Physical and acoustical performance of natural rubber foam prepared via microwave and convection heating techniques

Abstract

Conventional manufacturing techniques of natural rubber foam (NRF) require long processing time besides producing closed cell structure, a property that limits the application of the NRF. The NRF produced via compression moulding (CPM) and microwave-convection oven heating techniques were compared in this study. The correlation between different processing techniques with the physical, morphological, and acoustic properties of NRF was examined. The results indicated that in all the processing techniques, an increase in the blowing agent (BA) led to a decrease in the density of the NRF. Heating the material sequentially with 16 parts per hundred (phr) of BA in a microwave oven at 1000 Watts, and then, in a convection oven at 150 ℃ produced NRF with a density of 0.23 g/cm³. In contrast, the NRF produced by CPM with 16 phr of BA had a density of 0.35 g/cm³. Scanning electron microscope analysis revealed that the NRF generated by CPM had fewer interconnected and more closed cells. On the other hand, sequential heating using microwave and convection heating techniques and vice versa led to the production of NRF with more open and interconnected cells. The prepared NRF was examined for acoustic properties. The results showed that the NRF produced by CPM at 12 and 16 phr of BA had the lowest ability to attenuate sound wave energy. This was due to the highly solid surface of the sample, which caused high sound wave reflection. Open and interconnected cells significantly improved the acoustic efficiency. These findings indicated that microwave-assisted heating techniques can modify the cellular structure of NRF and produce the material within a shorter period.