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Hongzhang Chen - One of the best experts on this subject based on the ideXlab platform.
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carbohydrate elimination of alkaline extracted lignin liquor by steam explosion and its Methylolation for substitution of phenolic adhesive
Industrial Crops and Products, 2014Co-Authors: Guanhua Wang, Hongzhang ChenAbstract:Steam explosion pretreatment was proposed to eliminate carbohydrates in the alkali lignin liquor isolated from corn stalk and the obtained lignin liquor was concentrated and methylolated without further purification process for substitution of phenolic resin as plywood adhesive. Moreover, FTIR and GPC analysis technology was applied to characterize the lignin variation during the steam explosion treatment and the Methylolation modification. The results demonstrated that steam explosion could effectively decrease the carbohydrate content of lignin liquor and the operational parameters of steam pressure 1.8 MPa and pressure maintaining time 5 min were obtained as preferable conditions for less carbohydrate content and higher lignin yield. The lignin methylolated under optimized conditions was found to successfully substitute 50% of phenolic resin as wood adhesive with approved bonding strength and lower free formaldehyde and phenol contents. The FOR and GPC analysis suggested that lignin showed higher content of carbonyl group and narrower molecular weight distribution due to depolymerization effect during steam explosion and formaldehyde was mainly incorporated into the aromatic C-5 position of G unit in the Methylolation process. Overall, the study indicates that steam explosion is an effective treatment to improve the purity of lignin liquor and the direct substitution of phenolic adhesive by methylolated lignin liquor significantly reduces the costs for lignin recovery, which offers a promising approach for enhancing the commercial operation of a steam-explosion-derived biorefinery. (C) 2013 Elsevier B.V. All rights reserved.
Luísa Carvalho - One of the best experts on this subject based on the ideXlab platform.
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Study of the synthesis parameters of a urea-formaldehyde resin synthesized according to alkaline-acid process
International Journal of Adhesion and Adhesives, 2020Co-Authors: Carolina Gonçalves, Nádia Paiva, João Pereira, João Ferra, Fernão D. Magalhães, Jorge Martins, Ana Barros-timmons, Luísa CarvalhoAbstract:Abstract This paper presents a study of two crucial synthesis parameters of the alkaline-acid process of UF resin synthesis: condensation formaldehyde/urea (F/U) molar ratio and U feed rate during the Methylolation step. The differences in the polymeric structures and the performance of the ensuing resins on particleboards (PBs) properties were analyzed and compared with a standard resin. The molecular weight distribution of the resins was monitored by gel permeation chromatography/size exclusion chromatography (GPC/SEC) and the unreacted oligomers by high-performance liquid chromatography (HPLC). The PBs produced were analyzed following European standards for mechanical tests and formaldehyde emission. The data obtained were also submitted to a statistical analysis. The results obtained showed that the use of low molar ratios yield higher internal bond strength (IB) values and lower formaldehyde emissions (F). In turn, the effect of urea feed rate during the Methylolation step on IB values depends on the F/UII molar ratio used: (i) a reduction for the higher final molar ratio used, and no effect for the lowest final molar ratio used. Moreover, the statistical analysis carried out showed that F/UII molar ratio has significance on almost all of the resins’ characteristics. The resin used as standard yielded the best results when the final F/U molar ratio was 1.10 and the resulting PBs presented values of internal bond (IB) of 0.51 N mm−2 and formaldehyde content (F) of 5.1 mg/100 g o.d.b., complying with the market requirements. Additionally, the effect of resin ageing was also studied and the PBs prepared using the best resin upon fifteen days of its production presented similar IB values and even lower F content in relation to those obtained using fresh resin.
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Statistical evaluation of the effect of urea-formaldehyde resins synthesis parameters on particleboard properties
Polymer Testing, 2018Co-Authors: Carolina Gonçalves, Nádia Paiva, João Pereira, João Ferra, Fernão D. Magalhães, Jorge Martins, Ana Barros-timmons, Luísa CarvalhoAbstract:Abstract This work discusses the optimization of different synthesis parameters for a low emitting urea-formaldehyde (UF) resin. Industrially, this resin was synthesized using the alkaline-acid process (alkaline Methylolation and acidic condensation) at different values of pH, temperature (T) and final viscosity and characterized according to different analytical methods. Particleboards (PBs) were produced using different pressing times and characterized according to the standard tests. A statistical analysis (ANOVA) was performed, and the main conclusion is that small changes on the synthesis of resins parameters do not affect the performance of PBs.
