Influence of the Degree of Condensation on the Radial Penetration of Urea-Formaldehyde Adhesives into Silver Fir (Abies alba, Mill.) Wood Tissue

Jeong²,

2021

Forests

This paper reports a comparison of adhesion behavior of urea-formaldehyde (UF) with those of melamine-urea-formaldehyde (MU) resins in bonding wood by analyzing the results published in literatures. For this purpose, the adhesion behavior of UF resins prepared by blending low-viscosity resin (LVR) with high-viscosity resin (HVR) at five different blending and two formaldehyde/urea (F/U) molar ratios (1.0 and 1.2) was compared with those of two MUF resins synthesized by either simultaneous reaction (MUF-A resins) or multi-step reaction (MUF-B resins) with three melamine contents (5, 10, and 20 wt%). As the blending (LVR:HVR) ratio increased from 100:0 to 0:100, the viscosity and molar mass (Mw and Mn) of the blended UF resins increased while the gelation time decreased. The interphase features such as maximum storage modulus (E′max), resin penetration depth, and bond-line thickness of the UF resins increased to a maximum and then decreased as the blending ratio increased. In addition, both MUF-A and MUF-B resins also showed an increase in the Mw and Mn as the melamine content increased from 5% to 20%. However, the E′max, resin penetration depth, and bond-line thickness of the MUF resins decreased as the molar mass or melamine content increased. These results indicated that the adhesion of UF resins heavily depends on the interphase features while that of the MUF resins highly depends on the cohesion of the resins.

Section: Methodsmentioning

confidence: 99%

Section: Depth Of the Resin Penetration Into Wood In Bond Linementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A Comparison of Adhesion Behavior of Urea-Formaldehyde Resins with Melamine-Urea-Formaldehyde Resins in Bonding Wood

Jeong²,

2021

Forests

“…The penetration of an adhesive into the wood structure is believed to have a strong influence on bond strength, durability and performance [18,[36][37][38][39][40][41][42][43][44][45][46][47][48]. Adhesive penetration into wood can occur in various forms, including gross penetration and penetration into cell walls.…”

Section: Lower Porosity and Permeabilitymentioning

confidence: 99%

Barriers to the Effective Adhesion of High-Density Hardwood Timbers for Glue-Laminated Beams in Australia

Leggate

McGavin

Outhwaite³

et al. 2022

Forests

A number of international timbers of high commercial importance are extremely difficult to glue, which is significantly hindering access to global market opportunities for engineered wood products, especially for heavily demanded structural products. Some particularly problematic timbers in Australia are the dominant commercial hardwood species, including spotted gum (Corymbia spp.) and Darwin stringybark (Eucalyptus tetrodonta). These species are renowned for their very high mechanical properties, natural durability and attractive aesthetic appeal. However, they are notoriously difficult to glue, especially for sawn laminate-based engineered wood products, such as structural glue-laminated beams. Despite considerable effort and testing of diverse internationally established best-practice approaches to improve adhesion, glue-laminated beam samples of these timbers still frequently fail to meet the requirements of the relevant standard, mainly due to excessive glue line delamination. This paper discusses the key barriers to effective adhesion of these high-density timbers and particularly emphasises the necessity of achieving greater adhesive penetration. Greater adhesive penetration is required to enhance mechanical interlocking, entanglement and molecular interactions between the adhesive and the wood to achieve stronger and more durable bonds. Potential solutions to enhance adhesive penetration, as well as to improve gluability in general, are discussed in terms of their likelihood to satisfactorily prevent delamination and the potential to be applied at an industrial scale. This new fundamental understanding will assist the development of solutions, allowing industry to commercialise newly engineered wood products made from high-density timbers.

Journal of the Korean Wood Science and Technology

“…The properties and performance of MUF resins are closely related to the resin's synthesis method and the melamine level. Previous studies have shown that synthesis parameters such as F/(U+M) molar ratio, melamine content, and the sequence of melamine addition (in the case of MUF) significantly affect the properties of UF and MUF resins (Dunky, 1998;Pizzi and Mittal, -292 -2003;No and Kim, 2004;Hse et al, 2008, Gavrilović-Grmuša et al, 2010a, 2010bPaiva et al, 2012, Hong et al, 2017a. These results reported that thickness of the interphase region and the depth of penetration into the wood were related to the resin viscosity.…”

Section: Introductionmentioning

confidence: 99%

Effects of Storage Time on Molecular Weights and Properties of Melamine-Urea-Formaldehyde Resins

Jeong¹,

Park²,

Causin³

2020

As the properties of the melamine-urea-formaldehyde (MUF) resins were changing during their storage time, this study investigated the impacts of the synthesis method and melamine content of the MUF resins on the pH, apparent viscosity, molecular weights, and crystallinity to estimate these properties over storage times of up to 30 days. Melaminesat three addition levels (5, 10, and 20 wt% based on the resin solids) were simultaneously reacted with urea and formaldehyde (MUF-A resins), while those at the same addition levels were first reacted with formaldehyde and then with urea(MUF-B resins). The pH values of the MUF-A and MUF-B resins decreased linearly as the storage time increased; the apparent viscosity increased linearly for the low melamine contents (5% and 10%) but increased exponentially for 20%. As anticipated, the molecular weights (Mw and Mn) increased linearly with the storage time, with a steeper increase in the Mw of the MUF-B resins compared with that of the MUF-A resins. The crystallinity of the two resin types decreased with storage time at higher melamine content. The relationships between these properties and the storage time made it possible to estimate the property changes in these resins synthesized by the different synthesis methods and melamine contents; this could help predict the properties of such resins in the industry during their storage.