Study of glycidyl ether as a new kind of modifier for urea‐formaldehyde wood adhesives

In this work, the multiepoxy functional glycidyl ether (GE) modified urea‐formaldehyde (UF) resins were synthesized via a traditional alkaline‐acid process under low formaldehyde/urea (F/U) molar ratio. The synthesized resins were characterized by ¹³C magnetic resonance spectroscopy (¹³C‐NMR), indicating that GE can effectively react with UF resins via the ring‐opening reaction of epoxy groups. Moreover, the residual epoxy groups of GE could also participate in the curing reaction of UF resins, which was verified by Fourier transform infrared spectroscopy. The storage stability of GE‐modified UF resins and the thermal degradation behavior of the synthesized resins were evaluated by using optical microrheology and thermogravimetric analysis, respectively. Meanwhile, the synthesized resins were further employed to prepare the plywood with the veneers glued. For the modification on bonding strength and formaldehyde emission of the plywood, the influences of addition method, type, and amount of GE were systematically investigated. The performance of UF adhesives were remarkably improved by the modification of GE around 20–30% (weight percentage of total urea) in the acidic condensation stage during the resin synthesis. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Low‐volatility acetals to upgrade the performance of melamine–urea–formaldehyde wood adhesive resins

1,1,2,2‐Tetramethoxyethane (TME), a high boiling point acetal derived from glyoxol, lhas been shown to upgrade the performance of melamine‐urea‐formaldehyde (MUF) and some UF resins used for wood adhesives. This affords the possibility of decreasing the percentage of resin used in the preparation of wood panels without volatilizing the TME acetal used.     

Improving the performance of urea‐formaldehyde wood adhesive system using dendritic poly(amidoamine)s and their corresponding half generations

Full as well as half generations of dendritic poly(amido amine)s (PAMAMs) were introduced onto urea‐formaldehyde (UF) wood adhesive system as modifiers to increase its stability and enhance the performance of the bonded wood joints with it. The effect of the modifiers on the physical properties and mechanical performance was discussed on the light of gel times, curing exotherms using differential scanning calorimetry (DSC), infra‐red (IR), and shear strength measurements. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Differential scanning calorimetry of urea–formaldehyde adhesive resins,synthesized under different pH conditions

The purpose of this study was to investigate the effects of reaction pH conditions on thermal behavior of urea–formaldehyde (UF) resins, for the possible reduction of formaldehyde emission of particleboard bonded with them. Thermal curing properties of UF resins, synthesized at three different reaction pH conditions, such as alkaline (pH 7.5), weak acid (pH 4.5), and strong acid (pH 1.0), were characterized with multiheating rate method of differential scanning calorimetry. As heating rate increased, the onset and peak temperatures increased for all three UF resins. By contrast, the heat of reaction (ΔH) was not much changed with increasing heating rates. The activation energy (E_a) increased as the reaction pH decreased from alkaline to strong acid condition. The formaldehyde emission of particleboard was the lowest for the UF resins prepared under strong acid, whereas it showed the poorest bond strength. These results indicated that thermal curing behavior was related to chemical species, affecting the formaldehyde emission, while the poor bond strength was believed to be related to the molecular mobility of the resin used. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 422–427, 2006     

Thermoplastic polymers as modifiers for urea–formaldehyde wood adhesives. III. In situ thermoplastic‐modified wood composites

Acrylic monomers and free‐radical initiators were dispersed in an aqueous urea–formaldehyde (UF) suspension and polymerized in situ to afford a suspension containing 5 wt % thermoplastic (5 g of thermoplastic/100 mL of suspension). The viscosity of the thermoplastic‐modified UF suspension (65 wt % solids at 25°C) ranged from 240 to 437 cP versus 121 cP for the unmodified UF control. Wood‐flour composites (sugar maple and 50 wt % adhesive) were prepared with thermoplastic‐modified UF suspensions and cured with the same cycle used for the composites prepared with the unmodified UF adhesive (control). The effect of the thermoplastic‐modified UF adhesive was evaluated on the notched Izod impact strength and equilibrium moisture uptake of the wood‐flour composites. The notched Izod impact strength of the composites prepared with modified UF adhesives increased by as much as 94% above that of the control. The increase depended on the initiator and the monomer composition. The modification affected the equilibrium moisture uptake and rate of moisture uptake in the wood‐flour composites. Preliminary results for particleboard prepared with 10 wt % modified UF adhesive (5% thermoplastic in the UF resin) and unoptimized cure conditions confirmed a significant effect of the thermoplastic modification on both the internal‐bond strength and thickness swelling of the particleboard. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of addition of glycolysis products of poly(ethyleneterephthalate) wastes to urea‐formaldehyde resin on its adhesion performance to wood substrates and formaldehyde emission

