Browsing by Author "Njuguna, James"
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Item Open Access Assessment of nanoparticle release and associated health effect of polymer-silicon composites(2014-04-15) Zhu, Huijun; Irfan, Adeel; Sachse, Sophia; Njuguna, JamesThe fast advancement in the nanotechnology and manufacturing of engineering nanomaterials has inevitably caused concerns over their impact on environment and human health. Little information is currently available on possible release of nanomaterials or/and nanoparticles (NP) from conventional and novel products and associated health effect. The NEPHH project funded under the EU FP7 programme is aimed to assess the environment and health impact of polymer-silicon nanocomposites in comparison to conventional polymer composites from life cycle perspective. As part of the NEPHH project, this study focused on assessing the possible release of NP during the application stage of conventional and nanoproducts. NP release was monitored during physical processing of polymer-silicon composites, and the toxicity of both the released NP and the raw silica nanomaterials that were used as fillers in nanocomposites was assessed in vitro using human lung epithelial A549 cells.Item Open Access Design and optimization of a novel tri-axial miniature ear-plug piezoresistive accelerometer with nanoscale piezoresistors(Cranfield University, 2013-02) Messina, M.; Njuguna, JamesThis work aims at the advancement of state-of-art accelerometer design and optimization methodology by developing an ear-plug accelerometer for race car drivers based on a novel mechanical principle. The accelerometer is used for the measurements of head acceleration when an injurious event occurs. Main requirements for such sensor are miniaturization (2×2 mm), because the device must be placed into the driver earpiece, and its measurement accuracy (i.e. high sensitivity, low crosstalk and low nonlinearity) since the device is used for safety monitoring purpose. A micro-electro-mechanical system (MEMS)-based (bulk micromachined) piezoresistive accelerometer was selected as enabling technology for the development of the sensor. The primary accelerometer elements that can be manipulated during the design stage are: the sensing element (piezoresistors), the micromechanical structure and the measurements circuit. Each of these elements has been specifically designed in order to maximize the sensor performance and to achieve the miniaturization required for the studied application. To achieve accelerometer high sensitivity and miniaturization silicon nanowires (SiNWs) as nanometer scale piezoresistors are adopted as sensing elements. Currently this technology is at an infancy stage, but very promising through the exploitation of the “Giant piezoresistance effect” of SiNWs. This work then measures the potential of the SiNWs as nanoscale piezoresistors by calculating the major performance indexes, both electrical and mechanical, of the novel accelerometer. The results clearly demonstrate that the use of nanoscale piezoresistors boosts the sensitivity by 30 times in comparison to conventional microscale piezoresistors. A feasibility study on nanowires fabrication by both top-down and bottom-up approaches is also carried out. The micromechanical structure used for the design of the accelerometer is an optimized highly symmetric geometry chosen for its self-cancelling property. This work, for the first time, presents an optimization process of the accelerometer micromechanical structure based on a novel mechanical principle, which simultaneously increases the sensitivity and reduces the cross-sensitivity progressively. In the open literature among highly symmetric geometries no other study has to date reported enhancement of the electrical sensitivity and reduction of the cross-talk at the same time. Moreover the novel mechanical principle represents advancement in the accelerometer design and optimization methodology by studying the influence of a uniform mass moment of inertia of the accelerometer proof mass on the sensor performance. Finally, an optimal accelerometer design is proposed and an optimized measurement circuit is also specifically designed to maximize the performance of the accelerometer. The new proposed accelerometer design is capable of increasing the sensor sensitivity of all axes, in particular the Z-axis increases of almost 5 times in respect to the current state-of-art-technology in piezoresistive accelerometer. This occurs thanks to the particular newly developed approach of combination of beams, proof mass geometry and measurement circuit design, together with the use of silicon nanowires as nanoscale piezoresistors. Furthermore the cross-sensitivity is simultaneously minimized for a maximal performance. The sum of the cross-sensitivity of all axes is equal to 0.4%, well below the more than 5% of the state-of-art technology counterpart