Synthesis, structure, and characterization of glyoxal-urea-formaldehyde cocondensed resins

Investigation of Novel Thermosetting Copolymer-Based Monomethylolurea-Glyoxal for Wood Manufacturing

The purpose of this investigation was to design novel alternating copolymers (monomethylolurea-glyoxal, MMU-G) as adhesives for wood manufacturing. MMU-G were synthesized under acid (pH = 5) conditions. After the 120-day storage period, the MMU-G resins were used for plywood production, which exhibited a wet shear strength of about 2.15 MPa, similar to the freshly prepared MMU-G resin. The excellent water resistance and long storage stability showed that MMU-G has particular characteristics and properties all of their own, which, in certain respects, are very different from those of urea-formaldehyde (UF) adhesives. The X-ray diffraction results showed that only a few crystallinities occurred in MMU-G resins, indicating the presence of long side chains in the MMU-G polymer structures, leading to better adhesion strength than UF resins. The structure characteristics of the MMU-G resin were studied by Fourier transform infrared and electrospray ionization mass spectrometry, and a possible molecular structure has been inferred, which is consistent with spectroscopic results.

A Green Resin Wood Adhesive from Synthetic Polyamide Crosslinking with Glyoxal

Glyoxal is considered to be the most likely substitute for formaldehyde to synthesize resin adhesives for wood bonding due to its reactivity, structural characteristics, being non-toxic, low volatility, and acceptable cost. Regrettably, the performance of the resin synthesized using glyoxal to directly replace all formaldehyde is not totally satisfactory, especially as it has almost no water resistance. This makes such a simple alternative fail to be suitable for industrial production. To prepare an environment-friendly glyoxal-based adhesive with good bonding performance, the work presented here relies first on reacting citric acid and hexamethylene diamine, producing a polyamide, with glyoxal, and then crosslinking it, thus synthesizing a thermosetting resin (namely CHG) adhesive and applying it for plywood bonding. The plywood prepared exhibits excellent dry and wet shear strength, which are better than GB/T9846-2015 standard requirements (≥0.7 MPa), and even after being soaked in hot water at 63 °C for 3 h, its strength is still as high as 1.35 MPa. The CHG resin is then potentially an adhesive for industrial application for replacing UF (urea-formaldehyde) and MUF (melamine-urea-formaldehyde) adhesives for wood composites.

Vapor-deposited functional polymer thin films in biological applications

Functional polymer coatings have become ubiquitous in biological applications, ranging from biomaterials and drug delivery to manufacturing-scale separation of biomolecules using functional membranes. Recent advances in the technology of chemical vapor deposition (CVD) have enabled precise control of the polymer chemistry, coating thickness, and conformality. That comprehensive control of surface properties has been used to elicit desirable interactions at the interface between synthetic materials and living organisms, making vapor-deposited functional polymers uniquely suitable for biological applications. This review captures the recent technological development in vapor-deposited functional polymer coatings, highlighting their biological applications, including membrane-based bio-separations, biosensing and bio-MEMS, drug delivery, and tissue engineering. The conformal nature of vapor-deposited coatings ensures uniform coverage over micro- and nano-structured surfaces, allowing the independent optimization of surface and bulk properties. The substrate-independence of CVD techniques enables facile transfer of surface characteristics among different applications. The vapor-deposited functional polymer thin films tend to be biocompatible because they are free of remnant toxic solvents and precursor molecules, potentially lowering the barrier to clinical success.

Potential Use of Wollastonite as a Filler in UF Resin Based Medium-Density Fiberboard (MDF)

Urea-formaldehyde (UF) resins are primary petroleum-based, increasing their potential environmental footprint. Identifying additives to reduce the total amount of resin needed without adversely affecting the panel properties could reduce these impacts. Wollastonite is a mineral containing calcium and silica that has been used as an additive in a variety of materials and may be useful as a resin extender. Nanoscale wollastonite has been shown to enhance the panel properties but is costly. Micron-scale wollastonite may be a less costly alternative. Medium-density fiberboards were produced by blending a hardwood furnish with UF alone, micron-sized wollastonite alone, or a 9:1 ratio of UF to wollastonite. Panels containing of only wollastonite had poor properties, but the properties of panels with 9:1 UF/wollastonite were similar to the UF-alone panels, except for the internal bond strength. The results suggest that small amounts of micron-sized wollastonite could serve as a resin extender. Further studies are suggested to determine if the micron-sized material has similar positive effects on the resin curing rate.

