Wettability and Surface Adhesion of Hemicelluloses of Different Structures to Urea-Formaldehyde Resin Adhesives

( Eko Setio Wibowo ),( Byung-dae Park ) 한국목재공학회 2022 한국목재공학회 학술발표논문집 Vol.2022 No.1

As a way of understanding the complex adhesion of heterogeneous wood cell walls, this study examined the wettability and surface adhesion of hemicellulose, one of the primary components of wood, to urea-formaldehyde (UF) resin adhesives to understand a complex adhesion process of wood biopolymers. Chemical structure of hemicelluloses, such as arabinogalactan and xylan, was characterized using Fourier transform infrared, one-dimensional, and two-dimensional nuclear magnetic resonances. As a result, arabinogalactan had a hyperbranched structure, whereas xylan was more linear, which caused a distinctive morphology in their films, with the latter having a rougher surface. Further, the surface adhesion between hemicellulose and UF resins with various formaldehyde to urea molar ratios (1.0 and 1.6) were measured. Therefore, two techniques were employed: 1) the adhesion force between liquid droplets of UF resins and hemicellulose films, and 2) the work of adhesion between the hemicellulose films and UF resins via contact angle measurements. The adhesion force and work of adhesion of arabinogalactan with different UF resins were found to be greater than those of xylan due to the former film’s higher surface free energy, more exposed OH groups, and smoother surface. In addition, 1.6 UF resins exhibited greater adhesion than 1.0 UF resins, regardless of the hemicellulose type, demonstrating that dispersion force was dominant in their molecular interactions.

Synchrotron X-Ray Diffraction Studies on Crystalline Domains in Urea-Formaldehyde Resins at Low Molar Ratio

WIBOWO, Eko Setio,PARK, Byung-Dae,CAUSIN, Valerio,HAHN, Dongyup The Korean Society of Wood ScienceTechnology 2022 목재공학 Vol.50 No.5

The crystalline domain of thermosetting urea-formaldehyde (UF) resins at low formaldehyde-to-urea (F/U) molar ratios (≤ 1.0) is known to be responsible for their poor performance as wood adhesives. Crystallization has been observed in 1.0 F/U UF resins during the addition reaction stage and at the end of the synthesis process (neat UF resins). The crystallinity and X-ray diffraction (XRD) spectra of the uncured neat UF resins, on the other hand, differed significantly from those of the cured neat UF resins, raising the possibility that their crystal structures were also different. This study demonstrates for the first time that the crystalline domains in 1.0 F/U UF resins generated from uncured and cured samples are identical. Despite having a lower crystallinity value, the synchrotron XRD patterns of purified neat UF resins were equivalent to the XRD patterns of cured neat UF resins. Transmission electron microscope images of the cured UF resins showed that the crystals were lamellar structures. This finding suggests that the crystal at low molar ratio UF resins are isotropic polycrystals with random orientation.

Simultaneous Improvement of Formaldehyde Emission and Adhesion of Medium-Density Fiberboard Bonded with Low-Molar Ratio Urea-Formaldehyde Resins Modified with Nanoclay

( Eko Setio Wibowo ),( Muhammad Adly Rahandi Lubis ),( Byung-dae Park ) 한국목재공학회 2021 목재공학 Vol.49 No.5

In wood-based composite panels, low-molar ratio (LMR) urea-formaldehyde (UF) resins usually result in reduced formaldehyde emission (FE) at the expense of poor adhesion. However, the FE and adhesion of medium-density fiberboard (MDF) bonded with LMR UF resins were both improved in this study. The modified LMR UF resins with transition metal ion-modified bentonite (TMI-BNT) nanoclay simultaneously improved the FE and adhesion of MDF panels. The modified LMR UF resins with 5% TMI-BNT resulted in a 37.1% FE reduction and 102.6% increase in the internal bonding (IB) strength of MDF panels. Furthermore, thickness swelling and water absorption also significantly decreased to 13.0% and 24.9%, respectively. These results imply that TMI-BNT modification of LMR UF resins could enhance the formation of a three-dimensional network rather than crystalline domains, resulting in improved cohesion.

