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- ItemPoly(acrylonitrile-co-butadiene) as polymeric crosslinking accelerator for sulphur network formation(London [u.a.] : Elsevier, 2020) Hait, Sakrit; ValentÃn, Juan López; Jiménez, Antonio González; Ortega, Pilar Bernal; Ghosh, Anik Kumar; Stöckelhuber, Klaus Werner; Wießner, Sven; Heinrich, Gert; Das, AmitThe major controlling factors that determine the various mechanical properties of an elastomer system are type of chemical crosslinking and crosslink density of the polymer network. In this study, a catalytic amount of acrylonitrile butadiene copolymer (NBR) was used as a co-accelerator for the curing of polybutadiene (BR) elastomer. After the addition of this copolymer along with other conventional sulphur ingredients in polybutadiene compounds, a clear and distinct effect on the curing and other physical characteristics was noticed. The crosslinking density of BR was increased, as evidenced by rheometric properties, solid-state NMR and swelling studies. The vulcanization kinetics study revealed a substantial lowering of the activation energy of the sulphur crosslinking process when acrylonitrile butadiene copolymer was used in the formulation. The compounds were also prepared in the presence of carbon black and silica, and it was found that in the carbon black filled system the catalytic effect of the NBR was eminent. The effect was not only reflected in the mechanical performance but also the low-temperature crystallization behavior of BR systems was altered. © 2020 The AuthorsMaterials science; Materials chemistry; Crosslinking accelerator; Sulphur network; Solid state NMR; Curing kinetics; Activation energy; Acrylonitrile butadiene; Polybutadiene; Low-temperature; Crystallization. © 2020 The Authors
- ItemThermally triggered optical tuning of π-conjugated graft copolymers based on reversible Diels–Alder reaction(London : RSC Publishing, 2016) Ahner, J.; Micheel, M.; Kötteritzsch, J.; Dietzek, B.; Hager, M.D.In order to design a π-conjugated polymer film with tunable optical properties by thermally triggered activation of energy transfer after processing, two monodisperse phenylene ethynylene based oligomers with different optical properties were synthesized and attached to aliphatic polymers as π-conjugated side chains. Subsequently, the exchange of the side chain chromophores between the prepared donor and acceptor graft polymers in the solid state based on a reversible Diels–Alder reaction was studied in detail. The resulting donor–acceptor graft copolymer exhibits intra polymer energy transfer upon excitation of the donor moiety. The photophysical properties of the original and exchanged graft copolymers were investigated by means of absorption and emission spectroscopy. This novel concept opens the possibility for optical tuning of π-conjugated polymer films after processing as well as applications as thermally triggered sensor systems.
- ItemRedox chemistry in the pigment eumelanin as a function of temperature using broadband dielectric spectroscopy(Cambridge : Royal Society of Chemistry, 2019) Motovilov, K.A.; Grinenko, V.; Savinov, M.; Gagkaeva, Z.V.; Kadyrov, L.S.; Pronin, A.A.; Bedran, Z.V.; Zhukova, E.S.; Mostert, A.B.; Gorshunov, B.P.Conductive biomolecular systems are investigated for their promise of new technologies. One biomolecular material that has garnered interest for device applications is eumelanin. Its unusual properties have led to its incorporation in a wide set of platforms including transistor devices and batteries. Much of eumelanin's conductive properties are due to a solid state redox comproportionation reaction. However, most of the work that has been done to demonstrate the role of the redox chemistry in eumelanin has been via control of eumelanin's hydration content with scant attention given to temperature dependent behavior. Here we demonstrate for the first time consistency between hydration and temperature effects for the comproportionation conductivity model utilizing dielectric spectroscopy, heat capacity measurements, frequency scaling phenomena and recognizing that activation energies in the range of ∼0.5 eV correspond to proton dissociation events. Our results demonstrate that biomolecular conductivity models should account for temperature and hydration effects coherently.
- ItemBiowaste chicken eggshell powder as a potential cure modifier for epoxy/anhydride systems: competitiveness with terpolymer-modified calcium carbonate at low loading levels(London : RSC Publishing, 2017) Saeb, Mohammad Reza; Ghaffari, Mehdi; Rastin, Hadi; Khonakdar, Hossein Ali; Simon, Frank; Najafi, Farhood; Goodarzi, Vahabodin; Vijayan P., Poornima; Puglia, Debora; Asl, Farzaneh Hassanpour; Formela, KrzysztofBiowaste chicken eggshell (ES) powder was applied as a potential cure modifier in epoxy/anhydride systems. Cure behaviour and kinetics of composites filled with very low content (0.1 wt% based on epoxy resin) of ES, calcium carbonate (CaCO3), and terpolymer-modified fillers, mES and mCaCO3, were discussed comparatively. Surface analysis was performed by X-ray photoelectron spectroscopy. Cure kinetics was investigated by differential (Friedman) and integral (Ozawa and Kissinger-Akahira-Sunose) isoconversional methods using dynamic differential scanning calorimetry (DSC) data. Overall, protein precursors naturally existing in the structure of pristine ES facilitated crosslinking of epoxy and hardener of anhydride with functional groups resulting from terpolymer attachment to CaCO3 particles. Accelerated/hindered cure was observed depending on the filler type and surface characteristics, as investigated via the autocatalytic/non-catalytic nature of reactions and comparison of activation energy values of four types of composites. An enhanced cure was identified for composites containing untreated ES, which could be inferred on account of the lower competitive cure of carboxyl groups in the terpolymer backbone with epoxy compared to peptide groups existing in microporous pristine ES. On the other hand, mCaCO3 revealed low values of activation energy compared to pristine CaCO3, but still of the same order as ground biowaste ES.