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Maslosh, V. Z.; Kotova, V. V.; Маслош, Ольга Владимировна

doi:10.1023/a:1025629507584

Cited by 7 publications

(8 citation statements)

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“…1, curves 1`and 2`). It has been shown previously [7] that the UFR formed under such conditions is of mostly linear structure, with a high content of methylene ether bonds. The ready hydrolysis of the methylene ether bonds and the equilibrium character of MG formation account for the reproducibly high content of free FA in UFR samples prepared in alkaline solution.…”

Section: Methodsmentioning

confidence: 93%

Section: Methodsmentioning

confidence: 99%

“…2, 4, 6, and 8, the same amounts of urea were loaded uniformly in equal portions during the course of the process step. A detailed protocol of UFR preparation and the UFR structure were reported in [7,8].Experimental data show that the properties and toxicity of UFRs are appreciably influenced by such process factors as the mode of loading urea, pH of the medium, and reaction time, and also by the concentrations of urea and FA. In the UFR synthesis in an alkaline solution, when urea is loaded in a single portion, the content of free FA is 0.133 0.14, and that of MGs, 18.6 319.8 wt % (Fig.…”

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confidence: 99%

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Decreasing the Content of Free Formaldehyde in Urea-Formaldehyde Resins

2005

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The possibility of decreasing the content of free formaldehyde in urea3formaldehyde resins by varying the pH and urea3formaldehyde ratio in various synthesis steps was examined. Urea3formaldehyde resins containing no free formaldehyde were prepared.Urea3formaldehyde resins (UFRs) are widely used binders. Their significant drawback is the toxicity caused by the presence of free formaldehyde (FA); its content depends on the preparation conditions [1].The influence of process parameters on the properties and structure of UFRs was examined in numerous studies [23 4], but the problem is far from being solved because of the complexity of the reactions involved in UFR formation. Polycondensation in the urea3FA system is accompanied by many side reactions (hydrolysis, cyclization, addition, etc.), affecting the functional composition of the product. The kinetic features and mechanisms of these reactions are different [5]. An additional factor complicating the mechanism of UFR formation is the polyfunctional nature of urea and FA.In this study, we examined how the process parameters affect the content of free FA in UFRs prepared at varied pH values and urea : FA ratios in particular reaction steps. EXPERIMENTALUFRs were prepared at 82 + 3oC and varied pH in three steps. The urea : FA molar ratio in these steps was 1 : 4, 1 : 1.45, and 1 : 1.33. In the course of the synthesis, we monitored the content of free FA and methylol groups (MGs) [6]. The experimental results are shown in Fig. 1. In run nos. 1 and 2, step I was performed in an acidic solution (pH 4.535.0), and steps II and III, in an alkaline solution (pH 9.5310.0). In run nos. 3 and 4, step I was performed in an alkaline solution (pH 9.5310.0); step II, in an acidic solution (pH 4.535.0); and step III, again in an alkaline solution (pH 9.5310.0). In run nos. 5 and 6, steps I and III were performed similarly to run nos. 3 and 4, and step II, at pH 2.0 32.5. In run nos. 7 and 8, all the three steps were performed in an alkaline solution (pH 9.5310.0). In run nos. 1, 3, 5, and 7, urea was loaded in a single portion in each step; in run nos. 2, 4, 6, and 8, the same amounts of urea were loaded uniformly in equal portions during the course of the process step. A detailed protocol of UFR preparation and the UFR structure were reported in [7,8].Experimental data show that the properties and toxicity of UFRs are appreciably influenced by such process factors as the mode of loading urea, pH of the medium, and reaction time, and also by the concentrations of urea and FA. In the UFR synthesis in an alkaline solution, when urea is loaded in a single portion, the content of free FA is 0.133 0.14, and that of MGs, 18.6 319.8 wt % (Fig. 1d, curves 1 and 1`); when urea is loaded uniformly, the content of free FA is 0.053 0.09, and that of MGs, 18.5319.7 wt % (Fig. 1, curves 2 and 2`). A longer reaction in alkaline solution does not result in an appreciable decrease in the free FA content.In the synthesis of UFR in an alkaline solution, a steady decrease in the free FA content is ...

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Section: Methodsmentioning

confidence: 93%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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Decreasing the Content of Free Formaldehyde in Urea-Formaldehyde Resins

2005

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“…The reaction of urea with formaldehyde can yield a number of products whose content depends on the process factors: component molar ratio, pH, temperature, etc. [63] . Urea formaldehyde (UF) resins are prepared by a two -stage reaction.…”

Section: Crosslinking Through Polycondensationmentioning

confidence: 99%

Basic Features and Techniques

Bhattacharya

Ray

2008

Polymer Grafting and Crosslinking

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“…In 33 Some investigations were also focused on the influence of synthesis parameters in the structure of the resins examined by 13 C-NMR and their effect on the performance of wood-based panels [34][35][36][37][38][39] ; this was also done to establish suitable correlations between various properties of these wood-based panels and the chemical structure of the uncured resins used. 40,41 The achievement of reliable quantitative results is not always possible, because some of these techniques have limitations.…”

Section: Introductionmentioning

confidence: 99%

A very simple empirical kinetic model of the acid‐catalyzed cure of urea–formaldehyde resins

Carvalho

Costa

2006

J of Applied Polymer Sci

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ABSTRACT:The hot pressing operation is the final stage in MDF (medium density fiberboard) manufacture; the fiber mat is compressed and heated up to promote the cure of the resin. The aim of the investigations is to study the curing reactions of UF (Urea-Formaldehyde) resins as commonly used in the production of MDF, and to develop a simplified kinetic model. This investigation has combined Raman spectroscopy to study the reaction cure and 13 C-NMR for the quantitative and qualitative characterization of the liquid and still uncured resin. Raman spectroscopy was found very interesting for the study of the resin cure and permitted to obtain kinetic data as the basis for a simple empirical model, considering a homogeneous irreversible reaction of a single kind of methylol group and ureas with rate constants depending on their degree of substitution. Although these results can provide a better understanding of the composition and the cure of an UF resin, several issues remain open, such as the influence of the reversibility of the reactions taking place during the curing process as well as the possible formation of cyclic groups in the resin.

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Cited by 7 publications

References 5 publications

Decreasing the Content of Free Formaldehyde in Urea-Formaldehyde Resins

Decreasing the Content of Free Formaldehyde in Urea-Formaldehyde Resins

Basic Features and Techniques

A very simple empirical kinetic model of the acid‐catalyzed cure of urea–formaldehyde resins

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