Papers by Maurice Collins
Emergent materials, May 20, 2024
In this study, novel biocomposites composed of CO 2 -derived poly(propylene) carbonate and plant-... more In this study, novel biocomposites composed of CO 2 -derived poly(propylene) carbonate and plant-based cellulose were developed employing solvent casting technique. An innovative and rapid strategy was employed, whereby pre-dissolving cellulose improves dramatically the compatibility of poly(propylene) carbonate with cellulose whilst pristine cellulose powder displays inhomogeneous distributions of cellulose within the biocomposite. Resulting biocomposites produce flat homogeneous surfaces with low cellulose content, whilst rougher surfaces and thicker cross sections were observed in films with higher cellulose content. Developed biocomposites outperformed biocomposites produced from pristine cellulose powder in terms of homogeneity, thermal stability, antioxidant activity and biocompatibility. Higher cellulose content samples show the formation of a new hydrogen bonding network between PPC and cellulose polymer chains and this contributes to improved thermal stability. TGA results reveal improved thermal stability for high cellulose content films and show enhanced water vapor permeability. A cell viability study shows that the developed materials are biocompatible. Curcumin, a natural antioxidant, was incorporated into optimized biocomposites to produce active biocomposites with antioxidant features to accelerate wound healing. Curcumin is shown to display a sustained release profile over a time period of 3 days, and this is ideal for would healing. The curcumin-functionalized biocomposites also contributed to enhanced thermal stability and water vapor permeability. Thus, these biocomposite films show promise as active biocomposites which can be used for biomedical applications such as wound healing.
Renewable Energy, Dec 1, 2018
Theoretical modelling techniques are used to compare the thermohydraulic performance and thermal ... more Theoretical modelling techniques are used to compare the thermohydraulic performance and thermal storage characteristics of molten salt, liquid sodium, and lead-bismuth in a CSP solar receiver concept. For molten salt, the performance of a number of heat transfer augmentation techniques are also studied. Sodium and lead-bismuth both yield excellent receiver thermal efficiency (max ∼92%), when compared to molten salt (max ∼ 90%), due to high thermal conductivity values that lead to large heat transfer coefficients. A high pressure drop penalty for lead-bismuth largely offsets its thermal performance gain over molten salt, however sodium retains its advantage as a receiver working fluid with a low pumping parasitic. The implementation of heat transfer enhancement techniques can significantly improve the performance of a molten salt receiver when compared to smooth tube designs. The low specific heat capacity and high unit cost of lead-bismuth is prohibitive towards its use as a storage medium in storage-integrated plant designs, resulting in very high LCOE values. Sodium is the most economically feasible fluid for systems with low storage (< 3 hour), however the low per-unit cost and high specific heat capacity of molten salt means that this is the most effective working fluid in systems with larger storage requirements.
Applied Energy, Nov 1, 2018
The nature in which a solar receiver in a concentrated solar power plant interacts with an accomp... more The nature in which a solar receiver in a concentrated solar power plant interacts with an accompanying heliostat field plays a significant role in plant performance and economics. An appropriate heat flux distribution should help deliver maximum receiver thermal performance, while minimising mechanical damage -thereby maximising power production and reducing costs. The current work presents an investigation into the thermal performance and mechanical reliability of a sodium-cooled solar receiver operating under heat flux profiles generated by a novel heliostat aiming strategy. A modification of the HFLCAL model is used to generate heat flux profiles for individual heliostats in a representative plant, and simulated annealing optimisation techniques are used to produce a novel heliostat aiming strategy. The importance of giving consideration to receiver limitations under non-uniform thermal boundary conditions in the development of a heliostat aiming strategy is demonstrated in this study, with mathematical optical, thermal, and mechanical models used to complete the analysis. An investigation has been conducted for a pointin-time resulting in maximum thermal loading conditions, with theoretical modelling techniques used to calculate receiver tube temperatures for aiming strategy yielded heat flux profiles, thereby allowing for the determination of heat losses and mechanical reliability through creep-fatigue damage. Results show that the simulated annealing algorithm can significantly improve heat flux homogeneity on the receiver, potentially reducing peak heat flux to less than 10% that of a single aiming point strategy, given an appropriate spillage allowance and aiming point grid size. A satisfactory configuration of spillage allowance and aiming grid size exists so as to supply maximum power to the receiver, while uniformly distributing the incident heat flux in order to meet mechanical reliability requirements. Based on the receiver design and conditions simulated in the analysis, a grid constructed of more than 81 aiming points (receiver area coverage of 32.7%), and an additional spillage allowance of 10% allows the receiver to deliver maximum power output while retaining mechanical durability through a 30 year plant life cycle.
