Can Tho University Journal of Science Vol. 13, No. 3 (2021): 48-57 48 DOI: 10.22144/ctu.jen.2021.040 Synthesis of lignin-based phenol-formaldehyde adhesive - A sustainable alternative to petrochemical Nguyen Thi Nhu Y 1 , Nguyen Thi Yen Nhi 1 , Tran Thi Minh Thu 1 , Nguyen Thi Ven 2 , Tran Nguyen Phuong Lan 2 and Luong Huynh Vu Thanh 2* 1 Can Tho University of Technology, Viet Nam 2 Can Tho University, Viet Nam *Correspondence: Luong Huynh Vu Thanh (email: lhvthanh@ctu.edu.vn) Article info. ABSTRACT Received 05 May 2021 Revised 17 Jun 2021 Accepted 25 Jun 2021 This study is to investigate the capability of producing lignin-based phenol- formaldehyde adhesive (LBPFA) with lignin derived from coir pith collected in the Mekong Delta, Viet Nam. The LBPFA synthetic process underwent non chemical modifications to minimize petrochemicals and energy. Effective factors as reaction time, reaction temperature and various lignin contents of phenol substitution were examined. Physical, chemical and thermal properties containing formaldehyde content, viscosity, solid content, Fourier transformed infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), tensile strength, tensile modulus and tensile strain were conducted. LBPFA was successfully synthesized at various levels of lignin contents substituting for phenol. The LBPFA’s parameters were in accordance with GB/T14372-2006 standard. The optimum reaction time, reaction temperature and lignin replacement content for LBPFA synthesis process were identified at 180 minutes, 90 0 C and 40% wt/wt, respectively. The LBPFA showed the highest dry and wet tensile strengths of 14.42 MPa and 7.66 MPa on wooden boards compared to corresponding figures of commercial resin with 2.98 MPa and 0 MPa, respectively. For plywood, bending strength shown in LBPFA and commercial adhesive were 15.97 MPa and 20.16 MPa, respectively. Keywords Lignin-based adhesive, Coir pith, lignin-based phenol- formaldehyde adhesive, Phenolic resin 1. INTRODUCTION Coir pith is a common agricultural by-product in Mekong Delta especially in Ben Tre province. Due to low value, coir pith was not utilized completely, which resulted in polluted air and water environment at coconut fiber processing areas (Luong et al., 2017; Nguyen et al., 2018). Lignin is one of the main components of plants, acting as a natural adhesive polymer in plant cell walls, increasing mechanical strength and waterproofing. Lignin is a heterogeneous polymer containing several function groups: hydroxyl, phenolic and ester groups. Its physical and chemical properties are highly dependent on biomass sources, locations and extraction methods (Mansori et al., 2006; Duval et al., 2014). Poly (phenol-formaldehyde) resins are being used in about one-tenth of all plywood and particle board industries. The outstanding performance of phenolic resins are high strength, long-term mechanical and thermal stability, low toxicity, low formaldehyde content, high water resistance, low phenolic swelling, excellent electrical and thermal insulation. The drawback of these resin is that it is toxic due to