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.
Authors:K. Siimer, T. Kaljuvee, P. Christjanson, T. Pehk, and I. Saks
Thermal behaviour of cure-accelerated phenol-formaldehyde (PF) resins was studied using the addition of commercial mixture
of water soluble oil shale alkylresorcinols (AR) to PF resin, 5-MR being as model compound. The acceleration effect of AR
is based on the promotion of condensation of resin methylol groups and subsequent reaction of released formaldehyde with AR.
Commercial PF resins SFŽ-3013VL and SFŽ-3014 from the Estonian factory VKG Resins have been used. The chemical structure of
resins was characterised by 13C NMR spectroscopy. TG-DTA analysis was carried out using labsysTM instrument Setaram. By TG-DTA measurements, the shift of exothermic and endothermic peaks and the changes of mass loss rate
in the ranges of 1.5–10 g AR/100 g PF resin were studied. The effect of AR on the curing behaviour of PF resins was also followed
by gel time.
Testing of the plywood when using PF resin with 5 mass% of AR shows that the press time could be reduced by about 15%.
The complexes of lanthanides(III) with hemimellitic acid (1,2,3-benzenetricarboxylic acid, H3btc) of the formula Ln(btc)·nH2O, where Ln=lanthanide(III) ion and n=2−6 were prepared and characterized by elemental analysis, infrared spectra, X-ray diffraction patterns and thermal analysis.
The IR spectra of the complexes indicate coordination of lanthanides(III) through all carboxylate groups. The complexes of
La(III), Ce(III), Pr(III) and Er(III) are amorphous. On heating in air atmosphere all complexes lose water molecules and next
anhydrous compounds decompose to corresponding metal oxides.
By diffusion in gel medium new complexes of formulae: Nd(btc)⋅6H2O, Gd(btc)⋅4.5H2O and Er(btc)·5H2O (where btc=(C6H3(COO)33−) were obtained. Isomorphous compounds were crystallized in the form of globules. During heating in air atmosphere they lose
stepwise water molecules and then anhydrous complexes decompose to oxides.
Hydrothermally synthesized polycrystalline lanthanide trimellitates form two groups of isomorphous compounds. The light lanthanides
form very stable compounds of the formula Ln(btc)⋅nH2O (where Ln=Ce−Gd and n=0 for Ce; n=1 for Gd; n=1.5 for La, Pr, Nd; n=2 for Eu, Sm). They dehydrate above 250°C and then immediately decomposition process occurs. Heavy lanthanides form complexes
of formula Ln(btc)⋅nH2O (Ln=Dy−Lu). For mostly complexes, dehydration occurs in one step forming stable in wide range temperature compounds. As the final
products of thermal decomposition lanthanide oxides are formed.
Authors:Maurizio Ferrante, Paolo Dottore, Morena Petrini, Paolo Trentini, and Giuseppe Spoto
). Before proceeding with the TG/DTAanalysis, a double weighing with a Gibertini electronic (mod. E42 Milano, Italy) and a TG/DTA scale is made, through which the following thermogravimetric analyses have been carried out. 8 samples of each material (number
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, and I. Saks
Urea–formaldehyde (UF) and phenol–formaldehyde (PF) resins are the most widely used wood adhesives. The first stage in resin
manufacturing is the formation of methylol derivatives which polycondensation leads to building the tridimensional network.
Understanding the behaviour of methylol compounds in curing provides useful information for developing appropriate resin structures.
Thermal behaviour of N,N′-dihydroxymethylurea, 2- and 4-hydroxymethylphenols, urea and phenol as model compounds for UF, PF and phenol–urea–formaldehyde
(PUF) resins was followed by TG-DTA method. The measurements were carried out by the labsys instrument Setaram at 30–450 °C in nitrogen flow. The characteristic signals for model compounds and for some reaction mixtures
were measured by high resolution 13C NMR spectroscopy.