Structure and curing mechanism of resol phenol-formaldehyde prepolymer resins

Christjanson, Peep; Pehk, Tõnis; Paju, Jane

doi:10.3176/proc.2010.3.05

Cited by 19 publications

(22 citation statements)

References 21 publications

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“… provided evidence that these intermediates do exist in UF reaction mixtures. Literature is ambiguous on whether the formation of these components is favored under basic conditions during hydroxymethylation or under neutral to acidic conditions during condensation and curing. In this work, methoxymethylene bridges were not taken into account.…”

Section: Chemical Reaction Systemmentioning

confidence: 99%

Quantitative and qualitative ¹H, ¹³C, and ¹⁵N NMR spectroscopic investigation of the urea–formaldehyde resin synthesis

Steinhof

Kibrik

Scherr

et al. 2014

Magnetic Reson in Chemistry

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Urea-formaldehyde resins are bulk products of the chemical industry. Their synthesis involves a complex reaction network. The present work contributes to its elucidation by presenting results from detailed NMR spectroscopic studies with different methods. Besides (1)H NMR and (13)C NMR, (15)N NMR spectroscopy is also applied. (15)N-enriched urea was used for the investigations. A detailed NMR signal assignment and a model of the reaction network of the hydroxymethylation step of the synthesis are presented. Because of its higher spectral dispersion and the fact that all key reactions directly involve the nitrogen centers, (15)N NMR provides a much larger amount of detail than do (1)H and (13)C NMR spectroscopy. Symmetric and asymmetric dimethylol urea can be clearly distinguished and separated from monomethylol urea, trimethylol urea, and methylene-bridged urea. The existence of hemiformals of methylol urea is confirmed. 1,3,5-Oxadiazinan-4-on (uron) and its derivatives were not found in the reaction mixtures investigated here but were prepared via alternative routes. The molar ratios of formaldehyde to urea were 1, 2, and 4, the pH values 7.5 and 8.5, and the reaction temperature 60 °C.

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Section: Chemical Reaction Systemmentioning

confidence: 99%

Quantitative and qualitative ¹H, ¹³C, and ¹⁵N NMR spectroscopic investigation of the urea–formaldehyde resin synthesis

Steinhof

Kibrik

Scherr

et al. 2014

Magnetic Reson in Chemistry

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“…It is found that the compositions of phenol formaldehyde resins changed with the varying catalyst to phenol molar ratio, formaldehyde to phenol molar ratio, reaction temperature and pH [18,19] , we researched a series of PF resin synthesized with different synthesize conditions to identify suitable synthetic resin technology.…”

Section: Results and Discussion Materials Mixture Ratios Effect On Curmentioning

confidence: 99%

Chemical Structure and Curing Characteristics of Phenol Formaldehyde Resins Catalyzed with Calcium Oxide

Wang

Zhang

2012

Polymer-Plastics Technology and Engineering

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Phenol formaldehyde resin catalysed by calcium oxide was synthesised under controlled temperature, material mixture ratios. The effects of catalysts on chemical structure of phenol formaldehyde resin was investigated by high performance liquid chromatography, fourier transform infrared and differential scanning calorimetry. The results indicated that synthesis parameters, including formaldehyde to phenol molar ratio and catalyst to phenol ratio, influence the rate of cure. Phenol formaldehyde resin catalysed by calcium oxide showed higher addition of formaldehyde onto ortho positions of phenolic rings, whereas in the presence of sodium hydroxyde addition onto para sites was favoured. The result of DSC was applied to investigate that Phenol formaldehyde resin catalysed by calcium oxide could cure at a low temperature. INTRODUCTIONPhenol formaldehyde (PF) resins were the first commercial synthetic polymeric materials. This type of resin have been widely used as industrial impregnating resins and adhesives in various applications for more than 50 years [1,2] . One of the drawbacks of PF resin is its slow cure which requires longer hot-pressing time and higher hot-pressing temperature for the manufacture of composite products.There have been many attempts to cure PF resins faster, including mixed with various resins [3] , adding accelerators and different catalysts such as ester [4,5] , copolymerized urea [6][7][8] , carbonate [9,10] and amides [11,12] .Faster curing PF resins may also be prepared by metallic ion catalysis, which increases the proportion of the free higher reactive para positions available for the reaction during curing of the resin. It was investigated that the valence and ionic radius of hydrated cations of basic catalyst on the mechanisms and kinetics of phenol formaldehyde

