Low addition of melamine salts for improved melamine‐urea‐formaldehyde adhesive water resistance

The addition of melamine acetate salts to an adhesive glue mix can allow the use of melamine–urea–formaldehyde (MUF) resins of lower melamine contents (rather than just urea–formaldehyde resins) and lower total amounts of melamine. Performances can be obtained that are characteristic of the top‐of‐the‐line, generally higher melamine content MUF adhesive resins for the preparation of wood particleboard panels. Improvements in the panel internal‐bond strength of greater than 30% can be obtained by the addition of melamine acetate salts to top‐of‐the‐line MUF resins. The approach to the concept of increased melamine solubility with a melamine salt is compatible with the approach of increasing melamine solubility with solvents such as acetals (e.g., methylal). However, the synergy advantage of using the two approaches jointly is not very marked. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 287–292, 2003     

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     

NMR structural elucidation of amino resins

Urea formaldehyde, melamine formaldehyde, and melamine urea formaldehyde (MUF) are important industrial amino resins that find application in numerous diverse areas, most notably in the bonding of wood products. To understand the physical properties of these amino resins and, hence, optimize their performance, a knowledge of their chemical structure is necessary. This article reports the use of NMR spectroscopy to acquire this information in the solid and liquid states. ¹³C‐NMR experiments, supported and augmented by ¹H‐NMR and ¹⁵N‐NMR results, showed that the two stages of resin synthesis, methylolation followed by condensation, occurred in each type of resin. However, in the various MUF samples analyzed, the second step appeared to be predominantly the self‐condensation of melamine and urea rather than the cocondensation of melamine and urea. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3504–3512, 2004     

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.     

Upgrading melamine–urea–formaldehyde polycondensation resins with buffering additives. I. The effect of hexamine sulfate and its limits

Iminoamino methylene base intermediates obtained by the decomposition of hexamethylenetetramine (hexamine) stabilized by the presence of strong anions such as SO and HSO, or hexamine sulfate, were shown to markedly improve the water and weather resistance of hardened melamine–urea–formaldehyde (MUF) resins used as wood adhesives and of the wet internal bond strength performance of wood boards bonded with them. The effect was shown to be induced by very small amounts, between 1 and 5 wt % of this material on resin solid content. This strong effect allowed the use of MUF resins of much lower melamine content and also provided good performance of the bonded joints. Because the main effect was also present at the smaller proportion of hexamine as hexamine sulfate, it was not due at all to any increase in the molar ratio of the resin as a consequence of hexamine sulfate addition. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 203–214, 2003     

Co‐polymerization analysis of thermosetting resins using 1H‐15N‐13C triple resonance NMR spectroscopy

¹H‐¹⁵N‐¹³C correlation NMR spectroscopy techniques developed to identify and characterize co‐polymer fragments in melamine‐urea‐formaldehyde (MUF) and phenol‐urea‐formaldehyde (PUF) model systems have been applied to industrially prepared MUF, PUF, and phenol‐melamine‐formaldehyde (PMF) resins. The NMR data confirm that co‐polymers form in a commercially prepared MUF resin manufactured by Momentive Specialty Chemicals Pty. Ltd. Spectra from PUF model reactions were compared with those from a PUF resin and it was determined that PUF co‐polymers did not form in the resin prepared using typical temperature and pH. Finally, NMR spectroscopy was used to identify and characterize PMF co‐polymer bonds in a phenol‐melamine‐urea‐formaldehyde (PMUF) resin prepared using a procedure from Momentive Specialty Chemicals Pty. Ltd. With these NMR techniques in hand, it is now possible to relate co‐polymer structures to properties of commercial thermosets. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

改性三聚氰胺-尿素-甲醛共缩聚树脂胶粘剂的合成

通过三聚氰胺-尿素-甲醛(MUF)共缩聚树脂胶粘剂的合成,探讨了三聚氰胺的用量对该MUF树脂耐水性能的影响及其规律。实验结果表明,当w(三聚氰胺)=43%～65%时,该MUF树脂的湿强度从0.93 MPa增加到2.74 MPa,耐沸水性明显提高;但是,当w(三聚氰胺)>65%时,该MUF树脂的湿强度增长极其缓慢,其耐沸水性提高并不明显;通过引入复合改性剂和适量的水,可使该MUF树脂的游离甲醛含量降低50%、成本降低10%～15%、固含量基本不变、胶合强度和耐沸水性均有所提高且适用期良好。     

Colloidal aggregation of aminoplastic polycondensation resins: Urea–formaldehyde versus melamine–formaldehyde and melamine–urea–formaldehyde resins

