TY - THES
T1 - Hot-pressed Saloplastics as Sustainable Ion-exchange Membranes
AU - Krishna B, Ameya
N1 - Ameya was born in Bangalore, India. He was schooled at Shri Aurobindo Memorial School and high-schooled at Deeksha Center for Learning, with majors in Physics, Chemistry, and Mathematics, and a minor in Computer Science.
He pursued a bachelor’s degree in Chemical Engineering at BMS College of Engineering. As a research assistant, his 2 year project on low cost Solar distillation for purifying water won the Sustainable Energy Challenge in the International Year of Sustainability- 2012. His bachelor’s thesis was on Biodiesel production using sustainable natural catalysts sourced from local seashells and red soil.
In 2014, Ameya moved to Germany for a Master’s degree in Chemical and Energy Engineering at Otto-van Guericke Universität, Magdeburg. Minor projects as a research assistant included COMSOL simulations of the physical impacts on cow-liver, MATLAB/Star-CCM+ simulations for fluid dynamics around a micro-aircraft, and experimental Fuel cell stack testing. His low inclination towards coding and simulations, led him to work on an experimental thesis at the Max Planck Institute for Dynamics of Complex Technical Systems, on enhancing catalyst coated membranes for Hydrogen energy in Electrolysers and Fuel cells. After graduating, he worked as a guest Scientist at the same institute.
In 2018, he moved to the Netherlands where started working on Polyelectrolyte Complexation based ion-exchange membranes with Prof. Dr. ir. Wiebe M. de Vos (Membrane Surface Science, MST) and Dr. ir. Saskia Lindhoud (Dept. of Molecules and Materials) at the MESA+ Institute of Nanotechnology, University of Twente.
100% MST. But MNF is co-supervisor.
PY - 2022/7/14
Y1 - 2022/7/14
N2 - Ameya Krishna B is a researcher in the Membrane Surface Science group led by Prof. Dr. ir. Wiebe M. de Vos and Dept. of Molecules and Materials supervised by Dr. Saskia Lindhoud. In his work, complexes of charged polymers are softened with salt, and are used to fabricate dense material and further used as membranes for ion-exchange.The thesis begins with an introductory Chapter 1 that places the work in the context of the needs of today and describes its objective in a larger frame. It informs the reader about membranes, especially for ion-exchange, including the principles governing transport through such materials. Polyelectrolytes and their complexes are introduced, and their processing into saloplastics is discussed. The advantages, especially in terms of simplicity and sustainability, of saloplastic membranes, are highlighted.For the fabrication of dense saloplastics, the first pair of polyelectrolytes, PSS-PDADMA, is chosen in Chapter 2 and suitable conditions for their complexation are studied. Factors for complexation, such as molecular weight, concentrations, and salt content, and those for hot pressing, such as saltwater, temperature, pressure, and time, are explored. A mould is constructed and edges of different thicknesses are utilized to achieve control over the thickness of saloplastic films with a variation of just ̴5%. Suitable plastics are fabricated and their physical and mechanical properties are investigated. Increased mechanical strengths were observed following reinforcement of the saloplastics with woven and non-woven mats, all during the process of hot-pressing. Patterned projections in the micro-scale were also achieved by using suitable moulds.The dense and charged nature of hot-pressed plastics led to the exploration of their membrane characteristics in Chapter 3. PSS-PDADMA combined in a stoichiometric ratio resulted in a positively charged saloplastic. At low salt concentrations (0.01-0.05 M KCl), it was observed to have permselectivity up to 96%, while at higher salt concentrations (0.05-0.25 M KCl) the values were < 60%. These effects were attributed to a relatively low charge density, as confirmed by a higher degree of swelling and lower ion exchange capacity than commercial membranes. The resistances were low, and the membrane showed a relevant mono to divalent anion selectivity. The membrane also showed good stability at low and high pH, the latter being an advantage for applications at extreme pH values.To study the behaviour of other polyelectrolyte combinations, weak polyelectrolytes