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Study of influence of synthesis conditions on properties of melamine–urea formaldehyde resins
International Wood Products Journal, 2012Co-Authors: Nádia Paiva, João Pereira, João Ferra, Paulo Cruz, Luísa Carvalho, Fernão D. MagalhãesAbstract:AbstractThe aim of this work is to assess the differences in the polymeric structure and performance of melamine–urea formaldehyde (MUF) resins, when changing relevant synthesis variables: formaldehyde/amine groups [F/(NH2)2] molar ratio (both in the Methylolation and the condensation steps) and the feedrate of urea during the condensation step. This synthesis process differs from the traditional alkaline acid process, since the F/(NH2)2 molar ratio is different for the Methylolation and condensation steps. It was found that the F/(NH2)2 molar ratio and urea feedrate in the condensation step are the most influential variables on the product characteristics. A relationship was established between polymeric structure of the resin and the physicomechanical properties, as well as the levels of formaldehyde. A resin formulation was obtained that exhibits a formaldehyde content, evaluated both by perforator and desiccator methods, within the Japanese F**** requirements. This resin presents an overall performanc...
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Comparison of UF synthesis by alkaline-acid and strongly acid processes
Journal of Applied Polymer Science, 2011Co-Authors: João Ferra, Luísa Carvalho, Ana Henriques, Adélio Mendes, Mário Rui P. F. N. Costa, Fernão D. MagalhãesAbstract:This work discusses two processes for pro- ducing urea-formaldehyde (UF) resins. One is the alkaline- acid process, which has three steps: usually an alkaline Methylolation followed by an acid condensation and finally the addition of a final amount of urea. The other process, the strongly acid process, consists of four steps, in which the first step involves a strongly acid condensation followed by an alkaline Methylolation, a second condensa- tion under a moderately acid pH and finally, methylola- tion and neutralization under a slight alkaline pH. Two resins were produced using the two above described proc- esses. The molecular weight distribution (MWD) of the resins was monitored off-line by GPC/SEC and the final resins were characterized by GPC/SEC and HPLC. These studies showed that the two resins differ greatly in chemi- cal structure, composition, viscosity, and reactivity. The monitoring of MWD indicated that the first condensation under a strongly acid environment leads to the production of a polymer with a distinctly different chemical structure, therefore increasing the flexibility of polymer synthesis and opening the way to the improvement of end-use properties. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 000: 000-000, 2011
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evaluation of urea formaldehyde adhesives performance by recently developed mechanical tests
International Journal of Adhesion and Adhesives, 2011Co-Authors: João Ferra, Luísa Carvalho, Adélio Mendes, Mário Rui P. F. N. Costa, Martin Ohlmeyer, Fernão D. MagalhãesAbstract:Abstract In the open literature, two main strategies can be found for synthesizing urea-formaldehyde (UF) resins. One is the alkaline–acid process, which takes place in three steps, usually an alkaline Methylolation followed by an acid condensation and then the addition of a final amount of urea. The other process consists of four steps, the main difference being an initial condensation in strongly acid environment. In this work, we evaluate the curing behaviour of four resins produced using the aforementioned processes by the Integrated Pressing and Testing System (IPATES) and the Automated Bonding Evaluation System (ABES). The characterisation of the bond strength development during hot pressing by ABES and IPATES shows that the four resins will have different performances in the bonding process of wood-based composites. For each resin, the effect of pressing parameters such as temperature, adhesive and hardener ratios on shear strength (ABES) and internal bond (IPATES) during hot pressing is put into evidence.
Tuula T. Pakkanen - One of the best experts on this subject based on the ideXlab platform.
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Kraft lignin reaction with paraformaldehyde
Holzforschung, 2020Co-Authors: Hanna Paananen, Tuula T. PakkanenAbstract:AbstractLignin is the second most abundant biopolymer and will be an important source for carbon-containing compounds in the future. Based on their similar phenolic structures, lignin has great potential to become a valuable substitute for phenol in phenol-formaldehyde resin adhesives. To meet this aim, the sodium hydroxide (NaOH)-catalyzed reaction of kraft lignin with formaldehyde was studied by using paraformaldehyde (PFA) as a formaldehyde source. The advantage of using PFA, the solid polymer of formaldehyde, is the simple composition of the depolymerized solution. According to the results of differential scanning calorimetry (DSC), the lignin reaction was found to require a high NaOH concentration in order for the reaction with PFA to proceed at reasonably low temperatures compared to the curing temperature of phenol-formaldehyde resins (approximately 150°C). On the other hand, high alkalinity conditions are known to favor the disproportionation of formaldehyde to formic acid and methanol. Due to the moderate reactivity of lignin, the Cannizzaro reaction can compete with the Methylolation reaction of lignin. Based on the results of 13C, 31P and 1H-13C heteronuclear single quantum correlation nuclear magnetic resonance (HSQC NMR), Methylolation was found to be the main reaction occurring in the lignin-formaldehyde reaction.
