UF Resin Research Articles

Qualitative analysis of pre-curing process of UF resin

The rheological behavior, molecular weight distribution (MWD), reactivity, and chemical structures of UF resin during the pre-curing process were elucidated by rheometry, gel permeation chromatograph (GPC), differential scanning calorimetry (DSC), and 13C NMR, respectively. The unsynchronized increasing processes between viscosity and rigidity during the pre-curing process were closely related to the changes of activation energy, MWD, and chemical structures. The results indicated that, due to the pre-curing behavior showed significant influence on the activation energy, both the occurrence of pre-curing behavior and its degree could be accurately judged, and the change trend of MWD and the chemical structures of the pre-curing resin could be also predicted by the non-isothermal DSC method. Once the value of Ea was higher than that of E0, the degree of cross-linking was increased and the network structure was formed indicating that the pre-curing behavior of UF resin had taken place.

Effect of aluminosilicate powders on the applicability of innovative geopolymer binders for wood-based composites

In this research, a new binder class for wood based composites, named geopolymer binder, was developed based on pozzolanic by-products (e.g. fly ash). Additionally, effects of different amounts of silica fume, as a replacement agent with other aluminosilicate components (e.g. fly ash and metakaolin), have been evaluated in the innovative binder. The Automated Bonding Evaluation System technique was used to characterize the bonding shear strength of the developed geopolymer binder. It was shown that the best shear strength for fly ash based binders was obtained by the lowest press temperature and longest pressing time. The addition of silica fume (from 20% up to 100%) significantly influenced the bonding shear strength in all binder types. Due to the chemical and mineralogical compositions, silica fume displays higher pozzolanic activity than metakaolin whereas fly ash shows lower strength in comparison to metakaolin. The silica fume (100%) based binder has also superior shear strength compared to those of conventional UF resin and other geopolymer binders. Bonding shear strength like that for UF resin was achieved by substituting only 20% silica fume in geopolymer binder compositions.

Recognition performance and mechanism of the activated carbon based UF resin towards traces of Fe(III) in rare earth solutions

Some trace of non-rare earth impurities has serious damage on the performance of rare earth material. Therefore, efficient removing these impurities from rare earth is very significant. In this paper, a novel activated carbon (ACUF700) was synthesized by homemade urea formaldehyde resin carbonized at 700°C. The surface properties, chemical functional groups, element content, surface morphology, and XPS of ACUF700 were investigated. The adsorption behavior of ACUF700 towards Fe(III) were investigated by batch and column method. The BET specific surface area of ACUF700 was 712cm3g−1, and the average pore diameter was 2nm. The ACUF700 possesses strong adsorption affinity and excellent recognition selectivity for Fe(III). The adsorption capacity could reach to 13mgg−1, and relative selectivity coefficients relative to La(III) and Ce(III) was 28.0 and 25.3, respectively. Besides, ACUF700 could be regenerated easily and reused without losing significantly adsorption capacity.

Improving physical and mechanical properties of new lignin- urea-glyoxal resin by nanoclay

To eliminate toxic formaldehyde from wood based panels, glyoxal, a low volatility and nontoxic aldehyde, was used to react with urea and lignin to prepare a glyoxalated lignin- urea-glyoxal (LUG) wood adhesive resin. Moreover, another objective of this research work was to improve the physical and mechanical properties of the new LUG resins by nanoclay addition. For the preparation of LUG resin, glyoxalated lignin (15 mass%) was added instead of second urea to the urea-glyoxal resin synthesis under acid conditions. The LUG resin so prepared was mixed with 1, 2 and 3 mass% nanoclay by mechanically stirring for 5 min at room temperature. Then, the physicochemical and structural properties of the prepared resins as well as the water absorption and the mechanical properties of the plywood panels bonded with it were measured according to standard methods. The physicochemical test results indicated that the gel time of the LUG resin was markedly slower than that of the UF resin. Plywood panels prepared with the LUG resin also presented lower water absorption as well as weaker shear strength than those prepared with the UF resin. Addition of nanoclay changed the physicochemical properties of the resins as the gelation time of the LUG resin was shorter when adding sodium montmorillonite (NaMMT). Higher shear strength values and lower water absorption were achieved by continuously increasing nanoclay proportion from 1 to 3 mass%. Furthermore, addition of nanoclay had more influence on panels bending strength than their flexural modulus. X-ray diffraction (XRD) analysis also indicated that NaMMT exfoliated completely when mixed with LUG resin.

