Acid Ionic Liquids as a New Hardener in Urea-Glyoxal Adhesive Resins

Abstract

Abstract:The effect of acidic ionic liquid (IL) as a new catalyst on the properties of wood-based panels bonded with urea-glyoxal (UG) resins was investigated. Different levels of N-methyl-2-pyrrolidone hydrogen sulfate ([HNMP] HSO 4 (0, 1, 2, 3 wt %)) were added to prepared UG resin. The resin was then used for preparing laboratory particleboard panels. Then, the properties of the prepared panels were evaluated. The structure of the prepared UG resin was studied by 13 C NMR, and thermal curing behavior of the resin before and after the addition of IL was measured by DSC. Additionally, the main oligomers formed in the UG reaction were identified by matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) mass spectroscopy. The results indicated that IL can be used as an efficient catalyst for UG resin. The physicochemical tests indicated that the addition of [HNMP] HSO 4 from 0 to 3 wt % decreased the pH value of the glue-mix, and the pH decreased on curing to the same level as urea-formaldehyde resins. The gel accelerated with increasing catalyst content and with the decreasing of the pH in the UG resin. The panels prepared with IL had higher mechanical strength and dimensional stability compared to those made from UG resins containing NH 4 Cl. Scanning electron microscope (SEM) micrographs showed that the panels prepared with ionic liquid presented low porous. DSC analysis showed that the addition of IL to the UG resin decrease the energy of activation of the curing reaction to render possible cross-linking. The MALDI TOF results indicated a preponderant linearity of the oligomers formed, implying a high energy of activation of curing for UG resins.

Functionality of Beech Bark in Adhesive Mixtures Used in Plywood and Its Effect on the Stability Associated with Material Systems

“…On the other hand, filler helps to reduce the penetration of resin into the small pores of the wood [19]. Many types of fillers, mostly natural, were investigated by other researchers, for example, corn starch flour, wheat flour, soybean meal, sorghum flour, and palm kernel meal [20,21,22,23,24,25,26]. In recent years, some research studies have been conducted to prepare and study the reaction mechanism and structure of environmentally friendly urea-based aminoresins by choosing glyoxal to substitute formaldehyde [27].…”

Melamine–Glyoxal–Glutaraldehyde Wood Panel Adhesives without Formaldehyde

“…The same principle of using an ionic liquid as a hardener that has been used for urea–glyoxal resins [ 12 , 17 ] was applied to melamine–glyoxal (MG) and melamine–glyoxal–glutaraldehyde (MGG’) resins for which, N -methyl-2-pyrrolidone hydrogen sulphate ([HNMP] [HSO 4 − ]) was used as hardener. As this material is relatively expensive it was prepared in the laboratory according to the method of Wang et al [ 15 ] and used with a minimum of purification [ 12 , 17 ] ( Scheme 1 ).…”

“…Recently, much work has been conducted to prepare and study the reaction mechanism and structure of environmentally friendly urea-based aminoresins by choosing glyoxal (G) to substitute formaldehyde (F) partially or totally so as to eliminate or markedly decrease formaldehyde (F) emission [ 9 , 10 , 11 , 12 ]. Urea–glyoxal (UG) and urea–glyoxal–formaldehyde (UGF) resins have been successfully synthesized and used as wood adhesive for plywood, interior decoration and furniture material [ 10 , 11 ] as well as for particleboard [ 12 ]. Equally, melamine–glyoxal resins have been formulated and while they were capable of yielding reasonable bond strength to satisfy relevant plywood standards, they did not yield internal bond (IB) strength results for particleboard to the level needed to satisfy relevant standards [ 13 ].…”

“…Recently, the energy of activation of cross-linking of urea–glyoxal resins was effectively and markedly decreased by the use of ionic liquids (IL) as resin hardeners and additives [ 12 , 17 ]. This made it possible to obtain the same performance of UF resins by using UG + IL resins to even bond particleboard.…”

Assessment of the physico-mechanical, thermal, and morphological properties of rubber wood modified with silica sol in combination with GU/GMU resins

“…However, because formaldehydebased thermosetting resins pose major environmental concerns, it is necessary to replace the toxic formaldehyde in the synthesis of environmentally friendly wood adhesives. Among the various aldehydes available, the usage of glyoxal has yielded the best results, as it is nontoxic, has a low cost, is nonvolatile, and is easily biodegradable (Younesi-Kordkheili and Pizzi 2016;Younesi-Kordkheili and Pizzi 2017). Due to its two active merged aldehyde groups, it can be used to glyoxylate the lignins in cell walls or cross-link with the hydroxyl groups in cellulosic materials via a hemiacetal or acetal reaction in the presence of a catalyst (Lee and Kim 2005;Navarrete et al 2013).…”