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- ItemBlending In Situ Polyurethane-Urea with Different Kinds of Rubber: Performance and Compatibility Aspects(Basel : MDPI, 2018-11-02) Tahir, Muhammad; Heinrich, Gert; Mahmood, Nasir; Boldt, Regine; Wießner, Sven; Stöckelhuber, Klaus WernerSpecific physical and reactive compatibilization strategies are applied to enhance the interfacial adhesion and mechanical properties of heterogeneous polymer blends. Another pertinent challenge is the need of energy-intensive blending methods to blend high-tech polymers such as the blending of a pre-made hard polyurethane (-urea) with rubbers. We developed and investigated a reactive blending method to prepare the outstanding blends based on polyurethane-urea and rubbers at a low blending temperature and without any interfacial compatibilizing agent. In this study, the polyurethane-urea (PUU) was synthesized via the methylene diphenyl diisocyanate end-capped prepolymer and m-phenylene diamine based precursor route during blending at 100 °C with polar (carboxylated nitrile rubber (XNBR) and chloroprene rubber (CR)) and non-polar (natural rubber (NR), styrene butadiene rubber (sSBR), and ethylene propylene butadiene rubber (EPDM)) rubbers. We found that the in situ PUU reinforces the tensile response at low strain region and the dynamic-mechanical response up to 150 °C in the case of all used rubbers. Scanning electron microscopy reveals a stronger rubber/PUU interface, which promotes an effective stress transfer between the blend phases. Furthermore, energy filtered transmission electron microscopy (EFTEM) based elemental carbon map identifies an interphase region along the interface between the nitrile rubber and in situ PUU phases of this exemplary blend type.
- ItemFerric Ions Crosslinked Epoxidized Natural Rubber Filled with Carbon Nanotubes and Conductive Carbon Black Hybrid Fillers(Basel : MDPI, 2022-10-18) Damampai, Kriengsak; Pichaiyut, Skulrat; Stöckelhuber, Klaus Werner; Das, Amit; Nakason, CharoenNatural rubber with 50 mol % epoxidation (ENR-50) was filled with carbon nanotubes (CNTs) and conductive carbon black (CCB) hybrid fillers with various CCB loadings of 2.5, 5.0, 7.0, 10.0 and 15.0 phr, and the compounds were mixed with ferric ion (Fe3+) as a crosslinking agent. The ENRs filled exclusively with CNTs, and CNT–CCB hybrid fillers exhibited typical curing curves at different CCB loadings, i.e., increasing torque with time and thus crosslinked networks. Furthermore, the incorporation of CNT–CCB hybrid fillers and increasing CCB loadings caused an enhancement of tensile properties (modulus and tensile strength) and crosslink densities, which are indicated by the increasing torque difference and the crosslink densities. The crosslink densities are determined by swelling and temperature scanning stress relaxation (TSSR). Increasing CCB loadings also caused a significant improvement in bound rubber content, filler–rubber interactions, thermal resistance, glass transition temperature (Tg) and electrical conductivity. A combination of 7 phr CNT and CCB with loading higher than 2.5 phr gave superior properties to ENR vulcanizates. Furthermore, the secondary CCB filler contributes to the improvement of CNT dispersion in the ENR matrix by networking the CNT capsules and forming CNT–CCB–CNT pathways and thus strong CNT–CCB networks, indicating the improvement in the tensile properties, bound rubber content and dynamic properties of the ENR composites. Moreover, higher electrical conductivity with a comparatively low percolation threshold of the hybrid composites was found as compared to the ENR filled with CNTs without CCB composite. The superior mechanical and other properties are due to the finer dispersion and even distribution of CNT–CCB hybrid fillers in the ENR matrix.
- ItemEffect of prestrain on the actuation characteristics of dielectric elastomers(Basel : MDPI, 2020) Kumar, Mayank; Sharma, Anutsek; Hait, Sakrit; Wießner, Sven; Heinrich, Gert; Arief, Injamamul; Naskar, Kinsuk; Stöckelhuber, Klaus Werner; Das, AmitDielectric elastomers (DEs) represent a class of electroactive polymers that deform due to electrostatic attraction between oppositely charged electrodes under a varying electric field. Over the last couple of decades, DEs have garnered considerable attention due to their much-coveted actuation properties. As far as the precise measurement systems are concerned, however, there is no standard instrument or interface to quantify various related parameters, e.g., actuation stress, strain, voltage and creeping etc. In this communication, we present an in-depth study of dielectric actuation behavior of dielectric rubbers by the state-of-the-art “Dresden Smart Rubber Analyzer” (DSRA), designed and developed in-house. The instrument allowed us to elucidate various factors that could influence the output efficiency of the DEs. Herein, several non-conventional DEs such as hydrogenated nitrile rubber, nitrile rubber with different acrylonitrile contents, were employed as an electro-active matrix. The effect of viscoelastic creeping on the prestrain, molecular architecture of the matrices, e.g., nitrile content of nitrile-butadiene rubber (NBR) etc., are also discussed in detail.
