[Objective]Through adding melamine to lignin phenol formaldehyde resin(LPF),its bonding strength was enhanced and its cure temperature was decreased.Therefore,a novel strategy was presented for the environmentally friendly manufacture of wood-based panels.[Method]The performance of melamine-modified lignin phenol formaldehyde resin(MLPF)was tested to study the effect of different molar ratios of melamine and(phenol + lignin),melamine/(phenol + lignin)and formaldehyde,and find the best MLPF synthesis conditions.In addition,the performances of phenolic resin(PF)and LPF with the same phenolic ratio and lignin replacement rate were compared.The structure and curing temperature of PF,LPF,and MLPF were compared by FTIR and DSC.[Result]The MLPF gel time was shortest at 318.62 s,when the molar ratios of melamine to(phenol + lignin)and melamine/(phenol + lignin)to formaldehyde were 4:6 and 1:2,respectively.The MLPF plywood's dry and wet bonding strengths were 2.04 MPa and 1.43 MPa,respectively,and its formaldehyde release was 0.088 mg/m3.MLPF had a stronger bonding strength than PF and LPF plywood,fulfilling the performance requirements of GB/T 14732-2017 and GB/T 9846-2015 national standards.According to FTIR studies,MLPF differed from PF and LPF in that it possessed double peaks for-OH and-N-H at 3 327 cm-1 and 3 214 cm-1,N-C-N characteristic peaks at 1 079 cm-1 and 1 036 cm-1,and triazine torus absorption peaks at 809 cm-1.It was proved that melamine was hydroxymethylated and involved in the synthesis of MLPF.The exothermic peak temperature of MLPF was 140℃,which was lower by 17.16%and 22.22%compared to that of LPF and PF,respectively.[Conclusion]The addition of melamine decreased the curing temperature and shortened the gel time of MLPF.The performance of MLPF plywood was much superior to that of LPF in terms of bonding strength and water resistance.
melaminelignin phenolic resinbonding strengthgel timecuring temperature
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