Influence of acrylamide copolymerization of urea–formaldehyde resin adhesives to their chemical structure and performance

To lower the formaldehyde emission of wood‐based composite panels bonded with urea–formaldehyde (UF) resin adhesive, this study investigated the influence of acrylamide copolymerization of UF resin adhesives to their chemical structure and performance such as formaldehyde emission, adhesion strength, and mechanical properties of plywood. The acrylamide‐copolymerized UF resin adhesives dramatically reduced the formaldehyde emission of plywood. The ¹³C‐NMR spectra indicated that the acrylamide has been copolymerized by reacting with either methylene glycol remained or methylol group of UF resin, which subsequently contributed in lowering the formaldehyde emission. In addition, an optimum level for the acrylamide for the copolymerization of UF resin adhesives was determined as 1%, when the formaldehyde emission and adhesion strength of plywood were taken into consideration. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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.     

Adsorption of selenite and selenate ions onto thiourea‐formaldehyde resin

In the present work, thiourea‐formaldehyde (TUF) chelating resin was synthesized and used in the adsorptions of selenite (SeO) and selenate (SeO) ions. The effects of initial acidity and initial selenium concentrations on the adsorptions were examined by batch technique. The synthesized resin was applied to the elemental analysis to determine its composition. FT‐IR spectra and SEM/EDS were also recorded before and after selenite adsorption. It was found that selenite and selenate ions were adsorbed onto TUF resin at strong acidic conditions (3–5M HCl). The adsorption capacities of the resin were calculated as 833.3 mg g^?1 TUF resin for selenite ions and 526.3 mg g^?1 TUF resin for selenate. All the adsorption data obtained for both selenite and selenate ions fitted well to the Langmuir isotherm. It was seen that the adsorption mechanisms in the both adsorptions were governed by the reduction of selenite or selenate to elemental selenium, Se⁰. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Selective separation and concentration of Pd(II) from Fe(III), Co(II), Ni(II), and Cu(II) ions using thiourea‐formaldehyde resin

Thiourea‐formaldehyde (TUF), a well‐known chelating resin, has been synthesized and it was used in the adsorption, selective separation, and concentration of Pd(II) ions from Fe(III), Co(II) Ni(II), and Cu(II) base metal ions. The composition of the synthesized resin was determined by elemental analysis. The effect of initial acidity/pH and the adsorption capacity for Pd(II) ions were studied by batch technique. The adsorption and separation of Pd(II) were then examined by column technique. FTIR spectra and SEM/EDS analysis were also recorded before and after the adsorption of Pd(II). The optimum pH was found to be 4 for the adsorption. The adsorption data fitted well to the Langmuir isotherm. The maximum adsorption capacity of the TUF resin for Pd(II) ions was found to be 31.85 mg g⁻¹ (0.300 mmol g⁻¹). Chelating mechanism was effective in the adsorption. Pd(II) ions could be separated efficiently from Fe(III), Cu(II), Ni(II), and Co(II) ions using TUF resin. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Soy-based,tannin-modified plywood adhesives

In this research, two different types of commercial tannins, namely a hydrolysable tannin (chestnut) and a condensed flavonoid tannin (mimosa), were used to prepare two types of soy-based (soy flour (SF) and soy protein isolate) adhesives for making plywood. Thermogravimetric properties (TGA) and its derivative as function of temperature (DTG) of different soy-based adhesive were measured in the range 40°C–300°C. Thermomechanical analysis (TMA) from 25°C to 250°C was done for the different resin formulations. Duplicate three-ply laboratory plywood panels were prepared by adding 300 g/m² of the adhesives’ total resin solid content composed of SF or isolated soy protein (ISP), urea, chestnut, and mimosa tannin extracts with hexamine as hardener. Based on the results obtained, tannins can improve SF adhesion properties. The TMA showed that chestnut tannin extract appeared to react well with SF, while mimosa tannin extract appeared to react well with ISP. Matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrometry also showed that among other reactions, the soy protein amino acids reacted with the tannins. Furthermore, delamination and shear strength test results showed the good water resistance of plywood bonded with soy-based tannin modified adhesive.     