reported in the literature. Future work is finally outlined and includes the electro-mechanical characterization of the silicon nanowires and the fabrication of the proposed accelerometer prototype that embeds bottom up SiNWs as nanoscale piezoresistors.Item Open Access Design, modelling and testing of a novel energy harvesting device(Cranfield University, 2009-09) Longana, Marco Luigi; Zhu, Meiling; Njuguna, JamesThis work is a feasibility study to develop a novel energy harvesting device. Energy harvesting devices capture energy in various forms from the surrounding and transform it into usable electrical energy. These devices do not require any refuelling or recharging and are virtually a never ending source of energy. The energy harvesting devices rely on di erent mechanisms of energy conversion, depending on the energy source. This work focuses on conversion of mechanical energy from vibrations into electric energy using piezoelectric materials. Most of the existing devices are shaped like a cantilever beam, thus limiting the tunability to a single resonance frequency. It is believed that by modifying the geometry of the energy harvesting device and applying a pre-load to the active material (piezoelectric), a variable tunability can be achieved. Also, the application of an axial compressive pre-load helps to further increase the power output of the device. Therefore, in this present work, the performance of a simply supported beam shaped energy harvesting device is investigated both numerically and experimentally. For the numerical analyses nite element simulations are carried out using ANSYS. An electro-mechanical model of the simply supported beam has been developed through a series of approaching models with increasing complexity, starting from an analytical solution. The nal three-dimensional model was used as a base to create a model of the beam that has been used during the experimental tests. Shape optimization studies were carried out on this nite element model to analyse the power output of the device. It has been observed, through pre-stressed modal analyses, that the axial pre-load decreases the resonance frequency of the beam, thereby giving the beam the ability to be tuned. Also,it has been observed that an optimisation of the beam footprint shape can increase the power output by almost 40%.The experimental work focussed on the investigation of the harmonic behaviour of the simply supported beam under di erent pre-load conditions. It was observed that the experimental results were in disagreement with the nite element simulations and also with the reference literature. The disagreement was identi ed to be due to the hinge design that does not ensure the alignment of the two tips of the beam and therefore the application of a perfectly axial pre-load. From the work presented here it emerges that the possibility to develop a simply supported beam shaped energy harvesting device that rely on the application of an axial pre-load to obtain tunability and an higher power output is promising. The nite element simulations gave good results on the beam behaviour and on the possibility to further increase its output by optimising the shape of its footprint. The experimental work allowed to identify the hinge design as a problem area to design a pro table device.Item Open Access Effect of fibre treatments on mechanical properties of flax/tannin composites(Cranfield University Press, 2013-09-19) Zhu, Jinchun; Zhu, Huijun; Abhyankar, Hrushikesh; Njuguna, JamesDue to the inherent environmental benefits of using natural resin (tannin) and natural fibre (flax), flax/tannin composites could be potentially used for vehicle applications. One of the main limitations is the hydrophilic property of flax, resulting in the poor fibre/hydrophobic matrix interface quality. Alkali, acetylation, silane treatment and enzymatic treatment were selected to modify non-woven flax mats to prepare the composites. The fibre morphology was studied through scanning electronic microscopes (SEM). The effects of fibre pre-treatments on dynamic and static mechanical properties of composites were investigated through adequate experiments, such as dynamic mechanical analysis (DMA) and static tensile testing. The modified rougher fibre surface broadened the glass transition peaks of composites due to the improved surface adhesion. However, there is no big improvement of tensile strength after modifications. The pure NaOH (sodium hydroxide) treated composites remain the tensile properties and offer good flax/tannin wettability.Item Open Access The effect of temperature changes on to quasi-static tensile and flexural performance of glass fibre reinforced PA66 composites(Cranfield University Press, 2013-09-19) Butterworth, Ian; Abhyankar, Hrushikesh; Westwood, Keith; Njuguna, James; Brighton, James; Mouti, ZakariaA significant method of reducing CO2 emissions in road vehicles is to reduce the vehicle mass. One means in which this can be achieved is to adopt lightweight materials such as thermoplastic composites. Thermoplastics offer advantages in term of weight when compared to conventional steel and aluminium casting. In this study thermal mechanical testing has been conducted on two types of commercial polyamide 66 (PA66) with 35 wt.