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Online monitoring of synthesis and curing of phenol–formaldehyde resol resins by Raman spectroscopy
Polymer, 2008Co-Authors: Janne Monni, Pentti Niemelä, Leila Alvila, Tuula T. PakkanenAbstract:Abstract The synthesis and curing of phenol–formaldehyde resol resins were monitored online by Raman spectroscopy. The synthesis of the resins (F/P 2.0, alkalinity 4.5 wt%) was studied at rising temperature (40–90 °C) for 90 min and at constant temperatures (80 °C, 90 °C, 100 °C, and 110 °C) for 120 min. The progress of the curing was investigated isothermally (80 °C, 90 °C, 100 °C, and 110 °C) for 120 min for three resins with different degrees of condensation. The synthesis and curing of the resins were started in the reactor and the advancement of the Methylolation and condensation reactions was followed through the window of the reactor in the wave number region of 2000–400 cm−1 with use of a fiber optic probe for the data collection. The Raman spectra of six model compounds (formaldehyde, phenol, 2-hydroxybenzyl alcohol, 4-hydroxybenzyl alcohol, 2-benzylphenol, and 4-benzylphenol) were analyzed to facilitate the interpretation of the spectra of the resins. The consumptions of free phenol and free formaldehyde, as well as the progress of the Methylolation and condensation reactions were easily monitored by following the changes in intensity of the characteristic Raman bands. The results for the cured resins obtained by Raman spectroscopy were in good agreement with the structures and residual reactivities studied by CP/MAS 13C NMR spectroscopy and differential scanning calorimetry (DSC), respectively. The results of the study show Raman spectroscopy to be a promising tool for the online monitoring and control of phenol–formaldehyde resol resin synthesis and curing; in addition, Raman spectroscopy offers an effective and fast method for structural study of the solid state resins.
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Novel two‐stage phenol–formaldehyde resol resin synthesis
Journal of Applied Polymer Science, 2007Co-Authors: Janne Monni, Leila Alvila, Jouni Rainio, Tuula T. PakkanenAbstract:The synthesis of phenol–formaldehyde resol resins was carried out in two stages to facilitate the start of a conventional batch process. In the first stage, the starting material solution was preprocessed in a continuous-flow stirred-tank reactor with a 5-min residence time. In the second stage, synthesis was continued in a batch reactor. Samples were analyzed by titrimetric methods, gas chromatography, nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. Most of the starting materials were consumed in the preprocessing reactor, which allowed better control of the reactivity of the prepolymer solution in the second stage. The Methylolation and condensation reactions proceeded steadily during the production process in the batch reactor. The results of the study indicated that dividing a conventional one-stage batch process into two stages could facilitate the control of the initial stages of resol production. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:371–379, 2007
Ali Hebeish - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of Reactive Polymers and Their Applications to Cotton Fabrics as Permanent Size
Molecular Crystals and Liquid Crystals, 2020Co-Authors: Mohamed Hashem, Ali HebeishAbstract:Abstract Dextrin was first polymerized-with acrylamide. The so obtained polymeric hybrid was converted to a reactive hybrid through Methylolation of its amide groups by reacting the latter with formaldehyde. On the other hand, poly(vinyl alcohol) was converted to a reactive form via its reaction with N-methylol-acrylamide in alkaline medium. The two polymeric materials were then applied to cotton fabric with a view to achieve two objectives. The first is to prepare cotton fabric bearing permanent size. The second is to make use of these polymeric molecules in chemical finishing of cotton. In both cases the application involves acid catalyst. Besides, the application was carried out under different conditions including type and concentration of catalyst, curing time and the concentration of the reactive polymeric material. The treated fabrics were monitored for strength properties, size add-on, and durability in addition to crease recovery in case of the finished fabric.