Tobacco (Nicotiana tabacum) stalk particles as additive in urea formaldehyde bonded plywood

The study investigated the use of tobacco (Nicotiana tabacum L) stalk particles as additive with both extender and filler property in urea formaldehyde adhesive formulation used to bond Paraserianthes falcataria (L) Nielsen veneers into plywood. The effect of varying amount of tobacco stalk particles on adhesive working properties, shear strength and wood failure of 3-ply plywood was investigated. Adhesive mix containing urea formaldehyde resin with tobacco stalk particles up to 8% by mass blended very well and remained stable for atleast 1?hour. An increase or no significant effect on shear strength and wood failure up to 8% tobacco stalk loading was observed compared to plywood that used a commercial glue formulation. Based on shear strength and wood failure, panels containing 4–8% tobacco stalk particles would pass the requirements of ISO 12466-2. Examination of adhesive penetration and plywood strength suggest that tobacco particles could function as both filler and extender. Tobacco stalk particles offer an environmentally friendly, low cost, strong and non-abrasive alternative to conventional fibers used in plywood production.     

Phenolic resin adhesives based on chestnut (Castanea sativa) hydrolysable tannins

Chestnut hydrolysable tannins are phenolic materials that have been considered too unreactive to compete in the phenolic resin adhesives market for exterior boards for the building industry. However, an article in 1973 describing 3?years industrial application of chestnut hydrolysable tannins during the first oil crisis indicated that this was not the case. We have extended this old work by using superior phenolic resins formulations and producing phenol–formaldehyde–chestnut tannin adhesives where a substitution of up to 80% of the phenol is possible with remarkably good results. The reactions involved were clarified by ¹³C NMR and MALDI-TOF mass spectrometry.     

Lignin–phenol–formaldehyde resin adhesives prepared with biorefinery technical lignins

In this study, four biorefinery technical lignins were used to synthesize lignin–phenol–formaldehyde (LPF) resin adhesives with a proposed formulation that was designed based on accurate analysis of the active sites in lignin with ³¹P nuclear magnetic resonance (NMR). The properties of the LPF resin adhesives and the plywoods prepared with them were tested. The structural features and curing behavior of the LPF resin adhesives were thoroughly investigated by solution‐ and solid‐state ¹³C NMR. Results indicated that the proposed formulation exhibited favorable adaptability for all four of these technical lignins for synthesis of LPF resin adhesives. High‐performance plywood with low emissions of formaldehyde could be successfully prepared with the synthesized LPF resin adhesives. All the LPF resin adhesives exhibited similar structure and curing behavior with the commercial phenol–formaldehyde (CPF) resin adhesive. However, the LPF resin adhesives showed relatively higher curing temperatures as compared with the CPF resin adhesive. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42493.     

Hydrolytic and thermal stability of urea-formaldehyde resins based on tannin and betaine bio-fillers

In this work, betaine (trimethyl glycine) and tannin (complex biomolecules of polyphenolic nature) were used as bio-fillers. Urea-formaldehyde (UF) resin with a molar ratio of formaldehyde versus urea (FA/U) of 0.8 was synthesized in situ with tannin and betaine as bio-fillers, to obtain UF resin with reduced free FA content and increased hydrolytic and thermal stability by the principles of sustainability. The samples TUF (with tannin) and BUF (with betaine) were characterized by using X-ray diffraction analysis (XRD), non-isothermal thermogravimetric analysis (TGA), and differential thermal analysis (DTA), supported by data from Fourier Transform Infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). The percentage of free FA in modified BUF resin is 0.1%, while the percentage of free FA in tannin-modified resin is 0.8%. The hydrolytic stability of the modified UF resins was determined by measuring the concentration of liberated FA in the modified UF resins, after acid hydrolysis. The modified BUF resin is hydrolytically more stable because the content of released FA is 3.6% compared to the modified TUF resin, where it was 7.4%. Based on the value for T_5%, the more thermally stable resin is the modified TUF resin (T_5% = 123.1°C), while the value of the T_5% for the BUF resin is 83.1°C. This work showed how UF bio-composite with reduced free FA content and increased hydrolytic and thermal stability can be obtained using tannin and betaine as bio-fillers.     

