Plastic in Noise Reduction

Abstract

Polymer foams are suitable for noise reduction materials. The open pores in the foam permit confined airflow via the material thus absorbing sound. The selection of materials is essential for good sound absorption and noise reduction application. Flexible polyurethane (PU) foams with high porosity have been extensively used as noise control materials in many applications in industry due to effective sound absorption, light weight or excellent viscoelasticity properties. A case study was done to investigate the feasibility of epoxy foam (EF), renewable polymer foam (RF), epoxy/renewable polymer foam (ERF) for the noise reduction application. The effects of titanium dioxide (TiO2) filler with 1–3 wt% ratios on the properties of EF and RF were determined. The average porosity, foam morphology, acoustic property such as sound absorption coefficient, α and noise reduction coefficient (NRC) of the polymer foams after exposure to UV (250 h, 500 h, 750 h, 1000 h) were characterized. The density of all foams was evidently changed to the increment of pore sizes which contributed from the decrement of filler loading. The morphological study indicates that EF1–3 and RF1–3 has variety in size of the microporous cellular structure compared to EF, RF and ERF. The EF, RF and EFR shows higher α of 0.965, 0.995 0.945 at frequency absorption level of 2943, 3106 and 3684 Hz, respectively. Meanwhile the lowest α for EF, RF and ERF is 0.878 at 3181 Hz, 0.823 at 3184 Hz and 0.876 at 3526 Hz, respectively. The composites with added TiO2 filler of EF1–3 and RF1–3 shows highest α with 0.968 at 3928 Hz, 0.998 at 3728 Hz, respectively. While the lowest α for both composites are 0.836 at 3512 Hz, 0.878 at 3915 Hz, respectively. This suggests that the highest loading of TiO2 resulted in cell sizes reduction after UV irradiation exposure and contributed to the higher α. In other words, the decrement in cell sizes of higher TiO2 loading improved the sound absorption property at prolonged UV irradiation hours (e.g., 1000 h). Thus, the microporous plastic foam synthesized from recycled cooking oil is a potential product for noise reduction application.