% short glass fibre reinforcement. One of the materials was impact modified with an elastomer to increase material toughness. Experimental results showed both the reinforced PA66 materials to be temperature dependent. All test results demonstrated the trade-off in the mechanical properties of the two materials especially the impact modified. PA66 with 35 wt.% short glass fibre exhibits the best tensile strength, flexural strength and modulus for each temperature tested. Whereas the impact modified PA66 with 35 wt.% short glass fibre exhibits the higher strain and toughness for each temperature tested.Item Open Access In vitro toxicity of new engineered nanoparticles through their life cycle(Cranfield University, 2013-11) Irfan, Muhammad Adeel; Zhu, Huijun; Njuguna, JamesThe rapid development of nanotechnology has caused concerns about nanoproducts on human health throughout their lifecycle. As part of the consortium NEPHH (nanomaterial related environmental pollution on human health through their life cycle, funded by EU-FP7), this project aimed to assess the potential effect of novel polymer-silicon composites on human health from a lifecycle perspective, focusing on in vitro toxicity of raw silica nanoparticles (SiNP) and dust nanoparticles (NP) released from silicon-based polymer composites. The main objectives were to characterise a group of amorphous SiNP and dust NP in water and cell culture medium; assess NP toxicity potential in in vitro models; and establish mode of SiNP action. The selection of SiNP of size 7-14 nm was based on their wide use in developing polymer nanocomposites. Dust NP were generated from mechanical processing of polymer composites made of polyamide-6 (PA6), polyurethane (PU) and polypropylene (PP), each incorporated with SiNP or 3 other different silicon reinforcement materials. The dispersion and size of NP in water and in cell culture medium were characterized using dynamic light scattering, scanning electron microscopy and transmission electron microscopy. The chemical composition of NP was assessed by infra-red spectroscopy. NP were assessed in vitro for induction of membrane damage, intracellular reactive oxygen species (ROS), loss of cell viability, and cellular uptake by flow cytometry and confocal microscopy. In order to identify potential biomarkers for toxicity prediction, miRNA array and extracellular metabonomic assays were performed. The size of SiNP (10-100 µg/ml) ranged from ~200-500 nm in water and ~20- 500 nm in culture medium, indicating the presence of aggregates. The infra-red spectrum of SiNP dried from culture medium showed a slight difference as compared with that dried from water, indicating protein adsorption. SiNP induced acute ROS increase, cell membrane damage, and reduction in cell viability after 48 h in human lung carcinoma epithelial A549 cells, lung fibroblast MRC-5 cells and skin HaCaT keratinocytes. SiNP were up taken by all 3 cell types, and located in the cytosol. Six early (<48h) SiNP responsive miRNAs were identified in A549 cells. SiNP also induced early changes in metabolites including glucose, lactate, ethanol, phenylalanine, histidine and tyrosine. Dust NP generated from PA6 group materials were more toxic than those from other polymer composites when assessed at 25-100 µg/ml at 72 h in A549 cells. The results obtained from this study suggest that 1) both small and larger SiNP aggregates are taken up into the target cells; 2) conventional cytotoxicity assays combined with miRNA and metabonomic assays provide insight into the molecular mechanisms of the nanotoxicity; 3) metabonomics and miRNA assays can serve as robust tools for recognising sub-toxic dose-effect relationships; 4) the toxicity of dust NP from polymer composites depends on polymer type but not reinforcement materials. This study demonstrated the importance of lifecycle analysis as opposed to single stage analysis of novel materials. Further studies need to improve study design to enable interpretation of cytotoxicity in relation to NP size, physiochemical property and intracellular dose, and to simulate the health effect of polymer-silicon composites under more realistic scenarios.Item Open Access Localised low velocity impact performance of FLAX/PLA biocomposites(Cranfield University, 2015-06) Nassiopoulos, Elias; Njuguna, James; Brighton, James L.Natural fibre composites are fast emerging as a viable alternative to traditional materials and synthetic composites. Their low cost, lightweight, good mechanical performance and their environmentally friendly nature makes them