- ItemA Comprehensive Study about the Role of Crosslink Density on the Tribological Behavior of DLC Coated Rubber(Basel : MDPI, 2020) Bayrak, Suleyman; Paulkowski, Dominik; Stöckelhuber, Klaus Werner; Staar, Benjamin; Mayer, BerndThe friction and wear behavior of coated rubber components is strongly dependent on the substrate properties. This work deals with the impact of the crosslink density, i.e., the hardness of the rubber substrate on the tribological performance of uncoated and coated rubber. The hardness of nitrile butadiene rubber (NBR) is varied altering the sulfur content. Both the uncoated and coated rubber samples are characterized in terms of surface and mechanical properties. Tribological tests comprise the examination of the macroscopic contact area and the temperature in the contact zone. It was found that the functional layer enhances the wear resistance significantly. Apparently, the wear and friction behavior of the coated rubber correlates with the hardness and the bulk properties of the substrate material.
- ItemTemperature Scanning Stress Relaxation of an Autonomous Self-Healing Elastomer Containing Non-Covalent Reversible Network Junctions(Basel : MDPI, 2018-01-19) Das, Amit; Sallat, Aladdin; Böhme, Frank; Sarlin, Essi; Vuorinen, Jyrki; Vennemann, Norbert; Heinrich, Gert; Stöckelhuber, Klaus WernerIn this work, we report about the mechanical relaxation characteristics of an intrinsically self-healable imidazole modified commercial rubber. This kind of self-healing rubber was prepared by melt mixing of 1-butyl imidazole with bromo-butyl rubber (bromine modified isoprene-isobutylene copolymer, BIIR). By this melt mixing process, the reactive allylic bromine of bromo-butyl rubber was converted into imidazole bromide salt. The resulting development of an ionic character to the polymer backbone leads to an ionic association of the groups which ultimately results to the formation of a network structure of the rubber chains. The modified BIIR thus behaves like a robust crosslinked rubber and shows unusual self-healing properties. The non-covalent reversible network has been studied in detail with respect to stress relaxation experiments, scanning electron microscopic and X-ray scattering.
- ItemPoly(acrylonitrile-co-butadiene) as polymeric crosslinking accelerator for sulphur network formation(London [u.a.] : Elsevier, 2020) Hait, Sakrit; Valentín, 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
- ItemDevelopment of Liquid Diene Rubber Based Highly Deformable Interactive Fiber-Elastomer Composites(Basel : MDPI, 2022-01-05) Kamble, Vikram G.; Mersch, Johannes; Tahir, Muhammad; Stöckelhuber, Klaus Werner; Das, Amit; Wießner, SvenThe preparation of intelligent structures for multiple smart applications such as soft-ro-botics, artificial limbs, etc., is a rapidly evolving research topic. In the present work, the preparation of a functional fabric, and its integration into a soft elastomeric matrix to develop an adaptive fiber-elastomer composite structure, is presented. Functional fabric, with the implementation of the shape memory effect, was combined with liquid polybutadiene rubber by means of a low-temperature vulcanization process. A detailed investigation on the crosslinking behavior of liquid polybutadiene rubber was performed to develop a rubber formulation that is capable of crosslinking liquid rubber at 75 °C, a temperature that is much lower than the phase transformation temperature of SMA wires (90–110 °C). By utilizing the unique low-temperature crosslinking protocol for liquid polybutadiene rubber, soft intelligent structures containing functional fabric were developed. The adaptive structures were successfully activated by Joule heating. The deformation behavior of the smart structures was experimentally demonstrated by reaching a 120 mm bending distance at an activation voltage of 8 V without an additional load, whereas 90 mm, 70 mm, 65 mm, 57 mm bending distances were achieved with attached weights of 5 g, 10 g, 20 g, 30 g, respectively.
