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Heinze D.,FH Aachen | Mang T.,FH Aachen | Popescu C.,KAO Germany GmbH | Weichold O.,Institute of Building Materials Research
Thermochimica Acta | Year: 2016

Four members of a homologous series of chlorinated poly(vinyl ester) oligomers CCl3–(CH2CH (OCO(CH2)mCH3))n–Cl with degrees of polymerization of 10 and 20 were prepared by telomerisation using carbon tetrachloride. The number of side chain carbon atoms ranges from 2 (poly(vinyl acetate) to 18 (poly(vinyl stearate)). The effect of the n-alkyl side chain length and of the degree of polymerization on the thermal stability and crystallization behaviour of the synthesized compounds was investigated. All oligomers degrade in two major steps by first losing HCl and side chains with subsequent breakdown of the backbone. The members with short side chains, up to poly(vinyl octanoate), are amorphous and show internal plasticization, whereas those with high number of side chain carbon atoms are semi-crystalline due to side-chain crystallization. A better packing for poly(vinyl stearate) is also noticeable. The glass transition and melting temperatures as well as the onset temperature of decomposition are influenced to a larger extent by the side chain length than by the degree of polymerization. Thermal stability is improved if both the size and number of side chains increase, but only a long side chain causes a significant increase of the resistance to degradation. This results in a stabilization of PVAc so that oligomers from poly(vinyl octanoate) on are stable under atmospheric conditions. Thus, the way to design stable, chlorinated PVEs oligomers is to use a long n-alkyl side chain. © 2016 Elsevier B.V.

Kang B.-G.,RWTH Aachen | Hannawald J.,Institute of Building Materials Research | Brameshuber W.,RWTH Aachen
ACI Materials Journal | Year: 2011

To analyze the damage and failure mechanisms of a multifilament yarn embedded in concrete during a pullout test, an acoustic emission analysis was carried out for the identification and localization of ' filament ruptures. The different damage mechanisms (filament rupture, filament debonding, and concrete microcracking) causing acoustic emission were first characterized for separation. Tests were carried out to generate isolated signals, which were studied using signal and frequency analysis. A high localization accuracy of the filament ruptures in the yarn pullout test could be achieved, and the damage progress of the yarn during the pullout test could be analyzed in detail. Copynght © 2011, American Concrete Institute. All rights reserved,.

Tigges B.,RWTH Aachen | Popescu C.,RWTH Aachen | Weichold O.,RWTH Aachen | Weichold O.,Institute of Building Materials Research
Soft Matter | Year: 2011

In this article a nanocomposite hydrogel system consisting of isocyanate-terminated, star-shaped poly(ethylene oxide) and spherical silica nanoparticles is presented that allows tuning of the mechanical and sorption properties by varying the particle size. With 9 nm silica particles, an almost threefold increase in both the hardness and reduced modulus is observed compared to the pure gel without losing moisture-adsorption capacity. Krenchel's efficiency factors indicate a very weak interfacial interaction between the polymer network and the small particles. The 21 nm particles give rise to a more than 25-fold increase in the hardness and a more than one hundredfold increase in the reduced modulus. However, the maximum water-uptake is reduced to half of that for the pure gel. Surface amino-functionalisation of the particles that allows covalent binding to the polymer is detrimental as it leads to inhomogeneous materials. Thermodynamic investigations reveal a transition of the water molecules into a more ordered, but only weakly hydrogen-bonded state upon adsorption rather than a condensed water phase. This might be a general phenomenon in hydrogels with consequences for synthetic materials as well as biological tissue. © 2011 The Royal Society of Chemistry.

Weichold O.,Institute of Building Materials Research | Antons U.,Institute of Building Materials Research
Advanced Materials Research | Year: 2013

The effect of incorporating elastomeric domains in concrete is described from the point of fracture mechanics. Concrete is subject to brittle failure, since cracks propagate at an enormous speed in the crystalline matrix. However, micro cracks are attracted to volume elements with lower elastic moduli such as elastomeric domains. Cracks that encounter the concrete-elastomer interface are stopped since energy is dissipated by plastic deformation of and/or crack deflection by the elastomer. The domain size and the distribution of the elastomer as well as, and properties of the elastomer-concrete interface are crucial parameters. Such a combination differs substantially from previously prepared polymer-impregnated concretes, in which only glassy polymers were used. © (2013) Trans Tech Publications, Switzerland.

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