RELATIONSHIP BETWEEN THE TEMPERATURE AND FREQUENCY DEPENDENCE OF THE DAMPING PROPERTIES OF NATURAL RUBBER WITH DIFFERENT EPOXIDATION LEVEL

RELATIONSHIP BETWEEN THE TEMPERATURE AND
FREQUENCY DEPENDENCE OF THE DAMPING
PROPERTIES OF NATURAL RUBBER WITH DIFFERENT
EPOXIDATION LEVEL
MlSA Rahim' & P Bont'iglio2
☁Department of Mechanical Engineering. The University of Shefeld. Shefeld. 51 3.10. United
Kingdom
2Dipartimento di lngegneria. Universita degli Studi di Ferrara. Via Saragat 1, 44122 Ferrara. Italy
Corresponding email: mibsetharahim1shefeld.ac.uk (mibsetharahim1[at]shefeld[dot]ac[dot]uk)
1 INTRODUCTION
Two common ways to control noise is either by reducing the power radiated by the source or through
insulation☁. The latter method is used wider whenever it is not practical to reduce the power of the
source. This is done because the problem of air-bome noise and structure-borne vibrations has a
negative inuence on the human health and general quality of life 29. Numerous studies have been
carried out to develop new materials and technologies to improve the performance of vibration and
noise control products. Nowadays. the viscoelastic materials such as rubbers have beenused
extensively in vibration and noise control applications. These materials provide elastic and viscous
characteristic in a range of temperatures and frequencies. Important characteristics of these materials
are their dynamic mechanical properties. i.e. the dynamic modulus (stiffness) and loss factor
(damping). The stiffness represents the elastic nature of the materials while the damping represents
the viscous nature of the materials. It is essential to evaluate the dynamic material properties because
they control the ability of these materials to reduce noise and vibration levels☁.
Principally, material like rubber dissipates vibratory energy by converting it into heat energy. The
internal friction between the long polymer chains that form the material is the main energy dissipation
mechanism. This situation is known as ☁mechanical hysteresis'5. The loss factor. often denoted as tan
6. is a parameter used to measure the vibration energy dissipation or damping behaviour of the
materials. According to Lu and Li☜. materials with effective damping should display high loss factor in
the broad temperature and frequency range. However. the loss factor is normally greatest over a
narrow temperature range which is near to their glass transition temperature (T9).
In this context. natural rubber with different epoxidation level or known as Epoxidized Natural Rubber
(ENR) becomes the main focus in this study. This is an interesting altemative material to be studied
instead of synthetic rubber. ENR is produced by epoxidation of natural rubber at the latex stage and
is classied as a green material as it is produced from a renewable natural resource unlike synthetic
rubbers which are derived from petroleum based resources☝. In addition. the study would be an
interesting subject as epoxidation level in the natural rubber has been reported to inuence the
increment in T9☝.
Epoxidation is stereospecic process; which is also related to the replacements on the double bond
of the polymer backbone? In the case of natural rubber latex. a percentage of its double bonds react
to form epoxide groups. Figure 1 shows the reaction of natural rubber (NR) latex with peracetic acid
solution. In the reaction, the epoxide groups could be observed distributed randomly along the natural
rubber backbone. Specic levels of ENR can be produced under right reaction conditions; acid
concentrations and temperatures.
The reason for this work is because☁ this material has been studied extensively in the tire industry☝,
but its actual ability to control vibration and noise is poorly understood. particularly over a range of
frequencies and temperatures. Thus. one aspect of our study is to investigate the effect of the
Vol. 38. Pt. 1. 2016