Recycling of poly(ethyleneterephthalate) waste was achieved through glycolysis using diethyleneglycol (DEG) and poly(ethyleneglycol) (PEG 400), which yielded different fractions that exhibited hydroxyl numbers of 174.41 and 54.86 mg of KOH/g, respectively, whereas GPC profiles revealed bimodality in both cases corresponding to M_n values equivalent to 534 and 1648. The products of glycolysis from both cases were individually incorporated as modifiers during the synthesis of urea‐formaldehyde resins from both the basic as well as acidic stages, respectively. It was found that the free formaldehyde level was remarkably decreased for the modified resins while the gel time was slightly affected indicating some activation of the resins. In addition, the adhesion strength of wood joints bonded with the modified resins improved markedly in the dry state while the moisture resistance was significantly fortified with respect to the comparable joints formulated from unmodified resins where instant failure took place within few hours after immersion in water. The shelf life of the resins did not prolong and lasted maximum for about 2 months which was ascribed to the presence of reasonable amount of carboxyl terminal groups at the ends of a minor portion of the glycolyzed products that could actively act to self‐catalyze the polycondensation and crosslinking reactions during storage leading eventually to vitrification of the resin and shortening of shelf life. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Brominated phenol–formaldehyde resin as an adhesive for plywood

A brominated phenol–formaldehyde resin was investigated as a plywood adhesive to study the effect of bromine on the physical and flammability properties of this resin. The results of these studies showed that brominated phenol–formaldehyde resin of 10% bromine content by weight of the phenol–formaldehyde resin was suitable to be used as a plywood adhesive. The optimal compressing temperature and compressing time were 110°C and 30 min, respectively. The prepared plywood obtained from the optimal condition gave a high shear strength, good flame retardancy, and good resistance to both hot and cold water. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1918–1924, 2003     

Free volume,adhesion, and viscoelastic properties of model nanostructured pressure‐sensitive adhesive based on stoichiometric complex of poly(N‐vinyl pyrrolidone) and poly(ethylene glycol) of disparate chain lengths

Positron annihilation lifetime spectroscopy was used to characterize the size and content of subnanoscopic free volume in a model pressure‐sensitive adhesive based on a stoichiometric hydrogen‐bonded network complex of poly(N‐vinyl pyrrolidone) (PVP) and oligomeric poly(ethylene glycol) (PEG). Adhesive properties were examined with peel and probe tack tests, and mechanical properties were studied with tensile test. Nonequimolar stoichiometry and the structure of PVP–PEG model pressure‐sensitive adhesive blends were found to be determined by the length of PEG short chains. The size and number density of free volume domains in the PVP–PEG blends were determined as functions of blend composition and relative humidity of the surrounding atmosphere, which controls the amount of absorbed water. Correlating the free volume, adhesion behaviors, and tensile properties of the blends, the range of free volume favoring pressure‐sensitive adhesion in examined compositions was established. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Enhancing the properties of urea formaldehyde wood adhesive system using different generations of core‐shell modifiers based on hydroxyl‐terminated dendritic poly(amidoamine)s

Different generations of hydroxy‐terminated dendritic poly(amidoamine) (Gn? OH) with ethylenediamine as a core were prepared by successive alternative addition of methylacrylate and the core up to the third generation while employing ethanolamine only in the last step of every full generation. The different generations prepared were used as modifiers for urea‐formaldehyde (UF) resins. The enhanced durability and stabilizing effect of the (Gn? OH)s along with the reduced levels of free formaldehyde and improved mechanical performance of wood joints glued with the modified resins are discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Application of the biodegradable diblock copolymer poly(L‐lactide)‐block‐poly(L‐cysteine): Drug delivery and protein conjugation