Solar Energy, May 1, 2018
The receiver in a concentrated solar power (CSP) tower system accounts for a considerable proport... more The receiver in a concentrated solar power (CSP) tower system accounts for a considerable proportion of plant capital costs, and its role in converting radiant solar energy into thermal energy affects the cost of generated electricity. It is imperative to utilize a receiver design that has a high thermal efficiency, excellent mechanical integrity, minimal pressure drop, and low cost in order to maximize the potential of the CSP system. In the present work, thermal, mechanical, and hydraulic models are presented for a liquid tubular billboard receiver in a representative CSP plant. A liquid sodium heat transfer fluid as well as a number of receiver configurations of heat transfer area, tube diameter, and tube material have been analysed. The thermal analysis determines tube surface temperatures for an incident heat flux, thereby allowing for the calculation of thermal losses and efficiency. The mechanical analysis is carried out to establish creep deformation and fatigue damage that the receiver may undergo through a life service. The hydraulic analysis is concerned with calculating the required pumping power for each configuration. Results show that thermal efficiency increases for a decreasing heat transfer area, however reducing receiver area comes at the penalty of increasing tube surface temperatures and thermal stresses. The selection of tube diameter is critical, with small diameters yielding the greatest thermal efficiency and mechanical life, however the increased pressure drop reduces the overall plant efficiency due to a necessary increase in pumping power. The optimum receiver configuration is established by finding an appropriate trade-off between thermal performance, service life, pressure drop, and material costs, by using the levelized cost of electricity (LCOE) as the objective function. The analysis highlights necessary trade-offs required to optimise the design of a solar receiver.
Advanced Composites and Hybrid Materials
Peripheral nerve injury (PNI) often clinically relies on the use of nerve grafts taken from the p... more Peripheral nerve injury (PNI) often clinically relies on the use of nerve grafts taken from the patient to establish a therapeutic effect, though secondary site of injury and morbidity have prompted the medical community to find alternative solutions. A new trend in the development of biomaterials arises in the form of electro-conductive biomaterials, especially for electrically active tissues such as the peripheral nerves. In this work, novel poly(3,4-ethylenedioxythiophene) PEDOT nanoparticles (PEDOT NPs) were synthetized via the mini-emulsion method and were combined with silk fibroin (SF) to create conduits for PNI repair. The synthesized PEDOT NPs-loaded SF conduits showed optimal properties for peripheral nerve substitution from the physico-chemical and biological point of view. They displayed excellent mechanical and conductivity performance with the tensile moduli reaching 6.61 ± 0.55 MPa and the conduits reaching 5.4 · 10–4 S cm−1, respectively. The conduits did not possess...
Advanced Composites and Hybrid Materials/Advanced composites and hybrid materials, Mar 1, 2024
The efficient and economical conversion of low-grade waste heat into electricity has promising po... more The efficient and economical conversion of low-grade waste heat into electricity has promising potential to combat the greenhouse effect and expedite the shift towards sustainable development. This study presents an innovative and appealing approach through the utilization of lignin, an abundant waste product derived from the paper and pulp industry, to develop hydrogels as compelling and sustainable materials for application in ionic thermoelectricity. Various compositions were evaluated to examine the impacts of varying lignin concentrations, types of electrolytes, concentrations of crosslinkers, and electrolyte concentrations on the ionic thermoelectric performance of the hydrogels. The optimized lignin-derived hydrogel, infiltrated with a 6 M KOH electrolyte, demonstrates high ionic conductivity (226.5 mS/cm) and a superior Seebeck coefficient of 13 mV/K. This results in a remarkable power factor (3831 µW/m•K 2 ) that leads to an impressive Figure of merit (ZT i ) (3.75), surpassing most of the existing state-of-the-art materials and making it the most efficient sustainable ionic thermoelectric material reported until now. These findings underscore the exceptional performance of lignin-based hydrogels in the realm of low-grade waste energy harvesting applications. The present study contributes to address the challenges posed by waste heat through effectively harnessing low-grade waste heat through the utilization of sustainable lignin-based hydrogels while reducing the reliance on fossil fuels and minimizing greenhouse gas emissions.