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     

Synthesis,characterization, and metal adsorption properties of tannin–phenol–formaldehyde resins produced using tannin from dried fruit of Terminalia chebula (Aralu)

In this study, tannin extracted from Terminalia chebula (Aralu) was used to produce tannin–phenol–formaldehyde resins. They were produced to obtain resins with different tannin to phenol ratio in an attempt to optimize the ion exchange capacities of resins produced. The resins made were sulfonated to improve their properties further. Bivalent cations, such as Zn²⁺, Pb²⁺, Ca²⁺, Mg²⁺, and Cu²⁺, were used to estimate the adsorption properties of both unsulfonated and sulfonated resins. The glass transitions of representative resins were estimated using differential scanning calorimeter thermograms. Fourier transform infrared spectroscopic analysis was used to gauge changes on resins by sulfonation and adsorption of cations. The glass transition values of unsulfonated, sulfonated, and metal‐adsorbed sulfonated resins showed a similar increasing trend with the increase of phenol content in the resin. The glass transition temperature values reach a plateau beyond the tannin/phenol ratio of 1 : 0.5, indicating the formation of large molar masses facilitating entanglements beyond that ratio. The phenol ratio of 1 : 0.5 has shown the highest adsorption capacity for all the metal ions used. The highest adsorption capacity was shown for sulfonated tannin–phenol–formaldehyde resin with the tannin/phenol ratio of 1 : 0.5 for Pb²⁺, which is 0.610 meq/g. The adsorption equilibrium data obtained using the column technique were found fitting Freundlich isotherm. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Decreasing the formaldehyde emission in urea‐formaldehyde using modified starch by strongly acid process

The incorporation of the modified starch (MS) in urea‐formaldehyde resins at different stage of the synthesis was studied in this article. The synthesized resins were characterized by Fourier transform infrared spectroscopy, indicating that the ester bond can be introduced into the UF structure after the addition of MS. The curing reactions were examined with differential scanning calorimetry and it reveals that curing temperature of UF resin are slightly shifted to higher temperatures. To study the bonding strength and formaldehyde emission of the bonded plywood, the addition method and amount of MS are systematically investigated. The performance of the UF resins is remarkably improved by the addition of MS around 15% (weight percentage of the total resin) in the second stage. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40202.     

Synthesis and characterization of phenol‐urea‐formaldehyde foaming resin used to block air leakage in mining

In this study, phenol, urea, and paraformaldehyde were used as the monomers for the one‐step synthesis of phenol‐urea‐formaldehyde (PUF) foaming resin that was used to block air leakage in mining. An orthogonal test was used to study the effects of urea amount, catalyst amount, reaction temperature, and reaction time on the foaming property of the resin. The results showed that the optimum parameters for synthesizing PUF resin are as follows: 1 mol phenol, 0.5 mol urea, 3 mol formaldehyde equivalents of paraformaldehyde, and 0.05 mol catalyst at 75°C for 3 h. The infrared and ¹³C nuclear magnetic resonance spectra of the PUF resin showed that the chemical structure of the PUF resin was significantly different from that of phenol‐formaldehyde resin, indicating that a copolymerization reaction has occurred among the three components, that is, phenol, urea, and paraformaldehyde. In this study, PUF foam was prepared from catalysts and PUF resin. The results showed that the foaming capacity and oxygen index of the PUF foam were significantly improved by using urea, whereas the shrinking percentage decreased with no change in compression strength. POLYM. COMPOS., 35:2056–2066, 2014. © 2014 Society of Plastics Engineers     