Colloidal particles formation followed by their clustering have been shown to be the normal way of ageing of aminoplastic resins, namely urea–formaldehyde (UF) resins, melamine–formaldehyde (MF) resins, and melamine–urea–formaldehyde (MUF) resins. Ageing or further advancement of the resin by other means such as longer condensation times causes whitening of the resin. This is a macroscopic indication of both the formation of colloidal particles and of their clustering. It eventually progresses to resins, which are mostly in colloidal, clustered state, followed much later on by a supercluster formation starting to involve the whole resin. The initial, filament‐like colloidal aggregates formed by UF resins have different appearance than the globular ones formed by MF resins. MUF resins present a short rod‐like appearance hybrid between the two. GPC has been shown to detect the existence of colloidal superaggregates in a UF resin, while smaller aggregates might not be detected at all. The star‐like structures visible in the colloidal globules of MF resins are likely to be light interference patterns of the early colloidal structures in the resins. These star‐like interference patterns become more complex with resin ageing or advancement due to the advancement of the resin to more complex aggregates, to eventually reach the stage in which filament‐like and rod‐like structures start to appear. The next step is formation of globular masses that are representative of the true start of physical gelation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1406–1412, 2006     

Effects of diatomite inorganic fillers on the properties of a melamine–urea–formaldehyde resin

In this study, a low‐cost diatomite was used to partly substitute wheat flour as one type of melamine–urea–formaldehyde (MUF) resin filler. Five‐ply plywood was fabricated, and its performance was measured. The crystallinity, fracture surface, and functional groups were tested to determine the effects of diatomite on the performance of the MUF resin. The results show that diatomite was well distributed in the MUF resin system and formed an embedding structure; this improved the wet shear strength of the resulting plywood by 33% to 1.36 MPa. Diatomite captured the free formaldehyde in the resin and the microporous structure formed in the resin accelerate formaldehyde release of the plywood. Consequently, the formaldehyde emission of the plywood was reduced. The diatomite partly replaced wheat flour as an MUF resin filler and could be applied in the plywood industry. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44095.     

Hydrolytic stability of cured urea‐formaldehyde resins modified by additives

Urea‐formaldehyde (UF) resins are prone to hydrolysis that results in low‐moisture resistance and subsequent formaldehyde emission from UF resin‐bonded wood panels. This study was conducted to investigate hydrolytic stability of modified UF resins as a way of lowering the formaldehyde emission of cured UF resin. Neat UF resins with three different formaldehyde/urea (F/U) mole ratios (1.4, 1.2, and 1.0) were modified, after resin synthesis, by adding four additives such as sodium hydrosulfite, sodium bisulfite, acrylamide, and polymeric 4,4′‐diphenylmethane diisocyanate (pMDI). All additives were added to UF resins with three different F/U mole ratios before curing the resin. The hydrolytic stability of UF resins was determined by measuring the mass loss and liberated formaldehyde concentration of cured and modified UF resins after acid hydrolysis. Modified UF resins of lower F/U mole ratios of 1.0 and 1.2 showed better hydrolytic stability than the one of higher F/U mole ratio of 1.4, except the modified UF resins with pMDI. The hydrolytic stability of modified UF resins by sulfur compounds (sodium bisulfate and sodium hydrosulfite) decreased with an increase in their level. However, both acrylamide and pMDI were much more effective than two sulfur compounds in terms of hydrolytic stability of modified UF resins. These results indicated that modified UF resin of the F/U mole ratio of 1.2 by adding acrylamide was the most effective in improving the hydrolytic stability of UF resin. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Impact of curing condition on pH and alkalinity/acidity of structural wood adhesives

Nine formulations were selected for evaluating the effect of different curing methods on pH and alkalinity or acidity of various structural wood adhesives. These included four phenol–formaldehyde (PF) resins with high pH, one phenol–resorcinol–formaldehyde (PRF) resin with intermediate pH, two melamine–urea–formaldehyde (MUF) resins, and two melamine–formaldehyde (MF) resins with low pH. The four curing methods used in the study were: (1) curing at 102–105°C for 1 h (based on CSA O112.6‐1977), (2) four‐hour curing at 66°C followed by 1‐hour curing at 150°C (based on ASTM D1583‐01), (3) curing at room temperature overnight (based on ASTM D 1583‐01), and (4) cured adhesive squeezed out from glue lines of bonded shear block samples. The effect of the different methods on pH and alkalinity/acidity of the cured adhesive depended strongly on the individual adhesives. For the PF, the alkalinity was different for the different formulations in the liquid form, while in the cured form, the difference in the alkalinity depended on the curing method used. The MF and the MUF were the adhesives most affected by the method used. In particular, the MUF showed much higher cured film pH values when cured by method 2 compared to the other three methods, while both the cured MF and MUF exhibited quite variable acidity values when cured with the different methods. The PRF showed reasonably uniform cured film pH but varying acidity values when cured with the different methods. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Variation of MUF and PMUF resins mass fractions during preparation

