ABSTRACT
Citric acid (CA) is a weak organic acid. It exists most notably in citrus fruits, after which it is named. As a commodity chemical, CA is produced on a large scale by fermentation. In this chapter, we first briefly review the applied research and methods for commercial production of CA. Then we synthesize and discuss the recent research on CA as a wood adhesive additive. For the purpose of wood bonding, CA can serve as a minor additive, functioning as a cross-linking catalyst, a cross-linking agent, or a dispersing agent to improve the adhesive strength and/or operational properties (such as viscosity). CA, with or without sucrose, can also be a major adhesive component in manufacturing fiber and particleboards with a variety of lignocellulose raw materials. The formation of ester linkages between CA and lignocellulose molecules (raw materials and/ or sucrose) developed adhesiveness and contributed to the good physical properties of the particleboards made with CA. These laboratory research accomplishments demonstrate that application of CA as a renewable natural adhesive compound for wood and lignocellulosic composites is possible. Further effort is on optimizing practical manufacturing conditions for specific types of wood-based molding and medium or low density lignocellulosic particleboards, using CA as an adhesive additive.