an ideal choice for the automotive sector. The automotive industry has already embraced these composites in production of non-structural components. At present, however, research studies into composites made of natural fibres/bio-sourced thermoplastic resins are at infancy stage and such works are rare in the literature. This study therefore focuses on the mechanical properties of poly(lactic) acid (PLA) flax reinforced composites for structural loaded components. The aim was to investigate the performance of flax/PLA biocomposites subjected to localized low velocity impacts. To start with, a detailed literature study was conducted covering biocomposites and PLA in particular. Next, a series of composite samples were manufactured. Morphological and thermal studies were also conducted in order to develop an in-depth understanding of their thermo-mechanical properties, including crystallinity, thermal response and their related transition temperatures. This was followed by localized impact studies. The influence of temperature, water uptake and strain rates to the material tensile strength and modulus, as well as the damage characteristics and limits that lead to failure were studied. Furthermore, in the present work different methods and existing material models to predict the response of biocomposites were assessed. A case study was then performed using these models to understand, develop and improve the side crash performance of a superlight city car prototype. ...[cont.]Item Open Access Localised low velocity impact performance of short glass fibre reinforced polyamide 66 oil pans(Cranfield University, 2012-03) Mouti, Zakaria; Njuguna, JamesThis thesis focuses on the mechanical properties of short glass fibre reinforced polyamide 66 material used in automotive composite structures, and its impact resistance under localised low velocity impact. The main application of this research concerns the impact performance of an oil pan component susceptible to stone impact damage. The thesis reviews the current state-of-the-art of thermoplastic polyamide materials with an overview of the glass fibre reinforced polyamide under-the-hood components, as well as its manufacturing and processing techniques. The study explores much of the work published in the literature so as to identify the fundamental parameters determining the impact resistance. It then concentrates on assessing the mechanical properties of the material subjected to quasi-static loads and impacts considering the influence and consequences of atmospheric or weathering conditions such as the moisture and salt uptake and the variation of temperature. The experimental work employed a universal testing machine for the quasi-static tests, drop weight tower and projectile air gun to carry out the dynamic tests. The testing involves different polyamide grades and impact modifier material in small specimens and full-scale oil pan components so as to gain important insights into the material-geometrical coupling effects. In correlation with the experiments, a finite element analysis was conducted to predict capability and simulate impact events using LS-DYNA solver. The simulation allowed putting to the test and comparing different protective design features. The post-testing investigations focused on the damage assessment and failures at micro- and macro-scales on the structure using visual inspection, scanning electron microscopy and ultrasound flaw detector. This was intended to bring detailed understanding of the failure mechanisms and also shed some light into damage tolerance of typical under-the-hood thermoplastic polyamide components. Investigation results indicated that impact resistance properties of short glass fibre reinforced polyamide 66 grades are sensitive and influenced by moisture and salt uptakes, temperature ageing and air oxidation. In general, the increase of these parameters reduces the material strength but at the same time improves its strain. The study also compares different structures and shows the significant contribution of the design in terms of shock absorption and stress distribution. The proposed oil pan design with protective ribbing pattern combined with a superior material with rubbery phase considerably improves the impact resistance of the full-scale automotive component studied.Item Open Access Mechanical properties of three-phase polyamide 6 nanocomposites(Cranfield University Press, 2013-09-19) Gendre, Laura; Abhyankar, Hrushikesh; Njuguna, James; Ermini, ValentinaThis 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.