Modified Urea Formaldehyde Resin Research Articles

Eco-friendly fiberboards with low formaldehyde content and enhanced mechanical properties produced with activated soybean protein isolate modified urea-formaldehyde resin

Urea-formaldehyde (UF) resin is one of the most widely used resin adhesive for wood-based panels. The main concern of UF resin bonded wood-based panels is formaldehyde emission and poor water resistance. In this study, activated soybean protein isolate (SPI) was used to modify UF resin for the production of eco-friendly fiberboard panels. The effects of different activated SPI on the properties of UF resins and the resin bonded medium-density fiberboard (MDF) panels were investigated. The free formaldehyde content of the urea-activated SPI modified UF resin was only 0.13 %. Approximately 27.8 % lower than that of the unmodified UF resin. The resin bonded MDF panel with a density of 760 kg/m3 shows a modulus of rupture (MOR) and modulus of elasticity (MOE) of 45.73 MPa and 4005 MPa, which is increased by 25 % and 15 % compared to the unmodified UF resin group. The internal bonding strength (IB) reaches 0.71 MPa, which is about 15 % higher than that of the unmodified UF resin group. The tested 24-hour thickness swelling (24 h TS) of the modified UF resin group is only 8.1 %. The tested formaldehyde content of the sodium dodecyl sulfate (SDS)-activated SPI modified UF resin bonded MDF panel is only 4.8 mg/100 g, which is 20 % lower than that of the control UF resin group. The activated SPI modified UF resin shows great improvement in bonding strength and lower formaldehyde content for MDF panels as compared to the pure UF resin. The chemical groups, crystalline properties, and thermal stability of the pure and the modified UF resins were characterized via Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric (TG) analysis. It is confirmed that the activated SPI modified UF resin has similar chemical structure, higher ratio of crystalline regions, and slightly lower thermal stability with compared to the pure UF resin. This study proposes a practical and applicable solution for the utilization of eco-friendly UF resin in wood-based panel production.

Properties of Wood-Fiber Board Manufactured with the Use of UFC-FF Modified Urea–Formaldehyde Resin

Properties of Wood-Fiber Board Manufactured with the Use of UFC-FF Modified Urea–Formaldehyde Resin

Applicational properties of reinforced plywood with nanomaterials and kenaf fiber

Kenaf fibers were added as a reinforcement between wood veneers of poplar (Populus deltoides) bonded with urea–formaldehyde (UF) resin to improve the applicational properties of standard three-layered plywood. Additionally, the influence of two different nanomaterials (nanocellulose and nanosilica)-modified UF resins on the performance of plywood was evaluated. Then, thickness swelling (TS), water absorption (WA), shear strength, and flexural properties were examined. Results indicated that reinforced composites with kenaf fibers improved the modulus of rupture (MOR) and modulus of elasticity (MOE) in both directions. In addition, physical properties, such as TS and WA after 24 h, improved in the reinforced plywood with kenaf and use of nanosilica (KNS) as a filler. The results of the mechanical properties were better than blanks. The treated adhesive, with nanocellulose and nanosilica revealed similar mechanical behaviors. The shear strength of plywood in KNC specimens showed the best result (increased 64.6% compared to blank) and MOR for both the parallel and perpendicular directions to the grain of the surface layers for KNS (105% and 158%, respectively), and MOE for KNS (92.9% and 152%, respectively) compared to the blank.

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

AbstractIn 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 T5%, the more thermally stable resin is the modified TUF resin (T5% = 123.1°C), while the value of the T5% 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.

Ureido Hyperbranched Polymer Modified Urea-Formaldehyde Resin as High-Performance Particleboard Adhesive.

The performance of urea-formaldehyde (UF) resin and its formaldehyde emission is a natural contradiction. High molar ratio UF resin performance is very good, but its formaldehyde release is high; low molar ratio UF resin formaldehyde release is reduced, but the resin itself performance becomes very bad. In order to solve this traditional problem, an excellent strategy of UF resin modified by hyperbranched polyurea is proposed. In this work, hyperbranched polyurea (UPA6N) is first synthesized by a simple method without any solvent. UPA6N is then added into industrial UF resin in different proportions as additives to manufacture particleboard and test its related properties. UF resin with a low molar ratio has a crystalline lamellar structure, and UF-UPA6N resin has an amorphous structure and rough surface. The results show that internal bonding strength increased by 58.5%, modulus of rupture increased by 24.4%, 24 h thickness swelling rate (%) decreased by 54.4%, and formaldehyde emission decreased by 34.6% compared with the unmodified UF particleboard. This may be ascribed to the polycondensation between UF and UPA6N, while UF-UPA6N resin forms more dense three-dimensional network structures. Finally, the application of UF-UPA6N resin adhesives to bond particleboard significantly improves the adhesive strength and water resistance and reduces formaldehyde emission, suggesting that the adhesive can be used as a green and eco-friendly adhesive resource for the wood industry.

