Modification Of The Urea-formaldehyde Resin Adhesive With Enzyme-hydrolyzed Oxidized Starch And Hydrazine Hydrate

Formaldehyde emission limits the development of urea-formaldehyde resin adhesive,which possesses advantages of reasonable price,high bonding strength and easy operation.In this work,core starch was hydrolyzed by?-amylase and then oxidized by H₂O₂.To obtain the harmfulless adhesive,urea-formaldehyde resin was modified with hydrazine hydrate and enzyme-hydrolyzed oxidized starch.To research the manufacturing process of enzyme-hydrolyzed-oxidation starch and modified UF adhesive,a series of experiments were carried out.Treated with a solution of H₂O₂(50%in quality of starch,H₂O₂:Fe²⁺=100:1)at 60?for 2h,carboxyl content of enzyme-hydrolyzed-oxidation starch reached 2.12%.And the synthesis process of urea-formaldehyde resin is alkali-acid-alkali.Urea-formaldehyde resin modified with enzyme-hydrolyzed oxidized starch at?stage is better than that at?stage.Formaldehyde emission declined from 3.40mg/L to 1.00mg/L,meanwhile,bonding strength declined from1.12 MPa to 0.50 MPa.Urea-formaldehyde resin modified with hydrazine hydrate at?stage better than that at?stage.Formaldehyde emission declined from 3.40 mg/L to0.08 mg/L and bonding strength declined from 1.12 MPa to 0.32 MPa.when enzyme-hydrolyzed oxidized starch and hydrazine hydrate are both added,formaldehyde emission released from 3.40 mg/L to 0.08 mg/L and bonding strength released from 1.12MPa to 0.32 MPa.To achieve national standard of the type of?plywood,the optimal process of modified UF is that enzyme-hydrolyzed oxidized starch was added 5%at?stage and hydrazine hydrate was added 2 molar equivalent at?stage.And formaldehyde emission released to 0.30 mg/L and bonding strength reached 0.75 MPa.The results of Fourier transform infrared spectroscopy?FT-IR?,X-ray diffraction?XRD?and the Differential scanning calorimetry?DSC?indicated that starch was oxidized successfully,carboxyl of starch and amidogen of hydrazine hydrate can react with hydroxymethyl and formaldehyde in resin.And the modifiers improve the degree of crystallinity and release the bonding strength.