Studies on the improvement of cured two‐stage phenolics performance. III. Relation between conditions of heat treatment and properties of wood‐flour‐filled phenolics

摘要

AbstractThe effect of heat treatment on the properties of cured two‐stage phenolics was studied. Samples were compression‐molded from the compound that was prepared from novolac, wood flour (100 phr), and hexamethylenetetramine (15 phr). Samples were heat‐treated in conditions of four levels for temperature (150°C, 170°C, 190°C, and 210°C) and time (4, 8, 16, and 24 h). The properties of samples heat‐treated, such as weight loss, dimensional stability, water absorption after boiling, and flexural properties were measured. The relation between the properties and the conditions of heat treatment was examined statistically. From the results, it was decided that the optimum conditions of heat treatment for practical use were: (i) to decrease water absorption and to heighten electrical resistance, 210°C, 24 h; (ii) to improve flexural properties at room temperature and at 160°C; 170°C, 8 h, and 170–190°C, 24 h, respectively. It was concluded that the decrease of water absorption of moldings was due to the increase of hydrophobic nature of wood flour included in moldings by heat treatment and that the improvement of flexural property of moldings at 160°C was due to an increase of crosslinking density by heat treatment. The reasons for the improvement of the electrical properties by heat treatment w