Determination of formaldehyde and TVOC emission behavior from interior use plywood using various post heat treatment processes

To reduce the formaldehyde/TVOC emissions from plywood with melamine–urea–formaldehyde (MUF) resin, four heat treatment procedures were designed and applied. Five‐ply plywood was fabricated, and its formaldehyde/TVOC emissions and wet shear strength were tested. Results showed that a simple low/no pressure post heat treatment procedure was effective and practical to decrease the formaldehyde/TVOC emissions from plywood. This was attributed to completely cured of MUF resin, the breakage of unstable chemical bonds, the acceleration of free formaldehyde releasing, and the exposed surface of the plywood. Meanwhile, this process also balanced the interior force of the resultant plywood and improved its wet shear strength. Under a 12 h oven heat treatment procedure after hot press, the formaldehyde and TVOC emissions from plywood decreased to 0.020 and 0.036 ppm, respectively, while the surface and core layer wet shear strength of plywood was improved to 1.24 and 1.08 MPa. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44909.     

Improvement of white pinewood properties by impregnation with thiourea–formaldehyde resin and orthophosphoric acid

White pinewood was impregnated with thiourea–formaldehyde (TUF) resin and orthophosphoric acid (OPA) as a crosslinking agent. The best weight gains (55–138%) were obtained after impregnation with an aqueous solution of TUF resin for 1 h and impregnation with aqueous solutions of OPA at different concentrations for 1 h. Water uptake of treated wood was found to be 23% after a water‐soaking test of 168 h, and a maximum antiswell efficiency was found to be 18% for a 85% OPA solution. Compression strength of the treated wood also improved with the highest value 62 KN/m² for wood treated with a 70% OPA solution versus a value of 40 KN/m² for untreated samples. Fire retardancy of the treated wood samples was also improved based on concentration of OPA. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 390–397, 2000     

Phenol–urea–formaldehyde resin co-polymer synthesis and its influence on Elaeis palm trunk plywood mechanical performance evaluated by 13C NMR and MALDI-TOF mass spectrometry

This study evaluated a new method of producing phenol–urea–formaldehyde (PUF) adhesives formulated differently under actual “in-situ” resin synthesis conditions. This was carried out by co-polymerizing urea formaldehyde (UF) resin with phenol–formaldehyde resin in the core layer of low molecular weight (LMW) phenol–formaldehyde (PF) resin treated Elaeis palm trunk veneers during the gluing process of Elaeis palm plywood. Matrix assisted laser desorption Ionization time of flight (MALDI-TOF) mass spectrometry (MS) illustrated and confirmed a series number of the phenol–urea co-condensates repeating unit in the prepared PUF resins which corroborated well with its mechanical properties (modulus of elasticity and modulus of rupture), bonding quality (dry test and weather boil proof or WBP test) and physical properties. A series of PF, UF and PUF resins oligomers forming repeating units up to 1833 Da were identified. Besides that, the solid state ¹³Carbon nuclear magnetic resonance (NMR) interpretation identified that the signal at 44–45 ppm and 54–55 ppm corresponding to methylene bridges were co-condensated in between phenol and urea in the PUF resin system. The ¹³C NMR investigation showed that the synthesis process of PUF resin contained no free formaldehyde elements. Furthermore, the proportion of urea and methylolureas in the mixture to synthesis PUF resin were sufficient and incorporated well into the formulation by reacting with LMWPF units to form co-condensed methylene bridges. This study showed a new and useful method to synthesize PUF resin during the gluing process of manufactured Elaeis palm plywood which can also enhance the performance of Elaeis palm plywood panels for structural instead of utility grade applications.     

