Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
In this project, different MUF resins were synthesized with varying melamine content, F/NH2 molar
ratio, number of addition steps and with varying addition order of the reactants during synthesis.
Further, it was investigated how these synthesis parameters influenced resin properties including
storage stability and free formaldehyde content. Additionally, NMR spectroscopy was used in order
to study the resulting chemical structure of the resins and their molecular size and molecular size
distribution were examined by SEC and MALDI-TOF-MS. The curing kinetics of the resins were studied
by Raman spectroscopy. From the resins, cured glue joints were prepared and the mechanical
properties and water resistance of these were tested through tensile shear testing after different
pretreatments of the glue joints.
It was confirmed that synthesis under both alkaline and acidic conditions resulted in a higher amount
of ether bridges in the resin in comparison to synthesis under acidic conditions. Furthermore, a high
melamine content and fewer urea additions resulted in resins with a higher amount of methylol
groups and less substituted functional groups. Comparatively, when the F/NH2 molar ratio was
increased or when formalin was added in two steps, a resin with higher amount of substituted
groups and structures of higher degree of condensation was obtained. From the synthesis procedure
it was concluded that a long condensation time at alkaline conditions was the most efficient way to
achieve a low free formaldehyde content, while a high F/NH2 molar ratio resulted in the highest
amount of free formaldehyde. Furthermore, a high amount of flexible ether bridges, low amount of
methylol groups, low melamine content, high F/NH2 molar ratio and a high degree of branched
chains seem to be important structural parameters for achieving resins with a long shelf life.
Additionally, from the SEC-analysis it was found that the resins had an average molecular weight (Mn)
between 1000-1600 g/mol and a broad molecular weight distribution, which were further verified by
MALDI-TOF-MS. The resins with a high melamine content had shorter chains, and the molecular
weight distribution was most significantly increased when the number of addition steps were
Through analysis of the curing process it was found that a higher hardener-to-resin mixing ratio
resulted in a faster curing process and a higher final degree of cross-linking. Additionally, it appeared
as the reaction of methylol groups was less pH-dependent than the reactions of ether bridges and
methylene bridges, which both were favored at lower pH. From the kinetic profiles it was observed
that the resin with a higher amount of ether bridges and lower amount of methylol groups had a
more prolonged curing process. Furthermore, the mechanical testing of the resulting cured glue
joints showed no significant difference in tensile strength between the resins when tested in the dry
state. However, a reduced tensile strength were observed for the resin with higher melamine
content when tested in the wet state, hence indicating that the increased melamine content used in
this project is not enough in order to significantly improve the mechanical properties or water
resistance of the cured glue joint observable with the used method.
2015. , 78 p.