Optimization of processing parameters of medium density fiberboard using response surface methodology for multiwalled carbon nanotubes as a nanofiller

In the present work, medium density fiberboard (MDF) panels were produced using multiwalled carbon nanotubes (MWCNT) reinforced urea formaldehyde resin. Response surface methodology was employed to optimize the relationship between the three variables, viz. pressing time, percentage of UF resin and percentage of MWCNT, used in the fabrication of MDF, and the influence of variables on the internal bonding (IB) and modulus of rupture (MOR) was studied. The optimum conditions based on the IB strength were determined as 8.18 % of UF resin, pressing time of 232 s, and MWCNT of 3.5 %. Similarly, the optimized conditions for MOR are also reported in this paper.

Utilizing brewer's-spent-grain in wood-based particleboard manufacturing

Brewer's spent grain (BSG) is a major by-product of the beer industry, representing around 85% of their entire by-products. In this research, chemical, physico-mechanical and structural properties of particleboard made with brewer's spent grain (BSG) are presented first time. BSG had even-balanced contents of cellulose, lignin and hemicelluloses, which was at about 20% each. Wood particles were replaced by BSG at percentages of 10, 20, 30 and 50. These BSG-based particleboard types were produced with a common density of 620 kg/m3, bonded with UF resin, and they were tested for modulus of rupture, modulus of elasticity, internal bonding, thickness swelling and water absorption. Scanning electron microscopy was employed to study the inner structure of the boards. Overall, the mechanical properties of BSG-based particleboards were lower compared to wood-based control. Likewise, thickness swelling and water absorption of BSG-based particleboards were found to be higher. SEM images suggested that smaller fraction of BSG tend to cover wooden particles, which may have potentially restricted the internal bonding status. Further, smaller BSG have shown to fill voids in the boards, with the consequence of retaining more water and cause higher swelling and water absorption. Although BSG-based particleboards show altogether a reduced performance, it can also be stated that particleboards having 10% of BSG do meet the requirements for general purpose particleboards, used in dry conditions.

Urea–formaldehyde resin prepared with concentrated formaldehyde

The characteristics of UF resin prepared with concentrated formaldehyde were studied in this paper. With the molar ratio F/U = 1.1, the UF resin prepared with concentrated formaldehyde showed better mechanical properties than that with formalin. The 13C-NMR and FTIR results indicated that there were more methylene groups, ether groups and urons in a UF resin system prepared with concentrated formaldehyde than those in a normal UF resin. The differential scanning calorimetry and DMA results showed that the curing temperature of UF resin with concentrated formaldehyde was lower than that of a normal UF resin. UF resin with concentrated formaldehyde showed worse thermal stability and higher thermal decomposition temperature.

Change in Chemical Compositions of Leachate and Medium Density Fiberboard from a Laboratory-scale Simulated Landfill

The change in chemical compositions of leachate and medium density fiberboard (MDF) from a laboratory-scale simulated landfill which constructed in a plastic container containing alternating layers of soil and MDF was investigated to evaluate decomposing of MDF in soil. Four treatments were conducted: 1) MDF in soil, 2) MDF only, 3) cured UF resin in soil, and 4) soil only. Molecular weight (MW) distribution of compounds in leachate from soil only treatment did not change over time. In UF resin in soil treatment, the MW distribution shifted to a lower MW distribution over time, while the peak shifted to the left indicated changing to higher MW distribution in leachate from treatment 1 and 2 contained MDF. Higher percent nitrogen in leachate was observed in MDF containing treatments due to the UF resin in the MDF. The percent carbon slightly increased in MDF only while that greatly decreased in MDF in soil treatment maybe due to bacterial activity. The percent of extractable materials from the MDF decreased greatly on day 35 compare to day 0, and subsequently did not change much on day 77. In contrast, percent holocellulose and lignin did not change much over time. No structural change of the wood fiber in MDF occurs during the study. Water-soluble materials from MDF in soil contributed the change in chemical composition of leachate.

