Process and Chemical Engineering - Doctoral Theses

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    Dairy powder breakage: mechanisms, impact factors, and influences on powder properties
    (University College Cork, 2022-05) Han, Jie; Miao, Song; Fitzpatrick, John J.; Cronin, Kevin; Teagasc; University College Cork
    Dairy powders provide a good form for convenient and stable preservation and transportation of milk ingredients, and most commercial dairy powders are agglomerated to improve powder functionalities. However, particle breakage during production and transportation is an important issue for agglomerates and only a few studies on dairy powder breakage have been published. Therefore, there is limited information to understand this phenomenon and find ways to decrease it. The present study investigated the breakage mechanisms of dairy powders, the influence of dairy powder breakage on powder properties, and the impact of powder characteristics on dairy powder breakage. This provides more information to better understand and control dairy powder breakage in an effort to improve the functionalities of dairy powders. The main breakage mechanisms of agglomerated infant milk formula (IMF) during transportation and mixing included dispersion, chipping (surface breakage), and fragmentation (body breakage, which includes both disintegration and splitting), which correspond to an increasing extent of breakage. The breakage mechanism of whole samples was one or a combination of breakage mechanisms because the breakage behaviour of samples with different particle sizes at the same process condition was different. Dairy powder breakage significantly decreased the particle size and porosity of powders and increased the specific surface area, particle density, and bulk density of samples. It also changed the shapes and surface composition of particles as seen with the increase in lactose content and the decrease in protein and fat contents for most samples. These changes in physical properties significantly deteriorated the rehydration properties of dairy powders, including the wettability and dispersibility, while it had only a small influence on powder flowability. In addition, body breakage had greater influences on powder physical properties than surface breakage. Thus, surface breakage had no influence on water sorption and mechanical properties of powders but body breakage significantly deteriorated these properties as seen with the increase in water sorption rates and final water contents, the acceleration in the crystallization, and the decrease in the overall molecular mobility. Dairy powder breakage degree or mechanisms was determined by the process conditions and particle characteristics. Breakage increased with increasing intensity of processing conditions, such as the transportation velocity and air pressures. In addition, fatigue affected the breakage of agglomerates dairy powders. For powder characteristics, the breakage degree of dairy powders increased with increasing particle size and decreasing particle structural strength. Considering particle structure, the strength of crystals and continuum solids were the highest, followed by particles with numerous holes throughout the particle, followed by the hollow sphere particle with a very thin shell. Under the same spray drying conditions, the formulation of dairy powders significantly affects dairy powder breakage by influencing the physical properties of powder particles, especially for particle size and particle structure. For whey protein/lactose model agglomerated powders, the two higher whey-protein powders were smaller in particle size, were less irregular in shape and had higher particle densities, which resulted in less breakage in comparison to the two lower whey-protein powders. For agglomerated model IMF powders that contained different protein and carbohydrates, whey protein powders were bigger in particle size, weaker in structural strength, and more irregular in shape in comparison to pure casein powders. This resulted in the better rehydration properties of whey protein powders but more breakage. Similarly, sucrose IMF samples had better rehydration properties but suffered more breakage than maltodextrin and pure lactose powders because of their bigger particle size. Findings in this study indicate that body breakage significantly deteriorates powder properties, so breakage should be limited to surface breakage. Since powder breakage cannot be avoided, changes to processing conditions (using lower conveying speeds or air pressures) and powder physical properties (mainly particle size and particle structure by changing production conditions or formulations) should be done to reduce breakage intensity.
