@article{RangelovaRadevNenkovaetal.2011, author = {Rangelova, Nadezhda and Radev, Lachezar and Nenkova, Sanchi and Salvado, Isabel Miranda and Vas Fernandes, Maria and Herzog, Michael}, title = {Methylcellulose/SiO2 hybrids: sol-gel preparation and characterization by XRD, FTIR and AFM}, series = {Central European Journal of Chemistry}, volume = {9}, journal = {Central European Journal of Chemistry}, number = {1}, issn = {2391-5420}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-9636}, pages = {112 -- 118}, year = {2011}, abstract = {Methylcellulose (MC) / SiO2 organic / inorganic hybrid materials have been prepared from MC and methyltriethoxysilane or ethyltrimethoxysilane, and characterized by XRD, FTIR and AFM. XRD showed peak shifts. FTIR shows intermolecular hydrogen bonding between MC and SiO2. AFM depicts surface roughness which depends on the silica precursor and MC content.}, language = {en} } @article{DimitrovHerzogNenkova2013, author = {Dimitrov, Kiril and Herzog, Michael and Nenkova, Sanchi}, title = {Fe3O4 Modification of Microcrystalline Cellulose for Composite Materials}, series = {American Journal of Chemistry}, volume = {3}, journal = {American Journal of Chemistry}, number = {5}, issn = {2165-8781}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-9651}, pages = {140 -- 147}, year = {2013}, abstract = {A new synthesis method for producing cellulose ferrite micro- and nano- composites was developed and new material properties were studied. Microcrystalline cellulose was modified with a mixture of Fe+2/Fe+3 to produce surface bonded nanoparticles magnetite (Fe3O4). Optimal conditions were determined. Microsized hematite (Fe2O3) was mixed with microcrystalline cellulose and used as a reference. The magnetite modified microcrystalline cellulose and hematite filled microcrystalline cellulose were used together with polyurethane prepolymer. New composite crosslinked conductivity materials based on the magnetite modified microcrystalline or hematite filled microcrystalline cellulose and polyurethane were developed. Morphology, crystalline properties, water absorption and electro conductivity of these materials were characterized. The physical properties of these materials were characterized by different analytical methods: SEM, XRD, water absorption and electrical resistance.}, language = {en} } @article{TsonevHerzogNenkova2013, author = {Tsonev, Tsvetomir and Herzog, Michael and Nenkova, Sanchi}, title = {Shape memory polyurethanes based on recycled polyvinyl butyral. I. Synthesis and morphology}, series = {Central European Journal of Chemistry}, volume = {11}, journal = {Central European Journal of Chemistry}, number = {12}, issn = {2391-5420}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-9664}, pages = {2058 -- 2065}, year = {2013}, abstract = {Shape memory polyurethanes (SMPUs) were synthesized by 4,4′-diphenylmethane diisocyanate (MDI), hexane-1,6-diol (HD), polypropylene glycol (PPG), and recycled polyvinyl butyral (PVB). Dynamic mechanical analysis, differential scanning calorimetry and Fourier transformation infrared attenuated total reflection spectroscopy was used to characterize the poly (vinylbutyral-urethanes). Micro-phase domain separation of hard and soft segments and phase inversion were investigated. Increasing the hard segment content, i.e., average hard segment molecular weight, leads to an increase in the degree of micro-phase separation, hard domain order and crystallinity. The crystalline hard segment structures combined with the elastic nature of soft segment matrix provide enough physical and chemical crosslinks to have shape memory effect.}, language = {en} } @article{TsonevHerzogNenkova2013, author = {Tsonev, Tsvetomir and Herzog, Michael and Nenkova, Sanchi}, title = {Shape memory polyurethanes based on recycled polyvinyl butyral. I. Synthesis and morphology}, series = {Central European Journal of Chemistry}, volume = {11}, journal = {Central European Journal of Chemistry}, number = {12}, publisher = {Versita}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-20052}, pages = {2058 -- 2065}, year = {2013}, abstract = {Shape memory polyurethanes (SMPUs) were synthesized by 4,4′-diphenylmethane diisocyanate (MDI), hexane-1,6-diol (HD), polypropylene glycol (PPG), and recycled polyvinyl butyral (PVB). Dynamic mechanical analysis, differential scanning calorimetry and Fourier transformation infrared attenuated total reflection spectroscopy was used to characterize the poly (vinylbutyral-urethanes). Micro-phase domain separation of hard and soft segments and phase inversion were investigated. Increasing the hard segment content, i.e., average hard segment molecular weight, leads to an increase in the degree of micro-phase separation, hard domain order and crystallinity. The crystalline hard segment structures combined with the elastic nature of soft segment matrix provide enough physical and chemical crosslinks to have shape memory effect.