Effects of nano manganese dioxide on performances of urea-formaldehyde resin

In cured urea-formaldehyde (UF) resin with low molar ratio of formaldehyde/urea (F/U), existent crystalline regions are believed to affect the properties of wood-based composites bonded with UF resins. The effects of crystalline regions on physicomechanical properties and formaldehyde emission of the plywood bonded with UF resin modified by nano Manganese dioxide (MnO2) were studied in this work. Results show that the modified UF resins with 0.9% MnO2 has a higher ratio of crystalline regions than those of neat resins. They resulted in a 79% improvement in the wet shear strength and a 70% reduction in the formaldehyde emission. The X-ray diffraction (XRD) results show that the crystallinity in the cured UF increases with the amount of MnO2 added. No change in the structure of the cured UF was found in the Fourier transforms infrared spectroscopy (FT-IR) with the addition of MnO2.

Sustainable bio-based dialdehyde cellulose for transforming crystalline urea–formaldehyde resins into amorphous ones to improve their performance

Sustainable bio-based dialdehyde cellulose (DAC) was employed to transform crystalline urea–formaldehyde (UF) resins into amorphous ones for simultaneouly improving their adhesion strength and formaldehyde emission. Serial samples of the UF resins modified with DAC during the resin synthesis were extracted to understand the chemical reactions between the DAC and UF species. Fourier transform infrared, 1H-nuclear magnetic resonance (NMR), and 13C NMR spectroscopies confirmed the occurrence of reactions between the DAC and UF species. As the synthesis proceeded, the crystallinity of the modified UF resins decreased from 51.7% to 17.4%, transforming the crystalline domains into amorphous ones. Thermograms showed that the DAC in the modified UF resins was decomposed at temperatures over 200 °C as degraded form, resulting in a lower cross-linking density than that of the neat UF resins. The adhesion strength of the modified UF resins was statistically similar to that of the neat UF resins, and the formaldehyde emission of the modified UF resins dramatically decreased to ∼ 64.6%. These results evidence the significant application potential of bio-based DAC in improving the sustainability and performance of UF resins.

Synthesis and Properties of Melamine Modified Urea Formaldehyde Resin for Impregnation Under New Process

In this paper, the basic properties of UF and UMF resins for impregnation under conventional and new processes were compared, and their chemical structures were characterized by ¹³C NMR. The effects of synthetic process and melamine addition on the bonding strength and formaldehyde emission of UF and UMF resins were studied. The resin synthesized by the new process has higher linear and methylene ether bond content, relatively lower methylene content, longer curing time and storage life and lower free formaldehyde content than the conventional resin; When melamine was added at the initial stage of UF resin synthesis reaction, it did not significantly change the total amount of methylene ether and hydroxymethyl in the resin system, but the content of class I hydroxymethyl increased and the content of class II hydroxymethyl decreased. The reason may be that the added melamine and urea react not only with the remaining formaldehyde in the system, but also with the formaldehyde removed from hydroxymethyl due to dehydroxylation reaction, Hydroxymethylmelamine and monobasic substituted urea are produced. At this time, about 50% of melamine still exists in UMF resin in the form of free or low hydroxymethylate, and does not participate in the formation of the main structure of the resin. Melamine was added in the early stage of the reaction. The modified resin bonded plywood has high bonding strength and low formaldehyde emission.

Effect of Copper (II) Sulfate on the Properties of Urea Formaldehyde Adhesive.

The purpose of this work is to investigate the effects of copper (II) sulfate on the formaldehyde release and the mechanical properties of urea formaldehyde (UF) adhesive. Copper (II) sulfate has been used as a formaldehyde scavenger in UF resin, and its effects on the physical and chemical properties of UF adhesive have been studied. Moreover, the mechanical properties and formaldehyde release of plywood prepared with modified UF resin have been determined. The UF resin has been characterized by Fourier-transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). FTIR spectra showed that the addition of copper (II) sulfate to the UF resin does not affect the IR absorptions of its functional groups, implying that the structure of UF is not modified. Further results showed that the free formaldehyde content of the UF resin incorporating 3% copper (II) sulfate was 0.13 wt.%, around 71% lower than that of the untreated control UF adhesive. With a copper (II) sulfate content of 3%, the formaldehyde release from treated plywood was 0.74 mg·L−1, around 50% lower than that from the control UF adhesive, and the bonding strength reached 1.73 MPa, around 43% higher than that of the control.

