Synthesis And Properties Characterization Of Maltose-Melamine-Formaldehyde Resin

In this work, maltose-melamine-formaldehyde (MMF) resins were synthesized by maltose, melamine and formaldehyde under the cross-linking reaction of borax in basic solutions. Effect of reaction temperature, pH, molar ratio of formaldehyde and melamine (F/M), molar ratio of maltose and melamine (Mt/Ma) and the amount of borax on the physicochemical properties of resins and the plywood pressed with the resins was investigated. The thermal stability and curing reaction of MMF resin were examinated by TG and DSC, then the molecular weight of MMF was characterized by GPC and the structure of MMF resins was studied by FT-IR. The hot-pressing parameters of theplywoodwasoptimized with orthogonal experiment design. The malt syrup was applied to synthesize the maltose syrup-melamine-formaldehyde resins wood adhesives, and the performances were compared with MMF resin. The main results of study are listed as following:(1) The bonding strength of the plywood pressed by MMF resin increases firstly and then decreases, along with increasing of reaction temperature, pH, molar ratio of formaldehyde and melamine (F/M), molar ratio of maltose and melamine (Mt/Ma) and the amount of borax, the formaldehyde release of the plywood decreases along with increasing of molar ratio of maltose and melamine (Mt/Ma). MMF resin was transparent liquid with viscidity of 67mPa-s (25℃), solid content of 50.77%, storage period of 20d, Mn of 1726g/mol and the bonding strength of the plywood was 1.010MPa the formaldehyde release of the plywood was 1.562 mg/L was synthesized when F/M(mol:mol) was 3.0, Mt/Ma(mol:mol) was 0.4, reaction temperature was 90±1℃, pH was 9.0～9.5, and the amount of borax(the total mass of the resin) was 0.3%.(2) FI-IR results showed that there are methylene groups, ether bond and amidine groups in the structure of MMF resins. It is suggested that those groups was a bridge connected Melamine withmelamine hydroxymethyl and maltose molecules; It is possible that the decreased boiling water resistance of MMF resins was due to the hydroxyl groups and ether bond.(3) The results of TG and DSC showed that it was an endothermic process in the curing reaction for MMF which was due to the higher energy of evaporated volatile. Along with increasing of (Mt/Ma) (mol:mol), the curing peak temperature and carbon yield (600℃)of MMF resin will be higher, and thermal stability will be better. The curing temperature of resins will be lower and the process of thermal decomposition will be simple and improved thermal stability are mainly due to the curing reaction of NH4Cl.(4) The activation energy and reaction order of MMF resin were caculated with Kissinger and Crane methods. And the results showed that the activation energy was 32.37 kJ/mol and the reaction order was 0.9412.The kinetics model of the curing system was f(a)=da/dt=1.68×1014 e-32370/RTp(1-a)0.9412(5) The results of orthogonal optimization experiment show that:the influence order of these testing factors on the bonding strength of MMF resin plywood was:glue content>hot pressing temperature>hot pressing pressure> hot pressing time.The optimum technological parameters of plywood showed that the amount of adhesives on two faces is 330g/m2, hot pressing temperature is 152℃, and hot pressing pressure is 1.2MPa, hot pressing time is 62s/mm;(6) The pure maltose was instead by malt syrup to Synthesis maltose syrupMelamine-formaldehyde wood adhesives The results showed that the viscidity of resins was 71 mPas (25℃),the self-life was 15d,and the bonding strength of the plywood was 0.847MPa, And there are the same structure as the FT-IR showed.