Wood Composites and Their Polymer Binders

This review presents first, rather succinctly, what are the important points to look out for when preparing good wood composites, the main types of wood composites manufactured industrially, and the mainly oil-derived wood composite adhesives and binders that dominate and have been dominating this industry. Also briefly described are the most characteristic biosourced, renewable-derived adhesives that are actively researched as substitutes. For all these adhesives, synthetic and biosourced, the reviews expose the considerable progresses which have occurred relatively recently, with a host of new approaches and ideas having been proposed and tested, some even implemented, but with even many more already appearing on the horizon.

From prebiotic chemistry to supramolecular oligomers: urea-glyoxal reactions

A fundamental question in origin-of-life studies and astrochemistry concerns the actual processes that initiate the formation of reactive monomers and their oligomerization. Answers lie partly in the accurate description of reaction mechanisms compatible with environments plausible on early Earth as well as cosmological scenarios in planetary factories. Here we show in detail that reactions of urea-as archetypal prebiotic substance-and reactive carbonyls-exemplified by glyoxal-lead to a vast repertoire of oligomers, in which different five- and six-membered non-aromatic heterocycles self-assemble and insert into chains or dendritic-like structures with masses up to 1000 Da. Such regular patterns have been interpreted by experimental and computational methods. A salient conclusion is that such processes most likely occur through SN-type mechanisms on hydrated or protonated species. Remarkably, such supramolecular oligomeric mixtures can be easily isolated from organic solvents, thus opening the door to the generation of novel urea-containing polymers with potential applications in materials chemistry and beyond.

Carboxylic acid-capped ruthenium nanoparticles: experimental and theoretical case study with ethanoic acid

Given that the properties of metal nanoparticles (NPs) depend on several parameters (namely, morphology, size, surface composition, crystalline structure, etc.), a computational model that brings a better understanding of a structure-property relationship at the nanoscale is a significant plus in order to explain the surface properties of metal NPs and also their catalytic viability, in particular, when envisaging a new stabilizing agent. In this study we combined experimental and theoretical tools to obtain a mapping of the surface of ruthenium NPs stabilized by ethanoic acid as a new capping ligand. For this purpose, the organometallic approach was applied as the synthesis method. The morphology and crystalline structure of the obtained particles was characterized by state-of-the art techniques (TEM, HRTEM, WAXS) and their surface composition was determined by various techniques (solution and solid-state NMR, IR, chemical titration, DFT calculations). DFT calculations of the vibrational features of model NPs and of the chemical shifts of model clusters allowed us to secure the spectroscopic experimental assignations. Spectroscopic data as well as DFT mechanistic studies showed that ethanoic acid lies on the metal surface as ethanoate, together with hydrogen atoms. The optimal surface composition determined by DFT calculations appeared to be ca. [0.4-0.6] H/Rusurf and 0.4 ethanoate/RuSurf, which was corroborated by experimental results. Moreover, for such a composition, a hydrogen adsorption Gibbs free energy in the range -2.0 to -3.0 kcal mol-1 was calculated, which makes these ruthenium NPs a promising nanocatalyst for the hydrogen evolution reaction in the electrolysis of water.

