Citric Acid-modified Starch as an Environmentally Friendly Binder for Wood Composite Making

Conventional formaldehyde-based wood binders for composites have been reported as hazardous to humans after prolonged exposure to released fumes. Therefore, this research was conducted to evaluate suitability of citric acid-modified corn starch as binder for wood composites. Corn starch was gelatinized before it was reacted with citric acid, mixed with wood particles, pre-pressed, and finally hot-pressed before characterization and evaluation. Through Fourier transform infrared analysis, ester groups were detected at 1736.8 cm-1, which was characteristic for starch modified with citric acid. Bending test results on citric acid modified corn starch wood composites showed 16.8 N/mm2 and 4020 N/mm2 for modulus of rupture and modulus of elasticity, respectively. Addition of 2% urea-formaldehyde increased these numbers to 17.9 N/mm2 and 5190 N/mm2, respectively. Internal bonding additionally increased from 0.88 N/mm2 to 0.95 N/mm2. All test specimens passed mechanical strength requirements by JIS A 5908 (2003). Based on the demand specification for the final usage of the wood composite, it can be concluded that citric acid modified starch is a possible successful choice as the adhesive, with or without additional urea formaldehyde resin.