Abstract
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.
Highlights
Penniston et al [3] stated that lemons and limes are among the citrus fruits that contain a higher concentration of Citric acid (CA), which amount to 8% of the dry weight of the fruits
Doll et al [44] and Larnøy et al [52] suggested that 150 ◦ C and 140 ◦ C is a better curing temperature than other lower temperatures used in their respective studies, it could be concluded that temperature of at least 140 ◦ C is required to ensure the polyesterification occurs to a greater extent
The following summaries can be drawn based on the review of the present literatures and works: 1
Summary
Seng Hua Lee 1, * , Paridah Md Tahir 1 , Wei Chen Lum 2 , Li Peng Tan 3, * , Paiman Bawon 4, *, Byung-Dae Park 5 , Syeed SaifulAzry Osman Al Edrus 1 and Ummi Hani Abdullah 4. Faculty of Veterinary Medicine, Universiti Malaysia Kelantan, Pengkalan Chepa, Kota Bharu 16100, Kelantan, Malaysia
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