Thermosetting composites prepared using husk of pine nuts from Araucaria angustifolia

The high consumption of pine nuts as food leads to high amounts of husk dispensed as waste. The incorporation of the husk from pine nut into composites appears as a strategic route to explore the commercialization of the Araucaria angustifolia. The present study aims to prepare and characterize thermosetting composites of urea and phenol formaldehyde and husk of pine nuts. For this, husk particles, paraffin emulsion, ammonium sulfate, and resins, were mixed with a high‐shear mixer and then cured by flat‐pressing at 4 MPa, 120°C, for 5 min. SEM and optical images revealed good homogenization between resin and husk. DTG and DSC results showed chemical affinity between filler and matrix—tracked by shifts in the DTG peaks of the husk. The UF composites showed higher wettability and water absorption; therefore higher thickness swelling. The UF and PF composites with 30% of resin provided the greatest repellency to water, and the highest mechanical properties. It was possible to prepare composites of UF and PF resins loaded with 70% and 80% of husk from pine nuts. POLYM. COMPOS., 39:476–483, 2018. © 2016 Society of Plastics Engineers

Evaluation of UF resin content in MDF boards after hot-pressing by Kjeldahl method

Understanding resin behavior during hot pressing of medium density fiberboard (MDF) is important to optimize panel properties. Before gelation, the mobility of the resin can affect its distribution and penetration on the wood cells during pressing. The resin in MDF boards occurs as coverage on the fibers surface and also penetrates within the fibers. In this paper, the effect of final resin content and physical–mechanical properties of MDF panels was measured under different conditions of press time, temperature and initial resin content. The measurements were performed by the Kjeldahl method. Results showed that a higher amount of initial resin led to a higher resin content in MDF boards. At the same amount of initial resin, a higher final resin content was obtained by increasing the pressing temperature. Furthermore, the final resin content affects the board properties such as internal bond strength and modulus of rupture. The results showed good correlation between mechanical properties and thickness swelling.

Influence of a urea–formaldehyde resin adhesive on pyrolysis characteristics and volatiles emission of poplar particleboard

To investigate the influence of urea–formaldehyde resin (UF resin) adhesive on the thermal utilization of wood waste, the pyrolysis of particleboard and its main components (poplar and UF resin) are studied in this paper.

White mustard straw as an alternative raw material in the manufacture of particleboards resinated with different amount of urea formaldehyde resin

In this work the optimum resination rate of white mustard straw particles with UF resin in the production of straw particleboards was investigated. The resination rates used in this study were 10, 12 and 14%. For the selected resination rate, the possibility of reducing the density of the straw particleboards was also determined. In order to evaluate the hygienic parameters of the experimental boards, the formaldehyde content and volatile organic compounds (VOC) were determined. Moreover, using a thermogravimetric analysis (TGA) the boards’ disposal options by means of burning or co-incineration were investigated. The study results showed that a 10% resination rate enabled the production of white mustard particleboards of type P1 and P2, while the simultaneous reduction in their density to 600 kg/m 3 limited their application to dry conditions only, i.e. boards of P1 type. Thermogravimetric analysis revealed a variable thermal performance of the studied boards. The pine particleboards showed a higher thermal resistance, however, up to a temperature of 750°C, the samples of the experimental boards underwent a similar process of thermal destruction.

Effect of surface structure, wax and silica on the properties of binderless board made from rice straw

When boards were manufactured from rice straw with UF resin, morphological differences, wax and silica adversely affected the boards' properties. The effects of the surface structures such as trichomes and protuberances were examined owing to improve the properties of binderless boards made from rice straw. The effects of silica and wax on the properties of binderless boards were also investigated. Trichomes and protuberances were broken by fine grinding. Wax was removed by extraction with hexane. Silica content was conditioned by fractionation of rice straw. Binderless boards were manufactured by hot-pressing, and their mechanical properties and water resistance were evaluated. Fine grinding increased both the mechanical properties and water resistance of binderless boards. One of the reasons was that size reduction of particles increased the bonding area. Another important reason was that the trichomes and protuberances that inhibit self-bonding were removed by fine grinding. The removal of wax increased self-bonding, and did not decrease the water resistance of boards. De-dusting decreased silica by a small amount, but this did not affect self-bonding. Hence, extraction of hexane and fine grinding were effective in increasing self-bonding of binderless boards made from rice straw. Owing to these pretreatments, the internal bonding and thickness swelling of the binderless boards made from rice straw met the requirements for particleboard and MDF of Japanese Industrial standards (JIS).