- ItemFriction, abrasion and crack growth behavior of in-situ and ex-situ silica filled rubber composites(Basel : MDPI, 2020) Vaikuntam, Sankar Raman; Bhagavatheswaran, Eshwaran Subramani; Xiang, Fei; Wießner, Sven; Heinrich, Gert; Das, Amit; Stöckelhuber, Klaus WernerThe article focuses on comparing the friction, abrasion, and crack growth behavior of two different kinds of silica-filled tire tread compounds loaded with (a) in-situ generated alkoxide silica and (b) commercial precipitated silica-filled compounds. The rubber matrix consists of solution styrene butadiene rubber polymers (SSBR). The in-situ generated particles are entirely different in filler morphology, i.e., in terms of size and physical structure, when compared to the precipitated silica. However, both types of the silicas were identified as amorphous in nature. Influence of filler morphology and surface modification of silica on the end performances of the rubbers like dynamic friction, abrasion index, and fatigue crack propagation were investigated. Compared to precipitated silica composites, in-situ derived silica composites offer better abrasion behavior and improved crack propagation with and without admixture of silane coupling agents. Silane modification, particle morphology, and crosslink density were identified as further vital parameters influencing the investigated rubber properties. © 2020 by the authors.
- ItemUnderstanding the Coupling Effect between Lignin and Polybutadiene Elastomer(Basel : MDPI, 2021) Hait, Sakrit; De, Debapriya; Ghosh, Prasenjit; Chanda, Jagannath; Mukhopadhyay, Rabindra; Dasgupta, Saikat; Sallat, Aladdin; Al Aiti, Muhannad; Stöckelhuber, Klaus Werner; Wießner, Sven; Heinrich, Gert; Das, AmitFrom an environmental and economic viewpoint, it is a win–win strategy to use materials obtained from renewable resources for the production of high-performance elastomer composites. Lignin, being a renewable biomass, was employed as a functional filler material to obtain an elastomer composite with a higher degree of mechanical performance. In the presence of a suitable coupling agent, an elevated temperature was preferred for the reactive mixing of lignin with polybutadiene rubber (BR). It is quite fascinating that the mechanical performance of this composite was comparable with carbon black-filled composites. The extraordinary reinforcing behavior of lignin in the BR matrix was understood by an available model of rubber reinforcement. In rubber composite preparation, the interfacial interaction between polybutadiene rubber and lignin in the presence of a coupling agent enabled the efficient dispersion of lignin into the rubber matrix, which is responsible for the excellent mechanical properties of the rubber composites. The rubber composites thus obtained may lead to the development of a sustainable and cost-effective end product with reliable performance. This novel approach could be implemented in other type of elastomeric materials, enabling a genuine pathway toward a sustainable globe.
- ItemTemperature-Dependent Reinforcement of Hydrophilic Rubber Using Ice Crystals(Washington, DC : ACS Publications, 2017-2-2) Natarajan, Tamil Selvan; Stöckelhuber, Klaus Werner; Malanin, Mikhail; Eichhorn, Klaus-Jochen; Formanek, Petr; Reuter, Uta; Wießner, Sven; Heinrich, Gert; Das, AmitThis is the first study on the impact of ice crystals on glass transition and mechanical behavior of soft cross-linked elastomers. A hydrophilic elastomer such as epichlorohydrin-ethylene oxide-allyl glycidyl ether can absorb about ∼40 wt % of water. The water-swollen cross-linked network exhibits elastic properties with more than 1500% stretchability at room temperature. Coincidently, the phase transition of water into solid ice crystals inside of the composites allows the reinforcement of the soft elastomer mechanically at lower temperatures. Young's modulus of the composites measured at -20 °C remarkably increased from 1.45 to 3.14 MPa, whereas at +20 °C, the effect was opposite and the Young's modulus decreased from 0.6 to 0.03 MPa after 20 days of water treatment. It was found that a part of the absorbed water, ∼74% of the total absorbed water, is freezable and occupies nearly 26 vol % of the composites. Simultaneously, these solid ice crystals are found to be acting as a reinforcing filler at lower temperatures. The size of these ice crystals is distributed in a relatively narrow range of 400-600 nm. The storage modulus (E′) of the ice crystal-filled composites increased from 3 to 13 MPa at -20 °C. The glass transition temperature (-37 °C) of the soft cross-linked elastomer was not altered by the absorption of water. However, a special transition (melting of ice) occurred at temperatures close to 0 °C as observed in the dynamic mechanical analysis of the water-swollen elastomers. The direct polymer/filler (ice crystals) interaction was demonstrated by strain sweep experiments and investigated using Fourier transform infrared spectroscopy. This type of cross-linked rubber could be integrated into a smart rubber application such as in adaptable mechanics, where the stiffness of the rubber can be altered as a function of temperature without affecting the mechanical stretchability either below or above 0 °C (above the glass temperature region) of the rubber.