Kategorie: ‘Publication’
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
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
(Deutsch) Neue Veröffentlichung:
Federn als Bindemittel und Flammschutz
The increasing demand for sustainable building materials requires alternative flame retardants that are more sustainable than those used to date. In this context, we present our first results with recycled poultry feather waste for the production of flame-retardant fibreboards. Impregnated wood fibres show a significantly reduced decomposition rate and decomposition temperatures that are approx. 50 °C higher. In addition, decomposition takes place gradually and not immediately as with untreated wood. With a total protein content of approx. 10 % by weight, the boards produced using the wet process are self-extinguishing and do not smoulder. In the three-point bending test, these fibreboards failed at 15 N/mm2, the limit value required by DIN EN 622 for commercially available, formaldehyde-bonded MBH fibreboards. This shows that the recycled feather residues not only have an impressive flame-retardant effect, but can also be used as a fully-fledged binder for a new generation of ecological fibreboards. As these boards are based exclusively on natural materials, they can be shredded and composted at the end of their life cycle.
The article was selected by the Journal for the cover of issue 5(50).
M. Brenner, O. Weichold
Protein Hydrolysates from Biogenic Waste as an Ecological Flame Retarder and Binder for Fiberboards
ACS Omega 2020, 5, 32227−32233. https://dx.doi.org/10.1021/acsomega.0c03819
New publication:
Duroplasts with a difference
Nature avoids highly reactive functional groups, such as isocyanate and epoxy, by using highly specialised enzymes as catalysts in condensation reactions. Consequently, bio-based raw materials require in vitro reaction conditions that are often difficult to reconcile with the requirements for thermoset resins. In addition, condensation reactions release small molecules (often water), which leads to the formation of foams under standard reaction conditions. It would therefore appear that natural building blocks would not be suitable for the production of thermosetting resins.
We show here that the addition of chopped feathers prevents the previously reported foaming of highly cross-linked combinations such as citric acid/glycerol, increases conversion and improves flame retardant properties.
M. Brenner, C. Popescu, O. Weichold
Anti-Frothing E ffect of Poultry Feathers in Bio-Based, Polycondensation-Type Thermoset Composites
Appl. Sci. 2020, 10, 2150; https://doi:10.3390/app10062150
New publication:
Gentle dissolution of chitosan
Despite its very low pKa value, hydrochloric acid is one of the most commonly used acids in the production of chitosan hydrogels for biomedical applications. Although hydrochloric acid is widely used, the occurrence of unwanted depolymerisation in the production of hydrogels from chitosan hydrogels is often disregarded. In order to fully exploit the potential of chitosan as a renewable resource, a new, very mild method for the preparation of chitosan solutions is described here.
These solutions dry to clear, transparent films that remain completely water soluble and absorb up to 70 wt% water from the water in the 90 % RH vapour phase at 25 °C. Absorption follows simple first-order kinetics and the rate constants The rate constants increase with increasing humidity up to about 71 % RH, where a metastable chitosan trihydrate salt appears to be formed. Desorption is slightly faster, but more complex, as it involves two different first-order processes. In addition, the films produced in this way are thermally more stable than the usual chitosan hydrochloride.
M. B. Endres, O. Weichold
Sorption-active transparent films based on chitosan
Carbohydrate Polym. 2019, 208, 108–114. https://doi.org/10.1016/j.carbpol.2018.12.031
New publication
Corrosion current drives corrosion sensor
New corrosion sensor for reinforced concrete requires no external power source. Steel corrosion causes enormous economic damage every year, which could be reduced by installing suitable monitoring devices. These should be simple, reliable and durable and should not require any maintenance or servicing. The present electrochromic device is designed to use the macrocell current of an active, chloride-induced corrosion element as an energy source to trigger a colour change. In this way, the system remains inactive until corrosion occurs. The device consists of diheptyl viologen in a liquid polymer electrolyte of LiClO4 and poly(ethylene glycol). The addition of viologen lowers the resistance but does not cause any further changes in the electrochemical properties of the polymer electrolyte. The impedance spectra indicate that ion transport rather than capacitive effects dominate the electrochemical properties. Experiments with direct current in the μA range show electrochromic switching times of several minutes, which is sufficient for the intended monitoring application.
T. Juraschek, O. Weichold
Development of an electrochromic device triggered by the macrocell current in chloride‐induced corrosion of steel‐reinforced concrete
J. Phys. Org. Chem. 2017, e3739. https://doi.org/10.1002/poc.3739
New publication
Structure formation in oligomers
How can the thermal stability and crystallinity of oligomers be controlled? Four members of a homologous series of chlorinated poly(vinyl ester) oligomers from poly(vinyl acetate) to poly(vinyl stearate) with degrees of polymerisation of 10 and 20 were prepared by telomerisation with carbon tetrachloride. All oligomers are thermally degraded in two main steps, whereby HCl and side chains are lost before the backbone is degraded. The polymers with short side chains, up to poly(vinyl octanoate), are amorphous and show internal plastification, while those with long side chains are semi-crystalline due to side chain crystallisation. The glass transition and melting temperatures as well as the initial decomposition temperature are more strongly influenced by the side chain length than by the degree of polymerisation. Thermal stability is improved when both the size and the number of side chains increase, but only long side chains lead to a significant increase in decomposition resistance.
D. Heinze, T. Mang, C. Popescu, O. Weichold
Effect of side chain length and degree of polymerization on thedecomposition and crystallization behaviour of chlorinated poly(vinylester) oligomers
Thermochimica Acta 2016, 637, 143-153. http://dx.doi.org/10.1016/j.tca.2016.05.015
New publication
Poly(vinyl acetate) plasticises itself
No additional plasticiser required. Poly(vinyl acetate), PVAc, with a degree of polymerisation Xn≈10 was produced by free radical chain transfer polymerisation with carbon tetrachloride and used as an oligomeric plasticiser for commercial PVAc. After H/Cl exchange at the chain ends, the product exhibits high thermal stability and excellent melt compounding properties. Blends of oligomeric and commercial PVAc show simple glass transition temperatures, which decrease with higher oligomer content, and exhibit small negative deviations from Fox’s linear additivity rule. This suggests that plasticisation and miscibility are mainly due to entropic effects. Injection moulded thick specimens show ductile behaviour at oligomer contents >10 wt%, while sheets with a thickness of 0.2-0.5 mm appear flexible already at 7.5 wt%. The oxygen permeability coefficients are an order of magnitude lower than those of low-density polyethylene. Due to the sum of their properties, the plasticised sheets represent a promising alternative for the production of barrier materials.
D. Heinze, T. Mang, K. Peter, M. Möller, O. Weichold
Synthesis of Low Molecular Weight Poly(vinyl acetate) and Its Application as Plasticizer
J. Appl. Polym. Sci. 2014, 40226. https://doi.org/10.1002/APP.40226