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The effect of non‐cellulosic constituents on the behaviour of flax towards sodium chlorite, urea and dyes
Journal of The Society of Dyers and Colourists, 2008Co-Authors: A. Higazy, Mohamed Hashem, N Y Abou Zeid, Ali HebeishAbstract:Flax fibres containing different amounts of non-cellulosic constituents were prepared by subjecting the fibres to scouring and/or bleaching under different conditions. Scouring was based on treatment with an aqueous solution of either alkaline sulphite or alkaline dithionite followed by bleaching with an aqueous sodium chlorite/potassium permanganate system. The scoured flax fibres exhibited much greater bleaching effect than did the grey flax. Grey flax and the four bleached substrates were reacted with urea to yield flax carbamate. This was methylolated by reaction with formaldehyde. The extent of carbamation was related to the amount of the non-cellulosic material in the substrate and the presence of copper(II) chloride. The dyeability of the bleached flax was increased by the carbamation and Methylolation sequence. The colour strength of dyed fibres was influenced by the methylol group content of the modified flax, the dyebath pH and nature of the dye used.
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Synthesis and Application of Reactive Carbohydrates. Part VI: Application of Reactive Carbohydrates Derived from Starch and Hydrolyzed Starches to Cotton Fabric
Starch-starke, 2006Co-Authors: A. Bayazeed, A. Higazy, Ali HebeishAbstract:Native starch, 15 min, 30 min, 45 min and 60 min hydrolyzed starches were converted to reactive carbohydrates via graft polymerization with acrylamide followed by Methylolation with formaldehyde. The reactive carbohydrates so obtained were applied to cotton fabric according to the conventional pad-dry-cure method under different conditions. The latter included the catalytic system and the curing conditions. The pad-cure and the pad-batch methods were also applicated. Examination of the treated fabrics for nitrogen content as a measure of the extent of reaction, occuring between the methylol groups of the reactive carbohydrate and the hydroxyl groups of cotton cellulose, as well as durability of the finish on the fabric indicated the dependance of the reaction and durability on nature of both reactive carbohydrate and catalyst as well as curing conditions. Reactive carbohydrate derived from 15 min hydrolyzed starch along with mixed catalyst, namely MgCl2 · 6 H2O/citric acid (20:80), constitute the most appropriate finish/catalyst combination provided that application is carried out according to the pad-dry-cure method; drying is effected at 100°C for 2.5 min while curing is expedited at 130°C for 30 s. Synthese und Anwendung reaktiver Kohlenhydrate. Teil 4: Anwendung von aus Starke und hydrolysierten Starken gewonnenen reaktiven Kohlenhydraten auf Baumwollgewebe. Native Starke sowie 15, 30, 45 und 60 min lang hydrolysierte Starken wurden durch Pfropfpolymerisation mit Acrylamid und anschliesender Methylolierung mit Formaldehyd zu reaktiven Kohlenhydraten umgesetzt. Die so erhaltenen reaktiven Kohlenhydrate wurden nach dem konventionellen Walzen-(Foulard)-Trockenverfahren unter verschiedenen Bedingungen bei Baumwollgeweben angewendet. Letztere schlossen das katalytische System und die Verfahrensbedingungen ein. Das Walzenverfahren und die Walzen-Batch-Verfahren kamen ebenfalls zur Anwendung. Die Prufung der behandelten Gewebe auf Stickstoffgehalt als Mas fur die Reaktion, die zwischen den Methylolgruppen des reaktiven Kohlenhydrates und den Hydroxylgruppen der Baumwollcellulose stattgefunden hat, sowie die Dauerhaftigkeit der Appretur auf dem Gewebe zeigten die Abhangigkeit der Reaktion und der Dauerhaftigkeit von der Natur sowohl des reaktiven Kohlenhydrats und Katalysators als auch der Behandlungs-bedingungen. Das durch 15 min Hydrolyse in Gegenwart des gemischten Katalysators, und zwar MgCl2 · 6H2O/Zitronensaure (20:80), gewonnene reaktive Kohlenhydrat stellt die geeignetste Appretur/Katalysator-Kombination dar, vorausgesetzt, das die Anwendung nach dem Walzen-Trockenverfahren erfolgt: die Trocknung wird 2,5 min bei 100°C ausgefuhrt, wahrend die Behandlung bei 130°C innerhalb von 30 s bewerkstelligt wird.
