Abstract
The investigation is for improving the phenolic resin's properties, such as toughness, electrical insulation, and water-proof, was performed by lengthening the distance between two crosslinking nodes and lowering the concentration of OH groups in a phenolic resin. In the concrete, a phenolic resin was modified with undecenyl aldehyde (UA) as follows : At first, phenol (P) was reacted with UA under different molar ratios and an acid condition, producing a UA modified phenolic oligomer (UA modified phenol) by addition reaction of both double bond and carbonyl group of UA to phenolic nuclei. Next, formaldehyde was reacted with free phenol and the oligomer mentioned above, producing a UA modified novolac oligomer by co-condensation between them. The latter oligomer had higher average molecular weight than a conventional phenol formaldehyde novolac. Further, the investigation was made on the flowability and curing behavior of molding compounds which were prepared from both the UA modified phenol and novolac, hexamethylenetetramine as a curing agent, and wood flour as a filler. The flowability of the compound from UA modified novolac I (molar ratio UA/P = 0.1/1) and that from UA modified novolac II (UA/P = 0.2/1) were superior to that from the conventional novolac. Onset temperatures of curing reaction for the molding compounds from UA modified novolacs were similar to that from the conventional novolac. The properties of cured test pieces obtained by transfer molding were found as follows : toughness, electrical insulation and water-proof of cured resins from UA modified novolac I and II were superior to those from the conventional novolac, and heat resistance of cured resin from UA modified novolac 1-2 which had higher molecular weight than I or II was superior than that from the conventional novolac.
