Relationship between Mechanical Properties and Microstructure of Rigid Polyurethane Foams with Alternative Blowing Agents

The mechanical response of rigid polyurethane foams to compression, creep and stress relaxation in the rise and transverse directions was examined experimentally with alternative blowing agents and was related to their microstructures. Compression in the rise direction yields a three-stage stress-strain response; an initial linear elastic response leading to yield, a protracted post-yield plateau (plastic phase) and a final sharp rise in compressive stress (densification phase). Compression in the transverse direction however, gives a monotonously increasing stress-strain curve. It shows that CFC-11 makes rigid polyurethane foam stronger in both direction than the HCFC-141b and cyclopentane. Creep tests show different behavior in the rise and transverse direction. Stress relaxation experiments indicate different relaxation times for rigid polyurethane foams which were blown with alternative blowing agent. Stress relaxation time increases with increasing of strain in both directions. Foams microstructure were observed by optical microscope and related to the mechanical properties.

Keywords:

polyurethane foam , mechanical properties , microstructure , creep , stress relaxation time