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

Starost, Kristof Johan

Authors

Kristof Johan Starost



Contributors

Abstract

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.

Thesis Type Thesis
Institution Citation STAROST, K.J. 2020. Assessment of nanoparticle emission of polypropylene, polyester and epoxy nanocomposites during automated drilling process. Robert Gordon University [online], PhD thesis. Available from: https://openair.rgu.ac.uk
Keywords Nanoparticles; Nanocomposites; Nanoparticle release; Nanoparticle emission; Drilling; Nanofillers

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Copyright: the author and Robert Gordon University





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