Urea–formaldehyderesins are the most important type of the so-called amino plastic resins. Amino resins are often used to modify properties of other materials. These resins are added during the processing of
Authors:T. Zorba, E. Papadopoulou, A. Hatjiissaak, K. Paraskevopoulos, and K. Chrissafis
Urea-formaldehyde (UF) resins are the most used polycondensation resins today, in manufacturing particleboards. UF resins
possess some advantages such as fast curing, good performance in the panel, water solubility and low price. However, the main
chemical bonds of the UF resins macromolecules are hydrolysis sensitive. This causes low water and mositure resistance performance
and subsequent formaldehyde release from the UF-bonded panels. A multitude of pathways have been explored for the improvement
of UF resins’ behavior relating either to their synthesis procedure or application parameters during panel manufacture. In
this study, two UF resins (a conventional and an innovative one produced at very low pH and temperature conditions) were analyzed
for their specifications and characterized with TG-DTA technique in dynamic heating conditions and FTIR measurements both
in their pre-polymer and cured state.
Authors:Kadri Siimer, Tiit Kaljuvee, Tõnis Pehk, and Ilmar Lasn
Thermal behaviour of industrial UF resins modified by low level of melamine was followed by TG-DTA technique on the labsysTM instrument Setaram together with the 13C NMR analysis of resin structure and testing boards in current production at Estonian particleboard factory Pärnu Plaaditehas
AS. DTA curve of UF resin which has been cocondensed during synthesis with even low level of melamine shows the shift of condensation
exotherm and water evaporation endotherm to considerable higher temperatures. The effect of melamine monomer introduced to
UF resin just before curing was compared. The effect of addition of urea as formaldehyde scavenger was studied.
Authors:K. Siimer, P. Christjanson, T. Kaljuvee, T. Pehk, I. Lasn, and I. Saks
The thermal behaviour of MUF resins from different suppliers with different content of melamine was studied, along with the
13C NMR spectroscopic analysis of resin structure and the testing of particleboards in current production at Estonian PB factory
Pärnu Plaaditehas AS. The chemical structure of resins from DMSO-d6 solutions was analysed by 13C NMR spectroscopy on a Bruker AMX500 NMR spectrometer. The melamine level in different MUF resins is compared by the ratios
of carbonyl carbon of urea and triazine carbon of melamine in 13C NMR spectra. Curing behaviour of MUF resins was studied by stimultaneous TG-DTA techniques on the Labsys™ instrument Setaram.
The shape of DTA curves characterisises the resin synthesis procedure by the extent of polymerisation of UF and MF components
and is in accordance with structural data.
Authors:K. Siimer, T. Kaljuvee, P. Christjanson, and I. Lasn
analysis method was used to study the curing behaviour of urea-formaldehyde
(UF) adhesive resins in the presence of a wood substrate. The cure process
was followed using a Setaram labsysTM instrument
in flowing nitrogen atmosphere by varying the ratio of resin and wood. Resin
cure was catalysed with 2% of NH4Cl. Curing tests were
performed in the open standard platinum crucibles and in the sealed glass
capsules. To characterise the reactivity of curing system, the peak temperatures
in DTA curve and the mass loss values in TG curve were taken as the apparent
indices. The main attention was paid to phenomena which actually take place
in curing of UF resins during manufacturing of particleboards. Reactivity
of the curing system depends mostly on methylol content of resin and can be
adequetly evaluated by the maximum temperature of exothermic peak. The wood
substrate has a substantial influence on the resin and water diffusion in
system causing the changes in water/resin separation and water evaporation
conditions. The water movement in curing adhesive joint was a confusing parameter
in determining the peak positions. The rate of mass loss on a wood substrate
is higher as compared to curing UF resin alone.
The results of studies on urea and urotropine product distribution in solutions formed in microspherical nuclear fuel preparation by internal gelation are presented. It is shown that urea, urotropine and formaldehyde, the urotropine hydrolysis product, undergo various conversions in solutions, resulting in methylolurea and urea-formaldehyde resins formation. Results on the influence of acidity on the process as a function of time are presented. The organic content in the resulting solutions and microspheres has been determined.
Pentaerythritol diphosphonate melamine-urea-formaldehyde resin salt, a novel cheap macromolecular intumescent flame retardants
(IFR), was synthesized, and its structure was a caged bicyclic macromolecule containing phosphorus characterized by IR. Epoxy
resins (EP) were modified with IFR to get the flame retardant EP, whose flammability and burning behavior were characterized
by UL 94 and limiting oxygen index (LOI). 25 mass% of IFR were doped into EP to get 27.2 of LOI and UL 94 V-0.
The thermal properties of epoxy resins containing IFR were investigated with thermogravimetry (TG) and differential thermogravimetry
(DTG). Activation energy for the decomposition of samples was obtained using Kissinger equation. The resultant data show that
for EP containing IFR, compared with EP, IFR decreased mass loss, thermal stability and Rmax, increased the char yield. The activation energy for the decomposition of EP is 230.4 kJ mol−1 while it becomes 193.8 kJ mol−1 for EP containing IFR, decreased by 36.6 kJ mol−1, which shows that IFR can catalyze decomposition and carbonization of EP.