Stefan Spirk

Prof. Stefan Spirk

Institute for Paper, Pulp and Fibre Technology, Graz University of Technology, 8010 Graz, Austria
orcid

Research Focus & Metrics

Academic Career Length

22Years (2005-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

View All Publications
23 March 2021 in ACS Nano
Verified
Journal Article
Open access
RKRoland Kádár
Roland Kádár
Stefan SpirkStefan Spirk
Stefan Spirk
Tiina NypelöTiina Nypelö
Tiina Nypelö
Cellulose nanocrystals (CNCs) self-assemble and can be flow-assembled to liquid crystalline orders in a water suspension. The orders range from nano- to macroscale with the contributions of individual crystals, their micron clusters, and macroscopic assemblies. The resulting hierarchies are optically active materials that exhibit iridescence, reflectance, and light transmission. Although these assemblies have the potential for future renewable materials, details about structures on different hierarchical levels that span from the nano- to the macroscale are still not unraveled. Rheological characterization is essential for investigating flow properties; however, bulk material properties make it difficult to capture the various length-scales during assembly of the suspensions, for example, in simple shear flow. Rheometry is combined with other characterization methods to allow direct analysis of the structure development in the individual hierarchical levels. While optical techniques, scattering, and spectroscopy are often used to complement rheological observations, coupling them in situ to allow simultaneous observation is paramount to fully understand the details of CNC assembly from liquid to solid. This Review provides an overview of achievements in the coupled analytics, as well as our current opinion about opportunities to unravel the structural distinctiveness of cellulose nanomaterials.

1 January 2021 in Carbohydrate Polymers
Verified
Journal Article
Open access
Tiina NypelöTiina Nypelö
Tiina Nypelö
BBBarbara Berke
Barbara Berke
Stefan SpirkStefan Spirk
Stefan Spirk
JSJuho Antti Sirviö
Juho Antti Sirviö
Periodate oxidation of polysaccharides has transitioned from structural analysis into a modification method for engineered materials. This review summarizes the research on this topic. Fibers, fibrils, crystals, and molecules originating from forests that have been subjected to periodate oxidation can be crosslinked with other entities via the generated aldehyde functionality, that can also be oxidized or reduced to carboxyl or alcohol functionality or used as a starting point for further modification. Periodate-oxidized materials can be subjected to thermal transitions that differ from the native cellulose. Oxidation of polysaccharides originating from forests often features oxidation of structures rather than liberated molecules. This leads to changes in macro, micro, and supramolecular assemblies and consequently to alterations in physical properties. This review focuses on these aspects of the modulation of structural hierarchies due to periodate oxidation.

1 February 2015 in Carbohydrate Polymers
Verified
Journal Article
Closed access
Sergiu CoseriSergiu Coseri
Sergiu Coseri
ASAlina Spatareanu
Alina Spatareanu
LSLiviu Sacarescu
Liviu Sacarescu
CRISTINA MIHAELA RÎMBUCRISTINA MIHAELA RÎMBU
CRISTINA MIHAELA RÎMBU
DSDaniela Suteu
Daniela Suteu
VHValeria Harabagiu
Valeria Harabagiu

8 October 2020 in Angewandte Chemie International Edition
Verified
Journal Article
Open access
WSWerner Schlemmer
Werner Schlemmer
PNPhilipp Nothdurft
Philipp Nothdurft
APAlina Petzold
Alina Petzold
GRGisbert Riess
Gisbert Riess
PFPhilipp Frühwirt
Philipp Frühwirt
Stefan SpirkStefan Spirk
Stefan Spirk
We show the synthesis of a redox‐active quinone, 2‐methoxy‐1,4‐hydroquinone (MHQ), from a bio‐based feedstock and its suitability as electrolyte in aqueous redox flow batteries. We identified semiquinone intermediates at insufficiently low pH and quinoid radicals as responsible for decomposition of MHQ under electrochemical conditions. Both can be avoided and/or stabilized, respectively, using H3PO4 electrolyte, allowing for reversible cycling in a redox flow battery for hundreds of cycles.

9 August 2012 in Soft Matter
Verified
Journal Article
Closed access
PDF file
TMTamilselvan Mohan
Tamilselvan Mohan
Stefan SpirkStefan Spirk
Stefan Spirk
RKRupert Kargl
Rupert Kargl
ADAleš Doliška
Aleš Doliška
AVAlenka Vesel
Alenka Vesel
Karin Stana KleinschekKarin Stana Kleinschek
Karin Stana Kleinschek
The behavior of amorphous cellulose model thin films upon heat treatment is investigated. Upon heat treatment, a structural rearrangement in the films from a featureless to a fibrillar structure is observed which correlates with the regeneration time and total cellulose content as proven by atomic force microscopy and X-ray photoelectron spectroscopy. ATR-IR spectroscopy proves the presence of stronger hydrogen bonds in the heat treated surfaces which originate from a reorganization of the cellulose chains and pore structure. The rearrangement is accompanied with an increased surface hydrophobicity, a reduced swelling capacity and a reduction in the water content of the films. An increase in crystallinity of the films is not observed.

1 August 2021 in Carbohydrate Polymers
Verified
Journal Article
Open access
WSWerner Schlemmer
Werner Schlemmer
JSJulian Selinger
Julian Selinger
MHMathias Andreas Hobisch
Mathias Andreas Hobisch
Stefan SpirkStefan Spirk
Stefan Spirk
The increasing amount of electric vehicles on our streets as well as the need to store surplus energy from renewable sources such as wind, solar and tidal parks, has brought small and large scale batteries into the focus of academic and industrial research. While there has been huge progress in performance and cost reduction in the past years, batteries and their components still face several environmental issues including safety, toxicity, recycling and sustainability. In this review, we address these challenges by showcasing the potential of polysaccharide-based compounds and materials used in batteries. This particularly involves their use as electrode binders, separators and gel/solid polymer electrolytes. The review contains a historical section on the different battery technologies, considerations about safety on batteries and requirements of polysaccharide components to be used in different types of battery technologies. The last sections cover opportunities for polysaccharides as well as obstacles that prevent their wider use in battery industry.