Mechanical and Thermal Properties of Polyurethane Foams from Liquefied Sugar Beet Pulp

Polyurethane (PU) foams were prepared from microwave liquefied sugar beet pulp (LSBP) and polymethylene polyphenyl isocyanate (PAPI) by using a one-step method. The [NCO]/[OH] ratio was increased from 0.6 to 1.2, and the effect of this ratio on the mechanical, thermal and microstructural properties of the LSBP–PU foams was studied. The allophanate, isocyanurate and free isocyanate were detected in all the foams. The thermal degradation of these foams in air occurred in two main stages; the first one occurred at 200–350 °C and the second one occurred at 300–400 °C. The Tg of the foams increased when the [NCO]/[OH] ratio increased up to 0.9 above which it decreased. As the [NCO]/[OH] ratio increased, the less regular structure and broken cell shape (observed through SEM) indicated that severe damage in structural stability and mechanical properties of LSBP–PU foams occurred. The cellular structure of the foams could be controlled by controlling the gelling and blowing reactions through the control of NCO]/[OH] ratio.