A novel approach to self‐assembled and shell‐crosslinked (SCL) micelles from the diblock copolymer poly(L ‐lactide)‐block‐poly(L ‐cysteine) to be used as drug and protein delivery carriers is described. Rifampicin was used as a model drug. The drug‐loaded SCL micelles were obtained by self‐assembly of the copolymer in the presence of the drug in aqueous media. Their morphology and size were studied with dynamic light scattering and field emission scanning electron microscopy. The rifampicin loading capacity and encapsulation efficiency were studied with ultraviolet–visible spectrophotometry. The drug‐release rate in vitro depended on the oxidizing and reducing environment. Moreover, a straightforward approach to the conjugation of the copolymer with bovine serum albumin (BSA) was developed, and a gel electrophoresis test demonstrated that this conjugated BSA could be reversibly released from the copolymer substrate under reducing conditions. In conclusion, this L ‐cysteine copolymer can be used in drug delivery and in protein fixation and recovery. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Thermal properties and adhesion strength of amorphous poly(α‐olefins)/styrene–ethylene–butylene copolymer/terpene hot‐melt adhesive

The thermal stability and adhesion properties, such as lap‐shear strength of hot‐melt adhesives were obtained from amorphous poly(α‐olefins) and thermoplastic rubber [styrene–ethylene–butylene copolymer (SEBS)] blends. The addition of SEBS increased the toughness and viscosity and decreased the lap‐shear strength of the hot‐melt adhesive. Terpene tackifier resin offered enhanced lap‐shear strength; this was more effective when combined tackifier resin was added on the hot‐melt adhesive. Only a small amount of wax and antioxidant affected the thermal stability and lap‐shear strength of the hot‐melt adhesive. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Reactivity,chemical structure,and molecular mobility of urea–formaldehyde adhesives synthesized under different conditions using FTIR and solid‐state 13C CP/MAS NMR spectroscopy

This study was conducted to investigate the effects of reaction pH condition and hardener type on the reactivity, chemical structure, and molecular mobility of urea–formaldehyde (UF) resins. Three different reaction pH conditions, such as alkaline (7.5), weak acid (4.5), and strong acid (1.0), were used to synthesize UF resins, which were cured by adding four different hardeners (ammonium chloride, ammonium sulfate, ammonium citrate, and zinc nitrate) to measure gel time as the reactivity. FTIR and ¹³C‐NMR spectroscopies were used to study the chemical structure of the resin prepared under three different reaction pH conditions. The gel time of UF resins decreased with an increase in the amount of ammonium chloride, ammonium sulfate, and ammonium citrate added in the resins, whereas the gel time increased when zinc nitrate was added. Both FTIR and ¹³C‐NMR spectroscopies showed that the strong reaction pH condition produced uronic structures in UF resin, whereas both alkaline and weak‐acid conditions produced quite similar chemical species in the resins. The proton rotating‐frame spin–lattice relaxation time (T_1ρH) decreased with a decrease in the reaction pH of UF resin. This result indicates that the molecular mobility of UF resin increases with a decrease in the reaction pH used during its synthesis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2677–2687, 2003     

A honeymoon‐type adhesive for wood products based on acetoacetylated poly(vinyl alcohol) and diamines: Effect of diamines and degree of acetoacetylation

The honeymoon‐type adhesive for wood products based on acetoacetylated poly(vinyl alcohol) (AAPVA) was investigated focusing on the effect of acetoacetylation on performance, and that of amino compounds as a crosslinking agent. AAPVAs with different degrees of acetoacetylation were synthesized by the addition reaction of diketene in dimethylsulfoxide. Adhesive tests were carried out using aqueous solutions of AAPVA and six kinds of amino compounds, spread separately on test pieces of red meranti selected as the adherend. The mechanical strength of the bonded test pieces was then analyzed. It was found that the adhesive strength increased together with the degree of acetoacetylation at least until 3 h after the application of the adhesives. The degree of acetoacetylation had little effect on water resistance within the range 3.3–37.1%, and as a crosslinking agent, diamines containing primary amino groups were effective, although secondary amines and polyethyleneimine were not. It is assumed that the chemical structure of the amine influenced the crosslinking reaction at the adhesion interface. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2966–2972, 2004     

