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Oxidation of Natural Rubber based Magnetorheological Elastomers
KTH, Superseded Departments, Fibre and Polymer Technology.
KTH, Superseded Departments, Chemistry.
KTH, Superseded Departments, Fibre and Polymer Technology.
2004 (English)In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 86, no 3, 467-471 p.Article in journal (Refereed) Published
Abstract [en]

The Theological properties of magnetorheological (MR) materials can be changed continuously, rapidly and reversibly by an applied magnetic field. Solid MR materials consist of magnetically polarisable particles, generally iron, in an elastomer matrix. The high iron concentrations required (about 30% by volume) in order to get a substantial magnetorheological effect should influence the long-term stability of the materials. In this paper, the oxidative stability of natural rubber-based magnetorheological elastomers has been studied by chemiluminescence and oven ageing. The results show that the oxidative stability of natural rubber decreases dramatically when large amounts of iron particles are incorporated in the matrix. This is probably due to the large amounts of oxygen on the surface of the particles. Conventional antioxidants can be used to prolong the lifetime of magnetorheological elastomers, but in order to get acceptable lifetime of the materials a careful selection of the antioxidant system has to be made.

Place, publisher, year, edition, pages
2004. Vol. 86, no 3, 467-471 p.
Keyword [en]
Iron, Magnetorheology, Natural rubber, Oxidation
National Category
Chemical Engineering
URN: urn:nbn:se:kth:diva-5336DOI: 10.1016/j.polymdegradstab.2004.05.019ISI: 000225547600010ScopusID: 2-s2.0-5644268085OAI: diva2:8857
Available from: 2004-10-01 Created: 2004-10-01 Last updated: 2011-08-26Bibliographically approved
In thesis
1. Performance of Magnetorheological Rubber Materials
Open this publication in new window or tab >>Performance of Magnetorheological Rubber Materials
2004 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Magnetorheological (MR) rubber materials are the solid analogue of magnetorheological fluids; i.e. their rheological properties can be controlled continously, rapidly, and reversibly by an applied magnetic field. They consist of magnetically polarisable particles in an elastomer matrix and they can be made to respond to changes in their environment; hence, they are considered as "smart" materials. Examples of potential applications for these materials are adaptive tuned vibration absorbers, stiffness-tuneable mounts and suspensions, and automotive bushings.

The purpose of this work was to increase the knowledge relating to magnetorheological materials for damping applications. The materials should exhibit a large response to an applied magnetic field, and have good mechanical and long-term properties.

MR rubber materials were made from nitrile, natural and silicone rubber, with irregularly shaped iron particles several micrometres in size. The particles were not aligned by a magnetic field prior to the vulcanisation; hence, the materials can be considered to be isotropic. These materials show a large MR effect, i.e. an increase in the shear modulus when a magnetic field is applied, although the particles are not aligned within the material. This is explained by the low critical particle volume concentration (CPVC) of such particles. Similar behaviour can be obtained with materials containing carbonyl iron, if the particles are aggregated so that they behave like large irregular particles. The iron particle concentration must be very close to the CPVC in order to obtain a large MR effect without alignment of the particles.

The absolute MR effect (MPa) in an isotropic MR rubber material with large irregular iron particles is independent of the matrix material, and the relative MR effect (%) can thus be increased by the addition of plasticisers. However, the obtainable effect is limited by the reinforcement of the particles and by friction between the particles. Therefore, it is very difficult, if not impossible, to achieve an MR effect larger than 60%.

Other ways of increasing the MR effect are to increase the strength of the magnetic field, although the materials saturate magnetically at high field strengths, or to use small strain amplitudes. The strong strain amplitude dependence of the MR effect suggests that MR rubber materials are most suitable for low amplitude applications, such as sound and vibration insulation. Measurements at frequencies within the audible frequency range show that this is a promising application for MR rubber materials.

The incorporation of large amounts of iron into the rubber matrix decreases the oxidative stability dramatically. This is probably due to iron oxides on the surface of the particles, and to the fact that the oxidation rate is enhanced by iron ions, which are able to diffuse into the matrix. Standard antioxidants do not provide sufficient stabilisation for MR rubbers. Thus, proper stabilisation systems have to be found in order for these materials to be successful in applications.

Place, publisher, year, edition, pages
Stockholm: Fiber- och polymerteknologi, 2004
Trita-FPT-Report, ISSN 1652-2443 ; 2004:32
Materials science, magnetorheological rubber, Materialvetenskap
National Category
Materials Engineering
urn:nbn:se:kth:diva-31 (URN)91-7283-856-6 (ISBN)
Public defence
2004-10-01, K2, KTH, Teknikringen 28, Stockholm, 10:00
Available from: 2004-10-01 Created: 2004-10-01 Last updated: 2012-03-22

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