چكيده لاتين :
The influence of alternative blowing agents on the mechanical properties and microstructure of rigid polyurethane (RPU) foam and their relationship were examined. The compression, creep and stress relaxation tests were conducted on RPU foams. For compression test, loading was applied at a rate of 5 mm/min; and for creep tests, a constant stress (0.12 MPa) was applied for 15 min and the strain was
recovered for the next 15 min. In stress relaxation experiments the constant strain (3%) was applied for 15 min in the rise and transverse directions. The results of mechanical properties showed that the stiffness of the samples in the rise direction was higher than
the transverse direction . Furthermore, the yield strain for all the samples in the transverse direction was higher than the rise direction. Creep and stress relaxation results, showed that the RPU foam in the rise direction exhibited higher creep recovery , and lower stress decay than the transverse direction . RPU foam which was blown with
n-pentane showed the highest creep recovery and the lowest stress decay, and the foams blown with cyclopentane showed the lowest creep recovery and the highest stress decay at both directions. The microstructures of the foams were studied with an
optical microscope. The results of microstructural studies indicated that the RPU foam with the smallest cell size and the narrowest cell size distribution exhibited the highest compressive strength and modulus. RPU foam blown with n-pentane produced the
smallest average cell size and narrowest cell size distribution which led to the highest compressive strength and modulus, and the foams blown with cyclopentane produced the largest average cell size and the broadest cell size distribution leading to thelowest compressive strength and modulus.