Melamine⁻Glyoxal⁻Glutaraldehyde Wood Panel Adhesives without Formaldehyde

(MGG') resin adhesives for bonding wood panels were prepared by a single step procedure, namely reacting melamine with glyoxal and simultaneously with a much smaller proportion of glutaraldehyde. No formaldehyde was used. The inherent slow hardening of this resin was overcome by the addition of N-methyl-2-pyrrolidone hydrogen sulphate ionic liquid as the adhesive hardener in the glue mix. The plywood strength results obtained were comparable with those obtained with melamine⁻formaldehyde resins pressed under the same conditions. Matrix assisted laser desorption ionisation time of flight (MALDI ToF) and Fourier transform Infrared (FTIR) analysis allowed the identification of the main oligomer species obtained and of the different types of linkages formed, as well as to indicate the multifaceted role of the ionic liquid. These resins are proposed as a suitable substitute for equivalent formaldehyde-based resins.

The Major Chromophore Arising from Glucose Degradation and Oxidative Stress Occurrence during Lens Proteins Glycation Induced by Glucose

Glucose autoxidation has been proposed as a key reaction associated with deleterious effects induced by hyperglycemia in the eye lens. Little is known about chromophores generated during glucose autoxidation. In this study, we analyzed the effect of oxidative and dicarbonyl stress in the generation of a major chromophore arising from glucose degradation (GDC) and its association with oxidative damage in lens proteins. Glucose (5 mM) was incubated with H₂O₂ (0.5-5 mM), Cu²⁺ (5-50 μM), glyoxal (0.5-5 mM) or methylglyoxal (0.5-5 mM) at pH 7.4, 5% O₂, 37 °C, from 0 to 30 days. GDC concentration increased with incubation time, as well as when incubated in the presence of H₂O₂ and/or Cu²⁺, which were effective even at the lowest concentrations. Dicarbonylic compounds did not increase the levels of GDC during incubations. ¹H, ¹³C and FT-IR spectra from the purified fraction containing the chromophore (detected by UV/vis spectroscopy) showed oxidation products of glucose, including gluconic acid. Lens proteins solutions (10 mg/mL) incubated with glucose (30 mM) presented increased levels of carboxymethyl-lysine and hydrogen peroxide that were associated with GDC increase. Our results suggest a possible use of GDC as a marker of autoxidative reactions occurring during lens proteins glycation induced by glucose.

Force-induced retro-click reaction of triazoles competes with adjacent single-bond rupture

The highly controversial force-induced cycloreversion of 1,2,3-triazole, its well-known retro-click reaction, is shown to be possible only for 1,5-substituted triazoles, but competes with rupture of an adjacent single-bond. We draw this conclusion from both static and dynamic calculations under external mechanical forces applied to unsubstituted and 1,4- and 1,5-substituted triazoles. The JEDI (Judgement of Energy DIstribution) analysis, a quantum chemical tool quantifying the distribution of strain energy in mechanically deformed molecules, is employed to identify the key factors facilitating the force-induced retro-click reaction in these systems. For 1,4-substituted triazoles it is shown to be impossible, but the parallel alignment of the scissile bond in 1,5-substituted triazoles with the acting force makes it generally feasible. However, the weakness of the carbon-nitrogen bond connecting the triazole ring to the linker prevents selective cycloreversion.

Backbone-Degradable Polymers Prepared by Chemical Vapor Deposition

Polymers prepared by chemical vapor deposition (CVD) polymerization have found broad acceptance in research and industrial applications. However, their intrinsic lack of degradability has limited wider applicability in many areas, such as biomedical devices or regenerative medicine. Herein, we demonstrate, for the first time, a backbone-degradable polymer directly synthesized via CVD. The CVD co-polymerization of [2.2]para-cyclophanes with cyclic ketene acetals, specifically 5,6-benzo-2-methylene-1,3-dioxepane (BMDO), results in well-defined, hydrolytically degradable polymers, as confirmed by FTIR spectroscopy and ellipsometry. The degradation kinetics are dependent on the ratio of ketene acetals to [2.2]para-cyclophanes as well as the hydrophobicity of the films. These coatings address an unmet need in the biomedical polymer field, as they provide access to a wide range of reactive polymer coatings that combine interfacial multifunctionality with degradability.

