Alex Kwasi Kumi

Bio: Alex Kwasi Kumi is an academic researcher from Donghua University. The author has contributed to research in topics: Fire retardant & Regenerated cellulose. The author has an hindex of 3, co-authored 6 publications receiving 34 citations.

Perovskite solar cell-hybrid devices: thermoelectrically, electrochemically, and piezoelectrically connected power packs

Abstract: Findings and reports in the field of perovskite solar cells (PSCs) have been phenomenal and embrace diverse perspectives such as technical issues, yielding, marketing, and environmental concerns. Bottlenecks in the structure, manufacturing, and operation of PSCs have been frequently addressed; the use of various means including crystallography and kinetics studies, simulation, material, solution, and surface/interface engineering, as well as their outcomes, have yielded certified efficiency of 23.7%. However, the short lifecycle, large waste-to-harvest ratio, functional failure during bending and in the dark mode, environmental and stability issues, and lack of power storage hinder their commercial viability. As a remedy, PSCs can be teamed up with one or multiple mechanical or thermal energy-harvesting or electrochemical power storage devices that can fully or partially overcome these nonidealities. Here, the means of integrating different devices with PSCs to form hybrid packs are discussed. The factors contributing toward the efficiency and mechanical robustness of PSCs and their hybrid devices upon integration are investigated. As an essential bridging component, carbon electrodes are also considered. Furthermore, due to the pressing standards in the energy sector, hybrid devices with nontoxic lead (Pb)-free perovskites should form ideal power packs. Therefore, with reference to their lattice model, optical characteristics, and resulting photovoltaic (PV) performance, they have also been briefly highlighted.

Diffusion dynamics of 1-Butyl-3-methylimidazolium chloride from cellulose filament during coagulation process

Abstract: The diffusion dynamics of 1-Butyl-3-methylimidazolium chloride ([BMIM]Cl) during coagulation process of cellulose filaments with H2O as non-solvent were investigated in detail. The diffusion coefficients of [BMIM]Cl was calculated based on the Fick’s second law of diffusion according to the experimental data. Several factors which affect the coagulation process including polymer concentration, concentration and temperature of coagulation bath were discussed respectively. It is found that the diffusion rate of [BMIM]Cl decreased with the increasing polymer content in the spinning solutions and the initial concentration of [BMIM]Cl in the coagulation bath, while the diffusion coefficients increased largely with the coagulation temperature becoming higher. The diffusion coefficients of [BMIM]Cl is relatively lower, in contrast with the conventional solvent in the solution spinning process, which is coordinate with the result of polyacrylonitrile [BMIM]Cl system by Zhang et al. (Polym Eng Sci 48(1):184–190, 2008). Compared with the diffusion process of N-methylmorpholine-N-oxide (NMMO) from cellulose filament, the diffusion coefficients of [BMIM]Cl is lower, which suggested a stronger coagulation and washing conditions should be taken to produce regenerated cellulose fiber with [BMIM]Cl as solvent.

Interaction between N-Methylmorpholine N-Oxide, Water, and the Titanium Dioxide Surface in the Lyocell Process.

Abstract: Interaction between N-methylmorpholine N-oxide (NMMO), H2O, and the titanium dioxide (TiO2) surface was studied by spectral tests and molecular dynamics simulations as the theoretical foundation for the development of functional lyocell. The molecular structure, movement, and arrangement of the NMMO and water molecules, as well as the interaction energies between them, were characterized. The results show that both water and NMMO molecules can interact with the TiO2 surface, and the water molecule is stronger, which makes the water molecules near the TiO2 surface different from that of the bulk solution. With the increase of the NMMO concentration, NMMO molecules compete with the water molecules adsorbed on the TiO2 surface, and two adsorption conformations of NMMO on the TiO2 surface were found. When the NMMO concentration is higher than 50%, the N-O bond of NMMO is the main position interacting with the TiO2 surface, forming a more stable and complex adsorption molecular layer and enhancing the interaction between TiO2 and the solution, and finally promote the dispersion of TiO2 particle and increase the zero-shear viscosity of the lyocell solution. At the same time, the strong interaction also weakens the N-O bond of the NMMO molecules near the TiO2 surface with the bond length increasing; however, the influence cannot cause instability of NMMO. UV spectra also shows that there is no NMMO decomposition due to the addition of TiO2 during the dissolution process. In conclusion, NMMO can promote the dispersion of the TiO2 nanoparticles in the solvent, and the stability of NMMO is not affected, which is the basis for the preparation of the functional lyocell fiber.