}, language = {en} } @article{BauerFursenkoHeinrichetal.2022, author = {Bauer, Joachim and Fursenko, Oksana and Heinrich, Friedhelm and Gutke, Marko and Kornejew, Eckhart and Br{\"o}del, Oliver and Dietzel, Birgit and Kaltenbach, Alexander and Burkhardt, Martin and Edling, Matthias and Steglich, Patrick and Herzog, Michael and Schrader, Sigurd}, title = {Determination of optical constants and scattering properties of transparent polymers for use in optoelectronics}, series = {Optical Materials Express}, volume = {12}, journal = {Optical Materials Express}, number = {1}, publisher = {Optica Publishing Group}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-15666}, pages = {204 -- 224}, year = {2022}, abstract = {Knowledge of optical constants, i.e. refractive index n and extinction coefficient k, and light scattering properties of optical polymers are required to optimize micro-optics for light-emitting diodes in terms of efficiency, color properties and light distribution. We present here a model-based diagnostic approach to determine the optical properties of polymers, which should be particularly useful in the development of plastics for optical applications. Optical constants and scattering coefficients were obtained from transmission and reflection measurements in a wavelength range from UV to NIR taking into account scattering effects due to rough surfaces and volume inhomogeneity. Based on the models for the dielectric function, the molecular optical transition energies Eg, critical point energies, Urbach energies and exciton transition energies were determined. Rayleigh and Mie scattering model and van de Hulst\&\#x0027;s anomalous diffraction theory were applied to characterize scattering due to volume inhomogeneities. Scalar diffraction theory was applied to account for surface roughness scattering. Atomic force microscopy with nanomechanical characterization was used to characterize domains in size and shape and to assign optical scattering to a suitable morphological model. The combined optical and mechanical characterization help to improve the qualification of new polymer materials for optical applications.}, language = {en} } @article{ShchotkinaPalamarchukSkorokhodetal.2023, author = {Shchotkina, Nataliia and Palamarchuk, Y. and Skorokhod, Iryna and Dolinchuk, Liudmyla and Sokol, Anatoliy and Motronenko, Valentina and Besarab, A. and Gorchakova, N. and Frohme, Marcus and Herzog, Michael}, title = {Features of technological regulation for cardiac bioimplants}, series = {Cell and Organ Transplantology}, volume = {11}, journal = {Cell and Organ Transplantology}, number = {1}, publisher = {Institute of Cell Therapy}, address = {Kiev}, issn = {2311-021X}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-18248}, pages = {26 -- 33}, year = {2023}, abstract = {Patients with congenital heart defects and cardiovascular diseases are required new approaches to surgical intervention. The use of biological cardiac implants, which are made from the extracellular matrix, is a promising trend in modern regenerative medicine. These bioimplants can completely replace defective tissue or organs, and when manufactured with strict protocols and quality control measures, can be safe and effective for therapeutic applications. The process of manufacturing bioimplants involves various risks that need to be assessed and mitigated with ongoing monitoring and evaluation necessary to ensure the highest standards of quality. Overall, this study was successfully evaluated the requirements for introducing a new medical device into practice and created a technical file that meets all necessary documentation for certification.}, language = {en} } @article{BauerGutkeHeinrichetal.2020, author = {Bauer, Joachim and Gutke, Marko and Heinrich, Friedhelm and Edling, Matthias and Stoycheva, Vesela and Kaltenbach, Alexander and Burkhardt, Martin and Gruenefeld, Martin and Gamp, Matthias and Gerhard, Christoph and Steglich, Patrick and Steffen, Sebastian and Herzog, Michael and Dreyer, Christian and Schrader, Sigurd}, title = {Novel UV-transparent 2-component polyurethane resin for chip-on-board LED micro lenses}, series = {Optical Materials Express}, volume = {10}, journal = {Optical Materials Express}, number = {9}, issn = {2159-3930}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-13472}, pages = {2085 -- 2099}, year = {2020}, abstract = {In this work we present a novel optical polymer system based on polyurethane elastomer components, which combines excellent UV transparency with high thermal stability, good hardness, high surface tension and long pot life. The material looks very promising for encapsulation and microlensing applications for chip-on-board (CoB) light-emitting diodes (LED). The extinction coefficient k, refractive index n, and bandgap parameters were derived from transmission and reflection measurements in a wavelength range of 200-890 nm. Thermogravimetry and differential scanning calorimetry were used to provide glass transition and degradation temperatures. The surface tension was determined by means of contact angle measurements. As proof of concept, a commercial InGaN-CoB-LED is used to demonstrate the suitability of the new material for the production of microlenses.