Acoustic and thermal insulation properties of rubberhemp shive composite bonded with regenerated polyurethane resin

Studies on recycled materials for sound absorption and thermal insulation applications has emerged in recent years. This paper investigates the composite material made of the rubber granules and hemp shives. The rubber granule was gained from tyre recycling factory, and hemp shives which is still considered as waste in hemp fibre production. This paper analyses the hemp shives influence on acoustic and non-acoustic properties of rubber granule and hemp shive (RGHS) composites bonded with regenerated polyurethane resin. Tested composite material samples varied in rubber grain (RG) size (0.5-2 mm; 24 mm; 4-6 mm) and hemp shives (HS) (avg. length 7 mm; avg. width 2.2 mm). In this study the HS quantity was controlled and increased by ratio from 0 to 1:1. Samples of four thicknesses (10, 20, 30, 50 mm) were tested to find the HS influence on sound absorption coefficient. For non-acoustic parameters estimation gas pycnometry and inverse characterisation method according to Johnson-Champoux-Allard (JCA) model was used. The results showed that some of the parameters were influenced by change of hemp shive quantity in the composite panel. HS content in the composite increment influenced the airflow resistivity decrement by 50-57%, bulk density decrement by 21-28%, porosity increment by 12-17%. The acoustic sound absorption performance was tested using impedance tube transfer function method (ISO 10354-2). The peak sound absorption coefficient varied from 0.60-0.97 depending on the sample thickness and configuration. The correlation between hemp shive quantity and sound absorption was not significant. The test of thermal conductivity according to EN 12664 showed that minimum value of the RGHS panels of thermal conductivity coefficient was 0.07 W/m·K. Such results indicate that RGHS could be developed as multi-purpose material for sound absorption and thermal insulation applications. The aim of this paper was to incorporate HS into rubber granule panels and to investigate its influence on the acoustic and non-acoustic properties on the RGHS composite panels.