Converting crystalline thermosetting urea–formaldehyde resins to amorphous polymer using modified nanoclay

Eko Setio Wibowo,Muhammad Adly Rahandi Lubis,Byung-Dae Park,Jong Sik Kim,Valerio Causin 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.87 No.-

Thermosetting urea–formaldehyde (UF) resins as the most common adhesives for wood-basedcomposites emit formaldehyde, which forces producers to lower formaldehyde/urea (F/U) molar ratiofor the UF resins synthesis. However, low-molar-ratio (below 1.0) UF resins have low formaldehydeemission at the expense of poor adhesion, which is responsible for the formation of crystalline domainsas a result of hydrogen bonds between linear molecules. For thefirst time, this study reports theconversion of crystalline UF resins to amorphous polymers by blocking the hydrogen bonds, usingtransition metal ion-modified bentonite (TMI-BNT) nanoclay through in situ intercalation. The modifiedUF resins with 5% TMI-BNT showed an almost amorphous structure, faster curing and higher crosslinkingdensity compared with those of neat resins, and resulted in 56.4% increase in the adhesionstrength and 48.3% reduction in the formaldehyde emission. Thus, blocking hydrogen bonds in low F/Umolar ratio UF resins with TMI-BNT converted crystalline UF resins to almost amorphous ones, resultingin a significant improvement in their adhesion with a low crystallinity.

Determination of Crystallinity of Thermosetting Urea-Formaldehyde Resins Using Deconvolution Method

Eko Setio Wibowo,박병대 한국고분자학회 2020 Macromolecular Research Vol.28 No.6

Current low formaldehyde/urea (F/U) molar ratio urea-formaldehyde (UF) resins are quite different from high molar ratio UF resins used 20 years ago in terms of their crystallinity. For the first time, this paper reports a method of determining the crystallinity of thermosetting urea-formaldehyde (UF) resins of different molar ratios with the deconvolution method, using Voigt, Lorentzian, and Gaussian function. The Gaussian deconvolution of X-ray diffraction (XRD) patterns was the most suitable and reliable curve-fitting method, which gave the crystallinity value from 31.8% to 56.1% as the molar ratio decreased from 1.6 to 1.0. These results also indicated that low-molar-ratio (1.2 and 1.0) UF resins were semi-crystalline, whereas high molar-ratio (1.6 and 1.4) resins were amorphous. The Gaussian function was also employed to determine the crystallinity of the low-molar-ratio (1.0) UF resins cured at different curing and hardener conditions. Hardener level had greater influence on the crystallinity than hardener type even though the curing temperature and time affected the crystallinity.

Characterization of Acetone Fractionated Softwood and Hardwood Kraft Lignin

( Eko Setio Wibowo ),( Byung-dae Park ) 한국목재공학회 2022 한국목재공학회 학술발표논문집 Vol.2022 No.1

Lignin fractionation is one of the key strategies for transforming Kraft lignin into value-added materials. It is important to understand the structure-property relationship of fractioned lignin for its valorization. As a result, it's crucial to grasp the structure of fractioned Kraft lignin, as well as techniques of revealing its structure. In this study, we used a combination of FTIR, quantitative 31p-nuclear magnetic resonance (NMR), quantitative heteronuclear single quantum (HSQC) NMR, and gel permeation chromatography to compare the chemical structure, composition, and molecular weight of acetone soluble and acetone insoluble Kraft lignin for softwood and hardwood. Furthermore, differential scanning calorimetry (DSC) and thermogravimetric (TG) studies were also used to analyze their thermal characteristics. The results revealed that acetone insoluble Kraft lignin (AIKL) from softwood or hardwood species had higher molecular weight and polydispersity, as well as a variety of native lignin side chains and aliphatic hydroxyl groups, albeit in substantially lower quantity. And the acetone soluble Kraft lignin (ASKL) has lower molecular weight and polydispersity, as well as more aromatic hydroxyl groups and less lignin side chains. The DSC and TG results also imply that AIKL has higher glass temperature and thermal degradation activation energy than those of ASKL. In addition, this finding demonstrates that ASKL has the potential to replace phenolic component in phenolic resins adhesive.

