Effect of molecular weight of urea–formaldehyde resins on their cure kinetics, interphase, penetration into wood, and adhesion in bonding wood

Jeong, Bora; Park, Byung‐Dae

doi:10.1007/s00226-019-01092-1

Cited by 39 publications

(28 citation statements)

References 30 publications

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“…However, the release of formaldehyde in the production and use of UF resin and its products, and the deterioration of durability under high temperature or high humidity environments, have greatly affected the application of UF resin in the wood industry [ 3 , 4 , 5 ]. In addition, formaldehyde release from indoor panels is one of the main factors leading to sick building syndrome in indoor environment; therefore, formaldehyde release has always been one of the most important aspects of UF resin research [ 6 , 7 , 8 ]. In industrial production, the commonly used methods to reduce the release of formaldehyde mainly include reducing the molar ratio F/U of formaldehyde to urea; strictly controlling the reaction process conditions of UF resin synthesis, such as pH value, reaction temperature and reaction time; using formaldehyde traps, such as urea, polyvinyl alcohol, melamine; among these methods, the most effective is to reduce the molar ratio (F/U) [ 9 , 10 , 11 ].…”

Section: Introductionmentioning

confidence: 99%

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: Introductionmentioning

confidence: 99%

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

Zhang

2021

Polymers

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“…Synthetic, formaldehyde-based adhesives are mostly used in the composite industry. Urea-formaldehyde is widely used as an adhesive in the manufacture of wood-based composite panels because it is colorless, fast-curing, and inexpensive (Jeong and Park 2019). However, formaldehyde, which is a human carcinogen and not renewable, is emitted during the production and use of such composites.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of physical and mechanical properties of particleboard made from Petung bamboo using sucrose-based adhesive

Widyorini

2020

BioRes

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Bamboo is a potential non-wood lignocellulosic material from which to make particleboard. Sucrose-based adhesive is another potential ingredient, but its use in particleboard has been limited. Addition of ammonium dihydrogen phosphate (ADP) can be used to increase the bonding ability of sucrose-based adhesive and to reduce the required pressing temperature. Therefore, this research used different pressing temperatures and sucrose/ammonium dihydrogen phosphate (ADP) composition ratios to optimize the properties of particleboards. The physical and mechanical properties of the boards were analyzed and compared with the JIS A 5908 (2003) standard for particleboard. The results showed that the interaction of the sucrose-ADP composition ratio and the pressing temperature significantly affected the physical and mechanical properties of the particleboards. The particleboard using only sucrose as adhesive had optimum properties at 200 °C; however, after addition of ADP, the intended properties could be achieved at a 160 °C pressing temperature.

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“…Probably at high proportion of urea is made precipitation at unreacted form during polycondensation reaction [5]. The previous studies also stated that the solid content of UF resin is greater at higher F/U molar proportion [25]. Fig.…”

Section: Resultsmentioning

confidence: 86%

“…The viscosity of a polymer adhesive is controlled by temperature, pH and concentration. Plenty of researches have been studied the effect of reaction parameters on the viscosity of UF resin [24]- [25]. They interpreted the experimental results differently.…”

Section: Introductionmentioning

confidence: 99%

Effect of Synthesis Conditions on the Molecular Weight and Activation Energy of Urea-formaldehyde Prepolymer and Their Relationship

Anjum

Khan

2020

JEA

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The aim of this study is to find out the viscosity change of urea-formaldehyde (UF) resin with the synthesis parameters namely formaldehyde/urea (F/U) mole ratios, pH and temperature. The viscosity of UF resins, related to molecular weight and activation energy is very important factor of their usability. Urea-formaldehyde (UF) prepolymer was synthesized through polycondensation reaction with F/U ratio 0.8, 1.0, 1.2, 1.4, 1.6. The synthesis was carried out by two steps: alkali catalysis at reaction pH 8.3, 90°C for 60 min and thereafter acid catalysis at pH 4.3, 83°C for 15 min. Viscosity of prepolymer was determined at acid catalysis step by simple glass viscometer. Weight average molecular weight (Mw) was calculated from the viscosity data of UF prepolymer using Mark-Houwink equation. Highest Mw (2020.9) of prepolymer was obtained at F/U molar ratio 1.0 and pH 4.3. In addition, it was found that pH 4.0 yielded greater Mw (2049) UF prepolymer among the four reactions which were performed at pH 4.0, 4.3, 4.7, and 5.0. The energy of activation (Ea) of UF prepolymer was also calculated from the measured viscosity at temperature 70, 75, 80 and 85°C. The highest values of Ea were also found at F/U molar ratio 1.0 and pH 4.0 & lowest values was obtained at F/U molar ratio 1.6 and pH 5.0. From the experimental data, it was shown that the values of Ea and Mw were varied comparably with the change of reaction parameters.

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Effect of molecular weight of urea–formaldehyde resins on their cure kinetics, interphase, penetration into wood, and adhesion in bonding wood

Cited by 39 publications

References 30 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

Evaluation of physical and mechanical properties of particleboard made from Petung bamboo using sucrose-based adhesive

Effect of Synthesis Conditions on the Molecular Weight and Activation Energy of Urea-formaldehyde Prepolymer and Their Relationship

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