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Synthesis and Applications of Reactive Carbohydrates Part I: Behaviour of Carboxymethyl Starch Before and After Acid Hydrolysis Toward Grafting with Acrylamide
Starch-starke, 2006Co-Authors: A. Bayazeed, A. Higazy, Ali HebeishAbstract:Carboxymethyl starch (CMS) was subjected to acid hydrolysis at 50°C for different periods of time. The CMS sample and the hydrolyzed CMS samples were then subjected to two independent reactions, namely grafting with acrylamide using K2S2O8 as initiator and oxidation using K2S2O8 under the grafting condition but in absence of the monomer. The samples were analyzed for copper number and carboxylic content before and after these two reactions. Acid hydrolysis resulted in creation – in CMS structure – of aldehydic groups which underwent partial conversion to carboxylic groups during drying. Grafting reduced significantly the copper number and so did the oxidation. The latter increased the carboxylic groups but grafting exerted opposite effect. Hydrolysis of CMS for shorter or longer periods of time enhanced the susceptibility of CMS during the initial stages of grafting. The opposite held true for the later grafting stages. Methylolation and application of grafted prehydrolyzed CMS to cotton fabrics were reported. Synthese und Anwendung von reaktiven Kohlenhydraten. Teil 1: Verhalten von Carboxymethylstarke vor und nach der Saurehydrolyse gegenuber der Pfropfung mit Acrylamid. Carboxymethyl-starke (CMS) wurde bei 50°C unterschiedlich lange der Saurehydrolyse unterworfen. Die CMS-Probe und die hydrolysierten CMS-Proben wurden dann zwei unabhangigen Reaktionen unterworfen, und zwar der Pfropfung mit Acrylamid unter Verwendung von K2S2O8 als Startersubstanz und der Oxidation durch Verwendung von K2S2O8 unter den Bedingungen der Pfropfung, jedoch in Abwesenheit des Monomers. Die Proben wurden vor und nach diesen beiden Reaktionen auf die Kupferzahl und den Carboxylgehalt untersucht. Die Saurehydrolyse fuhrte zur Bildung von Aldehydgruppen in der CMS-Struktur, die der teilweisen Umwandlung in Carboxylgruppen wahrend der Trocknung unterlagen. Die Pfropfung verringerte die Kupferzahl und die Oxidation in signifikanter Weise. Die Oxidation erhohte die Anzahl der Carboxylgruppen, wahrend die Pfropfung einen entgegengesetzten Einflus ausubte. Die Hydrolyse der CMS erhohte die Angreifbarkeit der CMS wahrend der Anfangsstufen der Pfropfung. Das Gegenteil war bei den spateren Pfropfungsstufen der Fall. uber die Methylolierung und Anwendung von gepfropfter vor-hydrolysierter CMS bei Baumwollgewebe wird berichtet.
Fernão D. Magalhães - One of the best experts on this subject based on the ideXlab platform.
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Study of the synthesis parameters of a urea-formaldehyde resin synthesized according to alkaline-acid process
International Journal of Adhesion and Adhesives, 2020Co-Authors: Carolina Gonçalves, Nádia Paiva, João Pereira, João Ferra, Fernão D. Magalhães, Jorge Martins, Ana Barros-timmons, Luísa CarvalhoAbstract:Abstract This paper presents a study of two crucial synthesis parameters of the alkaline-acid process of UF resin synthesis: condensation formaldehyde/urea (F/U) molar ratio and U feed rate during the Methylolation step. The differences in the polymeric structures and the performance of the ensuing resins on particleboards (PBs) properties were analyzed and compared with a standard resin. The molecular weight distribution of the resins was monitored by gel permeation chromatography/size exclusion chromatography (GPC/SEC) and the unreacted oligomers by high-performance liquid chromatography (HPLC). The PBs produced were analyzed following European standards for mechanical tests and formaldehyde emission. The data obtained were also submitted to a statistical analysis. The results obtained showed that the use of low molar ratios yield higher internal bond strength (IB) values and lower formaldehyde emissions (F). In turn, the effect of urea feed rate during the Methylolation step on IB values depends on the F/UII molar ratio used: (i) a reduction for the higher final molar ratio used, and no effect for the lowest final molar ratio used. Moreover, the statistical analysis carried out showed that F/UII molar ratio has significance on almost all of the resins’ characteristics. The resin used as standard yielded the best results when the final F/U molar ratio was 1.10 and the resulting PBs presented values of internal bond (IB) of 0.51 N mm−2 and formaldehyde content (F) of 5.1 mg/100 g o.d.b., complying with the market requirements. Additionally, the effect of resin ageing was also studied and the PBs prepared using the best resin upon fifteen days of its production presented similar IB values and even lower F content in relation to those obtained using fresh resin.
