A rheological study of the gelling of UF polycondensates

Halász, László; Vorster, O.C.; Pizzi, A.; Alphen, J. van

doi:10.1002/(sici)1097-4628(20000307)75:10<1296::aid-app11>3.0.co;2-f

Cited by 14 publications

(3 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The gelling process of wood adhesives is important in terms of adhesion strength [25]. During the curing process, high molecular weight, three-dimensional networks formed and resulted in a strong, tight bond.…”

Section: Dynamic Viscoelasticitymentioning

confidence: 99%

Soy Protein Adhesive Blends with Synthetic Latex on Wood Veneer

Sun

2010

J Americ Oil Chem Soc

View full text Add to dashboard Cite

Environmental pollution has prompted an interest in and a need for bio-based wood adhesives. Modified soy protein has shown adhesion properties similar to those of formaldehyde based adhesives. The objective of this research was to investigate the compatibility of a modified soy protein (MSP) with six commercial synthetic latex adhesives (SLAs). Four different blending ratios of MSP and SLAs were studied. Adhesion; structural change; and rheological, thermal, and morphological properties of the MSP/SLAs blends were characterized. Dry adhesion strength of MSP, SLAs and their blends were all similar with 100% wood cohesive failure. Water resistance of all six SLAs was improved by blending with MSP in terms of the wet adhesion strength. The wet adhesion strength of MSP/PBG (40/60) blends was 6.416 MPa, as compared to 4.66 MPa of pure PBG (press bond glue, urea formaldehyde based resin). Viscosity of MSP/SLAs blends was reduced significantly and reached the lowest value at 40-60% MSP. Infrared spectra, thermal properties, and morphological images indicated that chemical reactions occurred between soy protein and PBG molecules. The MSP provided some functional groups, such as carboxylic (-COOH), hydroxyl (-OH) and amino groups (-NH 2 ), that cross-linked with hydroxymethyl groups (-CH 2 -OH) of PBG, and also acted as an acidic catalyst for the selfpolymerization of urea formaldehyde based resin.

show abstract

Section: Dynamic Viscoelasticitymentioning

confidence: 99%

Soy Protein Adhesive Blends with Synthetic Latex on Wood Veneer

Sun

2010

J Americ Oil Chem Soc

View full text Add to dashboard Cite

show abstract

“…Since a three-dimensionally crosslinked solid network is formed, the gelling process of wood adhesives is substantial for developing the strength of the bonded joints. 4 The GP of a UF resin is influenced by various parameters such as the molar ratio of formaldehyde to urea (F/ U), the pH value, the solid content, and the type and amount of the catalyst. 5 Aside from resin parameters, GP is also strongly influenced by other factors such as low-molecularweight extractives from the surrounding wood matrix which may have an accelerating or decelerating effect on curing depending on their chemical nature.…”

Section: Introductionmentioning

confidence: 99%

“…At the GP, a pronounced deceleration of the curing rate is observed because the reaction rate becomes no longer kinetically but diffusion controlled. Since a three-dimensionally crosslinked solid network is formed, the gelling process of wood adhesives is substantial for developing the strength of the bonded joints . The GP of a UF resin is influenced by various parameters such as the molar ratio of formaldehyde to urea (F/U), the pH value, the solid content, and the type and amount of the catalyst .…”

Section: Introductionmentioning

confidence: 99%

Determination of the Gel Point of Formaldehyde-Based Wood Adhesives by Using a Multiwave Technique

Nasseri,

Rosenfeld,

Solt

et al. 2023

ACS Appl. Polym. Mater.

View full text Add to dashboard Cite

Determining the instant of gelation of formaldehyde-based wood adhesives as an assessment parameter for their curing rate is important for optimizing the curing behavior. Due to the stoichiometrically imbalanced networks of formaldehyde-based adhesives, the crossover point of storage G′ and loss modulus G″ cannot unconditionally be assumed as the gel point in oscillatory time sweeps as the material response is frequency-dependent. This study aims to determine the gel point of selected adhesives by the isothermal multiwave oscillatory shear test. A thorough comparison between the gel and the crossover point of G′ and G″ is performed. Rheokinetic analysis showed no significant difference between the activation energies calculated at the gel point determined by a multiwave test and the crossover point obtained by the time sweep test. Hence, for resins with similar curing reactions, a reliable determination of gel point by applying a multiwave test is needed for a comparison of their reactivity.

show abstract

Rheology of polyflavonoid tannin–formaldehyde reactions before and after gelling. II. Hardener influence and comparison of different tannins

Garnier¹,

Pizzi²,

Vorster³

et al. 2002

J of Applied Polymer Sci

Self Cite

View full text Add to dashboard Cite

Good correspondence of the gel-time values obtained by two different methods, GЈ ϭ GЉ and 1/ 0 30, was observed for different types of natural and modified tannin extracts. The pH presents the predominant effect on both the activation energies and the gel times observed, while the proportion of a paraformaldehyde hardener has a much lesser effect on these parameters. The rate constants of the different phases of the reaction of polycondensation with formaldehyde, both before and after the gel point, were obtained for the six commercial tannin extracts tested. The viscoelastic properties of the different tannins/formaldehyde gels were measured. The gel stiffness S, relaxation coefficient n, and relaxation time were determined and their dependence on the proportion of the formaldehyde hardener, on the temperature, and on the type of tannin was determined. The gel stiffness S appears to be influenced considerably by the proportion of the formaldehyde hardener. Its value decreased as the percentage of the hardener increased: This was due to early network immobilization and the resulting lower level of crosslinking resulting from it. The influence on S of the temperature is not very pronounced. The relaxation coefficient n appears to depend mainly on the reactivity of the tannin used: The faster the reactivity, the higher was the value of n. This appears to be valid exclusively in tannin extracts where the colloidal state is still present, while it is not valid in extracts where the colloidal state was eliminated by, for example, solvent extraction.

show abstract

A rheological study of the gelling of UF polycondensates

Cited by 14 publications

References 14 publications

Soy Protein Adhesive Blends with Synthetic Latex on Wood Veneer

Soy Protein Adhesive Blends with Synthetic Latex on Wood Veneer

Determination of the Gel Point of Formaldehyde-Based Wood Adhesives by Using a Multiwave Technique

Rheology of polyflavonoid tannin–formaldehyde reactions before and after gelling. II. Hardener influence and comparison of different tannins

Contact Info

Product

Resources

About