Synthesis And Characterization Of Highly Etherified Melamine Formaldehyde Resin

Highly etherified melamine formaldehyde resin (HMMM) has been known for a number of years, which is widely used in coating, rubber, paper, leather, and other fields, for its excellent thermal stability and high crosslinking activity. It has been studied more early abroad, the production process is relatively mature. But the resin produced in our country cannot be applied to high-grade paint due to its poorer quality with a lower degree of methylation and higher concentration of oligomer. In this work the synthesis method and reaction kinetics of highly etherified melamine formaldehyde resin, the morphology and rheological properties of high methylol melamine formaldehyde resin (HMM) have been investigated.Firstly, the influence of a series of reaction conditions to the degree of methylolation and the content of free formaldehyde of the product in the methylolation reaction was studied using orthogonal experiment method. And the influence of various reaction conditions to the degree of methylation and the content of oligomer of the product in the methylation reaction was also conducted by the same method. Whereby the reaction conditions of the highly etherified product was optimized, and a HMMM crystal was prepared with a degree of methylation 5.6 and oligomer content 6.15 wt%.Secondly, methylolation reaction mass had been detected using high performance liquid chromatography-mass spectrometry technology, confirming that the monomethylolmelamine and two dimethylolmelamine isomers are existent under highly formaldehyde-to-melamine ratio reaction system. And the adjacent -CH2OH group will passivate the amino H, when formaldehyde reacts with -NHCH2OH. The variation of the molar concentration of methanol as the methylation reaction progresses had been analysed by gas chromatography. The methylation reaction mechanism was proposed, and the kinetic parameters were calculated.Finally, a series of HMM were prepared in different proportions of methanol, and its morphology were observed by SEM, found that they look like elongated strip. The HMM particle size becomes smaller and more tidy with increasing proportion of methanol. The viscosity research of HMM-water system by rotary viscometer indicates that the rheology characteristics of HMM-water system shows a Bingham flow under low solid content, but a Bingham- pseudoplastic flow with a evident shear-thinning phenomenon under high solid content; the apparent viscosity of the system increased exponentially as the solid content rising, with the same HMM size. Under higher solid content, the apparent viscosity of HMM-water is high with a small particle size and a width distribution, duo to the bonding floc phenomenon among particles; moreover, the apparent viscosity of HMM-water is high as well with a large particle size and a narrow distribution, duo to crowded interspace. Therefore, the minimum viscosity of HMM-water system is discovered at moderate particle size and distribution.