In-situ modification of low molar ratio urea–formaldehyde resins with cellulose nanofibrils for plywood

This study describes the in-situ modification of low molar ratio urea–formaldehyde (UF) resins with cellulose nanofibrils (CNFs) to improve the poor performance of resins synthesized with different methods (Synth 1 and Synth 2) when adding second urea. UF resins were in-situ modified with CNFs dissolved in a mixture of dimethyl sulfoxide (DMSO) and dimethylformamide (DMF) during the alkaline reaction step. Results showed that CNF addition enhanced the resin properties, such as shorter gelation time, faster curing rates at low activation energy, higher tensile shear strength (TSS), and lower formaldehyde emission (FE), compared to those of neat resins. The dry and wet TSS values of plywood bonded with UF resins modified with 3% CNFs synthesized using Synth 2 increased by 30% and 42%, respectively, and the FE value was decreased by 22% and 42%, respectively. These results reveal that in-situ modified UF resins with CNFs showed better performance than neat UF resins and that Synth 2 was more favorable than Synth 1.

Crystallinity of Low Molar Ratio Urea-Formaldehyde Resins Modified with Cellulose Nanomaterials

Inherent crystalline domains present in low formaldehyde to urea (F/U) molar ratio urea-formaldehyde (UF) resins are responsible for their poor adhesion in wood-based composite panels. To modify the crystallinity of low molar ratio (LMR) UF resins, this study investigates the additional effect of cellulose nanomaterials (CNMs), such as cellulose microfibrils (CMFs), cellulose nanofibrils (CNFs), and TEMPO-oxidized CNFs (TEMPO-CNFs) on the crystallinity of modified LMR UF resins. First, two modification methods (post-mixing and in situ) were compared for modified LMR UF resins with TEMPO-CNFs. The modified UF resins with TEMPO-CNFs decreased the nonvolatile solid contents, while increasing the viscosity and gel time. However, the in situ modification of UF resins with TEMPO-CNFs showed lower crystallinity than that of post-mixing. Then, the in situ method was compared for all CNMs to modify LMR UF resins. The modified UF resins with CMFs using the in situ method increased nonvolatile solid contents and viscosity but decreased the gel time. The crystallinity of UF resins modified with TEMPO-CNFs was the lowest even though the crystalline domains were not significantly changed for all modified UF resins. These results suggest that these CNMs should be modified to prevent the formation of crystalline domains in LMR UF resins.

Calcium carbonate modified urea-formaldehyde resin adhesive for strength enhanced medium density fiberboard production.

This study investigated the improved properties of calcium carbonate (CaCO3) modified urea–formaldehyde (UF) resin adhesive for medium density fiberboard (MDF) production. The CaCO3 modified UF resins were prepared by adding different proportions of CaCO3 to a low molar ratio UF resin at the initial stage of a typical synthetic process of the resin. The physicochemical properties of the resins were measured. The mechanical and environmental performances of the resin-bonded MDF panels were tested. The results show that the viscosity and free formaldehyde content of UF resins with or without CaCO3 modification were not significantly different. The solid content of the CaCO3 modified UF resin was significantly lower than that of the control group. In addition, the measured gel time of the CaCO3 modified UF resin was 111–149 s, which was longer than that of the control resin (82 s). The gel time was further extended with the increase of the CaCO3 content in the UF resin. The chemical group and crystal structure of UF resins with or without the modification of CaCO3 were not significantly different. The internal bonding (IB) strength of the MDF panels significantly increased from 0.75 MPa to 0.97 MPa when the UF resin was modified with 2% of CaCO3. This study provides scientific support for the preparation of inorganic mineral modified UF resins for strength enhanced wood-based panel manufacturing.