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“…This result was confirmed by previously published results. 8,30,31 The peak at 154-157 ppm is attributed to uron-type structures, because the carbonyl resonance is shifted toward a higher field in comparison to noncyclic components. The small value of uron ring structures observed just in the HCOOH-catalyzed (1.66, Table II) and HCl-catalyzed cases (0.13, Table II) is due to the fact that uron structures are generally in a very minor proportion when the F/U molar ratio is around 2.1.…”

Section: C-nmr Spectramentioning

confidence: 99%

Effect of different acids during the synthesis of urea‐formaldehyde adhesives and the mechanical properties of medium‐density fiberboards bonded with them

Dorieh

Mahmoodi

Mamaghani

et al. 2018

J of Applied Polymer Sci

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The characteristics of urea‐formaldehyde (UF) adhesives condensed by catalysis with four different acids, namely formic (HCOOH), hydrochloric (HCl), phosphoric (H3PO4), and sulfuric (H2SO4) acids, under alkaline–acidic–alkaline conditions at a molar ratio F/U = 1.12 were studied. The thermal curing properties of UF adhesives catalyzed with acid were characterized by differential scanning calorimetry at 10 °C/min heating rate. The resin structure examined by 13C‐NMR spectroscopy showed that the resin catalyzed with HCl had a lower proportion of methylol groups, resulting in a lower level of formaldehyde emission. It was interesting to note that HCOOH resulted in the best overall mechanical properties of the medium‐density fiberboard (MDF) panels. The HCl catalyst resulted in the poorest performance, providing the lowest internal bond strength, modulus of elasticity, and thickness swelling, with the exception of the free formaldehyde content. The resin catalyzed with H2SO4 had the highest free formaldehyde and the highest formaldehyde emission. H2SO4 and H3PO4 resulted in MDF mechanical properties relatively lower than for HCOOH. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47256.

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Structure and curing mechanism of resol phenol-formaldehyde prepolymer resins

Cited by 19 publications

References 21 publications

Quantitative and qualitative ¹H, ¹³C, and ¹⁵N NMR spectroscopic investigation of the urea–formaldehyde resin synthesis

Quantitative and qualitative ¹H, ¹³C, and ¹⁵N NMR spectroscopic investigation of the urea–formaldehyde resin synthesis

Chemical Structure and Curing Characteristics of Phenol Formaldehyde Resins Catalyzed with Calcium Oxide

Effect of different acids during the synthesis of urea‐formaldehyde adhesives and the mechanical properties of medium‐density fiberboards bonded with them

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Structure and curing mechanism of resol phenol-formaldehyde prepolymer resins

Cited by 19 publications

References 21 publications

Quantitative and qualitative 1H, 13C, and 15N NMR spectroscopic investigation of the urea–formaldehyde resin synthesis

Quantitative and qualitative 1H, 13C, and 15N NMR spectroscopic investigation of the urea–formaldehyde resin synthesis

Chemical Structure and Curing Characteristics of Phenol Formaldehyde Resins Catalyzed with Calcium Oxide

Effect of different acids during the synthesis of urea‐formaldehyde adhesives and the mechanical properties of medium‐density fiberboards bonded with them

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Quantitative and qualitative ¹H, ¹³C, and ¹⁵N NMR spectroscopic investigation of the urea–formaldehyde resin synthesis

Quantitative and qualitative ¹H, ¹³C, and ¹⁵N NMR spectroscopic investigation of the urea–formaldehyde resin synthesis