Studies On Urea-Formaldehyde-Modifier Co-condensed Resin Adhesive

To reduce the free formaldehyde content of UF resin and the formaldehyde emission content from wood products bonded by UF resin,this article used the modifier as resource to substitute formaldehyde partly and synthetized UFM resins,through measuring the viscosity,curing time,and free formaldehyde content of UFM resins,manufacturing plywood,testing formaldehyde emission content and bond strength in different hot-press tempreture,analysing the curing action tempreture with DSC,and examining with FTIR and ¹³C-NMR analysis,this article studied effects of the structure,amount and the synthetic process of modifier on reducing free formaldehyde content of UFM resins and formaldehyde emission content of plywood bonded by UFM resins.The conclusions are as following:(1) The more amount of modifier,the longer curing time,the lower viscosity values and free formaldehyde content of UFM resins,the most reduction of free formaldehyde content was about 60%. The synthetic process U1(added modifier with the first adding urea) and U2(added modifier with the second adding urea) of UFM had no distinct effect on free formaldehyde content.Generally speaking, the lower final mole ratio of UFM resin,the lower formaldehyde content.(2)On bond strength of plywood,adding modifier could improve bond strengh and water-proof leavel of plywood effectively,the bond strengh of plywood was better while the substituted mole ratio of modifier to formaldehyde was 0.025-0.05.Improving the hot-press tempreture could improve the bond strength of plywood effectively.Compared with synthetic process U2,the bond strength of plywood was better in synthetic process U1,and it could meet to the GB/T9846.3-2004 standard of the gradeâ… plywood.The plywood with UFM resin of 1.1 final mole ratio had a highest bond strength.(3)On formaldehyde emission content,adding modifier could decrease formaldehyde emission content of the plywood effectively.As the amount of modifier and the hot-press tempreture increased, the formaldehyde emission content decreased,the most reduction of the formaldehyde emission content was about 80.8%,it reached the GB/18580-2001 standard of E0.Compared with synthetic process U1, the formaldehyde emission content was lower in U2.The lower mole ratio of UFM resin,the lower formaldehyde emission content of plywood.(4) According to DSC analyzed,the UFM resins could not totally cure under lower tempreture (about 100℃),it had the second curing tempreture,.the second curing was much more distinctively as the amount of modifier increased.In the paper,the best hot-press tempreture was 140℃.(5) Comparing the FTIR and ¹³C-NMR spectrum of sample resins,the author inferred that the mechanism of how modifier descreased the free formaldehyde content of UFM resins and formaldehyde emission content of plywood was that the modifier descreased the mole ratio of formaldehyde to urea, while it reduced the amount of ether link(-C-O-C-) in the synthetic system.