%.Item Open Access Nano-sized particles emission during drilling and low velocity impact of silica-based thermoplastic nanocomposites(Cranfield University, 2012-10) Sachse, Sophia; Njuguna, James; Zhu, HuijunDuring the past decade, polymer nanocomposites have emerged as a novel and rapidly developing class of materials and attracted considerable investment in research and development worldwide. Driven by the certainty that by the integration of low nano ller amounts, existing material properties can be improved and moreover new material properties can be developed. Despite the clear bene t and therefore, increasing research, production and utilisation of nanomaterials, little is known about how nanocomposites will perform over their whole life cycle, especially in the usage and end of life phase. Under the in uence of environmental factors such as ultraviolet light, moisture, temperature and mechanical actions, nano-sized particles can be potentially released from nanocomposites and thus may have negative e ects on the human health and the environment. Within the scope of this work an extensive literature review has been conducted in which polymer nanocomposites are brie y introduced and release scenarios of engineered nano-sized particles from nanocomposites during their life cycle are discussed. In the experimental part of this work silica based polypropylene, polyamide and polyurethane composites were manufactured and particle exposure mechanism during mechanical processing and testing were monitored and analysed. A series of comprehensive physical characterisation techniques were utilised to assess particle size distribution, shape, and concentration in di erent mediums, once emitted by the solid composite materials. It was observed that during drilling of PA6 composites, the airborne particle emission rates were 10 times higher than those for the PP based composites. However, the characterisation of deposited particles showed exactly the opposite behaviour, were the total number of particles emitted by the PP based composites was 10-100 times higher than those of the PA6 based composites. To the best of our knowledge, this is the rst time such work has been reported in the literature. Further, the addition of secondary ller into a polymer/glass- bre composites changed the micro-mechanism during crash testing and therefore controlled the energy absorption characteristics of the composites. However, it was shown that once subjected to higher impact energies the geometric particle size of the released particles increased from approx. 25 nm for the 530 J to approx. 60 nm for the 1560 J impact. Additionally, the tensile modulus increased by 0.31 GPa and the speci c energy absorbed during impact test increased from 20.7 kJ to 22.6 kJ by using nano-SiO2 alternative to micro-SiO2 particles in PP/glass- bre matrix. Even though a respective enhancement in mechanical properties were observed by using nano llers over micro llers, no signi cant di erence in particle emission during impact test were measured. Further, it could be shown that during drilling and testing, nano-sized particles were released from all materials studied, regardless of whether they had nanoparticles integrated or not. In one particular case, the neat polymer matrix generated more nano-sized particles during drilling than the exfoliated PA6/nanoclay nanocomposite. Hence, the addition of nanoclay can have bene cial impact in terms of controlled particle release. However, in general the addition of nano llers increased the particle emission rates during drilling and impact testing of the nanocomposites. Further, the emitted nano-sized particles were not all free engineered pristine nanoparticles but also hybrid particles consisting of matrix/nano ller material. A signi cant set of data was obtained during this study and hence the outcomes sets an excellent foundation for risk assessment and life cycle analysis of silica based polypropylene, polyamide and polyurethane nanocomposites.Item Open Access Particle emission measurements in three scenarios of mechanical degradation of polypropylene-nanoclay nanocomposites(Elsevier, 2020-08-14) Blazquez, María; Marchante, Veronica; Gendre, Laura; Starost, Kristof; Njuguna, James; Schutz, Jurg A.; Lacave, José María; Egizabal, Ainhoa; Elizetxea, Cristina; Cajaraville, Miren P.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.Item Open Access Safety assessment of novel polymer-silicon composites - from LCA perspective(Publications Office of the European Union, 2012-12) Zhu, Huijun; Irfan, Adeel; Sachse, Sophia; Njuguna, JamesThe fast growing trend in the development of novel materials with potential applications in many industrial sectors has caused concerns over the environment and human health effect of the emerging activities and associated products. It is imperative that these concerns are addressed in a holistic manner as early as possible. As part of the NEPHH project, this study applied the LCA concept aiming to identify hazardous nanoparticles (NP) that could be released during the development and application of novel products, focusing on polymeric-silicon composites in recognition of their attractions to a wide range of industries, including construct engineering, automotive and aerospace.