Environmental Assessments of Leachate from Medium Density Fiberboard in a Simulated Landfill

This study investigated environmental assessments of leachate containing formaldehyde from medium density fiberboard (MDF) disposed in laboratory-scale simulated landfills. Environmental impact assessment of leachate was conducted by measuring formaldehyde, toxicity, biochemical oxygen demand (BOD), chemical oxygen demand (COD), bacterial enumeration, and pH. Amount of formaldehyde in leachate from MDF in soil decreased to the level of soil only treatment by 28 days, and toxicity decreased as the amount of formaldehyde decreased. BOD and COD levels in leachate from the treatments containing MDF exceeded permissible discharge levels of BOD or COD throughout the experimental period. The pH levels of all treatment were within permissible discharge range except on day 0. Fewer bacteria were observed in leachate from MDF in soil treatment than other treatments (MDF only, cured UF resin in soil, and soil only). Consequently, the leachate from disposal of MDF in soil detrimentally affect on environment. However, soil buffered formaldehyde leaching and pH on leachate in this study. Waste MDF may be required the pre-water soaking treatment for leaching formaldehyde to reclaim on land.

Influence of nanoclay on urea–glyoxalated lignin–formaldehyde resins for wood adhesive

ABSTRACTIn this research, the influence of nanoclay on urea–glyoxalated lignin–formaldehyde (GLUF) resin properties has been investigated. To prepare the GLUF resin, glyoxalated soda baggase lignin (15 wt%) was added as an alternative for the second urea during the UF resin synthesis. The prepared GLUF resin was mixed with the 0.5%, 1%, and 1.5% nanoclay by mechanically stirring for 5 min at room temperature. The physicochemical properties of the prepared resins were measured according to standard methods. Then the resins were used in particleboard production and the physical and mechanical properties of the manufactured panels were determined. Finally, from the results obtained, the best prepared resin was selected and its properties were analyzed by differential scanning calorimetry (DSC), Fourier transform infrared spectrometry (FTIR), and X-ray diffractometry (XRD). Generally the results indicated that the addition of sodium-montmorillonite (NaMMT) up to 1.5% appears to improve the performance of GLUF resins in particleboards. The results also showed that nanoclays improved mechanical strength (modulus of elasticity (MOE), Modulus of Rupture (MOR), and internal bond (IB) strength) of the panels bonded with GLUF resins. The panels containing GLUF resin and nanoclay yielded lower formaldehyde emission as well as water absorption content than those made from the neat GLUF resins. XRD characterization indicated that NaMMT only intercalated when mixed with GLUF resin. Based on DSC results, the addition of NaMMT could accelerate the curing of GLUF resins. The enthalpy of the cure reaction (ΔH) of GLUF resin containing NaMMT was increased compared with neat GLUF resin. Also the results of FTIR analysis indicated that addition of NaMMT change the GLUF resins structures.

Curing behavior of melamine-urea-formaldehyde (MUF) resin adhesive

In this work, MUF resin was tested by DMA method. It showed that G′ curves and strain curves together could be used to predict the curing behavior of MUF resins. The study showed that sequential formulation was preferred for the preparation of MUF resins. Hardener could accelerate the curing of MUF resins. But its addition amount should not be too high to affect the resins' shelf time. MUF showed medium thermal resistance when compared with UF and MF resins.

Urea formaldehyde resin with low formaldehyde content modified by phenol formaldehyde intermediates and properties of its bamboo particleboards

ABSTRACTPhenol formaldehyde reaction solution (PFS) was used to synthesize urea–formaldehyde resins (PFSUF resins) with low formaldehyde content. In addition, the prepared PFSUF resins were used as adhesives to bond bamboo particleboards. Mechanical properties, fracture morphology, water absorption ratio, and dimensional stability of bamboo particleboards have been studied by tensile tests, SEM tests, water absorption analysis, and swelling ratio analysis, respectively. The results demonstrate that the main ingredient of PFS is phenol formaldehyde intermediate 2,4,6‐trimethylolphenate and proper amount of PFS can be used to reduce the formaldehyde content of UF resins effectively. The results also show that bamboo particleboards bonded with PFSUF resins exhibit better mechanical properties, water resistance, and dimensional stability than that bonded with pure UF resin. However, the results of TG and mechanical properties analysis exhibit that alternative curing agents to ammonium chloride should be studied to improve the curing properties of the PFSUF resins with low formaldehyde content. Taken together, this work provides a method of preparing environment‐friendly PFSUF resins with low phenol and low formaldehyde content and the prepared resins have potential application in wood industry. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42280.

