New publication
New crosslinkers for diallylammonium gels
N,N’-methylene bisacrylamide (BIS) is a very popular crosslinker for radical polymerisation in water. It is highly reactive but tends to undergo alkaline hydrolysis and suffers from low solubility. This study shows that BIS forms only inhomogeneous networks with slowly polymerising systems such as N,N-diallyldimethylammonium chloride (DADMAC). As a result, gels with very low cross-linking densities, i.e. high swelling capacities, disintegrate during the swelling test. Coherent, i.e. highly cross-linked gels are not accessible due to the solubility limit. A promising alternative are multivalent tetraallyl compounds, such as tetraallylammonium bromide, N,N,N‘,N’-tetraallylpiperazinium dibromide and N,N,N‘,N’-tetraallyltrimethylenedipiperidinedibromide. In contrast to BIS, the copolymerisation with DADMAC is statistic. However, gelation with the new tetraallyl crosslinkers is much slower than with BIS and follows the order TAPB < TAMPB < TAAB, but the differences become significantly smaller as the content increases. At low contents, all three enable the production of gels with high swelling capacities of up to 360 g/g.
T. B. Mrohs, O.Weichold
Multivalent Allylammonium-Based Cross-Linkers for the Synthesis of Homogeneous, Highly Swelling Diallyldimethylammonium Chloride Hydrogels
Gels 2022, 8, 100. https://doi.org/10.3390/gels8020100
New PhD Student
In January, we welcomed Nils Münstermann to the area of bio-based building materials. As part of his dissertation, he is researching sustainable and biodegradable chitosan-based binders, adhesives and glazes for use on wood. We wish him every success with his research and welcome him to the working group.
External impact
The publication ‘Alkaline hydrogels as ion-conducting coupling material for electrochemical chloride extraction’ by A. Jung, A. Faulhaber and O. Weichold in the journal Materials and Corrosion is one of the most downloaded articles in 2021. More.
Completed Master Thesis
Congratulations to Nils Münstermann on successfully completing his Master’s thesis entitled ‘Synthesis and properties of superabsorbers based on chitosan hydrogels’ in the Chemistry degree programme. The thesis is part of the ongoing Biosuperabsorber project.
New publication:
Springs replace carbon black in rubber
Most elastomers (‘rubber’) used today are based on sulphur as a cross-linking agent and carbon black from fossil raw materials to change the mechanical properties. Here we show that natural keratin, e.g. from poultry feathers, can be a very promising substitute for both. Feathers are not only tough, but also contain a relevant amount of sulphur in the form of disulphide bridges. These can be activated under vulcanisation conditions and then covalently bind to EPDM rubber to form a cross-linked network. The presence of spring waste increases the tensile and compressive strength as well as the hardness and reduces the rebound resilience. Due to their high nitrogen content of approximately 17%, the springs also improve the thermal stability of the composite, shifting the main degradation step from 400°C to 470°C and significantly slowing down decomposition. As elastomers are a large market and springs in particular are a voluminous waste, the combination of the two offers enormous ecological and economic prospects.
M. Brenner, O. Weichold
Poultry Feather Waste as Bio-Based Cross-Linking Additive for Ethylene Propylene Diene Rubber
Polymers 2021, 13, 3908. https://doi.org/10.3390/polym13223908
New publication:
Feathers let plants grow
The global rise in temperature is leading to an increasing spread of semi-arid and arid regions and is accompanied by a deterioration of agricultural land. Polymers can help in many ways, but must not become a burden on the environment. In this context, we present here a method by which poultry feathers, representative of keratin waste in general, can be converted into hydrogels for use as a plant growth medium. Naturally cross-linked hydrogels are formed from suitably produced, aqueous keratin solutions during evaporation. The cress germination test showed that the gel contains no toxic substances and adheres strongly to the roots. This protects the plants from drought stress as long as the gel still contains moisture.
M. Brenner, O. Weichold
Autogenous Cross-Linking of Recycled Keratin from Poultry-Feather Waste to Hydrogels for Plant-Growth Media
Polymers 2021, 13, 3581. https://doi.org/10.3390/polym13203581
New project:Bio-based glazes and adhesives for wood
A new project focusing on bio-based building materials will start on 1 October 2021. Together with two industrial partners, we are developing glazes and adhesives for wood based on chitosan. The project is being supervised by Tobias Boehnke.
New Publication:Breaking Barriers in Ion Conductivity
We are proud to highlight another publication by Prof. Dr. Oliver Weichold. Together with Pia B. Sassmann, he co-authored the study Synergistic effects in cross-linked blends of ion-conducting PEO-/PPO-based unsaturated polyesters, which presents an innovative approach to enhancing ion conductivity.
In this work, unsaturated polyesters (UP) based on poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) were synthesized, doped with lithium perchlorate (LiClO₄), and cross-linked with styrene using a redox initiator. The findings reveal distinct behaviors in conductivity between PEO- and PPO-based polyester networks. While the conductivity decreases with increasing molecular weight for PEO, the opposite trend is observed for PPO.
Remarkably, the study discovered that targeted blending and cross-linking of PEO- and PPO-based polyesters can create synergistic effects. A 1:1 blend of short-chain PPO and long-chain PEO exhibited a resistivity five times lower than pure PEO and three times lower than pure PPO. These effects are attributed to enhanced chain mobility and intrachain hopping mechanisms, which are amplified by the cross-linking process.
Beyond improved ion conductivity, these networks offer rubber-like elasticity and high water tolerance, making them suitable for diverse applications, particularly under mechanical stress, in atmospheric conditions, or even in aqueous environments where standard ion-conducting systems often fail.
Sassmann, P.B., Weichold, O.
Synergistic effects in cross-linked blends of ion-conducting PEO-/PPO-based unsaturated polyesters
Ionics 27, 3857–3867 (2021). https://doi.org/10.1007/s11581-021-04149-z
Book chapter
Eine sehr grundlegende Einführung in das Thema Polymerchemie findet sich in
O. Weichold, Introduction to Polymer Chemistry. In: P. Richet, R. Conradt, A. Takada, J. Dyon (Hrsg.) Encyclopedia of Glass Science, Technology, History, and Culture Vol. 2. Wiley-VCH, New York, 2021, S. 1043–1055. https://doi.org/10.1002/9781118801017
Poster
Tim Mrohs presented a poster entitled: ‘Influence of Environmental Factors on the Swelling Capacities of Superabsorbent Polymers Used in Concrete’ at the 3rd International Conference on the Chemistry of Construction Materials (ICCCM) 2021 of the GDCh Bauchemie, which took place online.
