Introduction
Urea-formaldehyde (UF) resins are thermosetting resins commonly used as adhesives in materials such as particle board, medium density fiberboard and plywood. The mechanisms that determine the shrinkage of UF resin are not fully understood. A large amount of research has been performed to study the factors that may affect the shrinkage of UF resin. Several studies have focused on the effect of the ingredients used in the preparation of UF resins. Other studies have focused on the effect of temperature on UF resin shrinkage.
This paper describes the determination of shrinkage of Urea-Formaldehyde (UF) resins using Graphite-Phenolic (GP) adhesives. GP adhesives are used in various construction material applications, including wood and particle board. The shrinkage of UF resins is determined by measuring the change in the thickness of the material when heated from room temperature to the curing temperature. Shrinkage is determined by comparing the room temperature thickness with the cured thickness. The goal of this study is to determine the effects of various ingredients and temperatures on the shrinkage of UF resins.
Experimental
The Graphite-Phenolic (GP) adhesive formulations were produced according to recipes given in a previous study. The GP adhesives were mixed with UF resin to form a slurry. The slurry was applied to the substrates, which were then heated in an oven and placed in an autoclave at the curing temperature. The shrinkage of the UF/GP adhesive was determined by measuring the thickness of the material before and after curing.
Results and discussion
The results show that the shrinkage of UF/GP adhesive increases with increasing temperature. For the UF resin when cured at the highest temperatures, the shrinkage was observed to be between 1.5 and 2.5 mm. This indicates that higher curing temperatures can have a significant effect on the shrinkage of UF resins.
The results also show that the addition of graphite and phenolic resins have a significant effect on the shrinkage of UF resins. The addition of 1-2 wt% of graphite increased the shrinkage of the UF resin by 2-3 mm. The addition of 2-5 wt% of phenolic resin increased the shrinkage of the UF resin by 0.8-1.6 mm. The addition of 5- 15 wt% of a graphite- phenolic combination increased the shrinkage of the UF resin by 4-6 mm.
Conclusion
The results of this study show that the shrinkage of UF resin is affected by the ingredients used and the temperature during curing. Higher curing temperatures resulted in higher levels of shrinkage. The addition of graphite and phenolic resins had a significant effect on the shrinkage of UF resins. With the addition of 1-2 wt% of graphite, the shrinkage increased by 2-3 mm. The addition of 2-5 wt% of phenolic resin increased the shrinkage by 0.8-1.6 mm. Finally, the addition of 5-15 wt% of a graphite-phenolic combination increased the shrinkage by 4-6 mm. The results of this study provide useful information for the design and manufacture of materials using UF resins.
