Microspheres as a stabilizing element in polyurethane-cork composites

Abstract

Rigid polyurethane foam (RPUF) is a commonly used material for thermal insulation in buildings. Recent literature suggests a trend towards incorporating renewable additives in the synthesis of RPUF. For example, cork is a filler that can significantly improve polyurethane foam characteristics, particularly mechanical, thermal and acoustic properties. Conversely, the addition of cork to the polyurethane matrix results in material deformation. This article presents the innovative effect of microspheres as a stabilizing agent for size changes in polyurethane cork composites. Furthermore, the paper aims to describe the synthesis of RPUFs containing cork and microspheres – inorganic spherical beads with high thermal resistance. Unfortunately, the addition of filler can cause deterioration in other parameters, such as dimensional stability. An extensive analysis of the resulting composite is presented, including studies of the foaming process, morphology, physical properties, mechanical properties, and flammability. The incorporation of 10 wt% aluminosilicate microspheres resulted in 24 % higher compressive and tensile strengths, while the same amount of cork reduced the parameters by 52 % and 17 %, respectively. The greatest positive impact on thermal conductivity value was achieved by incorporating 10 wt% aluminosilicate microspheres, i.e. a reduction of 2.5 % compared to the control polyurethane foam. The addition of cork and microspheres increased the early-stage thermal stability by a maximum of 23 ºC and 5 ºC, respectively, while in conjunction with both fillers this was increased by a maximum of 3 ºC when 7.5 wt% cork and 2.5 wt% microspheres were used.