Irene Jansen

Polymeric light stabilizers based on siloxanes

Abstract Polymeric light stabilizers were synthesized by hydrosilylation of unsaturated 2-hydroxybenzophenone derivatives or pentamethylpiperidine derivatives with different hydridosiloxanes. Investigations of the hydrosilylation reaction by NMR and HPLC show that the stabilizer groups are mainly bound to the siloxane chain by non-hydrolysable SiC bonds. When allyl ethers are used as starting material, side reactions such as ether cleavage, hydrogenation and isomerization take place. To avoid these side reactions, unsaturated ethers or esters with long methylene chains between the double bond and the oxygen were used. The polymeric light stabilizers were tested as stabilizers of polypropylene and compared with TINUVIN 770. The activity of polymeric light stabilizers decrease, with increasing molecular weight. Extraction experiments demonstrate that the polymeric stabilizers are resistant against extraction by organic solvents while TINUVIN 770 is extracted under the same conditions. Thus, our polymeric HALS show a higher effectiveness than TINUVIN 770. The polymeric HALS derivatives with the best activity have molecular weights (Mn) between 2000 and 4000.

Synthesis and test of styrene—Cyclosiloxane and butadiene-cyclosiloxane block copolymers containing ultraviolet (UV) absorber and antioxidant groups

Block copolymers of polystyrene and poly(dimethylsiloxane) or of polybutadiene and poly(dimethylsiloxane) with nonhydrolyzably bound 2-hydroxybenzophenone and 2,6-di-tert-butylphenol residues were prepared by terminating the “living” block copolymers with glacial acetic acid to form siloxanol end groups, followed by condensation with diethoxysilyl derivatives of the stabilizers in the presence of dibutyltin dilaurate. The polymeric UV absorbers were proved to be nonextractable from polystyrene. At Xenotest aging (40°C) the polymeric UV absorbers were less effective than 2-hydroxy-4-octyloxybenzophenone. The polymeric antioxidants were superior to antioxidants of low molecular weight both in thermooxidative aging of vulcanized polybutadiene films at 70°C and in oxygen-uptake studies with stabilized polypropylene at 180°C over long periods.

Evaluation of mechanical and laser surface pre-treatments on the strength of adhesive bonded steel joints for the automotive industry

Abstract Recent research efforts in the automotive industry have been focused on the integration of high-strength steels within lightweight vehicles by using improved joining techniques. The present work falls in this subject area and is focused on the analysis of adhesive bonded dual-phase steel/epoxy joints for the automotive industry. Two quasi-static loadcases were considered, i.e. single-lap and T-peel tests, and various surface preparation strategies were evaluated. In particular, the mating surfaces were pre-treated by using pulsed laser irradiation with a fiber laser (1064 nm) and comparisons were made with degreasing and sand blasting. Moreover, the effects of bondline thickness and adhesive type were also assessed. To this aim, two epoxy adhesives with fairly different mechanical behavior (i.e. strain hardening versus elasto-plastic) were deployed for joints fabrication. Finally, T-peel tests were also carried out after sample cycling under controlled high humidity and temperature (i.e. accelerated aging). The obtained results highlighted the beneficial effect of laser irradiation on the joints’ mechanical behavior under both static and hydrothermal loadings.

Optimization of the aluminum oxide properties for adhesive bonding by laser surface pretreatment

The laser pretreatment of AlMg3 has been conducted to investigate the influence of the fluence on the oxide properties. Therefore, the aluminum surface is pretreated by a fiber laser and subsequently analyzed by SEM, EDX, and XPS. Finally, mechanical measurements are performed on adhesively bonded specimens to study the surface properties produced. For the purpose of comparison, the two state-of-the-art pretreatment methods etching and phosphoric acid anodizing are also investigated. The results show that laser pretreatment changes the properties of the aluminum surface and especially those of the oxide layer. The latter grows in comparison to the natural oxide layer of etched surfaces but does not reach the dimensions of an electrochemically formed oxide layer. Mechanical testing showed that the laser treated specimens reach and exceed the strength values of etched and anodized surfaces, respectively. However, strength after aging does not keep up with the good long-term resistance of anodized aluminum, ...