were introduced in Chapter 4. An important addition is the study of non-stoichiometry and its effect on the quality of the polyelectrolyte complex, and in turn, that of the plastic. A change in the polyelectrolyte ratio introduced changes in the quantity and sign of the net charge in the saloplastic, while also altering other properties. These changes were different for each pair and did not necessarily follow the change in type or percentage of excess polyelectrolyte introduced. A first negatively charged membrane was obtained from PSS-PVA and showed good ion-exchange properties. Weak-weak polyelectrolyte pairs were observed to lead to precipitates that were too soft and sticky to be processed.Excess Na+ is known to be a major cause of soil toxicity and abiotic stresses in plants, especially in greenhouses and dry regions. The agricultural importance of K+ selectivity over Na+ is explained in Chapter 5, and an approach to enrich the K+ concentration is proposed. PSS:PVA saloplastics fabricated at 1:2.5 ratio were found to be modestly monovalent-monovalent K+/Na+ cation-selective, improving the selectivities observed for commercial membranes. A hypothesis is presented and the possible causes are discussed.The ‘sustainability’ aspect of such dense saloplastics is further researched in Chapter 6 in terms of recyclability and non-autonomous self-healing properties. Saloplastics are shown to be recyclable over five times by the addition of high salt concentrations, filtering out any impurities, diluting to complexation conditions, and finally hot pressing. They are also demonstrated to be self-healing whenassisted by saltwater, which would be very handy, especially in saltwater applications. The advantage of salt-plasticized materials and their role in annealing is emphasized, leading to neutral plastics. Salt-annealing slightly loosens the chains and facilitates the incorporation of active enzymes in saloplastics. This is demonstrated using lysozyme, an antimicrobial enzyme that catalyzes the hydrolysis of bacterial cell walls. It is shown by lysozyme activity that the lysozyme is incorporated and remains active in the saloplastic.A final chapter puts forth a general discussion and some thoughts on possible directions the work can be continued in.
AB - Ameya Krishna B is a researcher in the Membrane Surface Science group led by Prof. Dr. ir. Wiebe M. de Vos and Dept. of Molecules and Materials supervised by Dr. Saskia Lindhoud. In his work, complexes of charged polymers are softened with salt, and are used to fabricate dense material and further used as membranes for ion-exchange.The thesis begins with an introductory Chapter 1 that places the work in the context of the needs of today and describes its objective in a larger frame. It informs the reader about membranes, especially for ion-exchange, including the principles governing transport through such materials. Polyelectrolytes and their complexes are introduced, and their processing into saloplastics is discussed. The advantages, especially in terms of simplicity and sustainability, of saloplastic membranes, are highlighted.For the fabrication of dense saloplastics, the first pair of polyelectrolytes, PSS-PDADMA, is chosen in Chapter 2 and suitable conditions for their complexation are studied. Factors for complexation, such as molecular weight, concentrations, and salt content, and those for hot pressing, such as saltwater, temperature, pressure, and time, are explored. A mould is constructed and edges of different thicknesses are utilized to achieve control over the thickness of saloplastic films with a variation of just ̴5%. Suitable plastics are fabricated and their physical and mechanical properties are investigated. Increased mechanical strengths were observed following reinforcement of the saloplastics with woven and non-woven mats, all during the process of hot-pressing. Patterned projections in the micro-scale were also achieved by using suitable moulds.The dense and charged nature of hot-pressed plastics led to the exploration of their membrane characteristics in Chapter 3. PSS-PDADMA combined in a stoichiometric ratio resulted in a positively charged saloplastic. At low salt concentrations (0.01-0.05 M KCl), it was observed to have permselectivity up to 96%, while at higher salt concentrations (0.05-0.25 M KCl) the values were < 60%. These effects were attributed to a relatively low charge density, as confirmed by a higher degree of swelling and lower ion exchange capacity than commercial membranes. The resistances were low, and the membrane showed a relevant mono to divalent anion selectivity. The membrane also showed good stability at low and high pH, the latter being an advantage for applications at extreme pH values.To study the behaviour of other polyelectrolyte combinations, weak polyelectrolytes were introduced in Chapter 4. An important addition is the study of non-stoichiometry and its effect on the quality of the polyelectrolyte complex, and in turn, that of the plastic. A change in the polyelectrolyte ratio introduced changes in the quantity and sign of the net charge in the saloplastic, while also altering other properties. These changes were different for each pair and did not necessarily follow the change in type or percentage of excess polyelectrolyte introduced. A first negatively charged membrane was obtained from PSS-PVA and showed good ion-exchange properties. Weak-weak polyelectrolyte pairs were observed to lead to precipitates that were too soft and sticky to be processed.Excess Na+ is known to be a major cause of soil toxicity and abiotic stresses in plants, especially in greenhouses and dry regions. The agricultural importance of K+ selectivity over Na+ is explained in Chapter 5, and an approach to enrich the K+ concentration is proposed. PSS:PVA saloplastics fabricated at 1:2.5 ratio were found to be modestly monovalent-monovalent K+/Na+ cation-selective, improving the selectivities observed for commercial membranes. A hypothesis is presented and the possible causes are discussed.The ‘sustainability’ aspect of such dense saloplastics is further researched in Chapter 6 in terms of recyclability and non-autonomous self-healing properties. Saloplastics are shown to be recyclable over five times by the addition of high salt concentrations, filtering out any impurities, diluting to complexation conditions, and finally hot pressing. They are also demonstrated to be self-healing whenassisted by saltwater, which would be very handy, especially in saltwater applications. The advantage of salt-plasticized materials and their role in annealing is emphasized, leading to neutral plastics. Salt-annealing slightly loosens the chains and facilitates the incorporation of active enzymes in saloplastics. This is demonstrated using lysozyme, an antimicrobial enzyme that catalyzes the hydrolysis of bacterial cell walls. It is shown by lysozyme activity that the lysozyme is incorporated and remains active in the saloplastic.A final chapter puts forth a general discussion and some thoughts on possible directions the work can be continued in.
KW - polyelectrolyte
KW - Polyelectrolyte complex
KW - Polyelectrolyte complex(es)
KW - Polyelectrolyte complexation
KW - polyelectrolyte multilayers
KW - Polyelectrolyte(s)
KW - membranes
KW - membrane
KW - Membrane filtration
KW - Membrane impedance
KW - Membrane potential
KW - Membrane preparation and structure
KW - Membrane resistance
KW - membrane transport
KW - membrane composition
KW - Membrane extraction process
KW - ion analysis
KW - Ion exchange
KW - Ion exchange membrane
KW - Ion exchange membranes
KW - Ion exchanger
KW - Saloplastic
KW - plastic
KW - plastic packaging waste; packaging recycling; circular economy; The Netherlands
KW - plastic packaging waste; recycling; recycling targets;polymer purity; quality of recycled plastics; limits
KW - Plastic deformation
KW - Plastic injection moulding
KW - plastic sorting
KW - plastic waste
KW - Plasticity
KW - Plasticization
KW - Plasticizer
KW - plastics
KW - Recyclability
KW - Recycling
KW - self healing materials
KW - Tensile
KW - tensile and compressive tests
KW - Tensile experiment
KW - Tensile properties
KW - Tensile property
KW - Tensile strain
KW - Tensile strength
KW - Tensile stress
KW - tensile test
KW - Tensile testing
KW - Tensile-compressive cyclic tests
KW - Resistance
KW - soil surface characteristics
KW - Soil loss
KW - soil
KW - Monovalent-selective
KW - Monovalent-selectivity
U2 - 10.3990/1.9789036554084
DO - 10.3990/1.9789036554084
M3 - PhD Thesis - Research UT, graduation UT
SN - 978-90-365-5408-4
VL - 1
PB - University of Twente
CY - Enschede
ER -