Effects of nanoclay modification with transition metal ion on the performance of urea–formaldehyde resin adhesives

As a way of reducing the formaldehyde emission and improving the adhesion of urea–formaldehyde (UF) resins, this study investigated the addition effects of pristine nanoclay (PNC) or modified nanoclay (MNC) with transition metal ion (TMI) on the performance of UF resin adhesives. Instead of a conventional simple mixing (SM) of MNC with UF resin (coded as MNC-SM), this study explored adding PNC or MNC into either the alkaline (ALK) or acidic (ACD) reaction during the synthesis of UF resins, which were coded as PNC-ALK, PNC-ACD, MNC-ALK, and MNC-ACD, respectively. For the first time, we report that the MNC-ALK resins result in almost amorphous UF resins with 25% crystallinity, which consequently increases the cross-linking, and improve the adhesion strength and decrease formaldehyde emission of modified UF resins. It is believed that the intercalated or exfoliated MNCs facilitate the formation of more cross-linking in the modified UF resins, leading to a better cohesive strength.

Enhancing the performance of low molar ratio urea–formaldehyde resin adhesives via in-situ modification with intercalated nanoclay

ABSTRACT Low molar ratio urea–formaldehyde (UF) resin adhesives are primarily used for the reduction of formaldehyde emission (FE) from wood-based composites, at the expense of poor reactivity and adhesion. This study aimed to enhance the performance of low molar ratio UF resins via in-situ modification, via the addition of octadecylamine (ODA)-modified bentonite (ODA–BNT) nanoclay. The molecular weights, curing behavior, chemical groups, and crystallinity of modified UF resins with different levels of ODA−BNT were characterized by gel permeation chromatography, differential scanning calorimetry, Fourier-transform infrared spectroscopy, and X-ray diffraction (XRD). The ODA–BNT/UF resins showed better reactivity and lower activation energy compared with neat resins. The XRD results clearly showed that ODA–BNT in modified UF resins had been intercalated. A 5% ODA−BNT addition resulted in a decrease in the crystallinity of the modified UF resins, leading to better adhesion strength and lower FE compared with neat UF resins. These results suggest that intercalation of ODA–BNT in low molar ratio UF resins improve their cohesion through the formation of a larger branched network in their cured state.

Converting crystalline thermosetting urea–formaldehyde resins to amorphous polymer using modified nanoclay

Thermosetting urea–formaldehyde (UF) resins as the most common adhesives for wood-based composites emit formaldehyde, which forces producers to lower formaldehyde/urea (F/U) molar ratio for the UF resins synthesis. However, low-molar-ratio (below 1.0) UF resins have low formaldehyde emission at the expense of poor adhesion, which is responsible for the formation of crystalline domains as a result of hydrogen bonds between linear molecules. For the first time, this study reports the conversion of crystalline UF resins to amorphous polymers by blocking the hydrogen bonds, using transition metal ion-modified bentonite (TMI-BNT) nanoclay through in situ intercalation. The modified UF resins with 5% TMI-BNT showed an almost amorphous structure, faster curing and higher cross-linking density compared with those of neat resins, and resulted in 56.4% increase in the adhesion strength and 48.3% reduction in the formaldehyde emission. Thus, blocking hydrogen bonds in low F/U molar ratio UF resins with TMI-BNT converted crystalline UF resins to almost amorphous ones, resulting in a significant improvement in their adhesion with a low crystallinity.

Preparation and Properties of Five Biomass-based Melamine Modified Urea Formaldehyde Resins

In this paper, shell (PS), rice husk (RH), rapeseed stalk (RS), toonaciliata wood (TW) and Sinocalamus affinis (SA) were served as the modifier to modify the melamine modified urea-formaldehyde resin (MUF). The PS, RH, RS, TW, SA were ultra-fine crushed to be the powder with less than 48 um. The reactivity of PS, RH, RS, TW, SA and formaldehyde solution was measured, and PS, RH, RS, TW, SA were added in the third stage of synthesis process of the MUF resin. The basic properties of the resin and plywood were tested. The results showed that, with addition of the PS, RH, RS, TW, SA, the reactivity with formaldehyde solution became better, while the gel time became longer, the resin viscosity and the solid content increased, and the free formaldehyde content of the resin decreased. The formaldehyde emission of the plywood decreased by 60.53%, 48.25%, 41.23%, 44.74%, 56.14%, respectively, and the wet ply strength of the plywood increased by 40.00%, 56.19%, 16.19%, 24.76%, 54.29%, respectively. The use of the ultra-fined PS, RH, RS, TW, and SA showed good effects on the formaldehyde elimination of the MUF resin.

