MRT Letter: High resolution SEM imaging of nano‐architecture of cured urea‐formaldehyde resin using plasma coating of osmium

Park, Byung‐Dae; Singh, Adya P.; Nuryawan, Arif; Hwang, Kiju

doi:10.1002/jemt.22272

Cited by 7 publications

(3 citation statements)

References 9 publications

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“…At the same time, the spherical particles also exist in the UF resin with a molar ratio of 1.4, but the quantity and size are small. This is essentially consistent with the observation of Park [32] et al for UF resins with different molar ratios. The formation and subsequent aggregation of colloidal particles have been shown to be the normal aging mode of amino resin.…”

Section: Fourier Infrared Spectrometer (Ft-ir)supporting

confidence: 93%

Morphology and Crystallinity of Urea-Formaldehyde Resin Adhesives with Different Molar Ratios

Zhang

2021

Polymers

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Using formaldehyde and urea as raw materials, a stable urea–formaldehyde resin (UF) is synthesized by the “alkali-acid-alkali” method. Unlike most thermosetting resins, UF often shows the appearance of crystal domains. In order to understand the relationship between the crystal and morphology of UF resin, analysis was carried out with the help of polarizing microscopy (POM), scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). The changes of two kinds of UF resins with molar ratios (F/U) of 1.4 and 1.0 before and after curing and under the influence of different curing agents and additives were studied. SEM results showed that the UF resins with low F/U (1.0) show spherical or flat structures before and after curing, and the diameter of the spherical structure increases with the increase of the content of curing agent, while in the UF resin with high F/U (1.4) it is difficult to observe the above phenomenon. At the same time, the possible accumulation mode of UF colloidal particles in the process of aggregation is explained, and the curing agent obviously promotes the development of the crystal structure, which may be the reason for the emergence of a large number of spherical particles. XRD results showed that the resin with low F/U has higher crystallinity than the resin with high F/U, indicating that the former shows more crystallization regions, while the latter shows more amorphous structure, and the crystallinity increases with the increase of the curing agent content, but the position of the crystallization peak does not change with the type of curing agent and the amount of curing agent. Observation of the selected area electron diffraction (SAED) pattern obtained by TEM shows that the cured low F/U (1.0) resin has a polycrystalline structure and a body-centered cubic unit cell. FT-IR results showed that the linear segment, branched structure, hydroxymethyl and methylene structure changes in UF affect the formation of crystal structure. This study also shows the possible contribution of hydroxymethylated species to the formation of crystals.

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Section: Fourier Infrared Spectrometer (Ft-ir)supporting

confidence: 93%

Morphology and Crystallinity of Urea-Formaldehyde Resin Adhesives with Different Molar Ratios

Zhang

2021

Polymers

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“…Solid UF resins with F/U mole ratio of 1.0 possess greater crystallinity, with larger crystallites compared to resins with higher F/U mole ratios [37,38]. Furthermore, the occurrence of simultaneous reactions among various molecular species that have their own constant activation energy could also have made contribution to the variation [31].…”

Section: Activation Energy Of Liquid and Solid Uf Resinsmentioning

confidence: 94%

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 particles within cured UF resin could be associated with the colloidal character of the resin [33,34], which has been linked to the crystalline regions [12,[35][36][37][38]. Larger and more abundant particles are found in low F/U resins [10,39], which also show crystallinity [12,28,29,[34][35][36][37][40][41][42][43].…”

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confidence: 99%

Micro-Morphological Features of Cured Urea-Formaldehyde Adhesives Detected by Transmission Electron Microscopy

Nuryawan

Singh

Park

et al. 2015

The Journal of Adhesion

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This work examined micro-morphological features responsible for the crystallinity of cured urea-formaldehyde (UF) adhesives, using transmission electron microscopy (TEM) to identify and characterize distinctive crystalline structures in resins obtained with different formaldehyde to urea (F/U) mole ratios and hardener levels. The TEM examination of cured UF resin adhesives impregnated into wood cell lumen revealed the presence of spherical particles with variable diameter and number per unit area. The diameter and number/area of the spherical particles increase for decreasing F/U mole ratio and decrease with an increase in the hardener levels, an effect which is closely related to their crystallinity. Therefore, the present findings suggest that the spherical particles are responsible for the crystallinity of cured UF resin adhesives. The results also indicate that crystalline structures represent an inherent feature of cured UF resin adhesives, particularly for low F/U mole ratios, even though these resins are usually classified as amorphous and cross-linked thermosetting polymers

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MRT Letter: High resolution SEM imaging of nano‐architecture of cured urea‐formaldehyde resin using plasma coating of osmium

Cited by 7 publications

References 9 publications

Morphology and Crystallinity of Urea-Formaldehyde Resin Adhesives with Different Molar Ratios

Morphology and Crystallinity of Urea-Formaldehyde Resin Adhesives with Different Molar Ratios

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

Micro-Morphological Features of Cured Urea-Formaldehyde Adhesives Detected by Transmission Electron Microscopy

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