Design of Experiment: A Statistical Approach to Understanding Factors Influencing Surface Properties of Sol-Gel Based Non-Stick Ceramic Coatings

Abstract: Ceramic coatings based on sol-gel method have increasingly gained much attention in recent times. In order to ascertain important experimental factors (variables) influencing surface properties, such as adhesion, pencil hardness and advancing contact angle (non-stick) of sol coatings, a 26-1-factorial screening design with six experimental variables, precursor mole ratio, low surface energy polymer concentration, silane coupling agent (SCA) concentration, silica nanoparticles concentration (SNP’s),curing temperature and three responses ( surface properties) were investigated. The results indicate that silane coupling agent concentration, SNP’s concentration and their interaction were the most significant experimental factors influencing advancing contact angle. None of the experimental factors studied were statistically significant with respect to hardness and adhesion.

Cellulose dissolution: insights on the contributions of solvent-induced decrystallization and chain disentanglement

Abstract: The dissolution of cellulose is a critical step for the efficient utilization of this renewable resource as a starting material for the synthesis of high value-added functional polymers and chemicals and also for biofuel production. The recalcitrance of semicrystalline cellulose microfibrils presents a major barrier to cellulose dissolution. Despite research efforts, important aspects of cellulose dissolution such as solvent-induced decrystallization and chain disentanglement are not well-understood. Here we address these fundamental issues with the practical goal of gaining insights into the swelling and dissolution of cellulose that cannot be obtained from macroscopic experimental data. To this end, we have used a newly-developed phenomenological model that captures the phenomena governing the dissolution of semicrystalline polymers as well as the thermodynamics and kinetics of dissolution. This model fits well experimental data for swelling and dissolution of cotton fibers in the ionic liquid [bmim]Cl, and allows the quantification of two important aspects, i.e., solvent effectiveness in cellulose (1) decrystallization and (2) chain disentanglement, the balance of which controls the mechanism and kinetics of cellulose dissolution. The activation parameters of cellulose decrystallization, estimated using the obtained decrystallization constant values, reveal that the decrystallization of cellulose in [bmim]Cl is associated with positive enthalpy and entropy and it is also very sensitive to temperature. When the solvent effectiveness in the disruption of cellulose crystals is relatively lower than its ability to disentangle the chains, the kinetics of dissolution are controlled by decrystallization. Furthermore, conditions that facilitate cellulose chain disentanglement, in addition to increasing the rate of dissolution, can result in faster decrystallization. The solvent effectiveness in chain disentanglement is the only factor that determines the decrease of the cellulose fiber radius. In cases where the fiber dissolution rate is lower than the decrystallization rate, the dissolution of cellulose is mostly controlled by the solvent ability to disentangle the chains. The insights obtained from this study improve the understanding of cellulose–solvent interactions underlying decrystallization and disentanglement and their contributions in controlling the kinetics of cellulose swelling and dissolution.

Ionic Liquid as Reaction Media for the Production of Cellulose-Derived Polymers from Cellulosic Biomass

Abstract: The most frequent polymer on nature is cellulose that is present together with lignin and hemicellulose in vegetal biomass. Cellulose can be, in the future, sustainable raw matter for chemicals, fuels, and materials. Nevertheless, only 0.3% of cellulose is processed nowadays due to the difficulty in dissolving it, and only a small proportion is used for the production of synthetic cellulosic fibers especially esters and other cellulose derivatives, normally in extremely polluting processes. The efficient and clean dissolution of cellulose is a major objective in cellulose research and development. Ionic liquids (ILs) are considered “green” solvents due to their low vapor pressure, that prevents them evaporating into the atmosphere. In addition, these molten salts present advantages in process intensification, leading to more than 70 patents in lignocellulosic biomass in ILs being published since 2005, most of them related to the production of cellulose derived polymers, e.g., acetates, benzoylates, sulfates, fuorates, phthalates, succinates, tritylates, or silylates. In this work, the use of ILs for production of cellulose derived polymers is thoroughly studied. To do so, in the first place, a brief summary of the state of the art in cellulose derivatives production is presented, as well as the main features of ILs in cellulose processing applications. Later, the main results in the production of cellulose derivatives using ILs are presented, followed by an analysis of the industrial viability of the process, considering aspects such as environmental concerns and ILs’ recyclability.