Temperature,pH, and reduction triple‐stimuli‐responsive inner‐layer crosslinked micelles as nanocarriers for controlled release

Temperature, pH, and reduction triple‐stimuli‐responsive inner‐layer crosslinked micelles as nanocarriers for drug delivery and release are designed. The well‐defined tetrablock copolymer poly(polyethylene glycol methacrylate)–poly[2‐(dimethylamino) ethyl methacrylate]–poly(N‐isopropylacrylamide)–poly(methylacrylic acid) (PPEGMA‐PDMAEMA‐PNIPAM‐PMAA) is synthesized via atom transfer radical polymerization, click chemistry, and esterolysis reaction. The tetrablock copolymer self‐assembles into noncrosslinked micelles in acidic aqueous solution. The core‐crosslinked micelles, shell‐crosslinked micelles, and shell–core dilayer‐crosslinked micelles are prepared via quaternization reaction or carbodiimide chemistry reaction. The crosslinked micelles are used as drug carriers to load doxorubicin (DOX), and the drug encapsulation efficiency with 20% feed ratio reached 59.2%, 73.1%, and 86.1%, respectively. The cumulative release rate of DOX is accelerated by single or combined stimulations. The MTT (3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide) assay verifies that the inner‐layer crosslinked micelles show excellent cytocompatibility, and DOX‐loaded micelles exhibit significantly higher inhibition for HepG2 cell proliferation. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46714.     

Synthesis and characterization of poly(dimethylamino ethyl methacrylate)–poly(ethylene oxide)–poly(dimethylamino ethyl methacrylate) triblock copolymers

Novel, monodispersed, and well‐defined ABA triblock copolymers [poly(dimethylamino ethyl methacrylate)–poly(ethylene oxide)–poly(dimethylamino ethyl methacrylate)] were synthesized by oxyanionic polymerization with potassium tert‐butanoxide as the initiator. Gel permeation chromatography and ¹H‐NMR analysis showed that the obtained products were the desired copolymers with molecular weights close to calculated values. Because the poly(dimethylamino ethyl methacrylate) block was pH‐ and temperature‐sensitive, the aqueous solution behavior of the polymers was investigated with ¹H‐NMR and dynamic light scattering techniques at different pH values and at different temperatures. The micelle morphology was determined with transmission electron microscopy. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Poly(9‐vinylcarbazole)/silver composite nanotubes and networks formed at the air–water interface

Silver‐nanoparticle‐doped poly(9‐vinylcarbazole) (PVK) nanocomposites were prepared via the reduction of Ag⁺ ions and the self‐assembly of PVK on AgNO₃ aqueous solution surfaces. The formed composite nanostructures depended strongly on the experimental temperature. Thick round disks of PVK surrounded by discrete Ag nanoparticles and/or with irregular holes formed at room temperature; nanotubes and micronetworks doped with Ag nanoparticles formed at about 30–40°C, and networks formed at higher temperature. Further investigation revealed that the nanotubes were transformed from thin round disks. The length of the PVK/Ag composite nanotubes were longer than 10 μm, and the average size of the embedded Ag nanoparticles was found to be about 3.5 nm. The composite networks were composed of round pores with diameters of several hundred nanometers and fine silver nanoparticles embedded in the thin polymer films that covered the pores. The formation of the nanotubes was a very interesting self‐assembly phenomenon of the polymer at the air–water interface that has not been reported before. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Rheology of poly(N‐vinyl pyrrolidone)–poly(ethylene glycol) adhesive blends under shear flow

The rheological properties of adhesive miscible blends of high‐molecular‐weight poly(N‐vinyl pyrrolidone) (PVP) with short‐chain poly(ethylene glycol) (PEG) under oscillatory and steady‐state shear flow have been examined with dynamic mechanical and squeezing‐flow analysis. The latter allows the rheological characterization of adhesive blends under conditions modeling adhesive‐bond formation as a fixed compressive force is applied to an adhesive film. The most adhesive PVP blend with 36 wt % PEG has been established to flow like a viscoplastic (yield stress) liquid with a power‐law index of about 0.12. The study of the apparent yield stress as a function of the PVP–PEG composition, content of sorbed water, molecular weight of PVP, and temperature shows that the occurrence of a yield stress in the blends results most likely from a noncovalent crosslinking of PVP macromolecules through short PEG chains by means of hydrogen bonding of both terminal OH groups of PEG to the complementary functional groups in PVP monomer units. A molecular mechanism of PVP–PEG interaction was established earlier by direct and independent methods. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 522–537, 2006     