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    Electrochemical materials for integrated magnetics
    (University College Cork, 2021-06-23) Smallwood, Daniel C.; Rohan, James; McCloskey, Paul; Science Foundation Ireland
    Next generation microinductors with magnetically enhanced VIA technology hold great promise for power converter applications in broad technology domains such as automotive, space, high-end computing, mobile devices, radio frequency (RF), artificial intelligence (AI) and the internet of things (IoT). Microinductor VIAs enable monolithic 3D device topologies with reduced footprint, increased inductance density and minimal parasitics. These qualities are essential for emerging 2.5/3D packaging architectures that require granular point-of-load (PoL) power delivery to efficiently supply a multitude of heterogeneously integrated devices. This thesis addresses the challenges of 3D monolithic microinductor design and fabrication, inclusive of magnetically enhanced VIAs comprising a clad laminated soft magnetic core. The current state-of-the-art utilizes 2D microinductor topologies and 2D fabrication methods, therefore significant advancement is required to enable fabrication of a novel 3D monolithic microinductor device comprising vertically oriented integrated magnetics. The major challenges addressed in this thesis fall into two main categories: 1) predictive modeling with computational lithography and computational electrochemistry to enable optimization of the VIA formation process and 2) the design and fabrication of a novel magnetically enhanced monolithic 3D microinductor device. A major contribution from the computational lithography is the derivation of a novel polychromatic light attenuation equation that is used to produce a succinct formula comprising a complete coupling between resist photochemistry and light diffraction effects. Additionally, new photoresist exposure dose determination methods are presented that negate the need for time consuming and costly in-situ metrology. These equations and methods enable fast and accurate predictive modeling of 3D photoresist VIA latent images, which are verified by comparison to directly corresponding experimental work, with highly positive correlation. These formulas converge quickly on the average modern computer and can be readily integrated into lithography simulators. Photoresist development is then investigated, wherein spin development is identified as the optimal method for wet etching VIA latent images. With computational electrochemistry, the electroforming process of Cu VIAs is explored using the FEM in COMSOL Multiphysics to perform 2D and 3D time-dependent simulation studies. Simulations are then verified by comparison to experimental results, with highly positive correlation. Special attention is given to electroformed surface topographies, which is valuable for sensor and flip chip applications. The major contributions from the microinductor device design and fabrication first include designing a unique device that meets target specifications for reduced footprint, increased inductance density and minimized parasitics. A novel fabrication process flow is next engineered to enable a vertically meandering current path with a repeating unit cell comprising a bottom interconnect, a first Cu VIA, a top interconnect and a second Cu VIA. This process flow is compatible with conformal deposition of a soft magnetic laminate (e.g., CoZrTa) for formation of a vertically oriented magnetic core clad on the Cu VIAs. Next, a 5-tiered photomask stack is designed and the corresponding SOPs are engineered. This enables fully in-house microinductor device fabrication, after which vital metrology and characterization is performed. The measured inductance density of our prototype magnetically enhanced monolithic 3D microinductor devices is 16.85 nH/mm2, which is comparable to previously reported metrics for fabricated 3D microinductors. This metric could be significantly improved in future devices by increasing the magnetic core thickness and/or optimizing the magnetic anisotropy characteristic of the integrated magnetic material and/or reducing the pillar diameter, wherein the VIA fabrication research presented in this thesis will be essential. Therefore, this novel microinductor research holds great promise for applications in next generation power converters.
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    Sustainability analysis of biopharmaceuticals manufacturing
    (University College Cork, 2020-04-30) Lalor, Fergal; Byrne, Edmond P.; Fitzpatrick, John J.; Sage, Colin
    The production of biopharmaceutical treatments is increasing globally at a rapid pace, leading to the treatment of more and more disorders, many of which historically were untreatable and debilitating. This increase in production poses sustainability concerns, with economic unsustainability from erratic returns on investment, societal concerns around treatment cost and access, and a dearth of published research on pathways to environmentally sustainable production methods. Recombinant protein production by perfusion cell culture under stainless-steel and single-use technologies was investigated using life cycle assessment (LCA) to determine the impact on environmental factors. The ReCiPe for LCA method was utilised, and the single-use scenario was found to result in 40% impacts than stainless-steel alternative across all production volumes. Factors influencing the difference in environmental impacts include infrastructural variables, such as the electricity source to the facility, and process variables, such as the interval between ultrafiltration/diafiltration batches. The feasibility of environmentally sustainable manufacturing processes were investigated, with novel technologies such as water-for-injection (WFI) production by reverse osmosis, the use of biologically-sourced polymeric materials for single-use items and the benefits of increased containment using single-use equipment on cleanroom maintenance evaluated. The results of this analysis indicate reductions in environmental impacts across both single-use and stainless-steel scenarios of 60%, but with further research required to fully understand the process impacts resulting from adopting these technologies. A multiple-criteria decision-making framework was developed to evaluate the economic, environmental and social sustainability of biopharmaceutical manufacturing processes under varying value orientations, enabling the comparison of treatments produced under different modalities. This framework may be utilised to assess treatments for regulatory approval and governmental reimbursement in a holistic manner, as opposed to a reductionist economic standpoint. Further research is required to account for greater complexities in the biopharmaceutical industrial system such as feedback loops between various stakeholders and to provide and document indices from existing processes to be used for evaluation of prospective treatments.