Journal of Applied Polymer Science, Jan 23, 2018
Currently, the most widely used binder in batteries is polyvinylidene fluoride (PVDF) with N-meth... more Currently, the most widely used binder in batteries is polyvinylidene fluoride (PVDF) with N-methyl-2pyrrolidone (NMP) used as a solvent. This solvent is flammable and toxic. Here we focus on the suitability of using water soluble sodium alginate (Na-alginate) and sodium carboxymethyl cellulose (Na-CMC) as alternative biobased binder materials for the anodes of lithium ion batteries. It reduces the environmental impact of current manufacturing processes. However, control of the rheological characteristics of the binder whilst containing active and conductive additives is key for optimised processing. Here we perform stability and rheological measurements of Na-alginate and Na-CMC solutions containing varying amounts of graphite and carbon black used as active and conductive materials respectively. Comparing to the benchmark Na-CMC, the degree of flocculation shows that for the same concentration of binder in water, Na-alginate suspensions are more stable. The rheology measurements show that Na-alginate slurries have a higher viscosity than Na-CMC at a shear rate of 50 s-1 with that for a 1.5% of Na-alginate binder being 1.26 Pa•s while for Na-CMC it was for 0.20 Pa•s. The loss factor was lower for Na-Alginate, between 2 and 3 against between 2.9 and 3.3 for Na-CMC, showing a more developed network structure.
Physical properties of crosslinked hyaluronic acid hydrogels
Journal of Materials Science: Materials in Medicine, Jun 5, 2008
In order to improve the mechanical properties and control the degradation rate of hyaluronic acid... more In order to improve the mechanical properties and control the degradation rate of hyaluronic acid (HA) an investigation of the structural and mechanical properties of the hydrogels crosslinked using divinyl sulfone (DVS), glutaraldehyde (GTA) and freeze-thawing, or autocrosslinking has been carried out. The thermal and mechanical properties of the gels were characterised by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and compression tests. The solution degradation products of each system have been analysed using size exclusion chromatography (SEC) and the Zimm-Stockmayer theory applied. Autocrosslinked gels swell the most quickly, whereas the GTA crosslinked gels swell most slowly. The stability of the autocrosslinked gels improves with a reduction in solution pH, but is still poor. GTA and DVS crosslinked gels are robust and elastic when water swollen, with glass transition values around 20 degrees C. SEC results show that the water soluble degradation products of the gels show a reduction in the radius of gyration at any particular molecular weight and this is interpreted as indicating increased hydrophobicity arising from chemical modification.
Solar Energy, Dec 1, 2019
An integrated optical-thermal-mechanical model is used to simulate the interaction between a heli... more An integrated optical-thermal-mechanical model is used to simulate the interaction between a heliostat field and sodium-cooled receiver through diurnal CSP plant operation. The cumulative heat flux on the receiver is controlled using a heliostat aiming strategy. A semi-empirical heat transfer model returns the receiver thermal profile based on the incident heat flux map, with aiming strategy solutions regulated by allowable flux density (AFD) data. A number of tube materials and inlet-outlet temperature combinations are investigated, with receiver thermal power output indicating suitable constructions for the delivery of elevated temperatures required for advanced power cycles. The selection of tube material is critical in maximising the heat absorption capabilities. The excellent creep-fatigue strength of Inconel 617 and Haynes 230 at high temperature yields a potential improvement in daily power output of up to 18% over more conventional heat exchanger materials. For these more traditional alloys, the aiming strategy requires a greater spillage allowance in order to generate a heat flux profile that satisfies lower mechanical reliability limits. The Ni-based superalloys alloys permit operation to temperatures far beyond conventional limits (> 700 • C), however the net power output is curtailed by greater heat losses at the receiver and an increased spillage requirement due to diminishing AFD levels.
