Study On Preparation And Properties Of Urea-Formaldehyde Resin Modified By L-Tyrosine/Hydroxyapatite

Urea-formaldehyde resin（UF）still has unshakable position in a short period of time,duo to low cost,excellent bonding performance and simple production process,but poor water resistance and formaldehyde release limit its indoor application.In order to further improve the performance of UF resin,the organic material L-tyrosine was subjected to hydroxymethylation（TYF）and hydroxyapatite was modified by silane coupling agent surface modification（HA-APTES）to modify urea formaldehyde resin,and L-tyrosine/urea formaldehyde resin（LUF）and hydroxyapatite/urea formaldehyde resin（HUF）were prepared respectively.The properties of resins and plywood were determined,and the thermal degradation and thermal curing properties of the resins were characterized by thermogravimetric（TG）and differential scanning calorimetry（DSC）,and the kinetics of thermal degradation and thermal curing were analysed.The main research contents and conclusions are as follows:（1）Compared with UF resin and plywood,it was found that TYF and HA-APTES had obvious effects on reducing formaldehyde emission and improving wet shear strength of plywood.The optimal addition amount of TYF was 3%,and the formaldehyde emission and wet shear strength of plywood were 0.57 mg/L and 1.47 MPa,respectively.The optimal addition of HA-APTES was 3%,and the formaldehyde emission and wet shear strength were 0.35 mg/L and 1.14 MPa,respectively.（2）The thermal degradation process of urea-formaldehyde resin could be divided into three stages:slow weight loss,rapid decomposition and carbonization.The peak temperature increases with the increase of heating rate,and the maximum thermal degradation peak shifts to higher temperature.The thermal stability of LUF and HUF was greater than that of UF,and the thermal degradation activation energies of LUF and HUF resins were 180.41 and 135.98 k J mol^-1 respectively,which were 45.64 and 1.2k J mol^-1higher than those of UF.Coats-Redfern method was used to determine the resin thermal degradation reaction model.The most possible reaction mechanism models of UF,LUF and HUF resins were G（α）=[（1-α）^-1/3-1]²、G（α）=[-ln（1-α）]⁴ and G（α）=[-ln（1-α）]³,respectively.（3）The thermal curing of the resin was analyzed with different heating rates.It was found that the three kinds of urea formaldehyde resins showed a single peak temperature,and with the increase of heating rate,the exothermic peak position of DSC curve shifted to the high temperature.The thermal curing activation energies of LUF and HUF resins were 101.92 and 115.91 k J mol^-1 respectively.LUF was 6.52 k J mol^-1 lower than UF,and HUF was 7.47 k J mol^-1 higher than UF.Therefore,the addition of TYF made the resin easier to cure,while HA-APTES delayed the curing of resin.The reaction orders of UF,LUF and HUF resins were 0.9474,0.9423 and 0.9494,respectively,which were all approximate first-order reactions.