Synthesis,characterization And Curing Mechanism Of Biomass Modified Phenol Formaldehyde Resin

Phenol formaldehyde(PF)resin is widely used in wood industry,especially in weather resistance wood panel products.The demand for wood-based panels increases continuously due to the rapid development of the wood construction industry.PF resin have shown a broader developing potential;however,the application of PF resin is greatly limited due to its high cost and poor environmental performance.To overcome these drawbacks,the modification using biomass is a new approach.However,the bonding strength and curing rate will be decreased when the ratio of biomass incorporation is high.In this project,aiming at these issues of biomass modified PF,tannin,soy bean meal and other resources were served as the biomass raw materials to modify PF resin.The chemical structure of modified PF was regulated through treatment of urea/sodium hydroxide aqueous solution,addition of urea and catalysis,which consequently improve the adhesive property and curing rate.In addition,the properties and chemical structure were characterized using FTIR,DSC,SEM,TG,NMR and MALDI-TOF.The main results of this research are summarized as follows:(1)Valonia tannin modified PF resins(VTPF)formed a copolycondensation structures,which improved the adhesion properties and other performances.When 40%phenol was substituted by valonia tannin,the bonding strength of prepared panels could reach the type I grade of polywood requirement and the formaldehyde emission can meet the E0 standard.The curing temperature of VTPF resin was lower than that of the PF resin.The copolycondensation structures of the VTPF resin could be confirmed by FT-IR,13C-NMR and MALDI-TOF measurements.(2)Urea could be copolymerized with VTPF resin to form a copolycondensation structures,which decreased the cost of biomass modified PF resins and reduced the formaldehyde emission of the bonded panels.The PTUF resin had hydroxymethylurea structures as compared with the tannin modified PF resins(PTF).In addition,as compared with the PTF resin,the formaldehyde emission of panels bonded with PTUF resin decreased by 59.37%,and the storage stability of the PTUF resin was significantly improved.(3)The catalysts(zinc acetate,magnesium oxide,and sodium carbonate)could improve the bonding strength and increase the curing rate of the biomass modified PF resin.High-ortho phenolic resin structures were formed with the addition of catalysts,thus it accelerated the VTPF resin curing and decreased the curing temperature.The curing peak temperature of the VTPF-Zn2+ resin was 126.6 0C,which was lower than that of the PF resin(134.89?).The bonding strength and formaldehyde emission of panels bonded with the modified phenolic resins was 1.3 MPa and 0.46 mg/L,respectively,when curing at 120?.(4)The pretreatment of biomass by urea/NaOH aqueous solution could significantly decrease the viscosity and improve the storage stability of the biomass modified PF resins.The pretreatment of soy isolate protein by urea/NaOH aqueous solution can improve the comprehensive properties of the soy isolate protein modified PF resins(SPF).As compared with the SPF resin,panels bonded with urea modified SPF resin(U-SPF)exhibited high bonding strength and low formaldehyde emissions.