Electrically conductive bio-scaffolds are being explored in the field of tissue engineering (TE) ... more Electrically conductive bio-scaffolds are being explored in the field of tissue engineering (TE) as a solution to address the clinical need of electroactive tissues, finding applications in nervous, cardiac, and spinal cord injury repair. In this work, we synthesise polypyrrole nanoparticles (PPy NP) via the mini-emulsion method with further combination with a gelatin/hyaluronic acid (HA) hydrogel to create electro-conductive Gel:HA:PPy-NP TE scaffolds. The electro-conductive Gel:HA:PPy-NP scaffolds possess excellent mechanical properties at 1.08 ± 0.26 MPa, closely matching to reported spinal cord mechanical performance. Scaffolds were designed with controlled porosity of 526.2 ± 74.6-403.9 ± 57.4 µm, and conductivities of 4.3×10− 6±1.1×10− 6 S.cm− 1 were reached. Rheological studies show that prior to lyophilisation, the Gel:HA:PPy-NP hydrogels display a shear-thinning behaviour. These gels were subsequently 3D printed into predefined 2 layer lattice geometries and displayed excel...
Synthesis and characterization of gelatin/lignin hydrogels as quick release drug carriers for Ribavirin
International Journal of Biological Macromolecules
Sustainable lignin precursors for tailored porous carbon-based supercapacitor electrodes
International Journal of Biological Macromolecules
Cinnamaldehyde was immobilized to O-amine functionalized chitosan via a coupling reaction. Fourie... more Cinnamaldehyde was immobilized to O-amine functionalized chitosan via a coupling reaction. Fourier transform infrared spectroscopy confirmed N-cinnamyl substitution. Wetting analyses demonstrate more hydrophobicity in the N-cinnamyl substituted O-amine functionalized chitosan compared to chitosan or unsubstituted O-amine functionalized chitosan. Thermal gravimetric analysis and differential scanning calorimetry demonstrates that the prepared N-cinnamyl substituted O-amine functionalized chitosan exhibits higher thermostability than unmodified chitosan at temperatures in which polysaccharides are commonly stored and utilised. The N-cinnamyl substituted O-amine functionalized chitosan, against four different bacteria strains [two gram-positive (Staphylococcus aureus and Bacillus cereus) and two gram-negative (Escherichia coli and Pseudomonas aeruginosa)], displays promotion of inhibition activity against these bacterial strains. Finally, the antioxidative activity of the N-cinnamyl su...
Physical properties of crosslinked hyaluronic acid hydrogels
Journal of Materials Science: Materials in Medicine, 2008
In order to improve the mechanical properties and control the degradation rate of hyaluronic acid... more In order to improve the mechanical properties and control the degradation rate of hyaluronic acid (HA) an investigation of the structural and mechanical properties of the hydrogels crosslinked using divinyl sulfone (DVS), glutaraldehyde (GTA) and freeze-thawing, or autocrosslinking has been carried out. The thermal and mechanical properties of the gels were characterised by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and compression tests. The solution degradation products of each system have been analysed using size exclusion chromatography (SEC) and the Zimm-Stockmayer theory applied. Autocrosslinked gels swell the most quickly, whereas the GTA crosslinked gels swell most slowly. The stability of the autocrosslinked gels improves with a reduction in solution pH, but is still poor. GTA and DVS crosslinked gels are robust and elastic when water swollen, with glass transition values around 20 degrees C. SEC results show that the water soluble degradation products of the gels show a reduction in the radius of gyration at any particular molecular weight and this is interpreted as indicating increased hydrophobicity arising from chemical modification.
Morphology of crosslinked hyaluronic acid porous hydrogels
Journal of Applied Polymer Science, 2010
Hydrogels, based on hyaluronic acid or hyaluronan (HA), are gaining attention as possible cell‐sc... more Hydrogels, based on hyaluronic acid or hyaluronan (HA), are gaining attention as possible cell‐scaffolding materials for the regeneration of a variety of tissues. This article describes how HA, a naturally occurring polymer, has been crosslinked to reduce its degradation rate and freeze dried to produce porous materials suitable for tissue engineering. The resulting pore architecture has been assessed as a function of freezing temperature and freezing rate, type of crosslinkers, and methods used in the crosslinking process. On comparing the average densities of crosslinked and uncrosslinked scaffolds, it is apparent that the chemical modification increases sponge density and wall thickness of the pores while decreasing the pore size. The mechanical response of the modified materials has been investigated by equilibrium‐swelling measurements and compression tests. These materials have an average pore size ranging from 167 to 215 μm, which suggests that they would be a suitable tempor...
