Lukas Munster

Microwave solvothermal decoration of the cellulose surface by nanostructured hybrid Ag/ZnO particles: a joint XPS, XRD and SEM study

The synthesis of hybrid silver/zinc oxide (Ag/ZnO) decoration on the cellulose surface is described. The structures were characterized with X-ray photoelectron spectroscopy (XPS) and corroborated with X-ray diffraction and scanning electron microscopy. Silver nitrate and zinc acetate dihydrate were used as soluble raw materials. Hexamethylenetetraamine was used as the precipitating and reducing agent. The surface of α-cellulose was always treated by hydrogen peroxide before synthesis with a relatively mild effect manifested in water contact angle measurement and XPS high-resolution spectra. The Ag/ZnO decoration system was identified as a true nanodispersed metal/semiconductor hybrid with a unique collective plasmonic structure observed on Ag 3d core lines for the first time. A series of experiments with a single precursor solution contributed to the characterization of the interaction of Ag+ and Zn2+ species with the surface and to the description of the reaction mechanism in the mixed precursor solution. In contrast to previous reports, a specific interaction between the cellulose substrate and Zn2+ was observed. No specific non-thermal effects of microwave heating were observed.

Hybrid nanostructured Ag/ZnO decorated powder cellulose fillers for medical plastics with enhanced surface antibacterial activity

Hybrid inorganic–organic fillers based on nanostructured silver/zinc oxide decorations on micro-cellulose carrier particles were prepared by stepwise microwave assisted hydrothermal synthesis using soluble salts as precursors of silver and zinc oxide. Hexamethylenetetramine was used as precipitating agent for zinc oxide and reducing agent for silver. The inorganics covered all available surfaces of the cellulose particles with a morphology resembling a coral reef. Prepared particulate fillers were compounded to medical grade poly(vinyl chloride) matrix. Scanning electron microscopy and powder X-ray diffractometry were used to investigate the morphology and crystalline phase structure of fillers. The scanning electron microscopy was used for morphological study of composites. With respect to prospective application, the composites were tested on electrical and antibacterial properties. A small effect of water absorption in polymer composites on their dielectric properties was observed but no adverse effect of water exposure on prepared materials was manifested. Electrical conductivity of fillers and composites was measured and no influence of water soaking of composites was found at all. The surface antibacterial activity of prepared composites was evaluated according to the standard ISO 22196. Excellent performance against Escherichia coli and very high against Staphylococcus aureus was achieved.

Antenna of silver nanoparticles mounted on a flexible polymer substrate constructed using inkjet print technology

This article describes the construction of an antenna that operates at frequencies of 1.07, 1.5, and 2.49 GHz and that is fabricated on a flexible polymer substrate using inkjet printing technology. In particular, this article is focused on the preparation and characterization of an antenna starting from the ink formulation for printing a homogeneous, electrically conductive layer using silver nanoparticles. The diameter of the prepared silver nanoparticles ranges from 50 to 200 nm. The inkjet printing technology on flexible polymer substrates offers a wide range of applications where there are high demands for flexibility. In combination with the polymer substrate, inkjet printing enables the production of more complex shapes and curves for antennas that are widely applicable not only in wearable electronic devices but also in plastic cases for portable communication devices.

Light-Induced Actuation of Poly(dimethylsiloxane) Filled with Graphene Oxide Grafted with Poly(2-(trimethylsilyloxy)ethyl Methacrylate)

This study serves to combine two approaches into one single step, to achieve a significant improvement of the light-induced actuation capabilities. Graphene oxide (GO) is an inert material, from the electrical and thermal conductivity point of view, and is incompatible with the usually-used poly(dimethylsiloxane) (PDMS) matrix. During surface-modification by surface-initiated atom transfer radical polymerization, the GO was transformed into a conducting and compatible material with the PDMS showing enormous light-induced actuation capability. The GO surface-modification with poly(2-(trimethylsilyloxy)ethyl methacrylate) (PHEMATMS) chains was confirmed by transmission electron microscopy and thermogravimetric analysis, with an on-line monitoring of gasses using FTIR. The improved compatibility was elucidated using contact angle and dielectric properties measurements. The PHEMATMS shell was investigated using gel permeation chromatography and nuclear magnetic resonance. The improved electric conductivity was measured using the four-point probe method and by Raman spectroscopy. The very important mechanical properties were elucidated using dynamic mechanical analysis, and with the help of thermo-mechanic analysis for the light-induced actuation. The excellent actuation capabilities observed, with changes in the length of around 0.8% at 10% pre-strain, are very promising from the point of view of applications.

Synthesis and Characterization of Poly(Vinyl Alcohol)-Chitosan-Hydroxyapatite Scaffolds: A Promising Alternative for Bone Tissue Regeneration

Scaffolds can be considered as one of the most promising treatments for bone tissue regeneration. Herein, blends of chitosan, poly(vinyl alcohol), and hydroxyapatite in different ratios were used to synthesize scaffolds via freeze-drying. Mechanical tests, FTIR, swelling and solubility degree, DSC, morphology, and cell viability were used as characterization techniques. Statistical significance of the experiments was determined using a two-way analysis of variance (ANOVA) with p < 0.05. Crosslinked and plasticized scaffolds absorbed five times more water than non-crosslinked and plasticized ones, which is an indicator of better hydrophilic features, as well as adequate resistance to water without detriment of the swelling potential. Indeed, the tested mechanical properties were notably higher for samples which were undergone to crosslinking and plasticized process. The presence of chitosan is determinant in pore formation and distribution which is an imperative for cell communication. Uniform pore size with diameters ranging from 142 to 519 µm were obtained, a range that has been described as optimal for bone tissue regeneration. Moreover, cytotoxicity was considered as negligible in the tested conditions, and viability indicates that the material might have potential as a bone regeneration system.

Dialdehyde cellulose crosslinked poly(vinyl alcohol) hydrogels: Influence of catalyst and crosslinker shelf life

Dialdehyde cellulose (DAC) derived from α-cellulose by periodate oxidation was solubilized and utilized as a suitable crosslinking agent for poly(vinyl alcohol) (PVA). The crosslinking occurs between reactive aldehyde groups of DAC on the C2 and C3 carbons of anhydroglucose unit and hydroxyl groups on PVA backbone in the presence of acidic catalyst. Two catalyst systems based on diluted hydrochloric or sulfuric acid were tested. Their influence on the PVA/DAC network has been investigated by solid-state 13C NMR, XRD analysis and in the terms of network parameters and mechanical properties. Because DAC undergoes structural changes and decays with time, the role of DAC solution age (1, 14 and 28 days old) on material properties of formed PVA/DAC samples was studied as well. Outlined, even after 28 days after solution preparation, DAC exhibited the capability to act as an efficient crosslinker for PVA. The resulting material properties of PVA/DAC hydrogels were found to be dependent on the molecular weight of solubilized DAC closely related to its age and the choice of catalyst system. Furthermore, the DAC potential for PVA crosslinking was investigated in a broad concentration range. Besides, the DAC crosslinking efficiency was also compared to that of common crosslinking agent glutaraldehyde. The results showed different network topology of prepared hydrogels and exceptional crosslinking potential of DAC in comparison to glutaraldehyde, which is most likely related to DAC macromolecular character.