DSC application for characterization of Urea/formaldehyde condensates

Szesztay, M.; László-Hedvig, Zs.; Kovacsovics, E.; Tüdős, F.

doi:10.1007/bf02663798

Cited by 36 publications

(20 citation statements)

References 4 publications

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“…These have clearly shown that UF (pH5) is faster in developing a dry strength while tannin-UF is faster in developing both dry and wet bond strength in comparison to PF resins. Previous work by Chow and Steiner (1975) and also more recently Szesztay et al (1993) suggested that the first exothermic peak for UF resin corresponded to the initial strength built-up during the manufacture of plywood. The position of the first peak centered at 87 °C for catalyzed UF (PH5), 113°C for tannin-UF-formaldehyde adhesive and 138°C for uncatalyzed UF (added for comparison) is in agreement with the expected order of reactivity for these adhesives while the relative position of the second peak is not (see Table 4 and Fig.…”

Section: Particleboard Test Resultsmentioning

confidence: 96%

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Characterization of Wattle Tannin Based Adhesives for Tanzania

Calve¹,

Mwalongo²,

Mwingira³

et al. 1995

HFSG

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Wattle tannin-based urea formaldehyde (UF) adhesives for exterior grade plywood panels were formulated and tested. Laboratory work was conducted in Canada and plant trials in Tanzania. Tests showed that tannin-based adhesives gave quite good plywood which met the Canadian Standard Association (CSA) exterior grade requirements under press conditions similar to those currently employed for UF (control) adhesives. Formulations containing formaldehyde and oil instead of paraformaldehyde were found to be slightly less reactive under mill conditions. For particleboard, hydrolysis of the tannin was required for producing adhesive with acceptable viscosity and "pot life" for commercial applications. The hydrolysis of tannin also improved mechanical properties of particleboard. Relatively long press cycles or high press temperatures were required to produce particleboard panels with aged modulus of rupture (MOR) strength above the CSA exterior grade requirements. Prior to particleboard making, size exclusion chromatography (GPC) and differential scanning calorimetry (DSC) were performed on tannin, hydrolysed tannin, tannin-UF adhesive and commercial PF and UF adhesives. GPC indicated, possibly due to aggregation, that the tannin average molecular weight increased upon heating in the presence of alkali. The thermal or kinetic cure characteristics of the tannin-based adhesives, which are activation energy, enthalpy of cure and reaction order, were determined to be comparable with those of UF adhesives. Tannin hydrolysis lowered the activation energy for cure and this resulted in lower press times, as shown in test results. IntroductionThe demand for imported wood adhesives in Tanzania is estimated at 1000 metric tonnes per annum. While Tanzania is importing tonnes of urea-formaldyde (UF) adhesives at high costs (US $ 0.75/kg), it is exporting at relatively low cost (US $ 0.45/kg) highly reactive tannin extract from the bark of the black wattle tree (Acacia mearnsii) which could be used as the main ingredient in the formulation of exterior grade wood composite adhesives (Dalton and many others).

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Section: Particleboard Test Resultsmentioning

confidence: 96%

“…1). In the case of UF, Szesztay et al (1993) indicated that a temperature of 150°C and above, elimination of formaldehyde as well as decomposition of methylene linkages take place. In fact, at these high temperatures both polymerization and decomposition are expected to occur.…”

Section: Particleboard Test Resultsmentioning

confidence: 98%

Characterization of Wattle Tannin Based Adhesives for Tanzania

Calve¹,

Mwalongo²,

Mwingira³

et al. 1995

HFSG

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“…Solid UF resins with higher F/U mole ratios (1.4 and 1.6) showed an endothermic peak around 190°C while low F/U mole ratio resins (1.0 and 1.2) had an endothermic peak around 250°C. These peaks ranged from 170 to 190°C, and are believed to be responsible for the melting of solid UF resins prior to the start of curing reaction [24]. However, exothermic T p values of solid UF resins were ranged from 240 to 274°C, depending on F/U mole ratio and heating rate (see Table 2).…”

Section: Resultsmentioning

confidence: 98%

“…A more branched structure of UF resins requires more energy to melt solid state to liquid state prior to starting the curing reaction. Therefore, polycondensation reactions among various hydroxymethylated ureas, occurring at the later stage of curing process, resulted in an exothermic peak [24,25]. The presence of exothermic curing of liquid and solid UF resins makes it possible to estimate their cure kinetics by calculating activation energy of the curing reactions using the cure kinetic theories.…”

Section: Resultsmentioning

confidence: 99%

Comparison of thermal curing behavior of liquid and solid urea–formaldehyde resins with different formaldehyde/urea mole ratios

Nuryawan

Park

Singh

2014

J Therm Anal Calorim

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This study was undertaken to compare thermal cure kinetics of urea-formaldehyde (UF) resins, in both liquid and solid forms as a function of formaldehyde/urea (F/U) mole ratio, using multi-heating rate methods of differential scanning calorimetry. The requirement of peak temperature (T p ), heat of reaction (DH) and activation energy (E) for the cure of four F/U mole ratio UF resins (1.6, 1.4, 1.2 and 1.0) was investigated. Both types of UF resins showed a single T p , which ranged from 75 to 118°C for liquid resins, and from 240 to 275°C for solid resins. As the F/U mole ratio decreased, T p values increased for both liquid and solid resins. DH values of solid resins were much greater than those of liquid resins, indicating a greater energy requirement for the cure of solid resins. The DH value of liquid UF resins increased with decreasing in F/U mole ratio whereas it was opposite for solid resins, with much variation. The activation energy (E a ) values calculated by Kissinger method were greater for solid UF resins than for liquid resins. The activation energy (E a ) values calculated by isoconversional method which showed that UF resins in liquid or solid state at F/U mole ratio of 1.6 followed a multi-step reaction in their cure kinetics. These results demonstrated that thermal curing behavior of solid UF resin differed greatly from that of liquid resins, because of a greater branched network structure in the former.

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“…The second exothermic peak at 110-130 °C was caused by the decomposition of the methylene ether bridges. [23] The peak temperature (T p ) for the condensation reaction of UF2 was a little lower than that of UF1, which might be related to the higher content of methylene and methylene ether groups proved by 13 C-NMR analysis. Activation energy (E a ) is a key factor to determine a reaction.…”

Section: Ftir Analysismentioning

confidence: 95%

Urea–formaldehyde resin prepared with concentrated formaldehyde

Lei

et al. 2016

Journal of Adhesion Science and Technology

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The characteristics of UF resin prepared with concentrated formaldehyde were studied in this paper. With the molar ratio F/U = 1.1, the UF resin prepared with concentrated formaldehyde showed better mechanical properties than that with formalin. The 13 C-NMR and FTIR results indicated that there were more methylene groups, ether groups and urons in a UF resin system prepared with concentrated formaldehyde than those in a normal UF resin. The differential scanning calorimetry and DMA results showed that the curing temperature of UF resin with concentrated formaldehyde was lower than that of a normal UF resin. UF resin with concentrated formaldehyde showed worse thermal stability and higher thermal decomposition temperature.

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DSC application for characterization of Urea/formaldehyde condensates

Cited by 36 publications

References 4 publications

Characterization of Wattle Tannin Based Adhesives for Tanzania

Characterization of Wattle Tannin Based Adhesives for Tanzania

Comparison of thermal curing behavior of liquid and solid urea–formaldehyde resins with different formaldehyde/urea mole ratios

Urea–formaldehyde resin prepared with concentrated formaldehyde

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