}, language = {en} } @article{MomanyiHerzogMuchiri2019, author = {Momanyi, Job and Herzog, Michael and Muchiri, Peter}, title = {Analysis of Thermomechanical Properties of Selected Class of Recycled Thermoplastic Materials Based on Their Applications}, series = {Recycling}, volume = {4}, journal = {Recycling}, issn = {2313-4321}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-12509}, year = {2019}, abstract = {Polypropylene and polystyrene are petroleum-based thermoplastics which are commonly used and disposed of in the environment after their service life, leading to environmental degradation. There is a need to recycle polypropylene and polystyrene, but the effect of recycling on thermo-mechanical properties is not well understood. This study aims to determine thermo-mechanical properties of the recycled polypropylene and recycled polystyrene and compare them with corresponding virgin polypropylene and newly produced polystyrene (general purpose polystyrene 1540 and high impact polystyrene 7240). The study was carried out by preparing bar-shaped samples of recycled polypropylene, recycled polystyrene, general purpose polystyrene 1540, and high impact polystyrene 7240 by compression molding using a hot press and thermally characterizing them to determine glass transition temperature and melting temperature using differential scanning calorimetry. The changes in Young\’s modulus, tensile strength, hardness, and toughness due to recycling activities were determined at room temperature (24 °C), 40 °C, 60 °C, and 80 °C. The thermo-mechanical properties of recycled polystyrene (PS) were found to be comparable to those of high impact polystyrene (HIPS) 7240. The study revealed that the hardness and toughness for the recycled polymers were higher than those of corresponding virgin polymers. On the other hand, tensile strength and Young's modulus for the recycled polymers were lower than those of the virgin polymers. Understanding the thermo-mechanical properties of the recycled polymers will contribute to more industrial applications hence increase the rate of recycling, resulting in a reduction in environmental pollution.}, language = {en} } @article{NjugunaMuchiriMwemaetal.2021, author = {Njuguna, James K. and Muchiri, Peter and Mwema, Fredrick M. and Karuri, Nancy W. and Herzog, Michael and Dimitrov, Kiril}, title = {Determination of thermo-mechanical properties of recycled polyurethane from glycolysis polyol}, series = {Scientific African}, volume = {12}, journal = {Scientific African}, issn = {2468-2276}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-14911}, year = {2021}, abstract = {Polyurethane foam is one of the most versatile polymers widely used in the automotive industry. However, due to the rising amount of polyurethane foam waste in the environment, there is growing research attention focusing on circular economy solutions to closing the material loop. This study aimed to determine the possible changes in thermo-mechanical properties between rigid polyurethane prepared using polyols derived from depolymerization of commercial polyurethane foam with benchmark rigid polyurethane (Ben PU). Polyurethane foams containing dispersion polyol were reacted with dipropylene glycol (DPG) and diethylene glycol (DEG) with a ratio of DPG: DEG of 1:1 in the presence of a consumable catalyst (Di-n-butyl amine). The recovered polyol was used as a raw material replacing 100\% benchmark rigid polyurethane petroleum-based polyester polyol to produce the recycled polyurethane (Rec PU). Thermal analysis was conducted to measure the recycled polyurethane's glass transition temperatures (Tg) using differential scanning calorimetry (DSC). Tensile strength, elastic modulus, toughness, and hardness test of the recycled polyurethane were conducted under three different temperatures; 24°C, 40°C, and 60°C. From the DSC results, the glass transition temperatures for the recycled and the benchmark rigid polyurethane occurred at 43°C and 50.4°C, respectively. Both polymers showed the brittle-ductile transition from 24°C to 40°C. Tensile strength for recycled polyurethane was lower than that of benchmark rigid polyurethane by 29-43\% and a corresponding 24-50\% decrease in elastic modulus. Recycled polyurethane recorded lower toughness than petroleum-based pure polyurethane by 13-16\%. However, the recycled polymer recorded high shored D values than the benchmark rigid polyurethane by 9-29\%. This study reveals that recycled polyol could be used as feedstock for polyurethane production with applications tailored to its mechanical properties.}, language = {en} }