Acetals‐induced strength increase of melamine–urea–formaldehyde (MUF) polycondensation adhesives. II. Solubility and colloidal state disruption

The strength improvement induced by addition of acetals such as methylal and ethylal in melamine–urea–formaldehyde (MUF) resins could be mostly ascribed to the increased effectiveness and participation of the melamine to resin cross‐linking. This phenomenon has been shown here, by matrix‐assisted laser desorption/ionization time of flight (MALDI‐TOF) mass spectroscopy, resin aging time stability, and mainly by laser light scattering, to be due to the following: (i) the increased solubility in water afforded by the acetals cosolvents of both the unreacted melamine and of the normally very much lower solubility, higher molecular weight, lower methylolated oligomers fraction, this leading to preferentially homogeneous and hence more effective reaction rather than heterogeneous reactions; and (ii) the effect that such acetals have on the size distribution of the resin colloidal particles, with the presence of acetals such as methylals markedly decreasing the average colloidal particles diameter of the resin. This latter effect appears to be due to the disruption of the molecular clustering of the MUF resin colloidal particles, but rearrangements in the size of the colloidal particles due to the decrease in surface tension of the system, which has also been noted, cannot be excluded. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1855–1862, 2002     

Thermosensitive self‐assembly micelles from A2BA2‐type poly(N‐isopropyl acrylamide)2‐b‐Poly(lactic acid)‐b‐Poly(N‐isopropyl acrylamide)2 four‐armed star block copolymers and their applications as drug carriers

A novel A₂BA₂‐type thermosensitive four‐armed star block copolymer, poly(N‐isopropyl acrylamide)₂‐b‐poly(lactic acid)‐b‐poly(N‐isopropyl acrylamide)₂, was synthesized by atom transfer radical polymerization and characterized by ¹H‐NMR, Fourier transform infrared spectroscopy, and size exclusion chromatography. The copolymers can self‐assemble into nanoscale spherical core–shell micelles. Dynamic light scattering, surface tension, and ultraviolet–visible determination revealed that the micelles had hydrodynamic diameters (D_h) below 200 nm, critical micelle concentrations from 50 to 55 mg/L, ζ potentials from ?7 to ?19 mV, and cloud points (CPs) of 34–36°C, depending on the [Monomer]/[Macroinitiator] ratios. The CPs and ζ potential absolute values were slightly decreased in simulated physiological media, whereas D_h increased somewhat. The hydrophobic camptothecin (CPT) was entrapped in polymer micelles to investigate the thermo‐induced drug release. The stability of the CPT‐loaded micelles was evaluated by changes in the CPT contents loaded in the micelles and micellar sizes. The MTT cell viability was used to validate the biocompatibility of the developed copolymer micelle aggregates. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4137–4146, 2013     

Performances of larch (larix gmelini) tannin modified urea–formaldehyde (TUF) resin and plywood bonded by TUF resin

Tannin from larch (Larix gmelini) bark extracts, as a natural renewable resource, was used to prepare tannin–urea–formaldehyde (TUF) resin. The chemical structures of larch tannin and TUF resin were characterized by matrix‐assisted laser desorption/ionization‐time of flight mass spectrometry and ¹³C nuclear magnetic resonance. The thermal behaviors of TUF resin were evaluated by differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). The performances of TUF resin were investigated by measuring the bond strength and formaldehyde emission of its bonded plywood. It was clearly shown that larch tannin is mainly composed of prodelphinidin repeating units. Phenolic groups were introduced into TUF resin mainly linked by methylene bond. Larch tannin has an adverse effect on the resin curing. However, it promoted the rigidity and flexibility of the glued system and upgraded the properties of plywood. Therefore, larch tannin could be applied in the modification of urea–formaldehyde resin. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41064.