Synthesis And Characterization Of Sodium Lignosulfonate-melamine-formaldehyde Resin

Using renewable resources to substitute oil-derived synthetic materials has drawn interest,mainly attributing to the global energy crisis.Sodium lignosulfonate,a byproduct of sulphite pulping and paper making,has many advantages,such as large output,renewable,degradability and non-toxicity.The study on sodium lignosulfonate modified melamine formaldehyde copolymer resin has important significance on the application of biomass waste in the environmentally friendly wood adhesive.At the same time,the utilization value of paper making wastewater is improved,which meets the requirements of energy conservation,environmental protection and sustainable development.The objective of this work is to evaluate the effects of sodium lignosulfonate content and synthesis methods on the physical and chemical properties,resin structure and thermal properties of SLMF resin,which were characterized by FT-IR,1H-NMR,13C-NMR,TG and DSC.The main research findings of this dissertation are as follows:(1)SLMF-a and SLMF-b resins were synthesized by sodium lignosulfonate,melamine and formaldehyde as the main raw materials under alkaline conditions using one-pot and two-step methods,respectively.When the molar ratio of formaldehyde to melamine(MF/Mm,)was 2.20 and the content of sodium lignosulfonate was 30 wt%,the SLMF-a and SLMF-b resins showed better performance.The synthesized resins were dark brown liquid,and the solid content of SLMF-a was 51.86%(66.50 mPa s).The bonding strength of SLMF-a reached 1.14 MPa,meeting the requirements of type I plywood.The free formaldehyde content of SLMF-a was 0.47%and storage life was 23 d.The solid content of SLMF-b was 51.05%(59.30 mPa s),the bonding strength reached 1.28 MPa,the free formaldehyde content was 0.38%,and the storage life was 25 d.(2)FT-IR,1H-NMR and 13C-NMR analysis showed that the lignosulfonate sodium was mainly composed of the guaiacyl and syringyl units,and the units were mainly connected by ?-O-4' and ?-5' bonds.SLMF resin was synthesized through Mannich reaction among sodium lignosulfonate,melamine and formaldehyde and the dehydration condensation reaction between primary alcoholic hydroxyl and methylol groups of sodium lignosulfonate.Sodium lignosulfonate could be stabilized in the resin system by absorbing low molecular weight polycondensate or the force of molecular interactions,such as the hydrogen bonds.(3)TG and DSC results showed that the curing process of SLMF resin is an exothermic reaction,and the curing activity and the temperature of the maximum thermal decomposition rate of SLMF resins decreased with the increase of the sodium lignosulfonate content due to the unreacted sodium lignosulfonate.The carbon residue rate of SLMF-a3 was 12.90%at 850?.The synthesis methods had a great impact on the thermal properties of SLMF resin,and the SLMF-a1 showed better heat resistance.