Mechanical properties of rigid polyurethane foams at room and cryogenic temperatures

摘要

Studies on the effect of the foams' polymeric matrix' properties on the tension and compression properties of pour rigid polyurethane (PUR) foams, apparent core density 65-70 kg/m~3, at 296 and 77 K were carried out. PUR foams were produced by the hand mixing method from polyol systems that comprised polyether, polyester polyols, and chain extenders. To produce PUR foams, crude MDI was used, and Solkane 365 mfc/227 ea was used as a blowing agent. The molecular weight per branching unit (M_c) of the polymeric matrix of PUR foams was varied in the range 300-1150. Cohesion energy densities of the blocks forming the polymeric matrix were calculated. The effect of M_c on the formation of hydrogen bonds between the urethane groups was estimated from FTIR spectroscopy data and ratio NH_(bonded)/NH_(free). It has been found that, with increasing polymeric matrix' M_c, the tensile strength and elongation at break of PUR foams at 296 and 77 K increases, while Young's modulus decreases. The increase in the parameter M_c promotes the decrease in the compressive strength and modulus of elasticity of PUR foams at 296 K, while compressive strength indices at 77 K are higher for the foams, whose polymeric matrix has the highest M_c. With increasing polymeric matrix' M_c, the concentration of the urethane groups bonded with hydrogen bonds increases. Structural and mechanical properties of layered spray polyurethane foams, apparent core density approx. 48 kg/m3, having two layers and polymeric matrix' M_c = 740 were investigated.