Characterization of the Low Molar Ratio Urea–Formaldehyde Resin with 13C NMR and ESI–MS: Negative Effects of the Post-Added Urea on the Urea–Formaldehyde Polymers

Wang, Hui; Cao, Ming; Li, Taohong; Yang, Long; Duan, Zhigang; Zhou, Xiaojian; Du, Guanben

doi:10.3390/polym10060602

Cited by 51 publications

(41 citation statements)

References 26 publications

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“…The crystallization of UF resin exists in both the synthesis process and the curing process [ 15 , 22 ]. Several previous studies have reported the role of linear structural segments in the formation of crystals in UF resins [ 19 , 20 , 26 ]. At the same time, it combines the characterization and analysis results of UF resin before and after curing.…”

Section: Resultsmentioning

confidence: 99%

“…As showed in Figure 14 , the growth model of crystals or spherical particles in UF resin is shown. In the synthesis process of urea–formaldehyde resin, the primary microcrystalline particles were formed in the linear molecular chain due to the decrease of solubility in the alkaline stage, and then a stable microcrystalline structure began to form with the adjustment of pH value and the addition of urea [ 19 , 22 , 26 ]. When the UF resin is cured by heating or adding a curing agent (H + ), the colloidal particles aggregate due to the decrease in stability.…”

Section: Resultsmentioning

confidence: 99%

“…Dazmiri [ 24 ] studied the effect of initial molar ratio on the adhesion properties of UF resin products, and found that the UF resin with the highest proportion of linear hydroxymethyl groups in the initial stage had the best adhesion properties, while the UF resin with the highest proportion of methylene bonds in the initial stage had the worst adhesion properties and the lowest formaldehyde emission. The properties of cured UF resin are closely related to the properties of finished UF resin and formaldehyde emission [ 9 , 10 , 25 , 26 ]. Therefore, the research on the properties and formation mechanism of resin cured materials has become a problem of close attention.…”

Section: Introductionmentioning

confidence: 99%

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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: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Zhang

2021

Polymers

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“…The preparation of urea formaldehyde (UF) resin as the adsorbent sample in our laboratory was presented following traditional alkaline‐acid‐alkaline reactions 25 . After this, the obtained sample was cured for 3 h at 120°C to ensure complete dryness.…”

Section: Methodsmentioning

confidence: 99%

The role of pore structure and nitrogen surface groups in the adsorption behavior of formaldehyde on resin‐based carbons

Liu

et al. 2020

Surface & Interface Analysis

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This study focused on the role of pore structures and nitrogen surface functional groups in the formaldehyde (HCHO) adsorption on the carbonized resin-based materials (UFC). After comparing the optimal sample UFAC-700 obtained by the activation of UFC at 700 C with the commercial activated carbon (CAC) and other UFC, the HCHO adsorption capacity for UFAC-700 (12.30 mg g −1) is more than three times and 10 times of that for CAC and UFC, respectively. Abundant pore structures could provide more adsorption sites for the initial stage of HCHO adsorption. Moreover, according to the density functional theory (DFT) calculations, pyrrolic-N could enhance the adsorption energy and polar interaction of HCHO due to electrostatic force between the positively charged H attached to the nitrogen group and the negatively charged O atoms in the HCHO molecule. This study introduced a novel way to specifically design the surface modifications for volatile organic compounds (VOCs) adsorption.

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“…Decreasing the formaldehyde molar ratio in these resins is among the approaches dedicated for controlling the formaldehyde emission from wood panels. Regrettably, there was a negative impact on the physical and mechanical properties, but even more, the curing rate was slowed down significantly leading to low production line efficiency [20]. Meanwhile, traditional and single curing agents cannot easily solve all the drawbacks of co-condensation resin systems.…”

Section: Introductionmentioning

confidence: 99%

Influence of Single/Collective Use of Curing Agents on the Curing Behavior and Bond Strength of Soy Protein-Melamine-Urea-Formaldehyde (SMUF) Resin for Plywood Assembly

Zhang

Zhou

et al. 2019

Polymers

Self Cite

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Soybean protein hydrolysate, melamine, urea, and concentrated formaldehyde were used to synthesize an environmentally friendly soybean protein-melamine-urea-formaldehyde (SMUF) co-condensation resin. (NH4)2SO4, (NH4)2HPO4, (NH4)2HPO4 + (NH4)2SO4, (NH4)2HPO4 + (NH4)2S2O8, and (NH4)2HPO4 + (NH4)2SO4 + (NH4)2S2O8 were employed as curing agents for SMUF resin. The curing and thermal behaviors of the SMUF resin were investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The results revealed the following: (1) (NH4)2SO4 alone could not cure the SMUF resin completely; thus, the final shear strength accomplished plywood with the resin was low, and its water resistance was poor, while the adhesive section was loose and porous/brittle after curing. (2) (NH4)2HPO4 could be hydrolyzed to generate H+ and promote SMUF curing, but it could also form polyphosphoric acids, resulting in crosslinking reactions with SMUF in parallel; thereby, the curing properties were improved. (3) When (NH4)2HPO4 + (NH4)2SO4 + (NH4)2S2O8 were engaged collectively as curing agent, the shear strength, water resistance, and heat resistance of SMUF attained were the best possible whereas the curing temperature was decreased and the heat released by curing was elevated substantially, which signifies maximized extent of crosslinking was achieved. Further, the adhesive section exhibited mostly a crosslinking intertexture as demonstrated by means of SEM. Accordingly, this study may serve as a guide for the curing of amino resins, with low-molar ratio of formaldehyde to amine in adhesives, which are applied to plywood production.

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Characterization of the Low Molar Ratio Urea–Formaldehyde Resin with 13C NMR and ESI–MS: Negative Effects of the Post-Added Urea on the Urea–Formaldehyde Polymers

Cited by 51 publications

References 26 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

The role of pore structure and nitrogen surface groups in the adsorption behavior of formaldehyde on resin‐based carbons

Influence of Single/Collective Use of Curing Agents on the Curing Behavior and Bond Strength of Soy Protein-Melamine-Urea-Formaldehyde (SMUF) Resin for Plywood Assembly

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