Journal of Applied Polymer Science, 2013
To ensure repeatability of these crosslinking procedures and thereby improve the degradation time... more To ensure repeatability of these crosslinking procedures and thereby improve the degradation time of hyaluronic acid (HA)‐based biomaterials in vitro, it is essential to have an understanding of the solution properties of HA. Control of HA dissolution is important because dissolution and solution degradation are concurrent processes during solution preparation. Complete dissolution is also important to maximize intermolecular crosslinking and reduce wasteful intramolecular reactions. Viscosity time profiles of HA solutions during dissolution have been obtained in order to optimize crosslinking efficiencies. Optimum dissolution occurs between 24 and 40 h when the HA is in a fully solvated disentangled state as indicated by the peak in the solvating curves which corresponds with Mark–Houwink α parameters of 0.76–0.85. The developed and characterized dissolution process was used to produce carbodiimide crosslinked HA films that were found to be reproducible and stable when immersed in ...
Journal of Applied Polymer Science, 2007
The effectiveness of four different reagents, glutaraldehyde (GTA), 1‐ethyl‐3‐(3‐dimethylaminopro... more The effectiveness of four different reagents, glutaraldehyde (GTA), 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide (EDC), poly(ethyelene glycol) diglycidyl ether (EX 810), and divinyl sulfone (DVS) as crosslinkers for cast hyaluronic acid (HA) films has been evaluated. Films were prepared by casting from solution and exposed to solutions of the crosslinkers in acetone–water solution. Swelling in water and in phosphate buffered saline (PBS) was then used to assess the effectiveness of the crosslinkers. GTA‐crosslinked films were found to be of low stability compared with those treated with EDC, EX 810, and DVS. Results suggest that instability in GTA‐crosslinked materials arises in part from residual acid catalyst. The effects of polymer molecular weight are not uniform. With GTA‐crosslinked film produced from higher molecular weight HA swells more, and this is attributed to reduced diffusion of the crosslinker, but with EDC, the opposite effect is observed, implying some additional ...
Research Square (Research Square), Jul 18, 2023
The use of carbon bre (CF) based composites is of growing global importance due to their applicat... more The use of carbon bre (CF) based composites is of growing global importance due to their applications in high end sectors such aerospace, automotive, construction, sports and leisure amongst others. It is forecast that composites will reach a global market value of $131.6 bn by 2024. However, their current high production cost, high carbon footprint and reduced production capability, limits their use to high performance and luxury applications. Approximately 50 % of the total cost of CF production is due to the thermal conversion of PAN precursor bre (PF) to CF as it involves the use of high energy consumption and low heating e ciency large furnaces. Looking at this scenario we propose in the present study to use microwave (MW) heating to convert PF to CF. This is scienti cally and technologically challenging since PF does not absorb microwave energy. Here, for the rst time we show how carbonisation temperatures of >1000 ºC can be reached in a matter of seconds through the use of a novel microwave (MW) susceptor nanocoating methodology developed via a Layer-by-layer assembly of multiwall carbon nanotubes (MWCNTs) on the PF surface. Remarkably, these CFs can be produced in an inexpensive domestic microwave and exhibit mechanical performance equivalent to CF produced using conventional heating. Additionally, we provide a life cycle and environmental impact analysis which shows that MW heating reduces the energy demand and environmental impact of lignin-based CF production by up to 66.8% and 69.5%, respectively.
Composites Based on Hyaluronic Acid and Inorganic Materials for Pharmaceutical and Biomedical Applications
Springer eBooks, 2023
Pb-free solder—microstructural, material reliability, and failure relationships
Elsevier eBooks, 2020
Abstract The establishment of near-eutectic Sn–Ag–Cu (SAC) alloys as replacements for eutectic Sn... more Abstract The establishment of near-eutectic Sn–Ag–Cu (SAC) alloys as replacements for eutectic Sn–Pb marked as the beginning for the development of lead-free solder alloy in electronic packaging industry. Second-generation lead-free alloys with lower Ag content were introduced to address the shortcomings such as poor mechanical shock performance and higher cost. Yet, the evolution has not stopped. In response to higher reliability requirements, third generation lead-free alloys are being developed to serve the applications operated in increasingly aggressive environments. In this chapter, case studies on thermal fatigue performance of various SAC-based lead-free solders and Sn–Zn-based low temperature solders have been made. The effect of solder size, solder composition, Sn grain morphology, printed circuit board surface finish, and thermal cycling profile on solder joint microstructure and reliability is evaluated. The relationship between microstructural evolution and thermal fatigue failure mechanism is discussed.
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Papers by Maurice Collins