Citric acid (CA) can be found naturally in fruits and vegetables, particularly citrus fruit. CA is widely used in many fields but its usage as a green modifying agent and binder for wood is barely addressed. Esterification is one of the most common chemical reactions applied in wood modification. CA contains three carboxyl groups, making it possible to attain at least two esterification reactions that are required for crosslinking when reacting with the hydroxyl groups of the cell wall polymers. In addition, the reaction could form ester linkages to bring adhesivity and good bonding characteristics, and therefore CA could be used as wood binder too. This paper presents a review concerning the usage of CA as a wood modifying agent and binder. For wood modification, the reaction mechanism between wood and CA and the pros and cons of using CA are discussed. CA and its combination with various reactants and their respective optimum parameters are also compiled in this paper. As for the major wood bonding component, the bonding mechanism and types of wood composites bonded with CA are presented. The best working conditions for the CA in the fabrication of wood-based panels are discussed. In addition, the environmental impacts and future outlook of CA-treated wood and bonded composite are also considered.

Forest covers 4.06 billion hectares (ha) or 31 of the total land area worldwide, where 93 (3.75 billion ha) are natural regenerating forests and the remaining 7 (294 million ha) are planted forests. Eucalyptus spp., being one of the most important plantation species, has been planted in 95 countries around the world, and the area of plantation has exceeded 22.57 million ha. In the southern hemisphere, it is a significant industrial fast-growing tree species. These plantations serve as a valuable resource for the timber and fibre-based industries. Eucalyptus is the main fibre resource for the pulp and paper industries in developed countries. Timber extracted from the planted eucalyptus trees has long been used for solid wood and its fibres were used for manufacturing medium-density fibreboard. In comparison to most softwood species, Eucalyptus timber is reported to have a higher rigidity, making it ideal for manufacturing structural products. Therefore, this paper presents a review and analysis of the recent state of research on the utilisation of planted eucalyptus for engineered wood products (EWPs) manufacturing. This study investigated Eucalyptus-based EWPs such as particleboard, fibreboard, oriented strand board, laminated veneer lumber, plywood, glue laminated lumber, and cross-laminated lumber. The feasibility of using planted Eucalyptus in the production of EWPs, as well as the challenges encountered, was also discussed.