Effects of Wood Flour and Curing Temperature on Some Properties of the Polyurethane Foam Core in a Wood-Based Sandwich Panel

Abstract

The objectives of this study were to examine the chemical, physical, and mechanical properties of polyurethane (PU) foam prepared with various wood flour contents and curing temperatures for use as a core layer in wood-based sandwich panels. The five alternative wood flour contents tested were 2, 4, 6, 8, 10, and 12%, and the alternative curing temperatures 100, 120, 140, and 160°C were studied with 10% wood flour content. The results showed that the cell size and density of the PU foam increased at wood contents above 6%, which reduced the compressive strength of the samples. It was also found for PU with 10% wood content that curing at 100 to 160°C caused a decrease in foam density by 50%, compared with PU foam cured under the standard conditions (i.e., at room temperature). SEM and cell size measurements show the anisotropy of PU foam and the increase of foam cell diameter when increasing the curing temperature from standard condition to 140°C. Consequently, the compressive strength and its specific value declined abruptly at elevated curing temperatures, starting from 100°C. These results suggest that elevated curing temperatures cause degradation of the properties of wood-filled PU foam, due to effects on foam cell structure.