The variation of molecular mass distribution with the progress of the reaction was studied for the following: (i) sequential‐type melamine–urea–formaldehyde (MUF) resin formulations in which the sequence of addition of chemicals follows well‐defined species reactivity principles; (ii) a nonsequential MUF formulation in which simultaneous melamine and urea competition for formaldehyde yields a MF resin cocondensed with small amounts of urea. This resin became soaked with reacted and unreacted monomeric urea species. (iii) A PMUF resin, namely a MUF resin with a small proportion of phenol (7.8% by weight on melamine and urea) cocondensed with the main MUF fraction. All the formulations used were industrial resins formulations in current use. Development and variation of molecular mass fractions, from which performance and other useful resin parameters depend, have been found to depend on the type of resin formulation used for these type of aminoplastic resins. The two very different MUF resin formulations yielded different variations in molecular mass fractions during the progress of the reaction and during the so‐called ambient temperature “maturing” of the resin. The PMUF resin also showed both similar and different fractions present during manufacturing and during short term ageing at ambient temperature. While similarities in recurrent fractions and in trends are common to all the three different formulations, differences between them are also clearly observed. A major proportion of the reaction of some of the aminoplastic resins examined also occurs on ageing (i.e.“maturing” of the resin at ambient temperature), this appearing to be an essential phase of the resin preparation process. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4842–4855, 2006     

Evaluation of melamine‐modified urea‐formaldehyde resins as particleboard binders

Particleboards bonded with 6 and 12% melamine‐modified urea‐formaldehyde (UMF) resins were manufactured using two different press temperatures and press times and the mechanical properties, water resistance, and formaldehyde emission (FE) values of boards were measured in comparison to a typical urea‐formaldehyde (UF) resin as control. The formaldehyde/(urea + melamine) (F/(U + M)) mole ratio of UMF resins and F/U mole ratio of UF resins were 1.05, 1.15, and 1.25 that encompass the current industrial values near 1.15. UMF resins exhibited better physical properties, higher water resistance, and lower FE values of boards than UF resin control for all F/(U + M) mole ratios tested. Therefore, addition of melamine at these levels can provide lower FE and maintain the physical properties of boards. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Curing of low level melamine‐modified urea‐formaldehyde particleboard binder resins studied with dynamic mechanical analysis (DMA)

Effects of resin formulation, catalyst, and curing temperature were studied for particleboard binder‐type urea‐formaldehyde (UF) and 6 ～ 12% melamine‐modified urea‐melamine‐formaldehyde (UMF) resins using the dynamic mechanical analysis method at 125 ～ 160°C. In general, the UF and UMF resins gelled and, after a relatively long low modulus period, rapidly vitrified. The gel times shortened as the catalyst level and resin mix time increased. The cure slope of the vitrification stage decreased as the catalyst mix time increased, perhaps because of the deleterious effects of polymer advancements incurred before curing. For UMF resins, the higher extent of polymerization effected for UF base resin in resin synthesis increased the cure slope of vitrification. The cure times taken to reach the vitrification were longer for UMF resins than UF resins and increased with increased melamine levels. The thermal stability and rigidity of cured UMF resins were higher than those of UF resins and also higher for resins with higher melamine levels, to indicate the possibility of bonding particleboard with improved bond strength and lower formaldehyde emission. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 377–389, 2005     

Phenol–formaldehyde‐type resins made from phenol‐liquefied wood for the bonding of particleboard

Liquefaction of southern pine wood in phenol in 30–40 : 70–60 weight ratios resulted in homogeneous liquefied materials, which were directly used to synthesize phenol–formaldehyde (PF)‐type resins. The synthesized resins showed good physical and handling properties: low viscosity, stability for storage and transportation, and resin applicable by a common sprayer. Particleboard panels bonded with the synthesized resins showed promising physical properties and significantly lower formaldehyde emission values than those bonded with the urea–formaldehyde resin control. One deficiency observed for the synthesized resins was lower internal bond values, which might be overcome the use of a hot‐stacking procedure. Overall, the process of wood liquefaction with limited amounts of phenol as a solvent was shown to have the potential of providing practical, low‐cost PF‐type resins with very low formaldehyde emission potentials. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Improving Hot-Water Resistance of Melamine-Urea-Formaldehyde by Addition of PolyFox PF-151N Polymer

Melamine urea formaldehyde (MUF) thermosetting wood adhesives have poor performance at elevated temperatures and humid conditions. PolyFox PF-151N polymer was mixed at different loadings (0.05, 0.1, 0.5, and 1%) with MUF to improve properties, especially water resistance and bond strength. The physical properties of the optimized MUF/PolyFox PF-151N resins were measured. In order to evaluate the quality of optimized MUF/PolyFox PF-151N resins, particleboards were produced and physical and mechanical properties were investigated.

