Viscosity and bond quality of urea formaldehyde adhesive extended with acid modified and phosphorylated sago (Metroxylon sp)

Graduation date: 1996It was the goal of this research to determine if sago\ud starch could be used to replace wheat flour as an adhesive\ud extender of Urea-formaldehyde plywood adhesives through\ud either chemical modification of the starch or modification\ud of the adhesive formulation strategy. Guiding principles of\ud the research would be that a useful adhesive would have a\ud viscosity of 1500 cPs and exhibit a curing rate and bond\ud strength comparable to a wheat-flour extended adhesive as\ud measured by the Automated Bonding Evaluation System (ABES)\ud machine.\ud The research was performed in three stages. In the\ud first stage, the effect of water content, chemical\ud modification, pH, retrogradation, viscosity, water intake\ud and bulk density on the physical properties of sago starch\ud were investigated. Two chemical modifications of sago starch\ud were employed, acid modification with dilute hydrochloric\ud acid and phosphorylation. In the second stage of experiments, the effect of sago\ud starch content (both natural and modified) on adhesive\ud viscosity was studied where the amount of Urea-formaldehyde\ud resin was held constant.\ud Data from the first two stages of research were used to\ud formulate adhesive mixtures with 1500 cPs viscosity which\ud were studied for curing rates and maximum bond strength.\ud This viscosity was chosen as one that would fit into current\ud Indonesian plywood production practices. It was found in\ud this stage of the research that all forms of the sago flour\ud studied, natural, acid modified and phosphorylated could be\ud formulated into a Urea-formaldehyde adhesive that gave\ud satisfactory curing rates and maximum bond strengths\ud compared to a wheat flour extended adhesive. For example, a\ud 30% resin solids formulation extended with natural sago,\ud acid modified sago, phosphorylated sago and wheat flour\ud exhibited curing rates of 0.035, 0.030, 0.022, and 0.027\ud MPa/s respectively. Maximum bond strengths for natural sago,\ud acid modified sago, phosphorylated sago and wheat flour\ud extended adhesives were 9.5, 9.8, 11.1 and 8.9 mPa\ud respectively. Indonesia uses the Japanese Agricultural\ud Standard for certification of its plywood. This standard\ud places paramount importance on bond strength.\ud Phosphorylated sago may be the best for initial scale\ud up to pilot plant tests since its physical properties were\ud closest to those of wheat flour