Multigrowth Factor Delivery via Immobilization of Gene Therapy Vectors

Molecules can be immobilized onto biomaterials by a chemical vapor deposition (CVD) coating strategy. Pentafluorophenolester groups react with amine side chains on antibodies, which can selectively immobilize adenoviral vectors for gene delivery of growth factors. These vectors can produce functional proteins within defined regions of biomaterials to produce customizable structures for targeted tissue regeneration.

Ultrasensitive In Situ Fluorescence Analysis using Modulated Fluorescence Interference Contrast at Nanostructured Polymer Surfaces

The precise modulation of fluorescence interference contrast is achieved by introducing a nanoscopically engineered spacer layer prepared by chemical vapor deposition (CVD) of functional polymers. These novel imaging substrates are chemically identical throughout their entire detection area, yet present patterns of nanoscale thickness. A protein binding cascade is studied in real time and in the presence of high background noise.

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

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] HSO₄ (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 ¹³C 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] HSO₄ 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 NH₄Cl. 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.

Chemical vapour deposition of soluble poly(p-xylylene) copolymers with tuneable properties

High-molecular weight poly(p-xylylene) (PPX)/2-hydroxy-ethyl methacrylate (HEMA) copolymers are synthesized by chemical vapour deposition. The copolymer coatings are hydrophilic and show good cytocompatibility.

Glyoxal-Urea-Formaldehyde Molecularly Imprinted Resin as Pipette Tip Solid-Phase Extraction Adsorbent for Selective Screening of Organochlorine Pesticides in Spinach

A new kind of glyoxal-urea-formaldehyde molecularly imprinted resin (GUF-MIR) was synthesized by a glyoxal-urea-formaldehyde (GUF) gel imprinting method with 4,4'-dichlorobenzhydrol as a dummy template. The obtained GUF-MIR was characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) and applied as a selective adsorbent of miniaturized pipet tip solid-phase extraction (PT-SPE) for the separation and extraction of three organochlorine pesticides (dicofol (DCF), dichlorodiphenyl dichloroethane (DDD), and tetradifon) in spinach samples. The proposed pretreatment procedures of spinach samples involved only 5.0 mg of GUF-MIR, 0.7 mL of MeOH-H2O (1:1, v/v) (washing solvent), and 0.6 mL of cyclohexane-ethyl acetate (9:1, v/v) (elution solvent). In comparison with other adsorbents (such as silica gel, C18, NH2-silica gel, and neutral alumina (Al2O3-N)), GUF-MIR showed higher adsorption and purification capacity for DCF, DDD, and tetradifon in aqueous solution. The average recoveries at three spiked levels ranged from 89.1% to 101.9% with relative standard deviations (RSDs) ≤ 7.1% (n = 3). The presented GUF-MIR-PT-SPE method combines the advantages of molecularly imprinted polymers (MIPs), GUF, and PT-SPE and can be used in polar solutions with high affinity and selectivity to the analytes in complex samples.

Superior Mechanical Properties of Epoxy Composites Reinforced by 3D Interconnected Graphene Skeleton

Epoxy-based composites reinforced by three-dimensional graphene skeleton (3DGS) were fabricated in resin transfer molding method with respect to the difficulty in good dispersion and arrangement of graphene sheets in composites by directly mixing graphene and epoxy. 3DGS was synthesized in the process of self-assembly and reduction with poly(amidoamine) dendrimers. In the formation of 3DGS, graphene sheets were in good dispersion and ordered state, which resulted in exceptional mechanical properties and thermal stability for epoxy composites. For 3DGS/epoxy composites, the tensile and compressive strengths significantly increased by 120.9% and 148.3%, respectively, as well as the glass transition temperature, which increased by a notable 19 °C, unlike the thermal exfoliation graphene/epoxy composites via direct-mixing route, which increased by only 0.20 wt % content of fillers. Relative to the graphene/epoxy composites in direct-mixing method mentioned in literature, the increase in tensile and compressive strengths of 3DGS/epoxy composites was at least twofold and sevenfold, respectively. It can be expected that 3DGS, which comes from preforming graphene sheets orderly and dispersedly, would replace graphene nanosheets in polymer nanocomposite reinforcement and endow composites with unique structure and some unexpected performance.