Study On Preparation Technology Of Lignin-based Phenolic Resin Adhesive

The outstanding performances in terms of mechanical properties,dimensional stability,chemical durability and flame resistance of phenol formaldehyde account for their vast application potentials.Phenol is one of the necessary raw materials for conventional phenolic resin.However,facing the issue of oil depletion or climate change,using biomass resources as raw materials to partially replace phenol has become a research hotspot.With the continuous progress of pulping industries and biorefining,the effective utilization of biomass resources has a better technical basis.As one of the three major components of woody biomass,lignin is a natural polymer with the most aromatic rings in nature.Lignin represents a viable option in terms of molecular composition.And in theory,the price of phenol is more than three times higher than the price of the same effective ingredient lignin.Therefore,the preparation of phenolic resin with lignin not only realizes the effective utilization of environmentally friendly biomass,but also saves costs,which is a very promising raw material for thermosetting resin materials.The specific research contents are as follows:?1?Firstly,the original real lignin was analyzed for composition and structure,and then the special molecular structure of the lignin was characterized by FT-IR and ¹³C NMR.The microstructure proved the feasibility of lignin to replace phenol which was suitable for the preparation of lignin-based phenolic resin.?2?Due to the three-dimensional highly cross-linked macromolecules of real lignin,the molecular structure had not been determined.So according to the functional group structure characteristics of the first part of the real lignin molecule,a lignin model compound was selected to simulate the preparation process of lignin-based phenolic resin.The free formaldehyde content and free phenol content were measured at intervals of half an hour,combined with FT-IR analysis,¹H NMR and ¹³C NMR analysis of the resin samples,the main characteristic reactions at each stage were obtained,and the experimental method used in this paper was proposed—Three-step copolymerization method.?3?Phenol was partially replaced by the lignin,and lignin-based phenolic resin binder was prepared by the three-step copolymerization.The viscosity of the lignin-based phenolic resin adhesive was investigated systematically by the process parameters,including alkali concentration,aldehyde-phenol ratio and lignin addition.The effects of solid content,free formaldehyde content,free phenol content and bonding strength were characterized by FT-IR,¹³C NMR and TG,respectively,in order to describe the functional structure and thermal curing characteristics for lignin-based phenolic resin adhesive.Interestingly,the results demonstrated that the resin synthesized with lignin content of 30%phenol equivalent had excellent molecular structure and curing properties compared to that under the other conditions.Fortunately,the phenolic resin prepared with lignin met the requirements of GB/T14732-2006"Wood adhesive:urea formaldehyde,phenol formaldehyde and melamine formaldehyde resins".?4?Urea and Nano-MgO as modifiers,phenol was partially replaced by the lignin,and lignin-based phenolic resin binder was prepared by a three-step copolymerization.The density,viscosity,solid content and free formaldehyde content of the lignin-based phenolic resin adhesive were investigated systematically by the process parameters,including urea addition,MgO addition and lignin addition.The functional structure and thermal curing characteristics for lignin-based phenolic resin adhesive were characterized by FT-IR and DSC,respectively.Interestingly,the results demonstrated that under the synergistic catalysis of urea and MgO,lignin addition could be increased to 45%,and the thermal curing performance was remarkably improved.