Aluminium preatreatment and the properties of adhesively bonded joints

SUMMERY: The influence of metal pretreating on the properties of adhesively bonded joints was investigated. AlMg3 and several pre-treatment methods were used. The pre-treated surfaces and the joints were characterized using: SEM/EDX, XPS, EIS, surface tension, DMA, μTA and the determination of mechanical parameters. The highest bond strengths were obtained using anodic oxidation in phosphoric acid as the pre-treatment method.

Full Polymer Dielectric Elastomeric Actuators (DEA) Functionalised with Carbon Nanotubes and High-K Ceramics

Dielectric elastomer actuators (DEA) are special devices which have a simple working and construction principle and outstanding actuation properties. The DEAs consist of a combination of different materials for the dielectric and electrode layers. The combination of these layers causes incompatibilities in their interconnections. Dramatic differences in the mechanical properties and bad adhesion of the layers are the principal causes for the reduction of the actuation displacement and strong reduction of lifetime. Common DEAs achieve actuation displacements of 2% and a durability of some million cycles. The following investigations represent a new approach to solving the problems of common systems. The investigated DEA consists of only one basic raw polymer, which was modified according to the required demands of each layer. The basic raw polymer was modified with single-walled carbon nanotubes or high-k ceramics, for example, lead magnesium niobate-lead titanate. The development of the full polymer DEA comprised the development of materials and technologies to realise a reproducible layer composition. It was proven that the full polymer actuator worked according to the theoretical rules. The investigated system achieved actuation displacements above 20% regarding thickness, outstanding interconnections at each layer without any failures, and durability above 3 million cycles without any indication of an impending malfunction.

Laser- und Plasmaverfahren im wirtschaftlichen Vergleich

Bei der Vorbehandlung von Aluminiumwerkstoffen wird noch immer vorwiegend auf nasschemische Prozesse zuruckgegriffen. Als Alternative dazu empfehlen sich sowohl fur den konstruktiven als auch dekorativen Automobilbau trockene Verfahren auf Basis von Plasma- und Laserprozessen. Welcher okonomische Nutzen erzielt werden kann, lasst sich am besten anhand eines Anwendungsbeispiels verdeutlichen.

Unsymmetric telechelic siloxanes with SiH and stabilizer end groups

Abstract Linear siloxanes were synthesized with SiH groups at one end of the chain and light stabilizer or antioxidant groups at the other end. Silanolates with hindered amine or hindered phenol groups were first prepared and subsequently used as initiators of the anionic ring opening polymerization of hexamethylcyclotrisiloxane. The termination of the anionic polymerization with chlorodimethylsilane yielded the desired unsymmetric telechelic siloxanes.

Polyelektrolytadsorption ergänzt Laservorbehandlung

Die Festigkeit und Langzeitbeständigkeit geklebter Aluminiumteile hängt bekanntlich sehr stark von der Vorbehandlung der zu klebenden Aluminiumoberflächen ab. Laserverfahren ermöglichen eine lateral definierte Aktivierung von Klebflächen, können aber nicht gewährleisten, dass der erzielte Reinigungsund Aktivierungseffekt bei Lagerung erhalten bleibt. Welche Wirkung zeigen in diesem Kontext geeignete wasserlösliche Funktionspolymere wie zum Beispiel Polyelektrolyte?

Lasergestütztes Fügen ohne Fugen

Die Lasertechnik ist aus dem Industriealltag nicht wegzudenken und hat sich aufgrund ihrer fertigungstechnischen Moglichkeiten in verschiedensten Anwendungen und insbesondere beim Fugen gleicher oder ungleicher Werkstoffpaarungen schon lange durchgesetzt. Auf welche Weise das Potenzial in der Mobelherstellung genutzt werden kann, verdeutlichen die folgenden Ausfuhrungen.