Methods for preparation of absorbent microspherical tannin resin

Tannin beads formed by reaction of Mimosa tannin (condensed-type tannin) with formaldehyde in nonpolar polybutenous medium were microspherical resins. Resins prepared with 37.5% tannin concentration were porous spherical resins with 139.22 m²/g of surface area (adsorption method of iodine in n-hexane, 2.1 m²/g for the dried beads by the Braunauer-Emett-Teller (BET) method) and were strong enough to withstand use on a column. The spherical resin adsorbed 3.7 mmol of Cr⁶⁺ ions per one gram dry weight of resin (by batch method), this adsorption being comparable to commercial adsorbent.     

Dynamic mechanical analysis of urea formaldehyde resin modified by ammonium pentaborate as wood adhesive

Urea formaldehyde (UF) resins with varied molar ratio of formaldehyde (F) to urea (U), modified by ammonium pentaborate (APB) at different loading level, was analyzed by dynamic mechanical analysis (DMA) and evaluated via bonding properties of its glued plywood. The result indicated that a higher loading of APB made a slower gelling and improved the ΔE′ (the difference of storage modulus) of UF resin with F/U molar ratio of 1.8. Hexamethylenetetramine, generated from the ammonium ion in APB and formaldehyde in UF resin and characterized by the covalent bond connections, was considered as the main reason to improve the rigidity of the cured UF resin system. The bond strength result confirmed the DMA analysis that the addition of APB improved bonding performance of UF resin with higher F/U molar ratio such as 1.8. A specific recommendation loading level of APB was made to modify UF resins, of which 6.0 to 8.0% APB should be used to modify UF resin with F/U molar ratio of 1.8, then 6% and 4% loading level of APB to UF resin with F/U molar ratio of 1.50 and 1.25, respectively. Finally, APB was n'ot suggested to modify UF resin at F/U molar ratio less than 1.20. POLYM. COMPOS., 37:2404–2410, 2016. © 2015 Society of Plastics Engineers     

Properties of poly(urea‐formaldheyde) microcapsules containing an epoxy resin

Physical properties of urea‐formaldehyde microcapsules containing an epoxy resin are presented and discussed. Microcapsules were prepared by in situ polymerization of monomers in an oil‐in‐water emulsion. Differential scanning calorimetry, thermogravimetric analysis, and scanning electronic microscopy were applied to investigate thermal and morphological microcapsule properties. Microencapsulation was detected by means of FTIR and Raman techniques. It was found that the amount of encapsulated epoxy resin as well as the extent of urea‐formaldehyde polymerization depends on the reaction temperature and the stirring speed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Examination of selected synthesis and room‐temperature storage parameters for wood adhesive‐type urea–formaldehyde resins by 13C‐NMR spectroscopy. V

The effects of posttreatments of particleboard adhesive‐type urea–formaldehyde resins were studied. The resins were synthesized with formaldehyde/first urea (F/U₁) mol ratios of 1.40, 1.60, 1.80, 2.10, and 2.40 and then the second urea was added to give a final formaldehyde/urea ratio of 1.15 in alkaline pH. The resins were posttreated at 60°C for up to 13.5 h and the 2.5‐h heat‐treated resin samples were stored at room temperature for up to 27 days. Resins sampled during the posttreatments were examined by ¹³C‐NMR and evaluated by bonding particleboards. In the posttreatments, hydroxymethyl groups on the polymeric resin components dissociated to formaldehyde and reacted with the second urea, and methylene and methylene–ether groups were formed from reactions involving the second urea. Methylene–diurea and urea groups bonded to UF polymers were identified. As a result, the viscosity of the resins initially decreased but later increased along with the cloudiness of the resins. Bond‐strength and formaldehyde‐emission values of particleboard varied with posttreatment variables as well as with the F/U₁ mol ratios used in the resin syntheses. The results would be useful in optimizing resin synthesis and handling parameters. Various reaction mechanisms were considered. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1896–1917, 2003