased concentration observed at 10 nm aerosol particle sizes measurements strongly suggest that there are independent CNTs being released at this range.The work is funded by and part of the European Commission Life project named Simulation of the release of nanomaterials from consumer products for environmental exposure assessment (SIRENA, Pr. No. LIFE 11 ENV/ES/596). We are also thankful to the funding by QualityNano Project through Transnational Access (TA Application VITO-TAF-382 and VITO-TAF-500) under the European Commission, Grant Agreement No: INFRA-2010-262163 for the access and use of the facilities at the Flemish Institute for Technological Research (VITO). The authors would like to acknowledge K. Tirez and R. Persoons at Vito for their XRF and SEM support. Kristof Starost is also thankful for partial funding by the School of Engineering for his studentship

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 Influence of Graphene Oxide on Nanoparticle Emissions during Drilling of Graphene/Epoxy Carbon-Fiber Reinforced Engineered Nanomaterials

Graphene oxide (GO) nanoparticles are increasingly being used to tailor industrial composites. However, despite the advantages, GO has shown conceivable health risks and toxicity to humans and the environment if released. This study investigates the influence that GO concentrations have on nanoparticle emissions from epoxy-reinforced carbon fiber hybrid composites (EP/CF) during a lifecycle scenario, that is, a drilling process. The mechanical properties are investigated and an automated drilling methodology in which the background noise is eliminated is used for the nanoparticle emissions measurements. Real-time measurements are collected using a condensation particle counter (CPC), a scanning mobility particle sizer spectrometer (SMPS), a real-time fast mobility particle spectrometer (DMS50) and post-test analytical methods. The results observe that all three nanoparticle reinforced samples demonstrated a statistically significant difference of up to a 243% increase in mean peak particle number concentration in comparison to the EP/CF sample. The results offer a novel set of data comparing the nanoparticle release of GO with varying filler weight concentration and correlating it the mechanical influence of the fillers. The results show that the release characteristics and the influence in particle number concentration are primarily dependent on the matrix brittleness and not necessarily the filler weight concentration within the nanocomposite

Nano particles Release and Emission from nanoreinforced polymer nanocomposites : A case study on Drilling process

<p>The aim of this study is to investigate the effect of different fillers (nanofillers and fibers) on dust generation during mechanical processing (Drilling) and structural testing of reinforced polyamide composite panels.</p