Effect of various compounding methods on acid red 18050- melamine modified urea formaldehyde resin compound as wood modifier

In order to simultaneously improve the strength and decoration properties of plantation wood, a multi-effect modifier was prepared by compounding acid red 18050(G) with melamine-modified urea formaldehyde resin (MUF). Various compounding methods for MUF synthesis such as adding dye with the first part urea (U1G) or with the second part urea (U2G), or direct blending with MUF resin (BG) were tested. Chinese fir plantation wood was impregnated with these modifiers separately, and its color, color fastness, and dyeing mechanism were studied. The results showed that G had good compatibility with MUF and could prolong its storage time, and all compound modifiers exhibited permeability and coloring effect on Chinese fir wood. Compared with G-dyed wood under the same conditions, all the compound dyed wood had better color fastness to water, and the U2G-dyed was the best, the color fastness to xenon light of U2G dyed wood was greatly improved.. Fourier transform infra-red (FTIR) analysis showed that compared with MUF-modified wood, the dye affected MUF hydroxyl-methylation reaction in U1G, lowered the polycondensation degree, and extended its storage time. The dye might have promoted the ionic reaction between resin amino and dye sulfonic groups in U2G, thus displaying better color fastness.

Synthesis and properties of rigid polyurethane foams synthesized from modified urea-formaldehyde resin

In this study, ethylene glycol modified urea formaldehyde resin (EUF) was synthesized from urea, paraformaldehyde and ethylene glycol, and then incorporated into rigid polyurethane foams (RPUFs) as a reactive-type liquid flame retardant. The structure of EUF was characterized by Fourier transform infrared spectroscopy, and the thermal degradation properties and fire behaviors of RPUFs were characterized by limiting oxygen index (LOI), cone calorimetry test and thermogravimetry analysis. The results show that the incorporation of EUF results in an increase in the thermal stability and LOI of RPUFs. As the EUF loading increases, the peak heat release rate, total smoke release and CO/CO2 weight ratio of RPUFs decrease significantly. This is because EUF can release non-flammable gases during the initial degradation of polyurethane foams and promote the formation of the compact char layer, which can serve as an effective shield against heat, oxygen and combustible volatiles during the combustion. However, EUF shows negative effect on the cell morphology and mechanical properties of RPUFs. In conclusion, EUF has excellent performance in flame retardancy and smoke suppression for RPUFs.

Oxidized polyethylene as a new alternative coupling agent for the fiberboards made from UF resin

ABSTRACTThe aim of this research was to improve the bonding of bagasse fiber panels with urea formaldehyde (UF) resins by incorporating oxidized polyethylene (OPE) as a new coupling agent. To reduce the panels formaldehyde emission and to improve their water resistance was an additional aim of this work. Thus, different proportions of OPE (5, 10 and 15%) were added during the UF resin preparation instead to the second urea. The resins were then used in the production of UF-bonded bagasse fiber panels. The physicochemical, structural and thermal properties of the resins as well as water absorption, flexural properties, internal bond strength (IB) and formaldehyde emission of the panels bonded with them were measured according to standard methods. According to the FTIR spectra, the absorbance related to C = C and C = O bonds increased due to the addition of OPE to the UF resin. DSC analysis indicated that in comparison to UF resin, the curing process of UF resin containing OPE occurred at a lower temperature. The gel time shortened and the viscosity increased by the addition of OPE to the UF resin. The panels containing OPE yielded higher IB, flexural modulus and strength compared to those made from pure UF resins. The panels bonded with modified UF resins also showed lower formaldehyde emission and water absorption. Based on finding of this work, the panels containing 15% OPE emitted less formaldehyde, had higher mechanical strength and better dimensional stability than other percentages OPE-modified UF adhesives.

Preparation and Properties of Coir-Based Substrate Bonded by Modified Urea Formaldehyde Resins for Seedlings

In order to form a firm root plug for the mechanical transplantation, modified urea formaldehyde (UF) resins were applied to bond coir based substrate and form substrate blocks. The physical and chemical structure, thermal stability, and crystallinity of the substrate blocks before and after nursery seedlings were characterized. The results showed that the -NH2 and -OH in the substrate reacted with the modified UF resins to form macromolecular structures. There was almost no difference between the XRD spectra of substrate blocks before and after the growth of seedlings. The modified resins in the substrate block were cured in the form of colloidal particles. The substrate block contained 53.8 At% carbon, 15.0 At% nitrogen, and 23.5 At% oxygen. When compared with the original substrate, the height, stem diameter, root length, and leaf area of tomato seedlings grown in substrate block were improved by 56.1%, 43.3%, 1.3%, and 63.3%, respectively. The qualification percentage of the substrate block was 94.3%, which was well above that of the original substrate (83.4%) according to JB/T 10291 (2013) standards. The substrate block bonded by the modified UF resins was suitable for tomato seedlings growth.