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Statistical evaluation of the effect of urea-formaldehyde resins synthesis parameters on particleboard properties
Polymer Testing, 2018Co-Authors: Carolina Gonçalves, Nádia Paiva, João Pereira, João Ferra, Fernão D. Magalhães, Jorge Martins, Ana Barros-timmons, Luísa CarvalhoAbstract:Abstract This work discusses the optimization of different synthesis parameters for a low emitting urea-formaldehyde (UF) resin. Industrially, this resin was synthesized using the alkaline-acid process (alkaline Methylolation and acidic condensation) at different values of pH, temperature (T) and final viscosity and characterized according to different analytical methods. Particleboards (PBs) were produced using different pressing times and characterized according to the standard tests. A statistical analysis (ANOVA) was performed, and the main conclusion is that small changes on the synthesis of resins parameters do not affect the performance of PBs.
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Study of influence of synthesis conditions on properties of melamine–urea formaldehyde resins
International Wood Products Journal, 2012Co-Authors: Nádia Paiva, João Pereira, João Ferra, Paulo Cruz, Luísa Carvalho, Fernão D. MagalhãesAbstract:AbstractThe aim of this work is to assess the differences in the polymeric structure and performance of melamine–urea formaldehyde (MUF) resins, when changing relevant synthesis variables: formaldehyde/amine groups [F/(NH2)2] molar ratio (both in the Methylolation and the condensation steps) and the feedrate of urea during the condensation step. This synthesis process differs from the traditional alkaline acid process, since the F/(NH2)2 molar ratio is different for the Methylolation and condensation steps. It was found that the F/(NH2)2 molar ratio and urea feedrate in the condensation step are the most influential variables on the product characteristics. A relationship was established between polymeric structure of the resin and the physicomechanical properties, as well as the levels of formaldehyde. A resin formulation was obtained that exhibits a formaldehyde content, evaluated both by perforator and desiccator methods, within the Japanese F**** requirements. This resin presents an overall performanc...
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Comparison of UF synthesis by alkaline-acid and strongly acid processes
Journal of Applied Polymer Science, 2011Co-Authors: João Ferra, Luísa Carvalho, Ana Henriques, Adélio Mendes, Mário Rui P. F. N. Costa, Fernão D. MagalhãesAbstract:This work discusses two processes for pro- ducing urea-formaldehyde (UF) resins. One is the alkaline- acid process, which has three steps: usually an alkaline Methylolation followed by an acid condensation and finally the addition of a final amount of urea. The other process, the strongly acid process, consists of four steps, in which the first step involves a strongly acid condensation followed by an alkaline Methylolation, a second condensa- tion under a moderately acid pH and finally, methylola- tion and neutralization under a slight alkaline pH. Two resins were produced using the two above described proc- esses. The molecular weight distribution (MWD) of the resins was monitored off-line by GPC/SEC and the final resins were characterized by GPC/SEC and HPLC. These studies showed that the two resins differ greatly in chemi- cal structure, composition, viscosity, and reactivity. The monitoring of MWD indicated that the first condensation under a strongly acid environment leads to the production of a polymer with a distinctly different chemical structure, therefore increasing the flexibility of polymer synthesis and opening the way to the improvement of end-use properties. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 000: 000-000, 2011
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evaluation of urea formaldehyde adhesives performance by recently developed mechanical tests
International Journal of Adhesion and Adhesives, 2011Co-Authors: João Ferra, Luísa Carvalho, Adélio Mendes, Mário Rui P. F. N. Costa, Martin Ohlmeyer, Fernão D. MagalhãesAbstract:Abstract In the open literature, two main strategies can be found for synthesizing urea-formaldehyde (UF) resins. One is the alkaline–acid process, which takes place in three steps, usually an alkaline Methylolation followed by an acid condensation and then the addition of a final amount of urea. The other process consists of four steps, the main difference being an initial condensation in strongly acid environment. In this work, we evaluate the curing behaviour of four resins produced using the aforementioned processes by the Integrated Pressing and Testing System (IPATES) and the Automated Bonding Evaluation System (ABES). The characterisation of the bond strength development during hot pressing by ABES and IPATES shows that the four resins will have different performances in the bonding process of wood-based composites. For each resin, the effect of pressing parameters such as temperature, adhesive and hardener ratios on shear strength (ABES) and internal bond (IPATES) during hot pressing is put into evidence.