Storage Stability of Phenol-Resorcinol-Formaldehyde (PRF) Resins with Methanol Addition

Eko Setio Wibowo,박병대 한국고분자학회 2023 한국고분자학회 학술대회 연구논문 초록집 Vol.48 No.2

Structure and Thermal Degradation Behavior of Acetone Fractionated Kraft Lignin

( Eko Setio Wibowo ),( Byung-dae Park ) 한국목재공학회 2022 한국목재공학회 학술발표논문집 Vol.2022 No.2

This study investigates the relation between the structure and thermal degradation behavior of industrial softwood and hardwood kraft lignin (KL) after acetone fractionation to obtain acetone soluble (AS) and acetone insoluble (AI) fractions with reduced structural complexity and polydispersity. Gel permeation chromatography, Fourier transform infrared, quantitative carbon-13 nuclear magnetic resonance spectroscopy, and thermogravimetric analysis were used to evaluate the structure and thermal degradation behavior of AS-KL and AI-KL. The AS-KL fractions had a reduced molecular weight, a lower polydispersity, less native wood lignin side chains, more aromatic hydroxyl groups, and a more condensed structure. The AI-KL fractions, on the other hand, had significantly higher molecular weight and polydispersity, as well as more aliphatic hydroxyl groups and native lignin side chains. As a result, the thermal degradation activation energy of AI-KL samples was higher than that of AS-KL samples because the former fractions had a higher molecular weight and more aliphatic OH groups, which promoted hydrogen bonding between lignin polymers and improved their thermal stability. These results show that acetone fractionation of KL can be utilized to investigate the association between industrial KL structure and thermal degradation. These findings also shed light on the thermal degradation behavior of acetone fractionated products with relevant chemical and physical characteristics for a given application, such as raw materials for lignin valorization.

Adhesion Force Measurements of Urea-Formaldehyde Resins on Wood and Cellulose Films

( Eko Setio Wibowo ),( Byung-dae Park ) 한국목재공학회 2020 한국목재공학회 학술발표논문집 Vol.2020 No.1

The development on wood adhesive research in the recent years mainly focuses on the modification of the resins to increase their cohesion force and resulted in the improvement of wood-adhesion. However, the interaction between adhesive and wood biopolymers itself remains unclear. This study aims to understand adhesion between wood biopolymer such as cellulose and urea-formaldehyde (UF) resins. The cellulose films were made by spin-coating of cellulose nanofibrils (CNFs) onto the silicon wafer and then compared with wood (Pinus densiflora) film for adhesive force analysis. Two methods are employed to calculate the adhesive force: van Oss-Chaudhury-Good (OCG) method and direct measurement using DCAT25 instrument. For OCG method, three liquids such as water, ethylene glycol, and diiodomethane were used for contact angle measurement of the films sample: CNFs, wood, and UF resins. In addition, the maximum adhesion force between UF resins droplet and sample films is obtained using DCAT25 instrument.

Cure Kinetics of Low-Molar-Ratio Urea-Formaldehyde Resins Modified with Nanoclay Using Different Kinetic Methods

( Eko Setio Wibowo ),( Byung-dae Park ) 한국목재공학회 2019 한국목재공학회 학술발표논문집 Vol.2019 No.2

This study reports cure kinetics of low-molar-ratio urea-formaldehyde (UF) resins modified with a transition metal ion modified bentonite (TMI-BNT) nanoclay using different kinetic analysis methods to understand the effect of TMI-BNT on the thermal curing behaviors of these modified resins. Differential scanning calorimetry (DSC) was used to determine the kinetic parameters using two types of kinetic methods, such as model-fitting (MF) method which consist of the Kissinger, the nth-order and autocatalytic method and the model-free kinetics (MFK) method which consist of Friedman (FR), Flynn-Wall-Ozawa (FWO) and the Kissinger-Akahira-Sunose (KAS) method. Among all kinetic methods, Kissinger, FWO and KAS method gave the best fit to explain the resins curing behavior, as showed that in general the activation energy (Eα) decreased as the TMI-BNT content increased, indicating a cure acceleration by TMI-BNT addition. It was explained that the proton released by the intercalation of linear oligomers of UF resins with TMI-BNT was the main cause of facilitating the condensation reaction.