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    Characterisation and improvement of the rehydration behaviour of high-protein milk powder
    (University College Cork, 2020-08-03) Wu, Shaozong; Fitzpatrick, John J.; Cronin, Kevin; Miao, Song; University College Cork; Teagasc; China Scholarship Council
    Milk protein isolate (MPI) has poor rehydration behaviours, particular in wetting and dissolution. The rehydration difficulty inhibited the achievement of MPI functionality. Methods were explored to solve rehydration difficulty. Agglomeration was a valid method for enhancing the wetting of dairy powder. Moreover, broadband acoustic resonance dissolution spectroscopy (BARDS) monitored gas release from powder through the alteration of speed of sound in solution. Thus, BARDS was utilised to study the gas release behaviour of agglomerated MPI, and MPI coated with emulsifiers. Meanwhile, as MPI composed mainly by casein, pH of solution affected the status of casein which possibility modify the rehydration process of MPI as well. Real-time measurement of particle size was applied to analyse the effect of pH on rehydrating MPI. Sodium carbonate, as an alkali food additive, was firstly studied at rehydrating dairy powder. However, alkalization of MPI followed by neutralization has been thoroughly investigated. Consequently, considering the effect of calcium chelation on MPI, citric acid was utilised to neutralise MPI from alkalization. Finally, the gelation behaviour of MPI was studied in a different sequence of neutralisation. Our results showed that as the porous structure modified the gas distribution in agglomerated MPI, interstitial air within agglomerates and vacuole air within agglomerates determined the gas release behaviour of agglomerated powder, while the vacuole air in primary powder particle became a crucial barrier for MPI dissolution. The BARDS profile showed that there was faster initial gas release from the agglomerates, indicating better wetting and dispersion ability of the agglomerates. The gas release of MPI during the wetting step was facilitated by lecithin and Tween 80 while the dissolution step was still poor. The wetting behaviour of MPI covered by the emulsifiers was greatly improved except for samples coated with 4% lecithin. The most instant wetting behaviour was observed when coating MPI with Tween at the larger size fractions. The swelling of the primary particle was observed in alkalization, which was ascribed to the swelling of casein micelle aggregates. This swelling of casein micelle aggregates indicates greater water penetration and loosening of the aggregate structure at higher pH, which facilitated the faster dissolution of MPI powder, especially at pH 8.4. As alkalization proved an excellent ability at the dissolution of MPI, sodium carbonate was utilised, which also showed improvement of MPI rehydration. Sodium carbonate was supposed as a calcium chelation as well to modifying the structure of casein micelle. The results showed that wettability worsened with higher sodium carbonate concentrations, due to strong films developing at the powder/water interfaces which inhibited water penetration into the MPI. However, appropriate agitation could effectively wet and disperse MPI. On the other hand, particle size and centrifugal sedimentation studies showed that increasing the sodium carbonate concentration greatly improved the dissolution ability of the MPI powder. The subsequent neutralisation process by citric acid enhanced the effects of calcium chelation due to reaction-product citrate. Besides, alkalization and neutralisation created larger colloidal particle size, which is hypothesised as being a dynamic balance between micellar casein and non-micellar casein. The sequence of neutralisation determined the process of rehydration, which in turn determine the gelation process. As for the gelation time and gel stiffness, performing alkalization firstly before neutralisation had a better result corresponding with increasing mobile casein molecule by improved rehydration, exhibiting homogeneous gel structure.
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    Mass transfer analysis of gas exchange through microperforated packaging films
    (University College Cork, 2017) Viana Ramos, Andresa; Oliveira, Jorge C.; Sousa Gallagher, Maria J; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior; Department of Agriculture, Food and the Marine
    The primary purpose of this work was to provide robust tools for the design of perforated packaging based on rigorous mathematical methods. A dimensionless correlation was established based on the identification of the variables affecting mass transfer through perforations. It was proved that the diameter of the perforation is the most important parameter. Air velocity and temperature (via its effect on viscosity and density of air) and diffusivity of gases through air are also relevant to this analysis. The Buckingham π Theorem was applied to identify the dimensionless numbers that provide a dimensionless correlation availing of the principle of dynamic similarity to predict the mass transfer coefficients of both oxygen and water vapour through perforations. As films tend to be much more permeable to water than to oxygen, a study on the effect of water (humidity) on films was also performed. It was found that diffusion and hence permeability can be significantly affected by the water content of the films and therefore the humidity of the atmospheres that the films are exposed to on both sides. A methodology was applied combining the William, Landel and Ferry and the Gordon-Taylor equations with the isotherm of water sorption to obtain the correct effective permeability of films during storage depending on the relative humidity. A methodology was also developed to analyse leakage flow in sealed packages in order to identify the relevant parameters that influence their variability and provide the most robust sealing conditions. The results on this thesis provide substantial data and rigorous mathematical approaches for a more efficient and accurate packaging design to achieve maximum shelf life.