Reduction of the thermal conductivity of the rigid polyurethane material with nano additives and design of microstructure

The modification and production of nano-clay from local clay sources have been studied. The nano-clay produced has been used in rigid polyurethane (PU) as an additive, and the structural changes of polyurethane such as cell size and distribution and the change of thermal and mechanical properties of rigid polyurethane have been evaluated. In addition to this, the recycling of the polyurethane rags to powder form and the usage of the powder in the rigid polyurethane to change the cell structure and the related thermal and mechanical property changes has been studied. Additionally, the control of the flow of the polyurethane to change the cell size and distribution and related changes of the thermal and mechanical properties has been studied. The hydrophilic clay has been modified by hexadecyltrimethylamonium bromide (CTAB), and the hydrophobicity of the clay is increased from 13° to 80°. The intergallery distance of the clay is increased from 12.5 Å to 18.8 Å. The cell size of the rigid polyurethane has been decreased by 65% by the addition of the modified clay, 15% by the addition of recycled PU powder , and the thermal conductivity is decreased by 8% and 2.5% respectively. With the flow control, the cell size has been decreased by 35%, and the thermal conductivity is decreased by 6.5%. At all the trials, the compressive strength of the polyurethane, which is a critical property for the refrigerator application has been followed and found to be not less than the lower critical value of 120 kPa. The lowest thermal conductivity attained in this study is 20.7 mW/mK.