Epoxidized Natural Rubber in Vibration and Noise Control Applications

The rise of the synthetic rubber and the fall in natural rubber prices are all motivations for the natural rubber industry to produce new specialty grades of natural rubber such as Epoxidized Natural Rubber (ENR). The optimal way to ensure the successfully of this ENR depends on the operational conditions and the potential applications. ENR is specialty grade chemically modified natural rubber and it is produced by epoxidation of natural rubber at the latex stage. There are two commercial grades available for ENR which have different epoxidation levels: 25 mol% and 50 mol%. These are referred as ENR-25 and ENR-50 respectively. ENR has been developed mainly to be used in the tyre industry, but its actual ability to control vibration and noise is poorly understood. Therefore, the aim of the research is to develop a method to design Epoxidized Natural Rubber (ENR) that can be used in vibration and noise control applications. In this study, dynamic properties of solid natural rubber with 0, 25 and 50 mol% epoxidation levels were firstly identified over a range of temperatures and frequencies, and a master curve for their dynamic properties was generated based on the time-temperature superposition principle. The natural rubber foams were then produced from the solid natural rubber formulations containing blowing agents using a two-roll mill mixer and a compression moulding. The foams were characterised physically with respect to their density, porosity and airflow resistivity. Dynamic properties of the foams were analysed over a range of temperatures and frequencies. The microstructure properties of the foams were scanned using Micro Computer Tomography (Micro-CT) scanner, and the mean pore size was generated based on the micrographs obtained, while the acoustic properties of the foams were measured using a two-microphone impedance tube to determine its sound absorption coefficient efficiency. This research provides new data on the physical, dynamic, microstructure and acoustical properties of natural rubber foam with different epoxidation levels. In addition, the modelling work was carried out to understand the relationship between the key non-acoustical parameters of natural rubber foam properties and its acoustic absorption performance. These observations are of a high value to help design natural rubber foams for noise control applications.