Synthesis and Comparison of Phenol-Urea-Formaldehyde (PUF) Thermosetting Resin with Commercial Synthetic Resins

Phenol-urea-formaldehyde (PUF) thermosetting resin was synthesized by reacting methylol phenol with urea under acidic condition and its bonding strength was compared with commercial synthetic resins (PF resin, UF resin and PUF resin made by mechanical blending of PF and UF resins). The results indicated that PUF resin made by this process performed better bonding strength than commercial UF resin and mechanical blending of PF and UF resins in both dry and wet conditions. Its bonding strength was found to be intermediate to UF and PF resins.

Surface characteristics and physical properties of wheat straw particleboard with UF resin

Agricultural fibers, such as straw and plant stalks, have been considered as renewable alternatives for making particleboard, which would ease the huge demand for wood. The objective of this study was to investigate surface characteristic (surface roughness and wettability) and physical properties (thickness swelling and water absorption) of wheat straw (Triticum aestivum L.)/poplar wood particleboard with UF resin and silane coupling agent. The effects of the silane coupling agent content and straw/poplar wood particles ratio on the surface characteristic and physical properties were examined. The ratios of the mixture of straw and poplar wood particles were 100:0, 85:15, 70:30 and 55:45. Silane coupling agent content was chosen at three levels of 0, 5 and 10 %. The experimental panels were tested for their physical properties according to the procedure in DIN 68763 (Determination of values of surface roughness parameters Ra, Rz, R max using electrical contact(stylus) instruments, concepts and measuring conditions, Berlin, Deutsches institut fur Norming, 1982) roughness measurements, average roughness (Ra), mean peak-to-valley height (Rz), root mean square roughness (Rq), were taken from the unsanded samples using a fine stylus tracing technique. Contact angle measurements were obtained by using a goniometer connected with a digital camera and computer system. Results indicated that physical properties (thickness swelling and water absorption (were improved by the addition of silane coupling agent, but use of poplar wood particles has a negative effect on physical properties (thickness swelling and water absorption). Statistical analysis showed that boards consisting of a greater amount of poplar particles exhibited lower wettability. Furthermore, panels made with higher amount of silane level, showed lower Rq values.

Effect of γ-irradiation on the hydrolytic stability and thermo-oxidative behavior of bio/inorganic modified urea–formaldehyde resins

In order to minimize emission of formaldehyde from urea–formaldehyde resins (UF) and to improve their thermo-oxidative behavior, the effect of low γ-irradiation on hydrolytic and thermo-oxidative stability of nano-silica modified UF resin, modified UF resin with wood flour (Pinus silvestris L.) as natural filler and modified UF resin with mixture of SiO2/WF fillers were investigated. The hydrolytic stability of modified UF resins was determined by measuring the mass loss and liberated formaldehyde concentration of modified UF resins after acid hydrolysis. The studied modified UF resins have been irradiated (50kGy) and effect of γ-irradiation was evaluated on the basis of percentage of liberated formaldehyde before and after irradiation. The minimum percentage (1.23%) of liberated formaldehyde and mass loss of a 25.35% were obtained in wood flour modified UF resin after γ-irradiation which indicate significant improvement in the hydrolytic stability compared to other modified UF resins. The effect of γ-irradiation was evaluated also on the basis of thermo-oxidative behavior of the same modified UF resins before and after irradiation. The thermo-oxidative behavior was studied by non-isothermal thermo-gravimetric analysis (TG), differential thermo-gravimetry (DTG) and differential thermal analysis (DTA) supported by data from IR spectroscopy. After γ-irradiation, the shift of DTA peaks a higher temperature indicates that thermo-oxidative stability of modified UF/SiO2/WF is increase.