The results show that it is possible to add PolyFox PF-151N up to 0.1% to the MUF resin without altering the mechanical properties of the commercial MUF. The mechanical properties of the particleboard panels bonded with the optimal MUF/PolyFox PF-151N (99.9/0.1 by weight) resin were considerably increased as compared to the panels glued with neat MUF resin. The use of PolyFox significantly reduced 2-h and 24-h thickness swelling compared to the control panels.     

Improvement of storage stability and physicochemical properties by addition of benzoguanamine in melamine‐formaldehyde resin synthesis

The improvement of melamine‐formaldehyde resin storage stability was achieved using benzoguanamine as partial replacement of melamine during synthesis (up to 15% substitution of melamine). The results showed that when benzoguanamine is added in the later stages of reaction, the resulting resins have improved storage stability (4 days or more, compared to 1 day in unmodified melamine‐formaldehyde resin). High‐pressure laminates produced with décor paper impregnated with the new developed resins showed surface properties equivalent to those obtained using commercial melamine‐formaldehyde resins. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45185.     

New melamine–formaldehyde–ketone resins. VI. Preparation of filled molding compositions and compression‐molding materials from reactive solvents based on cyclohexanone

The conditions and a method of preparing new molding compositions and filled compression‐molding materials from melamine–formaldehyde–cyclohexanone resins are described. The resins were obtained from melamine solutions in a reactive solvent prepared by the reaction of 1 mol of cyclohexanone with 7 mol of formaldehyde. The fillers were wood powder and sulfite cellulose. The thermal properties of the samples prepared from the compositions were studied with dynamic thermal analysis, thermogravimetry, and differential scanning calorimetry analysis. Selected mechanical properties [Brinell hardness, unnotched impact strength (Charpy method), and bending strength] of the cured resins were also measured. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mahua‐oil‐based resins for the high‐temperature curing of fly ash coatings

We attempted to prepare medium‐oil‐length glycerol alkyds based on Mahua oil. Fatty acids were isolated from the oil and used in the preparation of alkyds by the fusion method. The resins were characterized by IR spectroscopic analysis. The physicochemical and film properties of these resins were also studied. IR analysis of the resins revealed the formation of phthalate esters showing characteristic peaks at 1720 cm^?1. The resin was modified with melamine formaldehyde, which cured at high temperatures. Alternatively, the resin was made to air dry with ester gum, and the curing behavior was studied. The suitability of these resins for high‐temperature curing fly ash coating applications was established. Coatings were formulated with these resins and with 40% fly ash as an extender. The coatings were characterized by standard techniques, particularly for their anticorrosive and antiabrasive properties. Resistance to corrosion was evaluated in humidity and in salt‐spray conditions. We conducted a high‐stress (two‐body) abrasion test to test the abrasive wear resistance of the coatings. The Mahua‐oil‐resin‐based fly ash coatings were suitable for application in moderately corrosive and abrasive environments. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 110–120, 2003     

A 13C-NMR analysis method for MF and MUF resins strength and formaldehyde emission from wood particleboard. I. MUF resins

A method based on the use of ¹³C-NMR relative peak intensity rations for different characteristic chemical groups, known or supposed to contribute to melamine-urea-formal-dehyde (MUF) resin strength and formaldehyde emission, is presented. The method relates results obtained by ¹³C-NMR analysis of liquid MUF resins with their strength and form aldehyde emission in the resin hardened state. Sets of correlation equations are presented which can be used to predict some of the physical properties of a hardened MUF resin by studying the ¹³C-NMR peak ratios of well-defined chemical groups in the liquid MUF resin. A true class of MUF resins, with characteristics all of their own, appear only to exist in the copolymers in which the mass ratio of M: U is in the approximate range 55 : 45 to 34 : 66, mass ratios outside this range resulting in resins which behave almost as pure melamine or as pure urea resins. Contrary to what was found for MUF glue mixes in which lower condensation pre-resins are used as scavengers and accelerators, in pure MUF resins, the ratios of NMR peaks of the downfield substituted and unsubstituted triazine and urea signals, while still important, do not exclusively dominate the correlation equations, other chemical groups such as methylene (Me), methylol (Mo), and methylene ether groups assuming considerable importance. © 1996 John Wiley & Sons, Inc.